|
University of Berkeley, Site
link to Dinoflagellata, Neat explanation about red tide.
http://www.ucmp.berkeley.edu/protista/dinoflagellata.html
This next section is a great paper
explaining red tide exposure on humans: The paper is
Extremely informative, it was written by Mote
Marine, so check out their website for more interesting information.
This paper is well worth reading.
Literature Review of Florida Red Tide: Implications for Human Health
Effects
Barbara Kirkpatrick1, Lora E.
Fleming2, Dominick Squicciarini2, Lorrie C.
Backer3, Richard Clark4, William
Abraham2, Janet Benson5, Yung Sung
Cheng5, David Johnson4, Richard
Pierce1, Julia Zaias2, Gregory D.
Bossart2, Daniel G.
Baden6.
1
Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL,
34236
2NIEHS Marine and Freshwater Biomedical
Sciences Center, University of Miami, 4600 Rickenbacker Causeway,
Miami, FL, 33149
3National Center for Environmental Health,
Centers for Disease Control and Prevention, 1600 Clifton Rd NE,
Atlanta, Georgia, 30333
4Florida Department of Health, 4052 Bald
Cypress Way, Tallahassee, FL, 32399
5
Lovelace Respiratory Institute, 2425 Ridgecrest, SE Albuquerque, NM,
87108
6
Center for Marine Science, University of North Carolina, 5600 Marvin
K. Moss Lane, Wilmington, NC, 28409
Telephone (941)
388-4441 Ext. 226, Fax (941) 388-4312, E-mail: bkirkpat@mote.org
Author/proofs
address: Mote Marine
Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL,
34236
Key Words: Florida red tide, red tide, neurotoxic
shellfish poisoning, NSP, brevetoxins, harmful algal bloom, HAB,
Karenia brevis, shellfish poisoning, respiratory irritation,
marine toxin diseases
Abstract
Florida red tides
are a natural phenomenon caused by dense aggregations of single cell
or several species of unicellular organisms. Patches of discolored
water, dead or dying fish, and respiratory irritants in the air
often characterize these algal blooms. In humans, two distinct
clinical entities, depending on the route of exposure, are
associated with exposure to the Florida red tide toxins
(particularly the brevetoxins). With the ingestion of
brevetoxin-contaminated shellfish, neurotoxic shellfish poisoning
(NSP) presents as a milder gastroenteritis with neurologic symptoms
compared with other marine toxin diseases such as paralytic
shellfish poisoning (PSP) or ciguatera fish poisoning. With the inhalation of the
aerosolized red tide toxins (especially the brevetoxins) from the
sea spray, respiratory irritation and possibly other health effects
are reported in both humans and other mammals (Baden 1995, Fleming
1998a, Fleming 1998b, Fleming 1999a, Bossart 1998, Asai 1982,
Eastaugh 1989, Pierce 1986, Music 1973, Temple 1995, Anderson
1994).
This paper reviews
the literature on the known and possible human health effects of
exposure to the Florida red tides and their toxins. The review includes
discussion of the red tide organisms and their toxins, as well as
the effects of these toxins on both wild and laboratory animals as
they relate to possible human health effects and
exposures.
Background
Toxic red tides
have been observed in Florida since the 1840s. Since that time, multiple
episodes with significant fish kills, as well as cases of NSP have
been reported from the Gulf of Mexico (including the east coast of
Mexico), the east coast of Florida, and up to the North Carolina
coast; toxic blooms occur almost annually on the west coast of
Florida. Recently, these and other red
tides appear to be increasing in incidence, duration and geographic
spread (Viviani 1992, Smayda 1990, Van Dolah 2000, Tester 1991,
Tester 1997).
Anthropogenic influences (such as nutrient run-off inducing
red tide blooms and the transport of dinoflagellate cysts in ballast
water of ships have been suggested as possible causes. However, these red tides in
Florida occurred even before significant pollution and development
by human populations: during 1844- 1971, red tides and their
sequellae were noted along the west coast of Florida at least 24
times before the major industrial and agricultural development of
that area. Alternative
explanations (such as the effects of changing ocean temperatures,
currents and weather patterns associated with global warming, as
well as atmospheric transport of Sahara dust) are being investigated
(Tester 1997, Tester 1991, Viviani 1992, Tibbetts 1998, Morris 1991,
Ishida 1996, Anderson 1994, Sierra Beltran 1998, Cortes Altamirano
1995, Tommasi 1983, Epstein 1994, NRC 1999, Epstein 1998, Steidinger
1972, Kin Chung 1991, Smayda 1990, Walsh 2001).
Recent prolonged red tides in the Gulf of
Mexico have been associated with significant environmental, human
health, and economic impacts.
Beaches in Texas and shellfish beds from Florida to Mexico
have been closed.
Significant die-offs of fish, endangered manatees, and
double-crested cormorants, as well as reported adverse human health
effects, have resulted annually secondary to the red tide toxin
exposure along the coastline of the Gulf of Mexico (Bossart 1998,
Hopkins 1997, Kreuder 1998, Trainer 1999).
Organisms
The dinoflagellates
are ancient, single-celled, eukaryotic organisms that can exist in
benthic, parasitic, symbiotic, and free-living forms; ocean currents
can transport the latter easily. Many of the dinoflagellates include
in their life cycle at least one resting form or cyst. The cysts may serve as the
seeds for the red tides because they are the renewal of the motile
phase of the dinoflagellate when the environmental conditions are
appropriate; the motile forms create the blooms and the natural
toxins (Anderson 1994, de M Sampayo 1997, Baden 1995, Baden
1983).
The classic causative organism of Florida
red tides is Karenia brevis (formerly known as
Gymnodinium breve and Ptychodiscus
brevis).
K. brevis is a dinoflagellate restricted to
the Gulf of Mexico and the Caribbean, but has been carried by ocean
currents around Florida and up the east coast of the United States
as far as North Carolina.
Other species producing the same or similar toxins occur
throughout the world, particularly in New Zealand (Ishida 1996,
MacLean 1979, Hermes 1984 Chang 1998, Temple 1995, Morohashi 1999,
Anderson 1994, Anderson 1994, Sierra Beltran 1998, Cortes Altamirano
1995, Tommasi 1983, Horstman 1991, Khan 1997, Steidinger
1983). K.
brevis usually blooms in the late summer and autumn, almost
every year off the west coast of Florida, causing massive fish and
bird kills.
The K. brevis organism is relatively
fragile because it is unarmored. Therefore, particularly in
wave action along beaches, the organism is easily broken open,
releasing the toxins.
During an active in-shore red tide, the aerosol of
contaminated salt spray will contain the toxins and organism
fragments, both in the droplets and attached to salt particles;
these can be carried inland depending on wind and other
environmental conditions (Pierce 1990, Pierce 1989, Sakamoto 1987,
Music 1973, Backer submitted, Pierce 1986, Horstman 1991, ILO
1984).
Toxins
Associated with
these algal bloom episodes of K. brevis, a variety of
phytoplankton-related natural toxins have been identified. There are
reportedly hemolytic components and even cardiotoxic
anti-cholinesterase phosphorus-containing compounds (Mazumder 1997),
however the most important group is the neurotoxic brevetoxins
(Ptychodiscus brevis toxin, i.e., PbTx). As a group, the brevetoxins
are lipid soluble, cyclic polyethers with molecular weights around
900. Over 9 different
brevetoxins have been isolated in sea water blooms and K.
brevis cultures, as well as multiple analogs and derivatives
from the metabolism of shellfish and other organisms (Morohashi 1999, Baden and
Trainer 1993, Baden 1995, Mazumder 1997, Mattei 1999, Pierce and
Kirkpatrick, 2001). In
red tides, the major brevetoxin produced by concentration is PbTx-2,
as well as lesser amounts of PbTx-1 and PbTx-3 (Baden 1989, Pierce
et al., 1992).
As with many of the known marine toxins, the
brevetoxins are tasteless, odorless, and heat and acid stable. These toxins cannot be
easily detected, nor removed by food preparation procedures (Baden
1982a, Baden 1993, Baden 1995, Sakamoto 1987).
These brevetoxins
are depolarizing substances that open voltage gated sodium (Na+) ion
channels in cell membranes, leading to uncontrolled Na+ influx into
the cell (Baden 1983, Purkerson 1999). This alters the membrane
properties of excitable cell types in ways that enhance the inward
flow of Na+ ions into the cell; this current can be blocked by
external application of tetrodotoxin, a Na+ ion channel blocker
(Gallagher 1980, Baden 1983, Halstead 1988, Poli 1986, Viviani 1992,
Trainer 1991, Jeglitsch 1998).
Recent work by Purkerson et al. (1999) and others using
electrophysiology studies of single sodium channel of rat central
nervous system cells suggest that PBTx-3 may cause hyper
excitability as well as inhibitory effects in the intact brain
(Apland 1993, Templeton 1989a, Templeton 1989b). As a consequence of their
lipid solubility, these toxins are expected to easily pass through
cell membranes including the blood brain barrier, as well as buccal
mucosa and skin (Mehta 1991, Kemppainen 1991, Apland
1993).
The massive fish
kills associated with Florida red tides result from the neurotoxin
exposure, with possible contribution of the hemolytic fraction. In particular, PbTx-3 is
believed to be responsible for the respiratory irritation associated
with toxin inhalation (Baden 1982a, Baden 1982b). The brevetoxins ionically
depolarize nerve cells and lead to the characteristic disruptions of
respiratory and cardiac function known as neurotoxic shellfish
poisoning (NSP). When
Borison et al. (1985) and Koley et al. (1995) studied brevetoxin in
cats, they concluded that brevetoxin exerts its major toxic effects
on circulation and respiration through reflex and central actions,
largely sparing peripheral motor mechanisms. These toxins are also
directly cardiotoxic and hepatotoxic in various in vitro and
in vivo systems (Templeton 1989a, Templeton 1989b, Rodriguez
Rodriguez 1996, Bossart 1998, Rodgers 1984).
The respiratory
problems associated with the inhalation of aerosolized Florida red
tide toxins are believed to result from the opening of sodium
channels of nerve cell membranes by the brevetoxins (Baden 1982a,
Baden 1993, Asai 1982, Borison 1980, Franz 1989, Baden 1989). These effects can be blocked
by atropine (muscarinic blocker) as well as tetrodotoxin (sodium
channel blocker), but not by the interruption of vagal nerve
stimulation or by diaphragm dissection in experimental animals
(Baden 1982a, Gallagher 1980, Asai 1982, Trainer 1991, Baden 1989,
Tsai 1991, Watanabe 1988).
In isolated canine tracheal smooth muscle, neostigmine, an
acetylcholinesterase inhibitor, potentiated the brevetoxin-induced
contraction; mepyramine, phentolamine, methysergide, and
chlorisondamine did not effect the contraction (Asai 1982). In isolated human bronchial
smooth muscle, Shimoda et al. (1988) found similar results as well
as attenuation by verapamil (calcium and sodium channel
blocker). Therefore,
brevetoxin produces contraction of the lower airway smooth muscle by
stimulation of the cholinergic nerve fiber sodium channels with
acetylcholine release.
However, additional pathways may be important for
brevetoxin’s physiologic effects. For example, in the rat vas
deferens, Sakamoto et al. (1985) found that brevetoxin stimulated
sodium channels on adrenergic nerve fibers, releasing norepinephrine
from the nerve endings.
In addition, there
appears to be a role for mast cells in the brevetoxin-associated
respiratory effects. Watanabe et al. (1988) noted that brevetoxin
can combine with a separate site on the h gates of the sodium
channel, causing the release of neurotransmitters from autonomic
nerve endings. In
particular, this can release acetylcholine, leading to smooth
tracheal muscle contraction, as well as massive mast cell
degranulation. The mast
cell contribution to the adverse airway effects of brevetoxin is
supported by studies in a sheep model of asthma. In this model, aerosolized
brevetoxin causes bronchoconstriction that can be blocked by the
mast cell stabilizing agent cromolyn and the histamine H1 antagonist
chlorpheniramine (Singer 1998). Thus, in addition to the direct
neural component, brevetoxin appears to induce the release of
histamine from mast cells and the combination of these actions
results in adverse airway effects. Furthermore, because
brevetoxin exposure by the respiratory route results in systemic
distribution of brevetoxin, the initial bronchoconstriction may only
be part of the overall consequences associated with toxin
inhalation, including the central nervous system (Benson 1999, Apland
1993).
Computer modeling
suggests that brevetoxin is a possible enzymatic binding inhibitor
of cysteine cathepsins.
Cathepsins are powerful lysosomal proteinases and epitope
presenting enzymes, found within cytosol or lysosomes of macrophages
cells, lymphoid tissues and other cells (Bossart 1998, Sudarsanam
1992). Bossart et al.
(1998) postulated that the effects of aerosolized brevetoxins may be
chronic not just acute.
These chronic effects would begin with the initial
phagocytosis by macrophages, inhibition of cathepsins, and apoptosis
of these cells, followed by the phagocytosis of the debris by new
macrophages, ultimately resulting in chronic neuro-intoxication,
hemolytic anemia, and/or immunologic
compromise.
Brevetoxins undergo
biotransformation in rodents and fish (Poli 1990a, Poli 1990b,
Kennedy 1992). In fish,
the brevetoxins induce both cytochrome P4501A, and glutathione S
transferase with a variety of pathways for metabolism (Washburn
1996, Washburn 1994).
On the basis of evaluations of PbTx-3 on the sodium channels
of rat sensory neurons, Jeglitsch et al. (1998) suggested that
PbTx-3 metabolites may be more potent than PbTx-3 parent compound in
affecting sodium channels.
Work by Poli et al. (2000) evaluating metabolites in both the
urine of three persons suffering from NSP and from the contaminated
shellfish supported this conclusion; the authors suggested that
these toxic metabolites from both the shellfish and the humans may
be an additional cause of NSP and should be taken into account
during regulatory testing.
Animals
The major seafoods
contaminated by brevetoxins are shellfish, although no definitive
evidence exists of any health effects to the shellfish, with
possible exception of scallops (Cummins 1971, Sakamoto 1987,
Steidinger 1972, Summerson 1990, Ellis 1985).
Fish, birds, and
mammals are susceptible to the brevetoxins. In the mosquito fish
(Bambusia affinis) bioassay, the LD50 is reported at 0.011
µg/L (0.005-0.023) while with Japanese madaka (Oryzias
latipes) the LC50 was reported to be 0.015-25 µg/ml (Bossart
1998, Forrester 1977, Geraci 1989, O’Shea 1991, Laverty 1993,
Trainer 1999, Anderson 1994, Sierra Beltran 1998, Cortes Altamirano
1995, Ellis 1985, ILO 1984, Poli 1988). Fish kills associated with
these red tides have been estimated up to 100 tons of fish per day
during an active red tide.
The fish are killed apparently through lack of muscle
coordination and paralysis, convulsions, and death by respiratory
failure. In the toadfish model, Kennedy et al. (1992) found that
radiolabeled PbTx-3 was rapidly distributed within 1 hour of
intravenous administration (40.2% muscle, 18.5% intestine, and 12.4%
liver); after 96 hours, levels in the liver remained constant, but
those in bile, kidney, and skin increased, with a variety of
metabolites detected.
Birds die acutely with neurologic and hematologic
effects.
With respect to
mammals, the mouse LD50 is 0.170 mg/kg body weight (0.15-0.27)
intraperitoneally, 0.094 mg/kg body weight intravenously and
0.520 mg/kg body weight orally (Baden 1983, Baden 1995, ILO
1984). Franz and
LeClaire (1989) reported respiratory failure in less than 30 minutes
in guinea pigs exposed intravenously to 0.016 ng/kg PbTx-3. With intravenous
administration of PbTx-3 in rats, Poli et al. (1990a, 1990b) found
that approximately 90% was cleared within 1 minute from the
circulation.
Furthermore, radiolabeling distributed to the skeletal muscle
(70%), liver (19%), and intestine (8%) with little activity found in
the heart, kidneys, lungs, spleen, testes, or brain. Elimination over a 24-hour
period was primarily through the feces. The parent compound was
present in the skeletal muscle, but several metabolites of PbTx-3
excreted in the bile were found in the feces. Cattet and Geraci (1993)
orally administered sublethal doses (18.6 µg/kg) of PbTx-3 in rats,
and found wide distribution to all organs, with the highest
concentrations in the liver up to 8 days after exposure. Ingested PbTx-3 was
eliminated approximately equally in urine and
feces.
To evaluate
brevetoxin toxicokinetics from acute exposure up to 7 days, Benson
et al. (1999) exposed 12-week-old male F344/Crl BR rats to a single
exposure of 6.6 µg/kg PbTx-3 through intratracheal
instillation. More than
80% of the PbTx-3 was rapidly cleared from the lung and distributed
by the blood throughout the body, particularly the skeletal muscle,
intestines, and liver with low but constant amounts present in
blood, brain, and fat.
Approximately 20% of the toxin was retained in the lung,
liver, and kidneys for up to 7 days. The majority of the PbTx-3
was excreted within 48 hours after exposure, with twice as much
excreted in the feces than in the urine. The authors concluded that
potential health effects associated with inhaled brevetoxins may
extend beyond the reportedly transient respiratory irritation
reported by humans exposed to Florida red tide brevetoxin
aerosol.
Wells et al. (1984)
reported increased airway resistance in six unanaethestized female
Hartley guinea pigs when brevetoxin was inhaled as an aerosol or
applied to the nares as nose drops, compared with cross over
exposure to methacholine with and without pretreatment with
atropine. Furthermore,
the authors reported that the animals were significantly less
responsive to brevetoxin with pretreatment by atropine or by
diphenhydramine, although no observable effects on the sneezing,
drooling, and defecation of the animals with pretreatment. In the unanaesthestized
asthmatic sheep, picogram doses of PbTx-3 can cause a significant
and rapid increase in respiratory resistance (200 to 300x baseline);
as noted above, this brevetoxin-induced bronchospasm can be
effectively blocked by the mast cell stabilizing agent cromolyn and
the histamine H1 antagonist chlorpheniramine (Singer 1998). Thus in the lung, brevetoxin
appears to be a potent respiratory toxin involving both cholinergic
and histamine-related mechanisms.
Multiple die-offs
of marine mammals have been reported in association with Florida red
tide and brevetoxins (Geraci 1989, O’Shea 1991, Bossart 1998). In 1996, a prolonged Florida
red tide in the Gulf of Mexico resulted in the documented deaths of
149 endangered Florida manatees (Bossart 1998, Trainer 1999). The brevetoxin exposure of
the manatees appears to have been prolonged inhalation of the red
tide toxin aerosol and/or ingestion of contaminated seawater over
several weeks. This manatee die-off investigation revealed severe
catarrhal rhinitis, pulmonary hemorrhage and edema, and
non-suppurative leptomeningitis, as well as possible chronic
hemolytic anemia with multiorgan hemosiderosis and evidence of
neurotoxicity (particularly cerebellar) in the dead manatees. Therefore, the respiratory
tract, liver, kidneys, and brains of the manatees were primary
brevetoxin targets, and the brevetoxin exposures and effects were
believed to be chronic rather than acute. PbTx-3 and its metabolites
were identified by a immunohistochemical stain using a polyclonal
primary antibody to brevetoxin to be stored in the lung and other
organs in alveolar macrophages and in the brain within lymphocytes
and microglial cells.
Immunohistochemical staining with interleukin-1-beta
converting enzyme showed positive staining with a cellular trophism
similar to the brevetoxin antibody staining, suggesting that
brevetoxin may initiate apoptosis and/or release inflammatory
mediators that culminate in fatal toxic shock. Additional studies
demonstrated that brevetoxin binds to isolated nerve preparations
from manatee brain with a similar affinity as that reported for
terrestrial mammals (Trainer 1999), as well as causing significant
liver damage in in vitro mouse liver studies (Rodriguez
Rodriguez 1996).
Humans
The two known forms
of red tide toxins-associated clinical entities in humans first
characterized in Florida are an acute gastroenteritis with
neurologic symptoms after ingestion of contaminated shellfish (i.e.
NSP) and an apparently reversible upper respiratory syndrome after
the inhalation of the aerosols of the dinoflagellate and their
toxins (i.e., aerosolized red tide toxins respiratory irritation)
(Asai 1982, Baden 1995, Fleming 1999b, Fleming 1998a, Fleming 1998b,
Morris 1991, Music 1973, Fleming 2001, Baden 1982b, Poli 2000, Music
1973).
Ingestion of
brevetoxin
Neurotoxic
shellfish poisoning can be viewed clinically as a milder form of
paralytic shellfish poisoning (PSP) or ciguatera fish
poisoning. In human
cases of NSP, the brevetoxin concentrations present in contaminated
clams have been reported to be 30-118 Mouse Units (MU)/100 g (78-120
µg/mg). Poli et al.
(2000) reported on the measurement of brevetoxin in urine from three
persons who suffered from severe NSP after eating contaminated
shellfish from Florida; the urine brevetoxin levels ranged from
42-117 ng/ml by RIA analysis on admission to the emergency
department. As a
comparison, in PSP fatal paralysis can occur with as little as 1 mg
of saxitoxin, while picogram levels of ciguatoxin in ciguatera fish
poisoning have been reported to make adult humans severely ill. The shellfish reported to be
associated with NSP when contaminated with brevetoxin include
oysters, clams, coquinas, and other filter feeders (Keynes 1979,
Baden 1995, ILO 1984, Hughes 1976, ILO 1984, Poli 2000).
NSP typically
causes gastrointestinal symptoms of nausea, diarrhea, and abdominal
pain, as well as the neurologic symptoms primarily consisting of
paresthesias similar to those seen with ciguatera fish poisoning
(including reports of circumoral parathesiae and hot/cold
temperature reversal), beginning within minutes to 3 hours after
ingestion. Cerebellar symptoms such as vertigo and incoordination
also reportedly occur.
In severe cases, bradycardia, headache, dilated pupils,
convulsions, and the subsequent need for respiratory support have
been reported. Death
from NSP (rather than from PSP or ciguatera) is rare. Reportedly, symptoms resolve
within a few days after exposure, however, no studies have been
reported evaluating possible chronic health effects after acute NSP
(Morse 1977, Sakamoto 1987, Baden 1995, Fleming 1995, Fleming 2001,
Morris 1991, McFarren 1965, Viviani 1992, Hughes 1976, Noble 1990,
Martin 1996, Music 1973, Hopkins 1997, ILO 1984, Rheinstein 1993,
Dembert 1981).
Morris et al.
(1991) reported on an outbreak of NSP secondary to a red tide of
K. brevis (then known as P. brevis) in October 1987
along the North Carolina coast. Ultimately, over 48 persons
were diagnosed with NSP following consumption of cooked and raw
oysters at 20 different meals.
Acutely, 23% of the cases reported gastrointestinal and 39%
reported neurologic symptoms.
These symptoms were described as having a rapid onset (median
incubation of 3 hours), mild, and of short duration (maximum malaise
and vertigo up to 72 hours with median duration of 17 hours). Ultimately, 94% had multiple
symptoms, and 71% had more than one neurologic symptom. Although no deaths or
respiratory distress occurred, one woman was admitted to the
intensive care unit because of severe neurologic symptoms. The
illness attack rate increased significantly in association with the
number of oysters eaten.
Of note, 56% of the cases occurred before the first closure
of affected shellfish waters to harvesting in early November; North
Carolina had no red tide monitoring program at that time.
Inhalation of aerosolized
brevetoxin
Few reports have
been published about human exposure and health effects associated
with exposure to aerosolized red tide toxins in humans. The exposure usually occurs
on or near beaches with an active red tide bloom. Onshore winds and
breaking surf result in the release of the toxins into the water and
into the onshore aerosol
(Pierce 1986, 1989, 1990, 2001, Sakamoto 1987, Music
1973, Backer submitted, Horstman 1991, ILO 1984). After initial
reports in Florida and Texas, Woodcock (1948) reported respiratory
irritation during a severe red tide on the west coast of Florida in
1947. When seawater
containing the red tide organisms was sprayed as an aerosol into the
nose and throat of volunteers, coughing and a burning sensation
similar to that experienced on the beaches were reported (Woodcock,
1948). Pierce et al. (1990, 1989) simulated the red tide toxin
aerosol in the laboratory by bubbling air through seawater cultures of lysed
K. brevis cells; they recorded toxin enrichment in the
aerosol of 5 to 50 times the concentration of original
concentrations in the seawater. Collection of marine aerosol
along the Gulf coast of Florida and the North Carolina Atlantic
coast during natural red tide blooms showed that the aerosolized
toxins were the same as those in the water and as those resulting
from the K. brevis culture experiments (Pierce et al. 1989,
1990).
Inhalation of aerosolized red tide toxins
reportedly results in conjunctival irritation, copious catarrhal
exudates, rhinorrhea, nonproductive cough, and bronchoconstriction
(Music 1973, Asai 1982, Asai 1984, Franz 1989, Eastaugh 1989, Pierce
1986, Temple 1995, Sakamoto 1987, Baden 1982b, Davis 1994, Ahles
1974, Hughes 1976, Tommasi 1983, Hopkins 1997, ILO 1984, Dembert
1981, Cummins 1971).
Some people also report other symptoms such as dizziness,
tunnel vision, and skin rashes. In the normal population,
the irritation and bronchoconstriction are usually rapidly
reversible by leaving the beach area or entering an air-conditioned
area (Steidinger 1984, Baden 1983).
However, people with asthma are apparently
particularly susceptible; Asai et al. (1982) found that 80% of 15
asthmatic patients exposed to red tide aerosol at the beach
complained of asthma attacks.
Further studies by the same investigators (Watanabe 1988)
using human bronchial smooth muscle tissue from 12 non-asthmatic
persons, all with a smoking history, showed similar results to
canine smooth muscle studies: brevetoxins caused contraction with a
threshold of 0.1 µg/ml with peak response at 12.0 µg/ml (EC50=1.24
µg/ml); this response was blocked by verapamil, atropine and
tetrodotoxin, and it was potentiated by neostigmine. The possibility
of susceptibility of asthmatics to the brevetoxins is corroborated
by recent investigations with an asthmatic sheep model evaluating
the exposure of aerosolized red tide toxins discussed above (Singer
1998). Furthermore, there are anecdotal reports of prolonged
pulmonary symptoms even after exposure has ceased, especially in
susceptible populations such as the elderly or people with chronic
lung disease.
Reportedly, aerosolized red tide toxins
respiratory irritation is associated only with significant Florida
red tide blooms (including significant fish kills with dead fish on
the beaches) within a few feet of the breaking surf of an active
bloom. However,
exposure to aerosolized red tide toxins can cause respiratory
irritation, even in non-asthmatics and without obvious fish kills or
high dinoflagellate cell counts in the seawater within a few feet of
the seashore (K Steidinger, Florida Department of Environmental
Protection, verbal communication). This may be due to the
concentration of the brevetoxins in the aerosol of sea spray
generated by waves hitting the shore during a red tide (Pierce 1990,
Pierce 1989, Music 1973, Cummins 1971). How far inshore this red
tide toxins aerosol will travel, especially given strong offshore
winds during a red tide bloom, is not known.
Cummins et al. (1971) sampled water and
bivalves during a red tide along the west coast of Florida in
September 1967. In
addition to identifying K. brevis in the water samples and
showing toxicity in the mouse bioassay with shellfish samples, the
investigators reported burning of the eyes and respiratory
irritation during the course of sampling. These symptoms increased as
investigators approached the surf zone and were associated with
organisms in the water.
The investigators reported similar symptoms when they
received an inadvertent inhalation exposure from an aerosol of K.
brevis organism cultures being aerated in the laboratory during
oyster intoxication studies.
Music (1973) reported on a November 1972
K. brevis red tide on the east coast of Florida, after
currents and weather patterns had carried an existing red tide from
the usual epicenter of west coast of Florida. This red tide coupled with
strong easterly onshore winds resulted in multiple reports of
symptoms to the Palm Beach Health Department; the reports came from
people on the beach (swimmers, workers, lifeguards), as well as from
persons living on or near the beach throughout Palm Beach
County. Symptoms
reported included acute eye and nose irritation (e.g., profuse
watery eyes, copious rhinorrhea with burning of the eyes and nose),
non-productive cough, and respiratory distress similar to that
associated with the Florida west coast red tide. The symptoms were described
as having a sudden onset, i.e., occurring as soon as people got near
the beach areas or were exposed to the onshore winds in their
homes. The symptoms
reportedly resolved upon leaving the beach or wind exposure,
although less rapidly for those who were exposed for a longer
time. Exposure to
air-conditioning in homes or cars seemed to improve the symptoms
more rapidly. Persons
on boats or long piers not exposed to breaking surf with onshore
winds did not report any symptoms. All reports of symptoms
stopped when the winds changed direction.
Hopkins et al. (1997) briefly reported on a
prolonged Florida red tide with confirmed K. brevis
identification along the west coast of Florida from December 1995
through May 1996. The
Lee County Health Department conducted a mailed survey of 1100
residents and long-term visitors in areas adjacent to beaches. There were 416 (39%)
responses, with most respondents reported symptoms (although the
authors point out that response to the survey encouraged report from
symptomatic persons).
Eye and respiratory irritation were associated with the
amount of time spent at the beach, but more serious conditions
(i.e., bronchitis, pneumonia, and various neurologic problems) were
not. Six persons were
hospitalized for illnesses they attributed to red tide exposure
(although no definite diagnoses by physicians were
reported).
Kirkpatrick et al. (submitted)
conducted a similar pilot study in 1999 using scientists on K.
brevis red tide research cruises as volunteer study
subjects. Air and water
samples were analyzed for brevetoxins and personal interviews and
pulmonary function tests were conducted daily. On one day of the research
cruise when seas and winds were higher than on other days and cell
counts were up to 8 million cells/L, two scientists reported
shortness of breath and/or difficulty taking a deep breath. At that same time, both had
a decrease in pulmonary function. Although the pulmonary
function decrease was not clinically significant, it is worth noting
because neither scientist had any history of lung disease, both were
young (30 years old), and neither were
smokers.
In a pilot study of
aerosolized red tide, Backer et al (submitted) measured the
levels of brevetoxins in air and water samples and conducted
personal interviews and pulmonary function tests on people before
and after visiting Florida beaches during K. brevis red tide
events. One hundred
twenty-nine people participated in the study, which was conducted
during two separate red tide events in the west and east coasts of
Florida. During
these episodes, K. brevis and brevetoxins were measured in
the seawater, as well as brevetoxins in environmental and personal
air sampling. Exposure was categorized into three levels: little or
no exposure, moderate exposure, and high exposure. Lower respiratory symptoms
(e.g., wheezing) were reported by 8% of unexposed, 11% of moderately
exposed, and 28% of highly exposed people. A detectable inflammatory
response to the inhaled toxins was observed in over 33% of the
people examined after they visited the beach. During the moderate and high
exposure study periods, people were exposed to up to 36
ng/m3 or 80 ng/m3, respectively, of brevetoxin
in the air. If an
average adult breathes in about 25 liters of air per minute for
light exercise, then the authors estimated that people visiting the
beaches during the pilot study inhaled between 54 to 120 ng
brevetoxin each hour, or an inhaled dose of between 0.77 to 1.71
ng/kg (assuming an average weight of 70 kg) each hour. No clinically
significant changes occurred in pulmonary function test results;
however, the study population was small. The authors plan to further
investigate the human health impact of inhaled brevetoxins in future
epidemiologic studies.
Red tide events in the Gulf of Mexico are
usually reported from along the western coast of Florida and can
occur nearly annually (Kusek et al., 1999). Red tides along the Texas
coast are much less frequent (Villareal et al., 2001). Cheng et al. (submitted)
reported a red tide episode in the Gulf of Mexico near Corpus
Christi, Texas, in October 2000. At Marine Science Institute
(MSI) and Texas State Aquarium (TSA), airborne brevetoxin
concentrations between 1.6 ng/m-3 to 6.7 ng/m-3 were
reported, along with a few reports of upper respiratory symptoms
(throat irritation, nasal irritation, and itchy skin) and no reports
of lower respiratory symptoms. Although the number of workers was
too small for statistical analysis, the reported symptoms were
consistent with no/low exposure at the MSI and detectable exposures
at the TSA. This
suggests that at lower environmental concentrations of about 2
ng/m-3 to 7 ng/m-3, exposure to brevetoxin
could result in upper respiratory symptoms. This lower level of airborne
brevetoxin concentrations could be detected because of a more
sensitive LC/MS technique.
The brevetoxin particle size distribution with the impactor
samplers, the first time that particle size of brevetoxin was
reported. The MMAD was
between 7 mm to 9 mm (a range of 3 mm to 20 mm), a relatively large size for inhaled
ambient particles. Fine
particles below 2.5 mm were not detected. Inhaled particles of this
size would be deposited in the upper respiratory tract (nasal, oral,
and pharyngeal area) (ICRP, 1994; Yeh et al., 1996), and subsequent
respiratory irritation could result from the presence of the
particles themselves or from toxins associated with the
particles. Inhaled
particles also deposited on the face and exposed skin causing the
skin to itch.
Whether the inhalation of aerosolized
brevetoxins can result in other systemic health effects (such as
affecting the neurologic or immunologic systems) and in chronic
effects is not known The manatee evidence and other laboratory
animal studies suggest that this possibility should be explored
further (Fleming 2001, Fleming 1995, Bossart 1998, Benson
1999).
Diagnosis
In general, NSP is
a rare event in the United States. This is due in part to the
extensive monitoring of shellfish beds for toxins and organisms in
areas where red tide is endemic, resulting in shellfish bed closure
if either is elevated.
If shellfish are not available for testing, Florida red tide
toxins-associated human diseases is diagnosed primarily on
recognition of the clinical scenario of persons becoming ill with
gastrointestinal and neurologic symptoms after eating shellfish or
with acute respiratory symptoms after inhaling aerosols associated
with exposure to Florida red tide toxins.
The primary toxicity testing methods for
contaminated shellfish currently is the US Food and Drug
Administration (FDA) approved mouse bioassay. Several chemical,
pharmacologic, and immunologic techniques, and the in vitro
neuroblastoma cytotoxicity assay are available. In spite of specific
strengths, each of these methodologies suffers limitations (Hannah
1996). The mouse
bioassay in particular gives false positives and does not
conclusively prove the presence of a particular toxin (Kerr
1999).
Recent promising
brevetoxin research includes: HPLC, HPLC-MS, and micellar
electrokinetic capillary chromatography/laser induced fluorescence
detection methodologies for the identification of the K.
brevis toxins, as well as an experimental ELISA test using
antibodies to brevetoxin, radioimmunoassay, a cell based assay with
tritium labeled PbTx-3 and rat brain synaptosomes, a sodium channel
specific neuroblastoma cytotoxicity assay, and a neurophysiologic
method using in vitro rate hippocampal slices (Templeton 1988,
Melinek 1994, Fairey 1997, Hua 1995, Ishida 1996, Whitney 1997, Poli
1995, Naar in press, Trainer 1991, Hannah 1993, Dickey 1999, Kerr
1999, Poli 1990b, Shea 1997, Garthwaite 1996, Manger 1995, Van Dolah
1994). In particular,
the brevetoxin ELISA (based on goat anti-brevetoxin) is currently
being applied experimentally to detect brevetoxin in: contaminated
seawater, air, and contaminated shellfish (Naar in press). Although water sampling for
both the dinoflagellates and the toxins has been performed for many
years, red tide toxins air monitoring is presently
experimental. Air
monitoring could provide qualitative and quantitative time- and
geographic-based data.
Work with Florida
manatees (apparently killed by the inhalation of the red tide
toxins) has led to the development of a qualitative
immunohistochemical stain for the Florida red tide toxins found
within the macrophages and lymphocytes in nasal mucosa, lung, and
other tissues (Bossart 1998).
This staining technique has also been used to look for toxins
in the tissues of marine birds exposed to red tide toxins (Jessup
1998, Kreuder 1998).
This biomarker could be used as both an indicator of exposure
and effect. On the
basis of recent research in a sheep animal model using a modified
immunocytochemical technique on the bronchial lavage specimens of
animals exposed to aerosolized red tide toxins, this biomarker holds
promise as a diagnostic and prognostic tool. Initial work shows that the
immunocytochemical staining of throat and nasal swab specimens
reflect the bronchial lavage results, thus allowing for a more
human-applicable biomarker.
Currently, no tests are available for
measuring the brevetoxins in human fluids, although the work of Poli
et al. (2000) measuring brevetoxin and its metabolites in urine
using HPLC-MS and other methods, as well as the new brevetoxin ELISA
of Naar et al. (in press) are promising.
Treatment and
Prevention
Treatment for
shellfish poisoning is supportive (i.e., fluid replacement and
respiratory support if necessary). In PSP, emesis may not
occur, hence gastric lavage is commonly used. Ciguatera fish poisoning
caused by the natural marine toxin, ciguatoxin, was shown in a
clinical trial to respond to the early administration of intravenous
mannitol within 72 hours (Palafox 1988, Fleming 1997, Blythe
2001). Because
brevetoxin and ciguatera are similar structurally, intravenous
mannitol might be efficacious in treating early NSP (Mattei
1999).
Recent efforts have
been directed in experimental animals toward developing specific
monoclonal antibodies and antidotes against brevetoxin (Templeton
1989a, Templeton 1989b).
Furthermore, Templeton (1989a) and Poli (1990b) indicated
that in rats pretreated with an infusion of anti-brevetoxin IgG,
nearly all the neurologic symptoms were blocked. Additionally,
Purkerson-Parker et al. (2000) identified brevetoxin derivatives
that actually inhibit brevetoxin activity in electrophysiologic
experiments. Initial
data suggest that one of these derivatives, β-naphthoyl-PbTx-3 can
inhibit increases in pulmonary resistance in asthmatic sheep caused
by aerosols of K. brevis cultures as well as aerosols of pure
Pb-Tx-2 and PbTx-3.
In the case of
aerosolized red tide toxins respiratory irritation, the use of
particle filter masks may prevent or diminish the symptoms, and
retreating to air conditioned environment reportedly will provide
relief from the airborne irritation (Watanabe 1988, Woodcock 1948,
Music 1973, Backer submitted). Brevetoxin-induced
bronchospasm in asthmatic sheep and other animal models exposed to
aerosolized red tide toxins can be effectively blocked by the mast
cell stabilizing agent cromolyn and the histamine H1 antagonist
chlorpheniramine, as well as by the muscarinic blocker atropine, the
beta 2 agonists, the calcium channel blocker verapamil, and the
sodium channel blocker tetrodotoxin (Baden 1982a, Gallagher 1980,
Asai 1982, Trainer 1991, Singer 1998, Watanabe 1988). In the future, some of these
medications may be used to treat, and if used prophylactically, even
to prevent the bronchoconstrictive response. These medications may be
useful for people with asthma and for other susceptible persons
exposed to aerosolized red tide toxins.
In the laboratory,
C. virginica oysters accumulated K. brevis in less
than 4 hours in the presence of less than 5000 cells/ml of K.
brevis; the oysters will then naturally “detoxify” 60% of the
toxins in 36 hours when placed in K. brevis free water. There
is substantial variability between species of the potency of
depuration, even under laboratory conditions. Canning does not decrease
the brevetoxin concentration in bivalves. Commercial bivalves are
reportedly safe to eat 1 to 2 months after the termination of single
bloom episode (Baden 1983, Viviani 1992, Steidinger 1972). Successful ozone-assisted
depuration of red tide contaminated shellfish, both killing the
organism and inactivating the toxin, have been reported; depuration
with ultraviolet light and chlorination have proven unsuccessful
(Baden 1995, Blogoslawski 1975, Fletcher 1998, Roderick
1997).
Poli (1988)
reviewed laboratory procedures for the detoxification of equipment
and waste contaminated with brevetoxins PbTx-2 and PbTx-3. In particular, laboratory
equipment can be safely decontaminated using a dilute 0.1N NaOH
solution for at least 10 minutes, and disposable waste can be either
soaked in the NaOH solution before disposal or burned in an
incinerator with a combustion chamber of at least 500oC;
steam autoclaving is not a viable method of decontamination. Workers should be protected
from dermal, oral, and inhalation exposures to
brevetoxins.
Monitoring and
Surveillance
The most effective
way to prevent adverse health effects to humans from the red tides
is to prevent exposure to the toxins and organisms. In the case of NSP, this
means monitoring shellfish beds for organisms and toxins and closing
shellfish beds to harvest when specified levels are detected. For the aerosolized red tide
respiratory irritation, water and air monitoring could detect high
levels in the air, and warning notices can be posted along affected
coastal areas for susceptible subpopulations. Surveillance and reporting
of red tide disease in humans, other mammals, and animals are
important for early warning, prevention, and further understanding
of these diseases. In
addition, education and outreach programs to healthcare providers,
workers involved in the seafood and tourism industries, and the
general public are important components of successful monitoring and
surveillance programs (Fleming 1995).
Since the
mid-1970s, the Florida Department of Agriculture and Consumer
Services (DACS) has conducted a monitoring program of shellfish beds
in the Gulf of Mexico.
Beds are closed when the level of K. brevis exceed
5000 cells/liter near or in harvesting areas. The areas remain closed
until at least 2 weeks after a drop in cell counts below the action
level and mouse bioassay results in shellfish below 20 MU (mouse
units)/100g (Viviani
1984, Park 1995, Baden 1995).
No regulatory limit exists for brevetoxin in the seawater.
The regulatory limit for shellfish is 20 MU/100 grams of shellfish
meat, which is equivalent to 80µg brevetoxin /100 grams of shellfish
meat (Subcommittee 1970, Dickey 1999).
The standardized
mouse bioassay is used to test specimens for neurotoxicity. The bioassay is based on the
time until death of mice injected intraperitoneally with crude toxin
residues extracted from shellfish. Relative toxicity is
expressed in mouse units.
One mouse unit (MU) is the amount of crude toxin residue that
will on average kill 50% of test mice in 930 minutes. Although any detectable
level of toxin per 100 grams of shellfish tissue is considered
potentially unsafe for human consumption, in practice a residue
toxicity > 20 MU was adopted as the guidance level for the
prohibition of shellfish harvesting (Morris 1991, Dickey
1999).
These monitoring
programs should prevent ingestion NSP related to contaminated
shellfish consumption in most of the Florida human population but
not in areas where red tide is not an annual event or where
monitoring programs do not exist (e.g., North Carolina). Furthermore, such monitoring
programs do not prevent the respiratory irritation associated with
exposure to aerosolized red tide toxins, although they could serve
as early warning devices.
In Florida, where the red tides occur almost yearly, beaches
are not closed to recreational or occupational activities even
during active near-shore blooms.
Marine toxin
diseases such as NSP are believed to be significantly
underreported. This is
due to the public and medical misconception that all food poisoning
events result mainly from microbial contamination; furthermore, many
healthcare providers even in endemic areas do not realize that cases
of marine toxin disease are required to be reported to the public
health authorities.
Thus, in the case of ciguatera fish poisoning, the CDC has
estimated that only 2% to 10% of cases are actually reported in the
United States, even in endemic areas such as south Florida
(Sierra-Beltran 1998, Cortes Altamirano 1995, Fleming 1995, Fleming
2001, Ahmed 1993, McKee 2001).
In 1999, the Florida Department of Health added NSP to its
list of reportable diseases; however, aerosolized red tide toxins
respiratory irritation is not reportable.
The Florida Poison
Information Center at the University of Miami initiated a toll-free
24-hour/day Marine and Freshwater Toxin Hotline (1-888-232-8635) in
1997 to increase reporting of marine and freshwater related illness,
including the marine toxin associated diseases such as NSP and
aerosolized red tide toxin irritation. The Poison Information
Center passes on any cases of reportable illnesses by to the Florida
Department of Health for official reporting purposes. Efforts are
ongoing to increase knowledge and reporting of these illnesses by
healthcare providers and public health officials. These include a Video
Conference on the Human Health Effects of Marine Toxins in Florida
in June 1999, with a video and educational materials by the NIEHS
Marine and Freshwater Water Biomedical Sciences Center at the
University of Miami through funding from CDC, the Florida Department
of Health, and the Area Health Education Coalition (AHEC) (Fleming
1999b, Fleming 1998c).
Economic
Impact
The economic impact
of all the harmful algal blooms is difficult to quantify. This is due in part to their
unreported and unrecognized costs, including public health, seafood
industry and tourism (Anderson 2000, Martin 1976). In the case of K.
brevis, economic costs are associated with closure of shellfish
beds (as well as possible depressed commerce in shellfish, even
after the beds are re-opened, because of worried public perception),
the public health and medical costs of NSP and the aerosolized red
tide toxin respiratory irritation response, the impact on tourism
and related activities from the presence of active red tides in
recreational areas, the impact on marine mammals (including
endangered animals) and other animals, and the disposal of literally
millions of tons of dead fish on beaches and in canals and
rivers. For example, in
1971, St Petersburg, Florida, officials estimated that it cost
$155,763 to remove 2367 tons of fish from their beaches and canals
(Steidinger 1972). With
regards to potential fisheries impact, Sierra Beltran (1998)
reported that the shellfish beds are closed to harvest because of
active red tide contamination along the eastern coast of Mexico on
an average 60 days/year.
The 1987 closure of shellfish beds in North Carolina for an
entire season due to K. brevis cost an estimated $25 million,
without taking into account the NSP public health investigation and
other intangibles (Tester 1997).
Anderson et al.
(2000) estimated the annual economic impact for all the harmful
algal blooms (including K. brevis red tides) for the United
States. For 1987-1992
in 2000 dollars, the average 15 year capitalized impacts were
$449,291,987, with an annual average of $49 million/yr; of these
impacts, 45% were attributed to public health costs, 37% to
commercial fishery costs and losses, 13% to recreation and tourism,
and 4% to monitoring and management. The authors believe that
these estimates were highly conservative because of low monitoring,
reporting and data collection of harmful algal bloom events and
impacts.
Identified Research
Areas
Inexpensive,
reliable, and easily accessible testing for the brevetoxins in
multiple media (sea water, air, shellfish, and biologic fluids) are
essential for the understanding of the human health effects of
Florida red tide and its toxins. No established biomarkers of
exposure and effect for either of the Florida red tide
toxins-associated conditions in humans. Little information is
available on appropriate treatment and prevention methodologies
particularly of the respiratory irritation
illness.
The exact
composition, including droplet size, of the red tide brevetoxin
aerosol is unknown. It
is not known how far inshore this red tide toxins aerosol will
travel, especially given strong offshore winds during a red tide
bloom. Although water has been sampled for both the dinoflagellates
and the toxins for many years, red tide toxins air monitoring is not
widely conducted.
Expanded air monitoring could provide qualitative and
quantitative time- and geographic-based data.
Published
literature and formal epidemiologic studies are scarce on the human
health effects of the diseases, either ingestion NSP or inhalation
aerosolized red tide toxins respiratory irritation. Both NSP and aerosolized red
tide toxin respiratory irritation are likely to be under-reported
and under-diagnosed. No
population based statistics exist for the incidence of NSP or
aerosolized red tide toxins respiratory irritation, even in endemic
areas. Whether
inhalation of aerosolized brevetoxins can result in other systemic
health effects (such as neurologic or immunologic), and in chronic
effects is unknown. The
manatee evidence, as well as other laboratory animal studies,
suggests that this possibility should be explored further. These effects should be
considered particularly in possibly sensitive
subpopulations.
Finally, education
and outreach programs to healthcare providers, workers involved in
the seafood and tourism industries, and the general public are
important components of successful monitoring and surveillance
programs (Fleming 1995, Fleming 1998a, Fleming 1998b, Fleming 1999b,
Fleming 2000, Anderson 1993, Steidinger 1999, NRC 1999, Anderson
2000, Ahmed 1993, Pierce 1986, Kin Chung 1991, Smayda 1990, Martin
1998, ILO 1984).
AcknowledgementThe
authors thank the National Institute for Environmental Health
Sciences, grant P01 ES 10594, for funding this project.
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