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What are marine toxins?
What sort of diseases do marine toxins cause?
How can these
diseases be diagnosed?
How can these diseases be treated?
Are there long-term consequences to these
diseases?
How common are these diseases?
What can I do to prevent poisoning by marine
toxins?
What is the government doing about these diseases?
What else can be done to prevent these diseases?
How can I learn more about this and other
public health problems?
What
are marine toxins?
Marine toxins are naturally occurring chemicals that can contaminate
certain seafood. The seafood contaminated with these chemicals
frequently looks, smells, and tastes normal. When humans eat such
seafood, disease can result.
What sort of
diseases do marine toxins cause?
The most common diseases caused by marine toxins in United States
in order of incidence are scombrotoxic fish poisoning, ciguatera
poisoning, paralytic shellfish poisoning, neurotoxic shellfish
poisoning and amnesic shellfish poisoning.
Scombrotoxic fish poisoning also known as scombroid
or histamine fish poisoning, is caused by bacterial spoilage of
certain finfish such as tuna, mackerel, bonito, and, rarely, other
fish. As bacteria break down fish proteins, byproducts such as
histamine and other substances that block histamine breakdown
build up in fish. Eating spoiled fish that have high levels of
these histamines can cause in human disease. Symptoms begin within
2 minutes to 2 hours after eating the fish. The most common symptoms
are rash, diarrhea, flushing, sweating, headache, and vomiting.
Burning or swelling of the mouth, abdominal pain, or a metallic
taste may also occur. The majority of patients have mild symptoms
that resolve within a few hours. Treatment is generally unnecessary,
but antihistamines or epinephrine may be needed in certain instances.
Symptoms may be more severe in patients taking certain medications
that slow the breakdown of histamine by their liver, such as isoniazide
and doxycycline.
Ciguatera poisoning or ciguatera is caused by eating
contaminated tropical reef fish. Ciguatoxins that cause ciguatera
poisoning are actually produced by microscopic sea plants called
dinoflagellates. These toxins become progressively concentrated
as they move up the food chain from small fish to large fish that
eat them, and reach particularly high concentrations in large
predatory tropical reef fish. Barracuda are commonly associated
with ciguatoxin poisoning, but eating grouper, sea bass, snapper,
mullet, and a number of other fish that live in oceans between
latitude 35° N and 35° S has caused the disease. These
fish are typically caught by sport fishermen on reefs in Hawaii,
Guam and other South Pacific islands, the Virgin Islands, and
Puerto Rico. Ciguatoxin usually causes symptoms within a few minutes
to 30 hours after eating contaminated fish, and occasionally it
may take up to 6 hours. Common nonspecific symptoms include nausea,
vomiting, diarrhea, cramps, excessive sweating, headache, and
muscle aches. The sensation of burning or "pins-and-needles,"
weakness, itching, and dizziness can occur. Patients may experience
reversal of temperature sensation in their mouth (hot surfaces
feeling cold and cold, hot), unusual taste sensations, nightmares,
or hallucinations. Ciguatera poisoning is rarely fatal. Symptoms
usually clear in 1 to 4 weeks.
Paralytic shellfish poisoning is caused by a different
dinoflagellate with a different toxin, than that causing ciguatera
poisoning. These dinoflagellates have a red-brown color, and can
grow to such numbers that they cause red streaks to appear in
the ocean called "red tides." This toxin is known to
concentrate within certain shellfish that typically live in the
colder coastal waters of the Pacific states and New England, though
the syndrome has been reported in Central America. Shellfish that
have caused this disease include mussels, cockles, clams, scallops,
oysters, crabs, and lobsters. Symptoms begin anywhere from 15
minutes to 10 hours after eating the contaminated shellfish, although
usually within 2 hours. Symptoms are generally mild, and begin
with numbness or tingling of the face, arms, and legs. This is
followed by headache, dizziness, nausea, and muscular incoordination.
Patients sometimes describe a floating sensation. In cases of
severe poisoning, muscle paralysis and respiratory failure occur,
and in these cases death may occur in 2 to 25 hours.
Neurotoxic shellfish poisoning is caused by a third
type of dinoflagellate with another toxin that occasionally accumulates
in oysters, clams, and mussels from the Gulf of Mexico and the
Atlantic coast of the southern states. Symptoms begin 1 to 3 hours
after eating the contaminated shellfish and include numbness,
tingling in the mouth, arms and legs, incoordination, and gastrointestinal
upset. As in ciguatera poisoning, some patients report temperature
reversal. Death is rare. Recovery normally occurs in 2 to 3 days.
Amnesic shellfish poisoning is a rare syndrome
caused by a toxin made by a microscopic, red-brown, salt-water
plant, or diatom called Nitzchia pungens. The toxin produced
by these diatoms is concentrated in shellfish such as mussels
and causes disease when the contaminated shellfish are eaten.
Patients first experience gastrointestinal distress within 24
hours after eating the contaminated shellfish. Other reported
symptoms have included dizziness, headache, disorientation, and
permanent short-term memory loss. In severe poisoning, seizures,
focal weakness or paralysis, and death may occur.
How can these
diseases be diagnosed?
Diagnosis of marine toxin poisoning is generally based on symptoms
and a history of recently eating a particular kind of seafood.
Laboratory testing for the specific toxin in patient samples is
generally not necessary because this requires special techniques
and equipment available in only specialized laboratories. If suspect,
leftover fish or shellfish are available, they can be tested for
the presence of the toxin more easily. Identification of the specific
toxin is not usually necessary for treating patients because there
is no specific treatment.
How can these
diseases be treated?
Other than supportive care there are few specific treatments
for ciguatera poisoning, paralytic shellfish poisoning, neurotoxic
shellfish poisoning, or amnesic shellfish poisoning. Antihistamines
and epinephrine, however, may sometimes be useful in treating
the symptoms of scombrotoxic fish poisoning. Intravenous mannitol
has been suggested for the treatment of severe ciguatera poisoning.
Are there long-term
consequences to these diseases?
Ciguatera poisoning has resulted in some neurologic problems
persisting for weeks, and in rare cases, even years. Symptoms
have sometimes returned after eating contaminated fish a second
time. Amnesic shellfish poisoning has resulted in long-term problems
with short-term memory. Long-term consequences have not been associated
with paralytic shellfish poisoning, neurotoxic shellfish poisoning,
and scombrotoxic fish poisoning.
How common are
these diseases?
Every year, approximately 30 cases of poisoning by marine toxins
are reported in the United States. Because healthcare providers
are not required to report these illnesses and because many milder
cases are not diagnosed or reported, the actual number of poisonings
may be much greater. Toxic seafood poisonings are more common
in the summer than winter because dinoflagelates grow well in
warmer seasons. It is estimated from cases with available data
that one person dies every 4 years from toxic seafood poisonings.
What can I do
to prevent poisoning by marine toxins?
General guidelines for safe seafood consumption:
- Although any person eating fish or shellfish containing toxin
or disease-causing bacteria may become ill, persons with weakened
immune systems or liver problems should not eat raw seafood
because of their higher risk of Vibrio infection (see
Vibrio FAQ- http://www.cdc.gov/ncidod/dbmd/diseaseinfo/vibriovulnificus_g.htm).
- Keep seafood on ice or refrigerated at less than 38° Fahrenheit
to prevent spoilage.
Specific advise for avoiding marine toxin poisoning:
- Keep fresh tuna, mackerel, grouper, and mahi mahi refrigerated
to prevent development of histamine. Don't believe that cooking
spoiled or toxic seafood will keep you safe. These toxins are
not destroyed by cooking.
- Do not eat barracuda, especially, those from the Caribbean.
- Check with local health officials before collecting shellfish,
and look for Health Department advisories about algal blooms,
dinoflagellate growth or "redtide" conditions that
may be posted at fishing supply stores.
- Do not eat finfish or shellfish sold as bait. Bait products
do not need to meet the same food safety regulations as seafood
for human consumption.
What is the government
doing about these diseases?
Some health departments test shellfish harvested within their
jurisdiction to monitor the level of dinoflagellate toxins and
asses the risk for contamination. Based on the results of such
testing, recreational and commercial seafood harvesting may be
prohibited locally during periods of risk. State and federal regulatory
agencies monitor reported cases of marine toxin poisoning, and
health departments investigate possible outbreaks and devise control
measures. The Centers for Disease Control and Prevention (CDC)
provides support to investigators as needed.
What else can
be done to prevent these diseases?
It is important to notify public health departments about even
one person with marine toxin poisoning. Public health departments
can then investigate to determine if a restaurant, oyster bed,
or fishing area has a problem. This prevents other illnesses.
In any food poisoning occurrence, consumers should note foods
eaten and freeze any uneaten portions in case they need to be
tested. A commercial test has been developed in Hawaii to allow
persons to test sport caught fish for ciguatoxins.
How can I learn
more about this and other public health problems?
You can discuss any medical concerns you may have with your doctor
or other healthcare provider. Your local city, county, or state
health department can provide more information about this and
other public health problems that are occurring in your area.
General information about the public health of the nation is published
every week in the Morbidity and Mortality Weekly Report, by CDC
in Atlanta, GA (http://www.cdc.gov/mmwr/). Epidemiologists in
your local and state health departments are tracking a number
of important public health problems, investigating special problems
that arise, and helping to prevent them from occurring in the
first place, and from spreading if they do occur.
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