Pusulury S Babu(2000)
Zoonoses are diseases and infections that are naturally transmitted between vertebrate animals and man. These are of great public health importance in all developing countries including India. The subject of Zoonoses in taught in all veterinary and medical colleges, at under graduate and postgraduate levels, and is not included in the curriculum of fisheries sciences, inspite of several fish borne diseases communicable to man. There is need for creating awareness among the fisheries students, fish farmers and general public about the fish borne diseases communicable to man. In order to achieve this objective, a classification of Zoonoses is necessary. This can be done in many ways.
In addition the zoonoses can also be grouped as:
Utilization of natural water resources has increased considerably for the cultivation of aquatic livestock- particularly fish and shrimps. In addition several artificial ponds have been dug for the extensive and intensive fish farming in India. Under these changing situations fish borne zoonoses - Ithyozoonoses are likely to emerge as problems both for the producer and consumer. The fish farmer looses money by way of rejection of the produce resulting in economic loss. The consumer suffers from ill health due to the consumption of food containing zoonotic agents. Therefore there is an urgent need for familiarizing, the concerned persons about the Icthyo zoonoses. In order to create the awareness among the fish producers and scientists concerned with aquatic livestock this review is undertaken; incorporating the well-known Icthyozoonoses as well as the unfamiliar and recently recognized fish borne maladies.
Top ten aquaculture-producing countries are shown here under
China 56.30%, India 8.50%, Japan 4.10%, Indonesia 3.5%, Thailand 2.8%, USA 2.1%, Philippines 2.0%, Korea (ROK)1.8%, France 1.5%, Bangladesh 1.4%
- MN Kuttey,  Science Express, 8th September, 1988
India has 2.25 million hectors of ponds and tanks, 1.30 million hectors of lakes, 2.09 million hectares of reservoirs and 1.23 million hectors of brackish water areas. India has 9 major riverine systems besides several small sources of water with huge net work of canals besides several hundred reservoirs built for preserving the water resources. All the aquatic natural resources can be harnessed for increasing the production of fish and other edible livestock, in order to meet the protein requirement of the country. Besides India 8047 kilometers of coastline extensively used for harvesting marine livestock intended for human consumption.
In view of the ecological conditions prevailing not only in India but also in the above mentioned countries the prevalence of Ichthyo-zoonosis is expected to be in greater dimension than realized.
Several parasites found in fish can infect humans as nontraditional hosts. The mode of entry into humans is by ingestion of raw or undercooked infected fish. Proper cooking or freezing prevents transmission of ingested human pathogenic parasites. Some parasites are found only in tropical regions. The prevalence and importance of parasitic infections vary markedly depend on local risk factors and conditions.
Diphyllobothrium latum: lives in the small intestine of man and produces gastro-intestinal disturbances and anemia. The eggs are operculated and are liberated through feces in water. The eggs develop into a coracidium and are ingested by cyclops. In the intestine of the Cyclops the coracidium develops into a procercoid. Fresh water fish ingests the cyclops possessing procercoid. The procercoid changes into pleurocercoid. This is also called as sparganum. Man gets infection by ingestion of insufficiently cooked fish containing pleurocercoid. Thus the life cycle is completed. Salting, pickling or smoking does not destroy pleurocercoid and therefore remain infective to man. Laboratory diagnosis consists of microscopic examination of the patient's stool to demonstrate characteristic operculted eggs. Fish should not be consumed with out through cooking.
One of the most important nematode diseases of humans acquired from fish is anisakiasis or anisakidosis. Anisakis simplex is the most frequently associated Contracaecum osculatum species. Followed by Pseudoteranova dicipens has rarely been reported. This disease is caused by the larval stages of worms. These worms are natural parasites of whales, dolphins, porpoises, seals, sea lions, herring, cod, mackerel, salmon, squid, halibut, flatfish, etc. Major source of infection is traditional preparations such as raw herring, lomi lomi salmon, ceviche, sushi and sashimi. In man symptoms include abdominal pain, fever, nausea, vomiting, etc. Clinical diagnosis is based on the history of consumption of raw semi raw smoked inadequately cooked fish eisonophilia and leucocytosis are also seen on blood examination. Larvae can be demonstrated in the affected tissues. Serological tests may be of some value in the diagnosis. Endoscopic removal of the larvae from the stomach of the patients with four to six hours of ingestion may give relief. Surgical resection of the damaged wall can be resorted to. Control consists of evisceration of fish immediately after catch freezing the fish at -20 degrees Celsius. Avoiding consumption raw under cooked smoked or mildly salted fish will go a long way in the prevention of anisakiasis.
Dioctophyma renalae is a very large nematode producing renal colic hematuria, pyuria, and retention of urine due to the presence of parasite in the urinary system. Infection occurs by consumption of raw uncooked fresh water fish crayfish or crustacean containing infective larvae of the nematode. Microscopic examination of the urine for the presence of eggs of D renalae confirms the clinical diagnosis. Surgical removal of the affected kidney is the only treatment. If both kidneys are infected the prognosis is grave.
Besides health education of fish eating people thorough cooking of the fish should be ensured.
Thirty-three species of digenetic trematodes have been listed as transmissible to man through consumption of fish, crustacea or molluscs. Among these members of Heterophydiae family are significant. There are very small trematodes that inhabit the intestine of birds and mammals. The infective stage (metacercaria) can be found in a wide variety of fish. These parasites acquired by eating raw marinated or improperly cooked fish are frequently reported from human infections. Accumulation of large numbers of these parasites in the small intestine may cause inflammation, ulceration and necrosis. These trematodes are represented by the following species Heterophyes heterophyes, Paragonimus werstermonia, Metagonimus yokogawai, Clonorchis sinensis, Opisthorchis sps.,etc. The pathology caused by these parasites is similar and the risk cholangio- carcinoma (gall bladder cancer) may be high in chronic cases.
Nanophyetes salmoncola is a trematode parasite in the intestine of dogs and many wide piscivorous mammals. The disease however does not arise directly from the trematode but instead is due to a rickettsial hyperparasite "Neorickettsia helmonthoeca" which is pathogenic for dogs. Humans infected with this fluke do not develop salmon poisoning. The presence of large number of parasites can cause gastroenteritis popularly called as salmon poisoning.
Acanthocephalans or spiny-headed worms have been reported from humans. The adults of Chorinosoma stromosum are found in the stomach of pinnepids (sealions). The tiny crustacean intermediate hosts and fish, which eat the fish, are sources of infections.
Salmonellosis is a disease caused by any of the 2000 serotypes present in the man, animals, birds and fishes. The symptoms may be septicemia as in typhoid or bowel disturbances as in the case of infection due to Salmonella species. Sudden on set of abdominal pain, diarrhea, nausea, vomiting, fever, anorexia may be conspicuous. The disease is normally diagnosed in man and animals by bacterial examination of the blood, stool, urine etc. Fish grown in dirty waters may be a source of infection. Quinolins and other antibiotics along with supportive treatment are necessary to treat the affected patient. Hygienic production of fish in the processing plants is necessary to prevent human epidemics.
Erysipelothrix insidiosa (rheusiopathiae)is a slender rod shaped, non sporing, non motile, pleomorphic gram positive bacteria. Infection with this bacteria causes, itching, tingling and burning sensation at the site of inoculation /penetration of the organism in the thumb, forefinger and wrist. Erythyma, edema, artharlgia, lymphangitis, septicemia, endocarditis, anemia, and meningitis may be seen. This is an occupational hazard of the fishermen, anglers and workers in the fish processing plants. This bacterium is also amenable to antibiotic treatment if initiated early. Isolating the organism from the wound or other appropriate specimen makes diagnosis.
Listeria monocytogenes is a non capsulated, non sporing, pleomorphic, gram positive, rod shaped bacteria may also live a saprophyte in soil also and also infects wide range of animals and fishes and produces diseases in man. After an incubation period of 4 to 21 days the infected persons exhibits symptoms. It occurs in different forms. Septicemia, abortion, meningitis, glandular granulomatosis, conjunctivitis, papuler exanthema, pneumonia, urethritis endocarditis, hydrocephalus the usual manifestations. Tetracyclins, Ampicillins are the drugs of choice for the treatment of the affected patient.
Francisella tularensis is a small gram-negative non-sporulating, non-capsulated non-motile aerobic, rod shaped organism producing chills and fever with sudden onset. Erythymatous papulae, pustule, ulcer, regional lymphangitis, malaise, anorexia, head ache, nausea, gastro enteritis and broncho-pneumonia re also common. Laboratory diagnosis is based isolation and identification of the organism. Skin test gives positive result during the first week of the disease. Immunization of the high-risk groups and providing protective wears to the occupationally exposed persons constitute the control measures.
This bacterium is gram negative, curve shaped, halophilic in nature. On ingestion of the organism through insufficiently cooked for or by cross contamination in the kitchen man gets the infection. After an incubation period of 4 to 30 hours, acute gastroenteritis with diarrhea and vomiting, fever, headache, hypotension and cyanosis supervene. Laboratory diagnosis consists of isolation of the bacteria from the stool sample on thiosulphate citrate bile salt agar (TCBS) at 37 degrees Celsius. Eliciting the history of having eaten food of aquatic origin given indication of Vibrionic infection. Kanagawa test is helpful in the identification of the isolated from the patient's stool sample or food. Educating the fish eating community about the hazards of eating under cooked fish, besides kitchen hygiene are the two important ways of preventing the disease.
Vibrio cholerae and V.vulnificus are the dominant and emerging pathogenic sps. Among this genus V.cholerae in aquatic environment which are of concern with regard to human infections the primary vector for seafood borne illness is consumption of raw oysters. In several cases cooked crab has also been implicated.
Non cholera Vibrio sps. account for more cases of shell fish related disease than any other known agent. These are more halophilic and the consumption of seafood rather than contaminated water is the main source of infection.
In general healthy individuals are not infected by Vibrio vulnificus. Pre-existing liver disease, alcoholism, and other immuno-compromised states makes an individual very susceptible to V.vulnificus infection. Wound infections due to this bacterium are common due to recreational exposure.
Epidemiological and laboratory findings in certain countries have demonstrated the transmission of cholera by the fishery products. There appear to be a need for conducting more accurate evaluation of the risks of transmission of cholera through seafood. Considering the risk involved appropriate control measures should be undertaken.
Clostridium botulinum elaborates potent toxins in the proteinous food prepared unhygenically at home or factory and preserved improperly under anaerobic conditions. It is a gram positive sporebearing anaerobe usually contaminating the prepared foods. Several types of toxins are produced including powerful neurotoxins. Hygienic handing of the fish products and sanitary disposal of the wastes are the essential requisites in avoiding Botulinum toxicosis.
There are other bacteria pathogenic to fish, which cause infections in human, But the incidence is very low and symptoms are either localized wound infections or gastroenteritis. Such bacteria include Aeromonas hydrophila, Edwardsiella tarda etc., Plesiomonas shigelloides can be found in cultured fish and can cause food poisoning in humans when uncooked fish or shellfish are consumed. The majority patients may have some pre-existing health problems.
Toxic Food poisoning epidemics due to Staphylococcus aureus, Bacillus cereus, Clostridium perfringens are attributed to aquatic livestock. Home canned fish and other seafood preparations are potential sources of food poisoning. Infection type of food poisoning with salmonella sps. and Campylobacter sps. can also take place following contamination of prepared foods.
Shellfish including oysters, mussels and clams are filter feeding molluscs which can bio-accumulate human pathogens at levels higher than those in surrounding waters. Shellfish borne enteric viral illnesses have resulted in human disease outbreaks worldwide. The consumption of contaminated shellfish has resulted in illness due to hepatitis A and Norwalk-like viruses.
Entero-viruses in polluted waters have been studied since long time for their ability to survive in water sediment and shellfish. These have been isolated from Marine waters and shellfish. Bio-concentration and accumulation in shellfish may increase the concentration of viruses ten to hundred fold compared to the water column. Entero-viruses may remain infections for 9 days in marine waters and 19 days in sediment and up to 30 days in shellfish. These viruses may cause a wide range disease in different individuals ranging from aseptic meningitis, respiratory illness, myocarditis, fever, diarrhea, rash, nephritis, etc.
Small round viruses (SRVs) e.g.: Norwalk virus, Snow mountain agent, astroviruses, calciviruses and other SRVs have been implicated in adult gastroenteritis incidental to shellfish association. These viruses are heat stable and are resistant to chlorine.
Rotavirus and Adenovirus have not been documented as shellfish associated disease. This may be due to low survival in marine environment or due to improper diagnosis.
The public impact of these viruses is probably not fully appreciated.
TOXINS IN FISH AND SHELLFISH
Scombroid (Histamine) Poisioning
A laboratory in Canada first confirmed histamine poisoning in 75. Most in subsequently mahi-mahi or dolphin [Coryphaena hippurus] and marlin [Makaira spp.] are also implicated. Histamine levels of between 28 mg and 710 mg / 100 g were demonstrated. Symptoms of Scombroid poisoning are gastro-intestinal and neurological in nature. Histamine production is maximum at or near 30 degrees Celsius. Cooking has no impact on the toxin.
Ciguatera is a clinical syndrome characterized by the gastro-intestinal and neurological disorders. Ciguatera usually results from consumption of tropical reef fish or higher carnivores. Several benthic dinoflagellates are associated with a range of ciguatoxins. The epiphytic Gambierdiscus toxicus may be the main source of toxins other dinoflagellates thought to be responsible for ciguatera include Amphidinum carteri, A klebsi, Coolia monotis, Ostropcis ovata, O.siamensis, Prorocentrum concavum, P lima and P rhathymum. The principle toxins produced are ciguatoxin, scaritoxin, maiotoxin and palitoxin. Ciguatera related toxins are bio-accumulated. Higher carnivores consume herbivorous fish that feed on toxin benthic algae. The level of toxins in fish increases further up in the food chain. It is believed that disturbances to reeves during hurricanes and human recreations will result in the development of endemic (niche) for toxic algae.
Paralytic shellfish poisoning
Paralytic shellfish poisoning (PSP) is a serious illness which leads to neurological symptoms including paralysis terminating some times in fatality.
Dinoflagellates produce 20 derivatives of saxitoxin and accumulated in shellfish especially mussels, cockles, clams, and scallops. Saxitoxins are potent algal toxins. Alexandrium tamarensis and A.catinela have been implicated in PSP. The Cynobacterium Anabaena circinalis isloated from freshwater mussels produces 2 type to Saxitoxins, C-toxins, and gonyautoxins. Generally PSP is heat stable and outbreaks have occurred from consumption of cooked shellfish.
Puffer fish poisoning
Pufferfish poisoning (PFP) results in similar symptoms like PSP. Illness results from consumption of fish from Tetradontidae family including Pufferfish. The source is not considered to be diatoms or dinoflagellates. Bacteria implicated thus far include Listonella pelagia, Alteromonas sps. and Shewanella sps.
Neurotoxic shellfish poisoning
Neurotoxic shellfish poisoning (NSP) causes symptoms of numbness, gastro-intestinal disturbances, and muscular aches in man. NSP is caused by a concentration of a red tide dinoflagellate Gymnodium breve and its toxin (Brevitoxin) in shellfish.
Diarrhetic shellfish poisoning
Diarrhetic shellfish poisoning (DSP) causes gastrointestinal disturbances with abdominal cramps. DSP is the result of vocadic acid production by dinoflagellates concentrated in mussel, oyster, and scallop tissues. The algal sps associated are Dinophysis fortii and D accuminita, Prorocentrum sps is another potential DSP dinoflagellate.
Amnestic shellfish poisoning
Amnestic shellfish poisoning (ASP) results in gastro-intestinal and neurological symptoms, particularly memory loss. Symptoms often occur in elderly and resemble Alzheimer's disease. Nitzshia pungens was identified as producer of domoic acid that is responsible for an outbreak of ASP. Pseudonitzchia sps. also produce domoic acid.
Tetramine poisoning caused blurred vision, light-headedness, staggering, flushing, and weakness. Tetramine in 1.3 mg/g of whelk soft tissue Neptunea decemcostata whelks are large and are usually collecting during scallop -trawling. N.despecta tornata, Buccianium sps, Fusitriton sps are known to have caused severe headaches dizziness and abdominal cramps as a result of the presence of Tetramine (tetramethyl ammonium ion). In the salivary glands and a lesser concentration in other organs.
Boiling whelks for 1 hour will not destroy but removal of salivary glands is supposed to render the whelks edible.
Undetermined seafood toxin illness
Several illnesses have also been documented from other undetermined seafood toxins. Normally the symptoms are mild gastro-enteritis and sometimes burning peppery sensation in the mouth. Certain amines or other spoilage compounds are thought to be responsible for the fish-poisoning episodes. PREVENTION AND CONTROL Susceptible populations are those with underlying disease, diabetics, with impaired liver function, convalescents, cancer patients, HIV sero reactors. Indicator bacteria are inadequate to predict the prevalence of these infections and illnesses in the environment. Small round viruses [SRVS] are an emerging concern. Attention is now devoted to aquaculture product safety through Government programs, industry initiatives and new international standards such as "code of hygienic practice for the products of aquaculture". Hazard analyses and critical control point [HACCP] and good management practices [GMP] are very important. Aquatic foods are not only perishable but also act as ideal substrates for pathogens. Production and processing profiles have to be very strictly followed. Greater awareness among the public health personal about these rare diseases, by conducting periodical seminars, training programs and other communication methods. Creation of laboratory facilities for the rapid identification of these illnesses. Development of machinery for the monitoring, investigation and control of the episodes. Educating the population at risk, about the prevalence of these maladies in the area will go a long way in preventing the Ithyo-zoonoses.
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