Pathogenic Microorganisms in Fish: A Cause for Concern

Fishborne Zoonoses

The zoonotic infections in man reported from fish handling or eating are Mycobacterium infections, infections by Erysipelothrix spp. and various gut infections by Escherichia coli and Salmonella spp [2]. Campylobacter, Aeromonas, Vibrio, Edwardsiella, Escherichia, Salmonella and Klebsiella  are the pathogens which can be transmitted by contact with eroded skin or wounds or accidental ingestion of contaminated water, food, or other materials. Aeromonas  is commoner in fresh water and Vibrio is more likely to occur in salty water [2].

Bacterial Infections

Various bacterial infections can be acquired form eating fish, like: a) Gut infections: Vibrio and Aeromonas infections can be acquired by eating unclean or improperly cooked fish. Even Listeria gut infection has been reported form eating seafood. Vibrio vulinificus can cause gastrointestinal as well as soft tissue infection and even septicemia and can come from seafish [3]. The symptoms are similar to those of general food poisoning, like fever, vomiting, diarrhea, and abdominal pain. More serious symptoms are high fever, chills, low blood pressure, redness, swelling, and blisters on the skin [3]. Some severe cases of disseminated infections in Diabetic individuals with skin lesions have also needed amputations [4].

b) Skin infections: Mycobacterium marinum and Erysipelothrix spp. Can cause superficial infections and ulcers in man from handing raw or live fish [2]. Fish-handler’s disease occurs when cuts or scrapes in the skin get infected with the bacteria  Erysipelothrix rhusiopathiae and others. This is an erysipeloid infection, which means it is caused by an infection that resembles erysipelas but is caused by a different organism than that which causes erysipelas. Nodular lesions on fingers may also be seen [5].

According to our experience, we found Vibrio cholerae and Aeromonas species in freshwater fish in their scales. Thus this should be of utmost concern for people consuming fish and it should be cleaned and cooked thoroughly and properly before eating.

c) Fishborne botulism: Clostridium botulinum can also be found in fish, especially producing the tixins E, B and F, and are mostly found in fish intestine and gills [6]. Many outbreaks of Botulism have occurred from eating hot or a smoked fish. Eating it can cause Botulism if not cooked at very high temperatures. Thus one should be very careful while eating raw or semicooked fish.

Parasites in Fish

Nematodes like Anisakis spp., Gnathostoma spp. and Capillaria spp. are well transmitted from raw or improperly cooked fish to man. The practice of eating pickled or semi- raw fish preparations like Sushi and “Sashimi” has led to an increase in these infections across the globe [7]. Anisakis larvae cause damage to gastric mucosa. Japan sees roughly 3,000 cases of Anisakis infection annually, according to reports [4].

Cestodes like Diphyllobothrium latum infection has occurred in man after eating fish soaked or prepared in lime juice [8]. They can cause loose stools and lead later to Vitamin B12 deficiency and resultant Megaloblastic anaemia. Diphyllobothriasis in man causes minimal local pathology, but can cause reduced vitamin B12 absorption and changed gut mobility. The common symptoms include weakness, dizziness, salt craving, diarrhoea, and abdominal discomfort [9]. It is most prevalent in areas consuming partly cooked or raw or pickled fish, like Russia and other parts of Eastern Europe, North and South America and some Asian countries, like Japan [10].

Viruses

Viral infections like Noroviruses have been reported from eating shellfish [11]. Although shellfish are actually crustaceans, still it may be important from eating proper fish also. Noroviruses in lesser percentage has also been found in mussels and other varieties of seafood [12].

Fungal Infections from Fish

We have found Candida species in fish scales swab samples. They can cause yeast infections in skin and mucosa of the handler. There are reports of fungal infection of gut and colon by the fungus Monascus ruber in a patient with gastric Carcinoma [13]. The patient had consumed dried and salted fish which was the food responsible. Diagnosis of Fishborne Infections Diagnosis is both clinical and laboratory aided. Microscopy from swabs from the fish scales can be done in the form of screening for parasites. The patient’s clinical findings also help to a great extent in this case. The stool of the patient may be subjected to saline and Iodine mount to find out the eggs of the helminths and cestodes. Fish scales and meat can be subjected to culture on media like TCBS agar and Blood agar to detect the various bacterial pathogens. Viruses can be detected by more sophisticated methods like Tissue culture and other methods. We ourselves did culture on CLED agar and Sabouraud’s dextrose agar for finding out bacteria and fungi.

Treatment of Fishborne Infections

Bacterial infections may need antibiotics. Mycobacterium infections can be treated by antibiotics such as Rifampicin, streptomycin, sulfamethoxazole and trimethoprim, tetracyclines, and others. D. latum infection can be treated with drugs like Praziquantel. Disseminated or severe fungal infections need high-end drugs like Amphotericin B [13].