FOOD BORNE PARASITIC ZOONOSES
Food-borne zoonotic diseases (FBZD) pose a constant threat to public health, socioeconomic development and international trade. More than 200 known diseases are transmitted to human beings through food contaminated by pathogenic microbes such as bacteria and their toxins, viruses and parasites. The World Health Organization (WHO) in its initiative to estimate the global burden of food-borne zoonotic diseases reported illness caused by 31 food-borne zoonotic hazards, and estimated over 600 million illnesses and 4,20,000 deaths due to FBZD in 2010 (WHO, 2015). The disease burden was the highest in Africa (43%), followed by SouthEast Asia (24%) and Eastern Mediterranean (16%) sub regions. Around 40% of the FBZDs were reported from children under 5 years of age. The highest rates of under-5 mortality due to diarrhea were in sub-Saharan Africa and South Asia with India accounting for 1,05,000 deaths in the year 2015 (Troeger et al., 2017). Food-borne zoonotic diseases cost India about US$ 28 billion (Rs. 1,78,100 crore) or around 0.5% of the gross domestic product (GDP) every year (Kristkova et al., 2017). It is estimated that the current FBZD burden in India represents about 100 million cases per year. This corresponds to one in 12 people falling ill, which could be an underestimate as not all the cases are reported or recorded, and detailed information on the economic costs of food-borne diseases are largely missing. The risk of food-borne zoonotic illness has been rising due to several factors including pathogen behavior, rapid population growth and an increased global trade in foods and farm animals from the countries where appropriate microbiological safety procedures are not being followed or implemented. The improved transport logistics and conditions facilitate some microorganisms to survive on food products for longer periods and reach consumers in a viable form. The change in eating habits of consumers, for example, the consumption of lightly cooked food and a shift from low-to-high protein-based diets (like meat and fish products) has also increased the probability of occurrence of food-borne zoonotic illnesses. Further, the increased movement of human population facilitates easy spread of pathogens. These factors have escalated the severity of food-borne diseases and their impacts on health of the communities. Therefore, preventing illness and deaths due to food-borne zoonotic diseases remains a major public health challenge. Lack of accurate epidemiological data on the incidence and cost of foodborne diseases, particularly in the developing countries, has resulted in sketchy policies and resource allocations for mitigation of food-borne diseases. Further, the increasing antimicrobial resistance in bacterial pathogens all along the food chain has also impacted the public health. Considering the severity of the problem, a brain storming session on Food-borne Zoonotic Diseases was organized by the National Academy of Agricultural Sciences on November 21, 2019, to discuss strategic interventions to prevent FBZDs, and suggest a way forward to enable the governments to allocate resources and take appropriate measures for their prevention and control.
Food borne parasitic zoonoses (FPZ) are human infections transmitted through ingested food and caused by parasites whose natural reservoir is a vertebrate animal species. These diseases not only effect the health of humans and animals but also cause huge economic loss to food industry especially meat industry, because of condemnation of infected meet. Various factors such as food habits, socio economic status, lifestyle, lack of hygiene, poverty, occupation etc. affect the occurrence of these diseases in an area. In some parasitic diseases such as cysticercosis and sarcocystosis, cysts can be seen with naked eyes in meat, while in other cases cysts/parasitic stages are not visible. Further, FPZ can be classified under three categories;
- Meat borne parasitic zoonoses
- Fish borne parasitic zoonoses
- Vegetable and water borne parasitic zoonoses
- Meat borne parasitic zoonoses:
Common meat borne zoonotic parasites include Sarcocystis sp., Toxoplasma gondii, Taenia saginata, T. solium and Trichinella sp. These parasites can be transmitted to humans by consumption of raw contaminated pork and beef, however, parasitic species associated with pigs are more important than that of bovines. Sarcocystis spp. and T. gondii, are coccidian protozoans which have a global distribution.
Sarcocystosis:
The life-cycle is heterixenous with herbivores (domestic and wild) primarily acting as intermediate hosts and carnivores (domestic and wild), including humans, act as definitive hosts. Oocysts are passed in the faeces of definitive hosts. Intermediate hosts acquire infection by ingesting infective oocysts. Numerous species of Sarcocystis infect cattle, sheep, pigs, horses, camels, buffalo and wild game animals. Heavy infections in these intermediate hosts may cause abortion, anorexia, fever, anaemia and reduced live weight gain. Two species are recognised as zoonotic, namely: Sarcocystis hominis and Sarcocystis suihominis, although zoitocysts of unknown origin have also been found in humans. S. suihominis ( pigs as intermediate host ) is more prevalent in India than S. hominis(cattle as intermediate host). Humans acquire infection by consumption of uncooked beef/pork containing zoitocysts. S. hominis is only mildly pathogenic in humans, causing stomach pains, nausea and diarrhea. S. suihominis is more pathogenic than S. hominis, causing stomach pains, nausea, diarrhoea and dyspnoea within 24 hours of infection. No effective treatment is available for either intermediate or definitive hosts. Control is possible by avoiding eating undercooked meat.
Toxoplasmosis:
Toxoplasmosis is an important protozoan parasitic disease of all warm blooded mammals including humans. Oocysts are passed in the faeces of definitive host (cat). Cattle, buffaloes, sheep, goat, pigs and humans act as intermediate hosts in which consumption of oocysts leads to development of tachyzoite (fast multiplying cyst) in blood and ultimately bradyzoite i.e tissue cyst in various organs like heart, liver etc. Human also get infection by consumption of infected meat containing tissue cyst. Toxoplasmosis is a threat to immunocompromised individuals and pregnant females. In normally healthy individuals, fever, lymphadenopathy, muscle aches, and headache can be observed. Encephalitis is an important and severe manifestation of toxoplasmosis in immunosuppressed persons including AIDS patients. In pregnant woman, it causes abortion and congenital abnormalities in new born child. Congenitally infected children may suffer from impaired vision and mental retardation. Severely infected children show classic tetrad of signs i.e. retinochoroiditis, hydrocephalus, convulsions, and intracerebral calcifications.
Taeniasis:
Cysticercosis/ Taeniasis is an important cestode parasitic disease of zoonotic importance. This is a case of obligatory cyclozoonoses i.e. here man involvement is compulsory for the completion of life cycle of parasite. Man act as definitive host In case of T. saginata where as in case of T. solium man act as definitive as well as intermediate host. Man passes the eggs in the faeces, which are consumed by the cattle/ pig and causes cyst formation in the muscles of these animals. Again when this cyst containing beef and pork is eaten by human, life cycle is completed on passage of eggs in the faeces. Symptoms of taeniasis is mild in humans. But the major zoonotic importance is cysticercosis, which is caused by larva ( cysticercosis cellulosae) of T. solium resulting in nervous problems like seizures, epilepsy in humans. It occurs in man because of consumption of T. solium eggs in contaminated food and water and due to auto infection. Auto infection occurs because of poor hygienic practices of a person.
Trichinellosis:
Trichinellosis is an important nematodal parasitic disease which occurs because of ingestion of pork containing coiled larvae of Trichinella spiralis. People acquire infection after eating infected pork. Common clinical findings in humans include diarrhea, abdominal pain, swelling of eyelids or face, nausea and vomiting, muscle pain and tenderness.
1.Fish / crustacean borne parasitic zoonoses:
Fish is an important protein source and is consumed by majority of human population. But fish harbours many parasites which are of zoonotic importance. Along with fish, crabs and lobsters are also eaten which can also transmit zoonotic parasites to people. Contamination of the snail infested waters by egg laiden faeces from humans and use of human faeces, “night soil” as fertilizers helps in transmission of these fish borne parasitic diseases. Common fish/crustacean borne parasitic diseases of zoontic importance include; gnathostomiasis, clonorchiasis, opisthorchiasis, paragonimiasis, diphyllobothriasis, hetrophyiasis and anisikiasis etc. Eating of raw fish, salted, under cooked, lightly fermented fish, crabs and sea food containing encysted larvae of the parasites result in transmission of disease to human population.
Gnathostomiasis:
Gnatostoma spinigerum is widely distributed in Asia and has been considered to be the only species with human pathogenicity. Various fishes like cat fish, snake head fish etc harbour the parasites. Malaise, fever, urticaria, and nausea occurs after ingestion of larvae containing fish. Visceral larva migrans can occur in any part of the body. Migration of larva along the spinal cord into the brain cause paralysis, seizures & coma along with bloody CSF. It can also produce creeping eruptions known as cutaneous larva migrans by migration in skin & S/C tissue.
Diphyllobothriasis:
Diphyllobothriasis is an important fish borne disease caused by by the fish tapeworm Diphyllobothrium latum. and D. pacificum. Infective larvae (plerocercoid) of D. latum resides in the muscles of trout, salmon, pike, and sea bass. Eating of these raw fishes cause the disease. This parasitic infection leads to deficiency of Vit B-12 in the host & hence causes pernicious anaemia because of the competition of adult worm with the host for Vit B-12.
Paragonimiasis:
Paragonimiasis is caused by eating crabs and cray fish infected with Paragonimus lung flukes. P. westermani is the most common species in Asia and is the major source of human infection. Infective larvae metacercariae encysted in freshwater crabs and upon ingestion of larvae containing crabs, larvae penetrate the peritoneal cavity & migrate across the diaphragm into the pleural cavity. Abdominal symptoms are seen during the migratory phase and the parasites finally migrate into the lung parenchyma, where they mature and form solid worm cysts. Fever, chest pain, and chronic cough with hemoptysis (rusty-colored sputum) are the main clinical manifestations of this parasite.
Clonorchiasis and opisthorchiosis:
Clonorchiasis (caused by Clonorchis sinensis) and opisthorchiasis (caused by Opisthorchis sp.) is caused by consumption of raw or undercooked cyprinid fish containing the encysted metacercariae. The parasite develop & live in the bile duct for many year. Clinical manifestations are rare, but infection increases the risk of cholangiocarcinoma. Liver cirrhosis, Blocking & thickening of bile duct, Periportal fibrosis, dilated & tortuous intra hepatic duct are the other complications of this disease. Opisthorchiasis is the similar parasitic disease as is Chlonorchiasis. The main animal hosts are cats, dogs, pigs, rats and camels.
Hetrophyiasis:
Heterophyes heterophyes is an intestinal fluke found in mammals and birds which ingest encysted metacercariae in raw or undercooked fish. The life-cycle is similar to that of Clonorchis and Opisthorchis spp. and the operculated eggs passed in faeces are morphologically very similar. Clinical manifestations are rare and, if present, are usually due to eggs trapped in various tissues.
1.Vegetable and water borne parasitic zoonoses: Many diseases are transmitted through consumption of vegetables or contaminated water. Faciolopsis, giardiosis, cryptosporidiosis, cysticercosis, gastrodiscoidiasis, ameobiasis etc. are the important zoonotic parasitic diseases transmitted through vegetables and water. The most common mode of transmission of the these diseases is by ingestion of food and water contaminated with faeces from infected animals or humans and the consumption of raw leafy green vegetables irrigated with sewage water.
Fasciolopsis:
Fasciolopsis buski, is the fluke, commonly found in pigs. The metacercariae of this parasites attaches to the shell of water chestnuts (sanghera) which grow in seasonal ponds. These ponds are frequently visisted by pigs and hence contamination of water with pig faecal matter occurs. Disease occurs in human when they peel the chestnut with their teeths.
Giardiosis:
Giardia intestinalis (synonyms: Giardia duodenalis, Giardia lamblia) is a flagellate exhibiting a very simple and direct life-cycle. After ingestion of Giardia cysts through water and food the cysts pass through the duodenum and then the organisms leave the cyst and undergo binary fission to form new trophozoites that continue to proliferate and establish infection in the host. Morphologically, the trophozoite has a face-like or pearshaped appearance and, when viewed with the narrow end down, the paired nuclei look like eyes, the anterior flagella loop above the nuclei appears like eyebrows, and the median body resembles a down-turned mouth. Initial signs of giardiosis include anorexia, nausea, discomfort in the upper intestine and fatigue. This is followed by foul-smelling watery diarrhoea, flatulence and abdominal distension. Chronic infection is marked by recurrent brief episodes, or to a lesser extent, persistent episodes of foul-smelling loose stools, flatulence and abdominal distension.
Cryptosporidiosis:
Out of the eight recognised species of Cryptosporidium, only one, C. parvum, is of zoonotic importance. The parasite has been associated with outbreaks of diarrhoea in the young of cattle, sheep, goats, deer, horses, dogs, cats and turkeys. The first case of C. parvum in a human was reported in 1976. An increasing incidence has since been reported, mainly in immunocompromised patients with AIDS, in whom the infection is life threatening. Cryptosporidium parvum has been demonstrated to be responsible for sporadic outbreaks of water-borne illness in especially in immunocompetent individuals. Water-borne epidemics are facilitated by the ability of the oocyst to withstand standard water treatments (chlorination and sand filtration) and to remain viable for long periods in the environment.
Cysticercosis:
Cysticercosis is caused by larva ( cysticercosis cellulosae) of T. solium . Various manifestations of disease are neurocysticercosis, ocular cysticercosis and muscular cysticercosis. Neurocysticercosis resulted into nervous problems like seizures, epilepsy in humans. Disease occurs in man because of consumption of T. solium eggs in contaminated food and water and also due to auto infection. T. solium eggs can be ingested when agricultural land is irrigated with sewage water and vegetables and fruits are not washed properly before eating.
Gastrodiscoidiasis:
Gastrodiscoides hominis is primarily an intestinal fluke of pig, but also infect other vertebrates including human. Sometimes also known as colonic fluke, it infects the colon of pigs and rhesus monkey. But in case of humans the worms are attached on the wall of the caecum. Humans are considered an accidental host because the parasite can survive without humans. Humans acquire infection by ingesting the metacercaria by the contaminated vegetable. Disease manifestations in humans include diarrhoea, fever, abdominal pain, colic and an increased mucous production.
Amoebiasis:
Amoebiasis, also known as amebiasis or entamoebiasis is an infection caused by protozoans of the Entamoeba group especially by E. histolytica. Amoebiasis is usually transmitted by the fecal-oral route, but it can also be transmitted indirectly through contact with dirty hands or objects as well as by anal-oral contact. Amoebiasis can present with no, mild, or severe symptoms. Symptoms may include abdominal pain, mild diarrhoea, bloody diarrhea or severe colitis with perforation which may lead to peritonitis.
Prevention and control of FPZ:
Consumption of raw meat, offals and fish should be avoided. n Vegetables should be washed properly before eating especially carrots, raddish, cabbage etc. which are generally eaten as salad. n Proper cooking and freezing of meat should be done to render the parasites ineffective. n Proper hygienic measures should be followed. n Meat inspection should be done strictly and infected meat should be condemned accordingly. n Usage of sewage water for irrigation purpose should only be done after proper treatment and disinfection of sewage water.
Compiled & Shared by- Team, LITD (Livestock Institute of Training & Development)
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Reference-On Request.
