Prevention and control of parasitic zoonoses associated with water and food

Pashu Sandesh, 05th October 2018

¹R. K. Guptaand ²M. K. Verma

Introduction

Parasitic zoonoses directly affect human, livestock health and production. Transmission of parasitic zoonoses through food has public health as well as socioeconomic importance. Zoonoses are the diseases which are naturally transmissible between vertebrate animals and man. The environmental route of transmission is significant for many protozoan and helminthic parasites, with water, soil and food being particularly significant. Food borne parasitic zoonoses occur through consumption of infected meat, fish, contaminated vegetables/plant and water

Food-borne trematodosis including fasciolosis, were added to the list of helminthosis with a great impact on human development. The increased incidence of established protozoan zoonoses and the growing evidence of emerging parasitism’s give cause for concern to various stakeholders in public health. 

Contaminated vegetables/plants- and water-borne parasitic zoonoses

Fasciolopsiasis 

Fasciolopsiasis has a high prevalence (upto 33%) in the swine population of Assam. High infection rate of fasciolopsiasis had been recorded among people in the north east, particularly Assam.  Infection usually runs concurrently in pigs and humans but 29 per cent presence of F.buski in humans has been reported in Bombay city in the absence of porcine infection. Human foci were detected in Maharashtra.  In endemic areas, the disease is most prevalent in children in remote rural or semi-rural areas. Despite global interest and programme in control of food-borne trematode infections, there have been reports of a re-emergence of human fasciolopsiasis in Uttar Pradesh. 

Fascioliasis

Fascioliasis is an infection by the sheep liver fluke Fasciola hepatica. This fluke, which commonly infects sheep, cattle and other herbivores, is also an important parasite of man in many countries of the world. Fasciola gigantica is a larger species of Fasciola with a host range somewhat similar to F. hepatica, but this large fluke only rarely infects man. 

Inconsistent with the high endemicity of animal fascioliosis (F. gigantica and F.hepatica) reports of human infection have been rare so far.  Case reports dealing with hepato-biliary symptoms and obstructive jaundice in children attributable to Fasciola spp. are on record from Uttar Pradesh.  Similar report from Assam was also from a child with adult fluke in the gall bladder detected by ultrasonography. 

Recently, F. hepatica was detected on surgery in a woman from Delhi having multiple non-resolving liver abscesses cross-reactive to Echinococcus.  Human fasciolosis is a good example of a disease which is predicted to increase due to climate changes.  The ability of Fasciola to spread is related to the capacity of fasciolids to colonize and adapt to new environments, new definitive hosts as well as new lymnaeid intermediate hosts.

Diagnosis:  Fasciola eggs are similar to those of strongyles, but are larger (140 by 63 to 90 microns) and operculated. Presence of these eggs in faeces indicates a fluke infection. Finding adults or immature forms in the liver at slaughter is diagnostic.

Control: Snails must be eliminated from pasture by draining water. Infected animals are drenched with flukicide which will reduce pasture contamination. In Europe a fluke forecasting system proposes preventive control measures when persistent wet weather provides conditions conducive to snail proliferation and consequent Fasciola epidemics.

Schistosomiasis

It is a major parasitic disease infecting humans and domestic livestock, and caused by several species of flatworms in the genus Schistosoma.  According to the World Health Organization estimates up to 200 million people are infected in parts of South America, Africa and Asia.

Among human parasitic diseases, schistosomiasis ranks second only to malaria in terms of worldwide public health risks and socio-economic impact. Known also as bilharziasis, the disease was recognised since the time of the Egyptian pharaohs. Schistosomiasis is a tropical parasitic disease that is transmitted from mammals to snails and then back to mammals. It is most prevalent in areas where sanitation is poor. When human urine or feces containing schistosome eggs enters water that harbors the appropriate snail intermediate host, the snail can become infected. After an incubation period, the snail releases cercariae that can penetrate the skin of humans in the water. The cercariae penetrate the skin, enter the bloodstream, and travels to the liver. In the liver, the schistosome worms wait to pair up as male and female, with the larger male clasping the female with his body.

In acute infections, mental retardation, and even a type of bladder cancer are attributed to these intestinal trematodes. Eggs travel to and develop in the liver, bladder or intestine, and rarely to the brain and/or spinal cord, causing seizures, paralysis or meningitis.

Like the other forms of schistosomiasis, the blood flukes are carried by dirty water, placing farmers and fishermen particularly at risk. In addition to pharmaceutical treatment of infected persons, S. mansoni control through improvements in sanitation and water treatment, as well as snail control, is feasible. There is evidence that water resource development projects, such as damming of rivers, increase the prevalence of the disease as artificial shallow snail habitat is created in place of flowing waters.

The long-lived adult worms inhabit the hepatic portal vasculature (S. mansoni, S. japonicum) or vesicle veins of the bladder (S. haematobium), and the eggs laid by the females in the tissues are the cause of pathology, the severity of which is related to worm burden and intensity of the host response.  The most recent estimates suggest mortality rates directly attributable to schistosomiasis in sub-Saharan Africa at 280,000 per year, with millions of people showing clinical symptoms.  Schistosomiasis thus remains an important public health problem.

Some measures to prevent schistosomiasis  

• Avoid swimming in fresh water in countries where schistosomiasis occurs (Africa, South America, Caribbean, Middle East, and Southeast Asia).
• Bathe in water that is heated for 5 minutes. 
• Drink safe water. Boil water for one minute or filter water before drinking it. Boiling water will kill any harmful substances present. 

Neurocysticercosis

Although the disease has been discussed under meat borne parasitic zoonoses, contamination of vegetables with human sewage is major cause of the disease in India. In India, neurocysticercosis (NCC) is emerging as an important disease of the CNS, and next only to tuberculosis is the second most important cause of intracranial space occupying lesion. NCC is one of the principal causes of epilepsy.

Cryptosporidiosis

Cryptosporidiosis has been reported worldwide. Cryptosporidium parvum (genotype 2) is widespread in humans and other mammals. C. parvum is an emerging protozoan parasite of calves associated with diarrhoea among children. Cryptosporidium oocysts have also been detected from drinking water supplies. Cryptosporidium infection has been found to be significantly high in urban slum areas.

Cryptosporidiosis is increasingly recognised as a major cause of human diarrhoeal disease world-wide.  Transmission of zoonotic Cryptosporidium is through ingestion of oocysts of livestock origin.  In India, there have been reports from mid-1980’s on the prevalence of cryptosporidiosis among children in South India and in Chandigarh with detections based on microscopic demonstration of faecal oocysts (acid-fast staining) ranging between 1-13 per cent of the populations surveyed. 

The incidence is much higher in patients with AIDS (HIV) and other immunocompromised conditions.  The parasite has been recognised as the third commonest microbial infection in AIDS patients.  Its role as opportunistic enteric infection among HIV positive patients with or without diarrhoea has been widely reported from various centres viz. Chandigarh, Luckhnow, Pondicherry, Chennai, Amritsar, Vellore among others.

Ascariasis

Ascaris lumbricoides and Toxocara are common round worms found in the gastrointestinal tracts of man and animals. The embryonated eggs are ingested by the host; the infective larvae escape from the egg and penetrate the intestinal wall, pass through the liver to the lungs, break through the alveoli, gain entrance to the bronchi, ascend the trachea, are swallowed, and then develop into adults in the intestinal lumen.

Toxocariasis (Larva migrans): Upon entry in the internal organs of man larvae of mainly the dog ascarid (Toxocara canis) can set up this syndrome which is highly prevalent in South Asian Countries due to rampant faecal contamination of soil and opportunities for its contact with children as well as many kinds of workers . A vast majority of infections follow an inapparent course (convert toxocariasis). 

Clinical manifestations may take the form of invasion of either organs such as liver, lungs, heart and occasionally CNS or the other ocular tissues.  The incidence of toxocariasis has been reported from different parts of India. Recently a case has been reported with ocular toxocariasis from Kashmir.  High rate of sero-prevalence (33.33%) in children has been reported from Kashmir Valley than that of subjects residing in a rural area near Chandigarh. 

 Prevention and control of parasitic zoonoses

• Climatic changes due to global warming, increased vector population, world tourism, demand for livestock food products, changing socioeconomic conditions, poverty, lack of personnel hygiene, defecating in open space, scarcity of potable water, abundance of stray animals, high population density and culinary habits are responsible for rising zoonoses in India.
• Routine stool examination should desirably include new entities such as sporocysts of Sarcocystis and Cryptosporidium in the ambit of reportable infectious material.  The role of the veterinarian is paramount in coordinating with medical and public health personnel for the common objective of minimising the challenge to health and economy posed by food-borne parasites. 
• Emergence of diseases like human hydatidosis, neurocysticercosis, cryptosporidiosis, toxoplasmosis in acquired immune deficiency syndrome and reemergence of cutaneous leishmaniasis pose a great threat and challenge for prevention and control of parasitic zoonoses in India.
• Use of molecular epidemiological investigations, spatial analytical tools can help better understand current status of parasitic zoonoses in India.
• Health education, vector control, sanitary movements, controlled slaughtering, higher socioeconomic development and improved risk assessments can help control parasitic zoonoses in the country.
• There is need to have better coordination between medical and veterinary scientists in order to formulate appropriate control strategies.

¹R. K. Guptaand ²M. K. Verma

¹PG Scholar, Department of Veterinary Pathology

²Assistant professor, Department of Veterinary Pharmacology

Narendra Dev University of Agriculture & Technology

                  Kumarganj, Faizabad, Uttar Pradesh-224229

                       Email- manishverma307@gmail.com