The term zoonosis (zoonoses, plural) was coined by Rudolf Virchow to describe the disease transmitted from animal to man and vice versa. Zoonoses have been defined by the World Health Organization (WHO) as those diseases and infections the agents of which are naturally transmitted between animals and man. Zoonoses include only those infections with either proof or strong circumstantial evidence that there tra nsmissio n between animal a nd man. Zoono ses (zoonotic dise ases) ar e a heterogeneous group of diseases with a variety of causative agents. More than 300 such diseases of diverse etiology have been recognized.
Zoonoses are among the most frequent and dreaded risks to which mankind are exposed since their evolution. Increased mass movement of population, tourism, movement of animal population, trade with animal and animal products have often resulted in the spread of these diseases throughout the world by transcending the national and international borders. So zoonoses are not only an emerging health problem but also an international problem.
Zoonoses – an occupational hazard
There are certain groups of population who come in close contact with animals or animal products as part of their occupation. The attack rates are higher among these groups because of occupation than the rest of the population.
1. Agriculture: Farmers, agricultural workers, veterinarians, livestock transporters
and their family.
2. Animal product manufacturer: Butcher, slaughter men, handlers of meat, milk, egg, hide, fur, etc.
3. Sylvan and camp dwellers: Wildlife workers, foresters, hunters, surveyors, explorers, tourists, etc.
4. Recreational: Zoo-garden employees, wildlife park employees, visitors, pet or wild animal dealers and veterinarians.
5. Clinical laboratory workers: Animal autopsy performers, veterinarians, and laboratory animal handlers.
6. Epidemiological workers: Veterinary public health workers.
7. Emergency: Refugees, disaster victims and pilgrimage participants.
Socioeconomic aspects of zoonoses
Zoonoses in domestic animals impose a serious burden of ill health on people who live in rural areas and earn their livelihood through farming and other forms of agriculture. In some countries this high-risk group comprises up to 90 % of the total population. Also, zoonoses exert a double price by exacerbating the vicious cycle of protein-energy malnutrition and infection. Rejection of meat, fish and other animal products are the other losses because they are known to be commonly infected with harmful microbial and parasitic zoonotic infections.Further, the immense effect of zoonoses on the economy can be gauzed through the infection of animal species, such as cattle, buffaloes, horses, camels, yaks and llamas that still provide approximately 85 % of the world’s total draught power. In India, cattle alone account for 54 % of the energy used for all in rural areas. Besides, a large population of wild and semi-wild animals acts as reservoirs of infections and thus causing ill-health in persons coming in contact with them.
Factors influencing prevalence of zoonoses
Ecological factors: With the expansion of population, the man is entering the unaccustomed ecosystems in which potential pathogens form part of the biotic community (natural focus). These alterations greatly increase the risk of epidemic spread of zoonotic diseases.
Environmental pollution: The main problems are associated with faecal pollution of water supply, the soil and the vegetation. In polluted water reservoirs and streams, various microorganisms may develop and persist. Soil pollution by eggs and larvae of parasites and spores of bacteria and fungi is particularly hazardous where night-soil or inadequately treated sewage sludge is used for manuring crops, especially plants which are consumed raw.The large quantities of animal wastes from animal-breeding establishments (pig, poultry, cattle, etc.), dairies, abattoirs and carcass-disposal plants constitute other health hazards that must be taken into account.
Effects of human settlements: Rats, mice, bats, birds, lizards, etc., which live in and around human settlements are important in the epidemiology of zoonoses. Large human settlements (urban areas) are suitable not only for these animals but also to some other animals which are of primary importance in the transmission of zoonoses. Besides, a number of animals are also kept as pets. All these factors bring about a closer contact between man and animals resulting in zoonoses.
Human behavior and food habits: Socioeconomic, cultural and religious factors play an important role in the transmission of zoonotic diseases in man. For example, echinoccosis (hydatidosis) is more widely prevalent among Turkana people of Kenya, where, as per their religious customs the human dead bodies are exposed to hyenas and dogs, thus perpetuating the transmission of the disease.
Fluctuations in animal populations: The wild, semi-wild and other animal productions, including those of disease vectors, show the influence on factors like food supplies, climate and hydraulic changes. These fluctuations directly affect the extent and spread of zoonoses.