IMPORTANT CANINE AND FELINE ZOONOSES : ONE HEALTH APPROACH & PUBLIC HEALTH  IMPORTANCE

IMPORTANT CANINE AND FELINE ZOONOSES : ONE HEALTH APPROACH & PUBLIC HEALTH  IMPORTANCE

Zoonoses are defined by the World Health Organization as diseases and infections which are transmitted between vertebrate animals and man. Veterinary practitioners are often the first to address questions on possible transfer of disease from pets to owners who are their clients. The practitioner is expected to be the expert “on site” and provide accurate detailed information and solutions to problems. This challenging duty carries a great deal of responsibility and may also be associated with legal liability. The task of being knowledgeable about zoonoses is even more difficult when considering that the number of organisms known to cause zoonotic infections is greater than 250. Moreover, there is a constant flow of new data and information about these pathogens and newly discovered disease agents. Although human physicians are an important part of the network that should advise pet owners, they are often surprisingly ignorant about zoonoses which they consider to be rare and a relatively minor cause of illness in their human general practice.

The concept of the human-animal bond has a major importance in the modern society where pets are considered a part of the family and affection to them sometimes replaces relationships present in the traditional family. The interaction between humans and pets has a particular significance in special populations such as chronically-ill hospitalized patients, disabled people or prisoners. Contact of animals with people that have special needs could be very meaningful and rewarding to these individuals. But, particular consideration for zoonotic transmission of disease is often needed when relating to humans with immunosuppression or special susceptibility to infection. These individuals include HIV+ patients, cancer patients undergoing chemotherapy or radiation therapy, transplantation recipients undergoing immunosuppression to prevent organ rejection, patients with severe allergic or autoimmune diseases receiving immunosuppressive therapy, children or adults with congenital immunodeficiencies and more. Veterinary advice is often sought under these circumstances and practitioners should be prepared to provide helpful information on the risk of pet ownership to their clients. It should be borne in mind that having pets is of extreme importance to some immunosuppressed patients and therefore the benefits of having an animal should be weighed against the relative risk of acquiring infection from it. Normally, people do not need to be advised to part with their pets but rather to take precautions related to ectoparasite control, personal hygiene, feeding, vaccination and disease testing.

Fortunately, of the roughly 250 zoonotic organisms reported to be naturally transmitted to people, only about 40 are transmitted from dogs and cats. However, more pathogens are transmitted from pet birds, exotic reptiles and mammals, farm animals and wildlife animals.

The spectrum of zoonotic organisms is very wide and includes all classes of pathogens from viruses, through bacteria, algae, fungi, and protozoa to helminths. Furthermore, the transmission routes of these organisms are diverse and include spread by bites and through saliva, scratch or skin contact, aerogenic spread, urogenital dispersal, and vector-borne infections. The latter infections are commonly transmitted by pet ectoparasites such as ticks, fleas, flies, sand flies and mosquitoes.

The word ‘Zoonosis’ (Pleural: Zoonoses) was introduced by Rudolf Virchow in 1880 to include collectively the diseases shared in nature by man and animals. Later WHO in 1959 defined that Zoonoses are “those diseases and infections which are naturally transmitted between vertebrate animals and man”. Zoonoses include only those infections where there is either a proof or a strong circumstantial evidence for transmission between animals and man.

Zoonoses – an international problem

Historically, zoonotic diseases had a tremendous impact on the evolution of man, especially those cultures and societies that domesticated and bred animals for food and clothing. Zoonoses are among the most frequent and dreaded risk to which mankind is exposed. Zoonoses occur throughout the world transcending the natural boundaries. Their important effect on global economy and health is well known, extending from the international movement of animals and importation of diseases to bans on importation of all animal products and restrictions on other international trade practices. So, zoonoses no longer are solely a national problem. For effective control of zoonoses global surveillance is necessary.

With recognition of inter-relationships between countries, the internationalization of control efforts have become more relevant to technical, economic and social fields. The control of zoonoses retains its prominent place among the actions of international agencies according to the health and economic problems specific to each region.

Zoonoses – an emerging problem

Over the last two decades, there has been considerable change in the importance of certain zoonotic diseases in many parts of the world, resulting from ecological changes such as urbanization, industrialization and diminishing proportion of persons working in the so-called primary sector.

We do not know with what challenge nature will confront us in the world of constant interference with ecology. Most of the infections of man that have been discovered in the last twenty years are shared with lower animals and a number of other diseases previously thought to be limited to man have now been found to be zoonoses. Reference may be made to various types of encephalitis, eosinophilic meningitis, capillariasis, anisakiasis, lyme disease, monkeypox diseases in humans, lassa fever, Marburg disease and Ebola for all of which an animal link has been established.

Among those zoonoses recognized today as particularly important are anthrax, plague, brucellosis, Bovine tuberculosis, leptospirosis, salmonellosis, spotted fever caused by Rickettsiae, rabies, several common athropod borne viral infections (arboviral infection), certain parasitic diseases, especially cysticercosis, hydatid disease, trypanosomiasis and toxoplasmosis.

Classification

With the advanced laboratory techniques and increased awareness among medical and veterinary scientists, ecologist and biologists, more than 300 zoonoses of diverse etiology are now recognised. Thus, a very large number of zoonoses calls for classification especially for easy understanding. These are classified as follows:

According to the etiological agents

• Bacterial zoonoses :- e.g. anthrax, brucellosis, plague, leptospirosis, salmonellosis, lyme disease
• Viral zoonoses :- e.g. rabies, arbovirus infections, KFD, yellow fever, influenza, CCHF
• Rickettsial zoonoses :- e.g. murine typhus, tick typhus, scrub typhus, Q-fever
• Protozoal zoonoses :- e.g. toxoplasmosis, trypanosomiasis, leishmaniasis
• Helminthic zoonoses :- e.g. echinococcosis (hydatid disease), taeniasis, schistosomiasis, dracunculiasis
• Fungal zoonoses :- e.g. deep mycosis – histoplasmosis, cryptococcosis, superficial dermatophytes
• Ectoparasites :- e.g. scabies, myiasis

According to the mode of transmission

• Direct zoonoses – These are transmitted from an infected vertebrate host to a susceptible host (man) by direct contact, by contact with a fomite or by a mechanical vector. The agent itself undergoes little or no propagative or developmental changes during transmission, e.g. rabies, anthrax, brucellosis, leptospirosis, toxoplasmosis.
• Cyclozoonoses – These require more than one vertebrate host species, but no invertebrate host for the completion of the life cycle of the agent, e.g. echinococcosis, taeniasis
• Metazoonoses – These are transmitted biologically by invertebrate vectors, in which the agent multiplies and/or develops and there is always an extrinsic incubation (prepatent) period before transmission to another vertebrate host e.g., plague, arbovirus infections, schistosomiasis, leishmaniasis.
• Saprozoonoses – These require a vertebrate host and a non-animal developmental site like soil, plant material, pigeon dropping etc. for the development of the infectious agent e.g. aspergillosis, coccidioidomycosis, cryptococosis, histoplasmosis, zygomycosis.

According to the reservoir host

• Anthropozoonoses – Infections transmitted to man from lower vertebrate animals e.g. rabies, leptospirosis, plague, arboviral infections, brucellosis and Q-fever.
• Zooanthroponoses – Infections transmitted from man to lower vertebrate animals e.g. streptococci, staphylococci, diphtheria, enterobacteriaceae, human tuberculosis in cattle and parrots.
• Amphixenoses – Infections maintained in both man and lower vertebrate animals and transmitted in either direction e.g. salmonellosis, staphylococcosis

Factors Influencing Revelence of Zoonoses

1. Ecological changes in man’s environment

With the expansion of human population, man is forced to exploit the virgin territories and natural resources like harnessing the power of rivers, constructing roads and pipelines through virgin or thinly populated areas, clearing, irrigating and cultivating new land, deforestation. All this would lead to entering of humans in the unaccustomed ecosystem in which potential pathogens form part of the biotic community (natural focus).

Large scale expansion of agricultural and engineering resources, construction of dams, artificial lakes, irrigation schemes, clearing of forests -all these lead to changing of the biting habits of the blood sucking vectors and alteration in the population of reservoir animals which has led to the spread of leptospira, tuleraemia, helminthic infections etc.

2. Handling animal by-products and wastes (occupational hazards) – There is significantly higher attack rates in workers during the course of their occupation than the rest of the population, e.g. anthrax in carpet weavers, live stock raisers and workers with animal hair in the textile industry, leptospirosis in rice field workers, listeriosis in agricultural workers, erysipeloid in butchers and fish merchants, tularemia and trypanosomiasis in hunters, creeping eruptions in plumbers, trench diggers etc. Other examples of zoonoses as occupational hazards are Q-fever in abattoir and rendering plant workers, jungle yellow fever and tick borne diseases in wood cutters, salmonellosis in food processors, bovine tuberculosis in farmers etc.
3. Increased movements of man – Land development, engineering project work, pilgrimages, tourism, etc. expose the people to contaminated food and water leading to diseases like amoebiasis, colibacilliosis, giardiasis, salmonellosis, shigellosis, etc.
4. Increased trade in animal products – Countries which import hides , wool, bone meal, meat, etc. from an area where some of the zoonoses are endemic, are likely to introduce the disease into their territories, e.g. salmonellosis, foot and mouth disease, anthrax, Newcastle disease etc.
5. Increased density of animal population – Animals may carry potential risk of increased frequency of zoonotic agents in man e.g. dermatophytosis, tuberculosis, brucellosis etc.
6. Transportation of virus infected mosquitoes – Aircraft, ship, train, motor and other vehicles bring the viruses in to a new area, e.g. yellow fever Chikungunya fever, dengue fever etc.
7. Cultural anthropological norms – In Kenya, people allow the dogs and hyenas to eat human dead bodies infected with hydatidosis. This helps to perpetuate the transmission cycle of the disease.

Toxoplasmosis is a major protozoal zoonosis that threatens humans in particular HIV+ people and pregnant women. Toxoplasma gondii may infect any warm blooded animal with the cat being the definitive host. It can infect most cells types with a predilection to the central nervous system. Shedding of T. gondii oocysts in cat feces is usually restricted to a short period of time (7-10 days) during which large numbers of oocysts can be shed. Oocysts become infective only after sporulation which typically occurs 1-5 days after infected feces is excreted depending on the humidity and temperature conditions. However, infection of humans by meat containing cysts and not by ingestion of fecal oocysts appears to be the major route of infection to people. No association was found between cat ownership and T. gondii seroprevalence in a group of HIV+ people. Toxoplasmosis can be avoided by preventing the ingestion of sporulated oocysts and eating well cooked meat.

Bartonella henselae is a bacterium which is the major cause of cat scratch disease, bacillary angiomatosis, and peliosis hepatis. The two latter disorders are abnormal proliferation of small blood vessels resembling tumors which are common in AIDS patients, whereas cat scratch disease is mainly found in people with an intact immune system. Cats are mostly sub-clinical carriers of infection and fleas are responsible for transmission between cats. The prevalence of infection in cats is related to the extent of cat exposure to fleas and may reach more than 50% of the feline population in warm and humid regions where fleas are highly abundant. Humans appear to be infected by seeding of flea feces containing bacteria into the skin during cat scratch and possibly also during bites. Prevention of this infection in cat owners is especially important for HIV+ owners. It consists of flea control, clipping of cat claws, antiseptic cleaning of scratch and bite sites immediately after the event, screening and avoiding giving cats that are positive for B. henselae by PCR to HIV+ patients.

Rabies is still a very important lethal viral infection of warm blooded animals. Although it is not present or virtually eradicated in some countries, it is still prevalent in most countries in the world and responsible for the death of an estimated 55,000 humans per year worldwide. Vaccination of pets is compulsory in many countries and it is the cornerstone of the control of this disease. Campaigns to reduce and eradicate wild life rabies by distribution of oral vaccination have been successful in some countries. In addition, systems for quarantine of animals suspected of infection, routine post-mortem testing of animals for rabies, and post exposure preventative treatment to humans suspected of exposure to infection, are operated in many countries in which this disease is endemic.

Giardiasis is an enteric disease caused by the protozoa Giardia duodenalis in people. There is a large strain variation in giardiasis and pets can be infected with strains that are infectious to humans or species-specific strains that do not infect people. Giardia assemblages A and B are shared by humans and dogs. Assemblage A is shared by cats and humans and there are more specific assemblages infect animals but not humans such as assemblages C and D which infect dogs and assemblage F that infects cats. Waterborne outbreaks of giardiasis are mostly associated with infection related to Giardia from wild life and livestock. In contrast, infection from pets is usually associated with direct fecal contamination. Prevention consists of avoiding hand to mouth contact while handling animals, litter box hygiene and handling feces with gloves.

Q fever is caused by the gram-negative coccobacillus bacteria Coxiella burnetii. It is mostly a hazard in people who are in contact with domestic ruminants but is also sporadically reported in urban settings from people who have been in contact with infected cats or dogs. Cats can be infected by ticks which carry these bacteria, by ingestion of contaminated tissues, or by aerosol in a contaminated environment. Parturient cats are an important source for human infection and people become infected by aerosols from placental tissues. Pneumonia is the major clinical manifestation of Q fever in people.

Helminth parasites pose a threat to human health and it is the duty of the attending veterinarian to emphasize the potential zoonotic risks of these infections to pet owners and to offer preventative anthelminthic treatment. Early and repeated deworming of puppies and kittens is necessary for preventing and controlling these potentially zoonotic infestations. Ascarid worms can be transmitted transplacentally or transmammarily and puppies or kittens may be born infected or acquire infection very early in their lives. Humans become infected with animal ascarids when they accidentally ingest larvated eggs. Larvae hatch in the intestine and can migrate to visceral organs, the eye or the central nervous system resulting in larval migrans with symptoms depending on the effected tissues. Hookworms whose eggs are shed in animal feces are infectious to humans by accidental ingestion of infective larvae, or more commonly by skin penetration. Infective larvae that penetrate the epidermis cause cutaneous larval migrans. The tapeworms Echinococcus granulosus and E. multilocularis cause hydatidosis with large hydatic cysts in the internal organs of humans which necessitates surgical removal if resectable.

There is a long list of additional pet-related zoonoses that threaten human health. Pets may be directly related to the transmission of some infectious agents or in other cases merely sentinels for the presence of infection. Some additional zoonoses include tularemia, plague, salmonellosis, borreliosis (Lyme disease), leptospirosis, anaplasmosis, tuberculosis, cryptosporidiosis, blastomycosis and sporotrichosis.

To summarize, transmission of infection from pets to humans can be avoided by prevention of animal infection, vaccination, routine deworming, extermination of ectoparasites and strict observation of personal hygiene. The veterinarian has an important role in informing, educating and guiding pet owners to exercise these measures. The risk of disease transmission from pets to AIDS patients and other immunosuppressed individuals can be greatly reduced if guidelines for prevention of disease are followed. Thus, the mental benefit of having a pet in such conditions frequently greatly surpasses the risk of acquiring a contagious disease from it.

Zoonoses as a Public Health Problem

Although poorly documented, zoonotic diseases are a major public health problem in India. Plague has killed nearly 120 lakhs people since 1898. Rabies continues to be a serious health problem in the country. Approximately 20,000 deaths due to rabies are estimated to occur every year while more than 17 lakhs persons bitten by suspected rabid animals seek antirabies vaccination at rabies treatment centres. Typhus killed many people during World War-I. Brucellosis alone is estimated to cause annual loss of approximately 300 lakhs man days in addition to an annual economic loss of Rs.2400 lakhs through brucellosis in cattle and buffaloes. Japanese encephalitis is another emerging zoonotic disease in India causing several outbreaks and considerable morbidity and mortality. Studies on reservoir of this disease are yet in conclusive, Kala-azar although proved zoonotic all over the world, continues to be non zoonotic in India in spite of the epidemiological evidence suggesting it to be zoonotic. Cutaneous leishmanias is which was hither to consider an anthroponosis in India has been proved to be a zoonosis recently with the Indian desert gerbil Merriones hurriane as the animal reservoir. It is not surprising, that in India, where approximately 80%of population lives-in rural areas in close contact with large domestic animal population (5120 lakhs approximately, 7290 lakhs poultry and equally large populations of wild and semi-wild animals) abundance of vectors because of suitable climate, low socio-economic conditions and lack of proper medical care, zoonotic diseases assume great public health significance. However, because of inadequate diagnostic facilities, unfamiliarity of physicians with these diseases and lack of co-ordination between physicians, veterinarians, and epidemiologist, the extent of their existence is obscured.

Important Zoonotic Diseases: Prevention And Control

Important Zoonotic Diseases in India- Prevention And Control

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