Zoonotic Diseases, Zoonoses

Garden birds act as the primary reservoir of salmonella infection in humans. Most passerine salmonellosis outbreaks identified occurred at and around feeding stations, which are likely sites of public exposure to sick or dead garden birds and their feces. We, therefore, advise the public to practise routine personal hygiene measures when feeding wild birds and especially when handling sick wild birds.

Infectious diseases are the leading cause of death worldwide and, despite modern healthcare, infectious diseases remain a leading cause of death in the United States. The majority of pathogens that cause disease in humans are zoonotic (approximately 58% of all human pathogens). Many human infections are transmitted through contact with animals including dogs, cats, fish, birds, rabbits, hamsters, lizards, guinea pigs, snakes, frogs, turtles, ferrets, or gerbils. In the United States, the top five neglected parasitic infections include four zoonotic diseases, namely Chagas disease (infection with Trypanosoma brucei protozoa), cysticercosis (infection with tapeworm Taenia solium), toxocariasis (infection with immature roundworms), and toxoplasmosis (infection with Toxoplasma gondii protozoa). All of these parasites infect domestic dogs and cats.

Zoonoses with high incidence, severe symptoms in humans, prolonged duration of illness in humans and high transmission potential from animals to humans include leishmaniasis, Hendra virus, salmonellosis, cryptosporidiosis, Crimean-Congo hemorrhagic fever, babesiosis, anaplasmosis, paralytic shellfish poisoning, coccidioidomycosis, cysticercosis and Rocky Mountain spotted fever. Some of these zoonoses have high case fatality. 2

People may come into contact with animals outside of their homes such as in public settings (petting zoos, schools, fairs), through work-related activities, or recreation (parks). Animal bites are a serious public health problem, with an estimated 316,000 U.S. emergency room visits for a dog bite-related injury in 2008. Dogs are responsible for approximately 80% of all bites, cats accounting for less than 20% and other pet species and wildlife responsible for the remainder. Bites may lead to infection and rarely death. Animal scratches can also transmit pathogens. People also can acquire pet-associated zoonotic organisms through contact with animal saliva, urine and other body fluids or secretions, ingestion of animal fecal material, inhalation of infectious aerosols or droplets, and through arthropods and other invertebrate vectors.

Although any exposed person can become infected with a zoonotic pathogen, risks are particularly high for those with a compromised or incompletely developed immune system, such as the young, elderly, pregnant and those with immune function-reducing conditions or treatments, including diabetes, cancer, infection with human immunodeficiency virus (HIV), and radiation therapy. The increased disease risk for children is additionally imparted through closer physical contact with household animals, reduced hand hygiene and behaviors that include pica and exploration of the environment through mouthing.1 Park employees may have prolonged exposure to wildlife and arthropods, placing them at increased risk of infection with endemic zoonoses. For example, U.S. National Park Service employees showed evidence of prior infection with a variety of zoonotic agents, including California serogroup bunyaviruses, Bartonella henselae (26.7%), spotted fever group rickettsiae (22.2%), Toxoplasma gondii (11.1%), Anaplasma phagocytophilum (8.1%), Brucella spp. (8.9%), flaviviruses (2.2%), and Bacillus anthracis (1.5%). Sporadic cases and outbreaks of zoonotic diseases have been reported previously among NPS employees and visitors.3

Veterinarians are at increased risk of zoonotic infections. The most common zoonoses encountered in clinical practice are ringworm, rabies, and methicillin-resistant Staphylococcus aureus (MRSA) for companion animal veterinarians; Campylobacter, ringworm, and rabies for food animal veterinarians; West Nile virus (WNV) for equine veterinarians; and ringworm, rabies, and Campylobacter for mixed animal veterinarians.5

Body louse Pediculus humanus
Body louse

As diagnostic and research capabilities have advanced, pathogens able to infect both humans and animals have increasingly been recognized as a major source of human diseases. With the emerging nature of zoonotic pathogens, it seems that domestic animals may play as potential sources of new zoonotic diseases. Forty-five bovine zoonotic pathogens were identified. Of the emerging bovine zoonotic pathogens, 13 (52%) are bacteria, six (24%) are viruses, four (16%) are parasites, one (4%) is fungal, and one (4%) is a prion. Given the importance of cattle, not only in terms of human health but also to the food supply, a number of bovine zoonoses have been classified as potential bioterrorism agents. Twenty-four (53%) of the recognized cattle zoonotic pathogens are on CDC's bioterrorism list. Groups with greater exposure to cattle and cattle products have increased risk of contracting bovine zoonotic infections (livestock handlers, veterinarians, abattoir workers, meat inspectors, laboratory staff handling biological samples from infected cattle, and persons consuming unpasteurized milk or other diary products and improperly prepared meats). As with many other infectious diseases, infants, the elderly, the immunocompromised, and those with other underlying health conditions are at increased risk of contracting bovine zoonotic infections.

Bird Zoonoses

There are from 11 to 16 million companion and exotic birds in the United States. Many families own their “kitchen pet bird”, which represents a lucrative business for pet shops or local breeders. Bird fairs and live bird markets also gather a lot of people. In addition, some species are bred for their very high value. Exotic birds like ara or cockatoo, legally or illegally traded from for example Asia or South America, remain high in the ranking of popular pets and are also profusely represented in zoos and parks. However, these animals are potential carriers and transmitters of zoonotic diseases and spreading parasites which include:

List of Zoonoses

Image Provider: CDC/K. Mae Lennon, Tulane Medical School; Clement Benjamin




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