Zoonotic Infectious Disease

In This Month’s Issue:

1 January – Zoonotic Infectious Disease – What Diseases Can We Catch from Animals?:

Ever wonder about the likelihood of contamination from pets or other animals that could create diseases in human? The Center for Disease Control and Prevention provides some interesting parallels.

Pretty Scary Information: Most emerging infectious diseases are actually zoonotic; wildlife constitutes a large and often unknown reservoir of disease source. Emerging infectious diseases do have a major effect on human health and can create tremendous economic losses. Animals, particularly wild animals, are thought to be the source of more than 70% of all emerging infections. These infections are termed zoonoses. The diseases are mainly of viral origin, and likely to be vectorborne. The emergence and rapid spread of West Nile virus in North America and the monkeypox outbreak in pet prairie dogs have been major awakening public health events. Bird flu fear is widespread.

It is believed that the damage done to ecosystems and human intrusion into wildlife areas are contributory and necessitate better worldwide surveillance. Similarly, the increase of ecotourism, often in primitive settings with limited hygiene, can be associated with the acquisition of zoonotic agents. Most animal pathogens for which surveillance programs exist relate to farm animals, and few or no programs are specifically aimed at wildlife. Recommendations are being made to monitor the pathogens that can infect humans to attempt to prevent emergence of new reservoirs of potential diseases.

Public health services and clinical practitioners are encouraged to more actively educate the public about the risks of owning exotic pets and adopting wild animals.

Human activities may also be a source of wildlife infection, which could create new reservoirs of human pathogens. The recent outbreak of tuberculosis caused by Mycobacterium tuberculosis in suricats and mongooses was one of the first documented spillovers of a human disease within a wildlife population. Banded mongooses were observed feeding regularly at garbage pits and were therefore exposed to human excretions and any infectious material from tuberculosis-infected humans.

Farming of wild animal species led to reemergence of zoonoses such as bovine tuberculosis in captive deer populations. Deer at low population densities on natural range are less likely to be affected to any major extent by disease. However, disease becomes a factor in intensive management of deer. Wildlife may become new reservoirs of infection and may recontaminate domestic animals; examples include bovine tuberculosis in the United Kingdom associated with Mycobacterium bovis infection in badgers (Meles meles)and brucellosis in outdoor-reared swine in Europe that resulted from spillover from the wild boar brucellosis (Brucella suis biovar) reservoir.

Wildlife trade provides mechanisms for disease transmission at levels that not only cause human disease outbreaks but also threaten livestock, international trade, rural livelihoods, native wildlife populations, and ecosystem health. Worldwide, an estimated 40,000 primates, 4 million birds, 640,000 reptiles, and 350 million tropical fish are traded live each year. International wildlife trade is estimated to be a US $6-billion industry.

Illegal trade can also be a possible source of human infection. In March 1994, psittacosis developed in several customs officers in Antwerp, Belgium. A customs officer had been hospitalized with pneumonia 10 days after exposure to parakeets illegally imported by an Indian sailor. Similarly, a highly pathogenic avian influenza A H5N1 virus from crested hawk eagles smuggled into Europe by air travel has been isolated and characterized.

The avian influenza epidemic, which began in Southeast Asia in 2003 and recently spread to other parts of the world, is directly related to infected birds sold live in traditional markets. Live bird markets facilitate the spread of this avian H5N1 virus by wild birds. Similarly, the newly discovered severe acute respiratory syndrome–associated coronavirus was linked to trade of live, wild carnivores, especially civets, in the People’s Republic of China. However, recent data suggest that civets may be only amplifiers of a natural cycle involving trade and consumption of bats.

Trichinellosis has long been associated with consumption of undercooked meat from wild animals, such as bears, and now consumption of uncooked meat from deer and wild boar has recently been associated with emergence of severe cases of hepatitis E in hunters in Japan. Industrialized nations’ new taste for exotic food has also been linked with various zoonotic pathogens or parasites, such as protozoa (Toxoplasma), trematodes (Fasciola Paragonimus), cestodes (Taenia, Diphyllobothrium), and nematodes (Trichinella, Anisakis, Parastrongylus).

Adventure travel is the largest growing segment of the leisure travel industry; growth rate has been 10% per year since 1985. This type of travel increases the risk that tourists participating in activities such as safaris, tours, adventure sports, and extreme travel will contact pathogens uncommon in industrialized countries. The most commonly encountered rickettsial infection in travel medicine is African tick bite fever, caused by Rickettsia africae and transmitted in rural sub-Saharan Africa by ungulate ticks of the Amblyomma genus. Most patients are infected during wild game safaris and bush walks. Moreover, because ecotourism is becoming increasingly popular with international travelers, more cases of imported rickettsioses are likely to occur in Europe, North America, and elsewhere in years to come.

Petting zoos, where children are allowed to approach and feed captive wildlife and domestic animals, have been linked to several zoonotic outbreaks, including infections caused by Escherichia coli, salmonellae, and Coxiella burnetii. More than 25 outbreaks of human infectious diseases associated with visitors to animal exhibits were identified during 1990–2000. In an outbreak of salmonellosis at a Colorado zoo, 65 cases (most of them in children) were associated with touching a wooden barrier around the Komodo dragon exhibit. Salmonella organisms were isolated from 39 case-patients, a Komodo dragon, and the wooden barrier. Children who did not become infected were more likely to have washed their hands after visiting the exhibit.

Exotic pets are also a source of several human infections that vary from severe monkeypox related to pet prairie dogs or lyssaviruses in pet bats to less severe but more common ringworm infections acquired from African pygmy hedgehogs or chinchillas. Epidemiologic and animal trace-back investigations confirmed that the first community-acquired cases of monkeypox in humans in the United States resulted from contact with infected prairie dogs that had been housed or transported with African rodents imported from Ghana.

Similarly, an outbreak caused by Francisella tularensis type B occurred among wild-caught, commercially traded prairie dogs; F. tularensis antibodies in 1 exposed person documented the first evidence of tularemia transmission from prairie dog to human.

In the United States, the number of commercialized reptiles, especially iguanas, imported per year has increased considerably to ˜1 million. The number of human cases of salmonellosis, especially in very young children, increased dramatically in parallel with iguana pet ownership. The Centers for Disease Control and Prevention estimates that ˜7% of human infections with salmonellae in the United States are associated with having handled a reptile. Most iguanas have a stable mixture of Salmonella serotypes in their intestinal tract and intermittently or continuously shed Salmonella organisms in their feces.

The educational process must focus on the potential risks of
* Owning/handling exotic pets
* Hygiene after visiting a zoo
* Traveling, particularly in areas of high infectious probability
* Cross contamination of meat products
* Wildlife cross contamination with domestic cattle (and people)