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Category: Clinical Microbiology
Viruses are usually classified according to structural principles and genetic homology. Agents causing zoonoses exist in various virus groups that have similarities in the disease patterns that they induce. There may also be similarities involved in hosts and vectors. In this chapter, we have chosen a sequential arrangement following viral classifications for the most part. This sequence makes it possible to point out similarities within individual virus groups. Tables include the geographical distribution and clinical signs that are important for differential diagnosis. Viral zoonoses are also compared with nonviral zoonotic diseases.
Beside the “classical” bacterial zoonoses, this chapter covers infectious diseases such as listeriosis, in which the causative agents are frequently found in animals and that are traditionally regarded as zoonoses. However, since these agents may also be found in the environment and are not necessarily transmitted directly from animals to humans, diseases caused by them have also been termed “sapronoses,” “geonoses,” or “saprozoonoses.”
Dermatophytoses are chronic fungal infections caused by dermatophytes, that is, keratinophilic fungi that are able to utilize keratin-containing structures (hair, nails, scales, etc.) from humans and animals. They belong to the genera Epidermophyton, Microsporum, and Trichophyton of the family Arthrodermataceae. Individual species may be anthropophilic, zoophilic, or geophilic. Zoophilic species from warm-blooded animals with overt or latent infections may, if transmitted to humans, give rise to severe cases of dermatitis. Transmission from human to human is possible, although infectivity decreases with each passage and dies out after three to four passages. Anthropophilic dermatophytes, such as Trichophyton rubrum, T. tonsurans, and Epidermophyton floccosum, can also (although rarely) be transmitted from humans to animals, in whom they may cause skin diseases. In turn, these animals could be a source for human infections. The same chain may operate in primarily geophilic species, such as Microsporum racemosum and M. gypseum.
Parasitic zoonoses belong to the most important human diseases worldwide. They are caused by protozoa, helminths [trematodes (flukes), cestodes (tapeworms), and nematodes (round worms)], Acanthocephala (thorny-headed worms), pentastomids (tongue worms), and arthropods. The last of these plays an additional role as a transmitter of viruses, rickettsiae, bacteria, protozoa, and helminths.
In the United States, approximately 4 to 5 million episodes of animal bites occur every year, resulting in approximately 300 000 visits to emergency departments, 10 000 hospitalizations, and 20 deaths, mostly among young children. In England and Wales, 200 000 people per year seek medical help in hospitals after dog bites; in France, the number is 500 000. In Germany, 35 000 people per year are bitten by dogs; 1 to 2% of them are treated in ambulatory care units.
In a recent survey of foodborne illnesses requiring hospitalization, viruses were found as causative agents three times more frequently than bacteria. The death toll of foodborne viral infections, however, is less than one-fifth of the death toll of foodborne bacterial illnesses. Norwalk-like agents are the most important causes of foodborne illness with 23 million cases per year worldwide, followed by rotaviruses, astroviruses, and hepatitis A virus ( Tab. B1 ).
Iatrogenic transmission of pathogens is generally possible for agents that circulate in the blood or infect tissues to be transplanted. Severe complications may arise, particularly if the agent is able to subsequently proliferate in the recipient. Apart from using contaminated tools, for instance, needles and syringes, iatrogenic transmission occurs mainly in the course of transfusion of blood or blood products and in organ transplantation. Major problems arise by the fact that usually relatively large amounts of agents are transmitted and the recipient is, in general, a sick person, impaired by an eventually reduced resistance or immunocompetence. Transmissions of the following zoonotic agents by transfusion of blood and blood products have been reported:
Appendix D contains a table titled, Diseases Notifiable at the National Level, United States (2012) and Canada (2014)
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