Zoonoses

ZOONOSES (from Greek zoon-animal and nosos-disease), a term that was initially used in its literal sense and referred to all diseases of animals in general. Gradually its meaning narrowed, and it came to denote only diseases transmitted from animals to humans. At present, it is rarely used and again in a somewhat broader sense, referring to infectious and parasitic diseases common to animals and humans, which according to modern terminology constitutes one branch of comparative pathology. Diseases that can only be caused experimentally, through artificial infection, are not included in this category. The number of known infections that occur naturally in both humans and animals constantly increases as new pathogens are discovered and the biology of less-studied diseases becomes better understood.-From an etiological point of view, zoonoses can be divided into the following groups. I. Diseases caused by bacteria. Anthrax; the causative agent, Bac. anthracis, is cultivated mainly in the bodies of herbivorous animals. Glanders; the causative agent, Bac. mallei, affects mainly single-hoofed animals-horses, donkeys, mules, mules. Psittacosis; the causative agent of parrot disease, Bac. psittacosis, discovered by Nocard, is determined by French authors as standing between Bac. paratyphi B and Bac. Gartneri; it causes a typhoid-like disease, often with a fatal outcome. Malta fever; the causative agent, Micrococcus (Microbacillus) melitensis, causes chronic disease in goats (of certain breeds), cows, and some other domestic animals; it is excreted in milk and urine.-In addition, diseases common to humans and animals include tuberculosis, plague of rodents and humans (pestis), tetanus, malignant edema, and other anaerobic wound infections. The connection between paratyphus A and B and meat poisoning with diseases in animals caused by bacilli belonging to the Salmonella group cannot yet be considered definitively established.- II. Diseases caused by filamentous fungi. Actinomycosis; the causative agent, the ray fungus, exists in numerous varieties; of these, only some varieties are pathogenic to humans and animals. Ringworm, favus; the causative agent, Achorion Schönleini, in some varieties affects besides humans most often mice and rats, from which cats and dogs become infected, then horses, donkeys, chickens and ducks. Tinea tonsurans, herpes tonsurans; the causative agent, Trichophyton, is easily transmitted by its spores to susceptible individuals; horses, cattle, dogs, cats, pigs, sheep, goats, rabbits are affected by tinea; from them the infection passes to humans, especially young people, and then from person to person both by contact and through infected objects. Thrush, Soor, and some diseases caused by molds (Aspergillus fumigatus, Mucor corymbifer) are also common to humans and animals, but mutual transmission of infection is practically not observed.--III. Diseases caused by spirochetes. Weil's disease, Botkin's disease, icterus haemorrhagicus; the causative agent - Spirochaeta icterogenes (Leptospira icterohaemorrhagica)-occurs in nature in wild rats (Mus decumanus and alexandrinus), in domestic mice (Mus musculus) and the field mouse (Microtus montebelli); sick animals excrete the spirochete in urine, contaminating water and food products, which then serve as a source of human infection. Rat-bite disease, in Japanese "Sodoku" (see Sodoku); the causative agent, Spirochaeta morsus muris, affects under natural conditions rats (Mus decumanus and alexandrinus), the vole (Microtus montebelli), cats, ferrets, weasels, African squirrels.-Seven-day fever, in Japanese "Nanukayami"; the causative agent, Spirochaeta hebdomadis, has been found among animals so far only in the field mouse Microtus montebelli, which excretes it in urine; the routes of human infection are not precisely established. - IV. Diseases caused by so-called "filterable viruses". Foot and mouth disease (see), aphthae epizooticae; the nature of the causative agent has not yet been established; the ultramicroscopic bacillus discovered by Frosch and Dahmen, Loeffleria neve-manni, has not gained general recognition. Foot and mouth disease causes extensive epizootics among cattle; on a smaller scale, pigs, sheep, goats, buffaloes, deer, camels, wild even-toed ungulates are infected; very rarely-horses, dogs, cats; among birds, chickens and pigeons become ill during epizootics in cattle. Transmission occurs either by contact or through infected objects, including milk and dairy products. Smallpox. According to the prevailing view, human smallpox (variola), which in former times had an endemic and even pandemic character, served as a source of infection for cattle, in which the disease (vaccina) proceeded in a very mild form, manifesting only in the form of individual pustules in those places where the human virus was brought by human hands (mainly on the udder). Reverse infection of humans from cattle with the mitigated form (cowpox) was also often observed earlier and served as the basis for vaccination discovered by Jenner. Rabies, hydrophobia. According to some researchers, the causative agent belongs (as in smallpox) to the chlamydozoa and has besides its filterable form its larger formations-Negri bodies, which are found in the ganglion cells of the central nervous system. However, this view is not generally accepted, and the causative agent of rabies is still unknown. All warm-blooded animals, including birds, are apparently susceptible to rabies infection. Particular practical interest is represented by the morbidity of domestic and wild carnivores, as they are the main spreaders of rabies, infecting in a sick state by biting other animals and humans with their saliva containing the rabies virus. - V. Diseases caused by protozoa. Malarial diseases (see Malaria); usually are not classified as infections common to humans and animals, although mutual infection with plasmodia occurs between humans and Anopheles, in which pathological processes occur in the body of the latter, bearing the character of a quite definite disease. Sleeping sickness, African human trypanosomiasis; the causative agent - Trypanosoma gambiense and Tr. rhodesiense; the transmitter-the tsetse fly (Glossina palpalis); the main "reservoir" of the virus in nature is man, but it is allowed that domestic cattle and antelopes can also serve as such, and mutual infection between man and the mentioned animals can occur through the tsetse fly. Carlos Chagas' disease, American human trypanosomiasis. The causative agent of Chagas' disease - Schizotrypanum cruzi; the transmitters-large bugs, Triatoma megista, Rhodnius prolixus, Eratyrus cuspidatus. The main source of infection is a sick person. In nature, the virus of the disease has been found in armadillos, some marsupial animals, in cats. In view of the ease with which artificial infection of dogs and other domestic animals can be achieved, it is assumed that they also participate in maintaining the virus and in mutual infection. Kala-azar, tropical splenomegaly. The causative agent, Leishmania donovani, occurs in sick people and sick dogs. Oriental sore, bouton d'Orient, Pendian sore, Sart sore, Delhi boil; the causative agent - Leishmania tropica; lesions similar to human ones are also found in some animals (dog, horse, cat, camel), however their etiological identity is not proven, and therefore the question remains open whether they can serve as a source of human infection, and vice versa.-VI. Diseases caused by parasitic worms, helminths. Numerous helminthic diseases (see Helminthiases, as well as individual helminthic diseases) should also be classified as zoonoses, in which animals serve as intermediate hosts. - VII. Diseases caused by arthropoda. Scabies; the causative agent of human scabies, the scabies mite, Sarcoptes scabiei, does not affect animals, but most of its varieties parasitic on animals can pass to humans (most often from horses and dogs, but also from pigs, cats, sheep, goats, camels, etc.); infection usually occurs by contact, but transmission through objects is not excluded. (For more details-see individual infections.)