Home Economics American Trypanosomiasis Chagas Disease, Second Edition: One Hundred Years of Research
1CIRAD-Bios, UMR177-Trypanosomes, Montpellier, France, 2Kasetsart University, Bangkok, Thailand
The various ways of infection of animals (and humans) 284
The problem of diagnosis in animals 286
Natural infections in domestic animals and livestock 288
Experimental infections in livestock 290
New cycles establish in the United States 291
Trypanosoma cruzi is a parasite in man but it is also a parasite in many other animal species both wild and domestic; human infection can occur in rural as well as in urban areas, which reveals various roles of insects and other mammals in its epidemiology.1 Even if the main mammalian hosts and/or reservoirs are considered to be humans, marsupials, dogs, and cats,2 a nonexhaustive list of 150—200 wild animals (including the vampire bat Desmodus rotundus) and some 10 domestic or peridomestic animals, which are found to be infected, has been compiled.3,4 In particular, T. cruzi can be naturally found in dogs, cats, cattle, goats, sheep, rabbits, and equines.3,5—7 Among susceptible domestic animals, guinea pigs may play an important epidemiological role, particularly in Peru where they are bred for meat. In Paraguay, it was suggested that cattle, pigs, dogs, and cats provide reservoirs for T. cruzi. In French Guiana, the studies have shown that Didelphis marsupialis and Philander opossum are frequently infected,8 as well as domestic dogs,9 however, T. cruzi was not reported in livestock and humans.10 Indeed, T. cruzi is rarely reported in livestock, but is it due to a lack of presence or a lack of investigation and a lack of an efficient diagnosis method?
From a veterinary point of view, it is difficult to classify these various categories of animals since their role is variable from one situation to another, and, in some instance, may be underestimated. As a first attempt to gather animals into categories, we can consider (1) animal species which are known to have a potential role in the epidemiology of the disease; they may be wild (opossum, armadillo, raccoons, rats, mice, etc.)
American Trypanosomiasis Chagas Disease. DOI: http://dx.doi.org/10.1016/B978-0-12-801029-7.00013-7
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or domestic (dog, cat, guinea pig etc.); and (2) animals that are receptive but are not known to be reservoirs, although they may have a role in the epidemiology; they may be wild animals such as monkeys, deer, and wild pigs or domestic and/or livestock such as equidae, bovines, ovines, caprines, and suidae. A third category would be the experimental model animals which have been very useful to study the human disease, such as mice, rats, guinea pigs, hamsters, rabbits, dogs, and monkeys.
Wild animals as reservoir, domestic animals as reservoir, and animals as experimental models are studied respectively in three specific chapters, so the present chapter will focus on livestock infections. Due to the lack of knowledge on this latter part, it is important to overview the potential ways of infection of livestock and the difficulties encountered to establish a reliable diagnosis in these animal species. Indeed, a study aiming at establishing the seroprevalence of T. cruzi infection in livestock (or dogs) would meet the problem of species specificity due to the interference of Trypanosoma vivax and/or Trypanosoma evansi in the detection of T. cruzi infection, as well as Leishmania infections which are known to cross-react with trypanosomes antigens11; conversely, T. cruzi can interfere with the diagnosis of trypanosomoses in livestock, in particular serological diagnosis of T. vivax in ruminants and T. evansi in equines.10
In rodents, monkey, and dog—infections which have been observed under natural and experimental conditions—information on the pathogenicity and evolution of the infection is available; on the contrary, the information on the livestock aspects of T. cruzi infection is very limited, probably due to the following reasons: (1) T. cruzi infection is not suspected to be of medical and economical significance in livestock; (2) some of the symptoms are greatly delayed from the infection, far beyond the duration of most of the experimental designs in livestock species; (3) the lack of specificity of the diagnosis tools; (4) the existence of a high risk of human infection when handling experimentally infected animals, especially large animals such as horses and bovines; and (5) the existence of a great number of other obviously more important hosts and reservoirs of the parasite.
This chapter will present the scarce information on T. cruzi’s natural and experimental infections in livestock, but it will also focus on the specific natural way of infection of these animals and the potential and possible risks and way back of the infection from these animals toward other animals including humans. A part of it will be speculative due to the very poor information available on the real status and role of livestock in the epidemiology of the infection.
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