New and Emerging Parasitic Zoonoses

Abstract

Parasitic zoonoses are widespread throughout the world and commonly are associated with foodborne infections and insect bites, but they receive little media attention and many are neglected tropical diseases. Comprehending the complex population biology and transmission ecology of multihost parasites is one of the major challenges of biomedical sciences for this century. This chapter will review zoonotic parasites, which rarely infect humans but are increasingly recognized in Asia and affecting tourists such as sarcocystic species, and newly recognized zoonoses in humans previously considered strictly animal pathogens. Sarcocystosis causes myositis in humans and two species can be acquired from eating undercooked meat: Sarcocystis hominis, from beef, and Sarcocystis suihominis, from pork. A species from reptilian host, Sarcocystis nesbitti, can be acquired from ingesting feces-contaminated water or food from endemic areas. Other emerging zoonotic parasites including the raccoon roundworm, Baylisascaris procyonis, Onchocerca lupi, Dirofilaria species, and Trypanosoma evansi, are also reviewed in this chapter. B. procyonis is widespread in raccoons but infects a wide range of vertebrates and has been increasingly recognized to cause infections in humans for more than a decade, predominantly young children. This parasite can cause severe visceral larva migrans with grievous neurological disturbance and ocular disease and it is endemic in North America. O. lupi is a filarial nematode that infects the scleral conjunctival tissue of dogs, wolves, and cats, and canine cases have been on the increase in the USA and Europe. The first human case of O. lupi was reported in Europe in 2001 and the first case in the USA in 2013. Unlike the cases reported in other countries, the American experience have not had subconjunctival nodules but present with more invasive disease, such as spinal, orbital, and subdermal nodules. Trypanosoma are major zoonotic parasites recognized to cause substantial disease burden in sub-Saharan Africa [sleeping sickness] and Latin America [Chagas disease], but other less known animal species can occasionally cause human disease [T. lewisi, T. congolense, and T. evansi]. T. evansi was first reported to cause human infection in India in 2005 and more recently in Vietnam, with nonspecific febrile illness. However, a high burden of disease is present in bovids and horses [approaching 30%] in central and southern Vietnam and possibly in other parts of Asia, and human infections may be more common than recognized and have the potential to cause larger burden of human infections. Dirofilariasis is also considered an emerging parasitic zoonosis in Europe. Dirofilariasis is caused by the dog heartworm, D. immitis, transmitted by mosquitoes and produces pulmonary nodules in humans or by D. repens which can cause subcutaneous nodules or ocular lesions. Global surveillance should be implemented to monitor these emerging and novel parasitic zoonoses.