Agriculture Reference
In-Depth Information
3
Soil-Transmitted Helminthic Zoonoses in
Humans and Associated Risk Factors
Vamilton Alvares Santarém
1
, Guita Rubinsky-Elefant
2
and Marcelo Urbano Ferreira
3
1
School of Veterinary Medicine, Universidade do Oeste Paulista (Unoeste)
2
Institute of Tropical Medicine of São Paulo, Universidade de São Paulo (USP)
3
Institute of Biomedical Sciences, Universidade de São Paulo (USP)
Brazil
1. Introduction
The soil is an important route for transmission of numerous human pathogens, including the
five major soil-transmitted helminths (STHs), also known as geohelminths, namely:
roundworm (
Ascaris lumbricoides
), whipworm (
Trichuris trichiura
), hookworms (
Ancylostoma
duodenale
and
Necator americanus
), and threadworm
Strongyloides stercoralis
(Brooker et al.,
2006). An estimated one billion people are currently infected with STHs worldwide,
particularly in resource-poor settings (WHO, 2011). Although overall mortality due to STH
infections is low, morbidity may be significant given the pronounced impact on nutrition,
growth, physical fitness, cognitive functions among infected infants, schoolchildren and adults
from developing countries (Bethony et al., 2006). In Africa, an estimated 89.9 million children
harbor STHs, many of whom are co-infected with two or more STH species (WHO, 2011).
Zoonotic agents, comprising a wide variety of bacteria, viruses, and parasites, account for
almost two thirds of all known human infections. Some helminthoses that commonly infect
canids and felids are typically soil-transmitted. This chapter focuses on two major groups of
STHs that cause disease in humans: (a) the ascarids
Toxocara canis
and
T. cati
, associated
with visceral and ocular larva migrans, and (b) the hookworms
Ancylostoma braziliense
and
Anc. caninum
, associated with cutaneous larva migrans. We review the current geographic
distribution, laboratory diagnosis and clinical spectrum of these infections, examine the
relative contribution of some risk factors for infection and disease, and discuss potential
control measures for reducing the burden of disease in companion animals and humans.
A third soil-transmitted ascarid species that can cause human disease is
Baylisascaris procyonis
,
commonly found in raccoons in North America. Human infections are characterized by severe
neurological disease, leading to death or long-lasting sequelae (Watts et al., 2006). Another
nematode species,
Gnathostoma spinigerum
, has occasionally been found in biopsy sample from
patients with suspected VLM. More recently species of
Toxocara
including
T. malayensis
, a
parasite of the domestic cat, and
T. lyncus
, which infects the caracal, have been identified, but
their role in human disease remains unknown (Despommier, 2003). Soil-transmitted larval
infection with other common canine and feline hookworms, such as
Anc. ceylanicum
,
Anc.
tubaeforme
and
Uncinaria stenocephala
, can also cause occasional dermatological lesions in
humans, and
Anc. ceylanicum
can readily develop in adults causing severe enteritis (Bowman
