Agriculture Reference
In-Depth Information
Human CLM, known or presumed to be caused by
Anc. braziliense,
has been reported in
many tropical and subtropical regions, including North and South America, Southern
Europe, India, and the Philippines. The distribution of human infection overlaps with the
geographic range of
Anc. caninum
. CLM is the most common dermatologic condition that
affects North American and European tourists returning from tropical countries. These
imported cases are often reported after exposure to beaches in regions where
Anc. caninum
is
commonly found in their definitive hosts.
6. Laboratory diagnosis, clinical spectrum and treatment of human
toxocariasis
Because larvae do not develop into adult worms in humans, these paratenic hosts do not
pass
Toxocara
eggs in their feces. As a consequence, fecal examination does not contribute to
the laboratory diagnosis of human toxocariasis. Definitive diagnosis of current infection can
only be obtained by histological examination of infected tissue, but biopsies are rarely
obtained for diagnostic purposes. Less commonly, ultrasonography, computed tomography,
and nuclear resonance imaging are also used to detect and localize lesions suggestive of
granulomas (Magnaval et al., 2001; Watthanakulpanich, 2010).
Virtually all
Toxocara
infections in humans are diagnosed serologically. The standard test to
diagnose human toxocariasis is the indirect ELISA with antigens excreted-secreted by
T.
canis
(TES) L3 larvae (de Savigny, 1975, 1979). The TES-based ELISA for IgG antibodies has
been reported to be 78% sensitive and 92% specific (Glickman et al., 1986), although
putatively more specific recombinant antigens have been obtained for serology. Since cross-
reactive antibodies elicited by exposure to other helminths may reduce the specificity of
TES-based serology in tropical populations (Lynch et al., 1988b; Watthanakulpanich et al.,
2008), serum samples are usually pre-incubated with antigens of related nematodes, to
remove cross-reacting antibodies. Our test samples are routinely pre-incubated with an
adult worm extract of
A. suum
(Elefant et al., 2006).
Positive ELISA results can be confirmed by Western blot (Magnaval et al., 1991), but this
technique is more expensive and labour-intensive than ELISA. Recombinant
T. canis
antigens, which are species-specific, have been expressed and used in prototype ELISAs for
detection of antibodies, with promising results (Yamasaki et al., 2000). Among the four
human IgG subclasses, specific IgG2 antibodies to TES antigens yield the highest sensitivity
in ELISA (Watthanakulpanich et al., 2008), while detection of IgG4 antibodies contributes to
increased specificity (Noordin et al., 2005).
Immunoblotting (IB) techniques, based on TES antigens, have been applied to improve
serodiagnosis, and for follow-ups after chemotherapy (Rubinsky-Elefant et al., 2011).
Antigen-capture ELISAs with monoclonal antibodies have been developed (Gillespie et al.,
1993; Robertson et al., 1988) but poor specificity precludes their use in routine diagnosis.
Polymerase chain reaction (PCR)-based methods for
Toxocara
identification in clinical and
environmental samples have been described (Fogt-Wyrwas et al., 2007; Zhu et al., 2001), but
are not widely available.
The clinical spectrum of toxocariasis in humans, ranging from asymptomatic infection to
severe organ injury, is determined by parasite load, sites of larval migration, and the hosts
inflammatory response. Two severe clinical syndromes are classically recognized: VLM
(systemic disease caused by larval migration through major organs) and OLM (disease
limited to the eye and optic nerve). Half a century ago, Beaver and colleagues described
