Agriculture Reference
In-Depth Information
infections with
Toxocara
, however, cause much less severe systemic manifestations, if any,
and treatment is not required.
Eosinophilia and elevated levels of IgE are commonly found in toxocariasis, as well as high
titres of
Toxocara
antibodies. Covert and common toxocariasis are likely to represent slight
variations in the clinical spectrum of mild infections in children and adults, respectively.
Although wheezing is a common presenting feature of VLM, whether or not
Toxocara
infection predisposes to asthma remains uncertain. Some epidemiological studies have
shown a positive association between wheezing or asthma and
Toxocara
seropositivity
(Desowitz et al., 1981; Ferreira et al., 2007; González-Quintella et al., 2006), while others
failed to detect such an effect (Fernando et al., 2009; Sharghi et al., 2001). Asthma symptoms
can result from larval migration through the lungs, but a role has also been proposed for
parasite-induced atopy (Cooper, 2009).
Compared with systemic disease, ocular toxocariasis or OLM usually affects older children,
with an average age at onset of 7.5 years (range, 2-50 years) (Taylor, 2001). About 80% of
cases are diagnosed in patients younger than 16 years of age (Brown, 1970). Males tend to be
more frequently affected than females (Brown, 1970; Taylor, 2001). The clinical condition
currently known as OLM or ocular toxocariasis was first described by Wilder (1950), who
found nematode larvae or their residual hyaline capsules during the histological analysis of
24 eyes that had been enucleated from children with suspected retinoblastoma.
The clinical presentation of OLM depends on the primary anatomic site involved and the
immune response of the host. A single eye is affected in most patients (Taylor, 2001). The
most common symptoms are strabismus, unilateral decreased vision and leukocoria (white
eye). Peripheral, posterior pole retinal granuloma and endophthalmitis are the usual
presentations on the eye exam.
The presence of a vitreous band, or a membrane extending between the posterior pole and
high-reflective peripheral mass, detected by ocular ultrasound, may help in the diagnosis
when the ocular medium is opaque (Figure 3).
Fig. 3. Clinical presentation of ocular toxocariasis. A. Peripheral retinal and vitreous lesion, a
localized mass of whitish tissue involving the retina and peripheral vitreous with a fibro-
cellular band running from the periphery toward the optic nerve or posterior retina. B.
Ocular ultrasound showing a vitreous band or membrane (arrow) extending between the
posterior pole and high-reflective peripheral mass. (Image Courtesy: Ophthalmology Clinic
of the University of São Paulo - Medical School General Hospital, HC-FMUSP).
