IN HUMANS continued
unilateral diminished vision, leukocoria, photophobia and ocular granulomas. Blindness can occur. The extent of visual impairment depends on the larval burden. It is possible that children with OLM have a repeated small- dose inoculation of larvae over a long period of time that escape the host’s immune defence mechanisms to lodge in the retinal vessels. 13-15 - Covert toxocariasis in children or common toxocariasis in adults is typically non-specific and describes patients that demonstrate positive Toxocara serology linked to a number of systemic and local symptoms. Fever, anorexia, headache, wheezing, nausea, abdominal pain, vomiting and lethargy may be seen. 13,16 - Neurotoxocariasis or neural larva migrans (NLM) is considered rare and predominantly occurs in middle- aged individuals. Migration of larvae through the central nervous system results in clinical signs such as meningitis, encephalitis, cerebral vasculitis, or myelitis, usually associated with other symptoms such as fever or headache. 13,17,18 - Systematic reviews have identified associations between Toxocara seropositivity and asthma in children and epilepsy, although further studies are needed. 19,20 A cross- sectional study from the United States demonstrated reduced cognitive function in children seropositive for Toxocara independent of other known confounding factors (e.g. socioeconomic status), however due to the nature of the study, a causal association cannot be confirmed. 21
Unilateral leukocoria caused by toxocariasis (© American Academy of Ophthalmology)
covert or “common” toxocariasis, and neurotoxocariasis (NLM). 13 - Visceral larva migrans (VLM) is considered the most common syndrome and is predominantly documented in young children, but considered rare in practice. Most cases are asymptomatic or subclinical. Clinical signs associated with VLM pertain to the organs involved and may include coughing, wheezing, abdominal pain, hepatomegaly and myalgia. 13 - Ocular larva migrans (OLM) is usually unilateral in presentation and most commonly reported in children. 13 Cases occur every year in Australia and are considered rare, estimated at one case per 1.6 million head of population annually. 2 Clinical findings include strabismus,
KEY CONSIDERATIONS 1. Veterinarians should educate dog owners regarding the potential risks of improper parasite control in dogs. 2. As the prepatent period of T. canis is approximately five weeks and T. cati five to eight weeks, monthly deworming of dogs and cats is recommended. 3. Daily removal of pet faeces and covering sandpits when not in use is essential to reduce environmental contamination.
Monthly deworming of
adult dogs and cats is recommended to reduce environmental contamination and minimise zoonotic risk.
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Companion Animal Zoonoses Guidelines 86
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