Toxocariasis: Zoonotic Roundworm

Toxocariasis is a zoonosis caused by roundworms of cats and dogs, with Toxocara canis as its main representative (Fan et al., 2004). This zoonotic roundworm is not only present worldwide in its definitive host; it also occurs in different paratenic hosts which consist of other animals, including humans (Strube et al., 2013). Unembryonated eggs are passed by infected dogs into the environment during defecation. Optimal temperatures and humidity allow these eggs to embryonate, making them infectious to both final and paratenic hosts (Fan et al., 2004). Transmission to humans normally occurs through accidental ingestion of embryonated eggs from contaminated soil (Khademvatan et al., 2013), from food contaminated with eggs or from ingestion of

Its clinical manifestations are non- specific and may vary widely from asymptomatic cases to systemic infections. In many cases, infected hosts were asymptomatic; however, it can also be clinically manifested in four forms based on organs and tissues affected, as well as their signs and symptoms. These are visceral larva migrans, ocular larva migrans, neurological toxocariasis, and covert toxocariasis (Despommier, 2003; Magnaval et al., 2001; Roldan et al., 2010). Furthermore, toxocariasis has also been known to cause blindness, hepatomegaly, liver necrosis, spleen enlargement, and pulmonary symptoms. It is also known to affect the neuropsychological performance and cognitive development of the infected human hosts. Toxocara eggs cannot be detected in human feces since they do not develop into adults in paratenic hosts. Definitive diagnosis is challenging since it requires direct observation of the larva in tissues. However, due to migration of larvae and their very small size, there is a difficulty in detecting larvae in human tissues (Akao and Ohta, 2007). Hence, diagnosis of the disease is largely based on clinical, epidemiological, and serological data (Bojanich et al.,