Global Burden of Toxocariasis: A Common Neglected Infection of Poverty

Abstract

Toxocariasis is a zoonosis of global importance, yet our understanding of the burden of human disease is limited by insufficient clinical awareness, absence of standardized diagnostic criteria and lack of coordinated epidemiological surveillance (Macpherson in Int J Parasitol 43(12–13):999–1008, 2013; Smith et al. in Trends Parasitol 25(4):182–188, 2009; Rubinsky-Elefant et al. in Ann Trop Med Parasitol 104(1):3–23, 2010). Human infection results from zoonotic transmission of the nematode Toxocara canis, and to a lesser extent T. cati, whose definitive hosts are dogs and cats, respectively (Despommier in Clin Microbiol Rev 16(2):265–272, 2003). Toxocara canis and T. cati are distributed worldwide, and seroprevalence studies have shown that toxocariasis is especially prevalent among socioeconomically disadvantaged children in both developing and developed nations (Smith et al. in Trends Parasitol 25(4):182–188, 2009; Hotez in PLoS Negl Trop Dis 3(3):e400, 2009). Infection in humans occurs after accidental ingestion of embryonated eggs containing Toxocara larvae present in contaminated soil or food (Despommier in Clin Microbiol Rev 16(2):265–272, 2003), or by ingestion of encapsulated larvae in raw tissues of paratenic hosts, such as cows, sheep and chickens (Akao and Ohta in Parasitol Int 56(2):87–93, 2007). Clinical manifestations range from asymptomatic infection to severe organ injury, and treatment varies according to symptoms and location of the larvae (Macpherson in Int J Parasitol 43(12–13):999–1008, 2013). Improved understanding of the global health impact of toxocariasis would assist control of this common neglected infection.