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CAB Review

Toxocara and its species.


This systematic review focuses on the nematode genus Toxocara and its zoonotic and non-zoonotic species and provides an update to that published by Warren almost half a century ago. Currently, 26 species of Toxocara have been described morphologically and four differentiated by molecular techniques. The most frequently reported and wide spread zoonotic species is Toxocara canis. Zoonotic infection with T. cati remains controversial and only a few infections, mostly in children with ocular larval migrans (OLM), have been reported. To date, none have been confirmed using molecular techniques. Only a single-suspected case of human infection with T. pteropodis has been reported and this species has yet to be confirmed as zoonotic. Of the non-zoonotic species T. vitulorum is of major economic importance and there are 13 minor species: T. alienata, T. apodemi, T. genettae, T. indica, T. leonine, T. mackerrasae, T. malaysiensis, T. paradoxura, T. pearsei, T. sprenti, T. surkattae, T. tanuki and T. vajrasthirae. Nine species have been reported only once: T. canarisi, T. cynonycteridis, T. elephantis, T. herpestum, T. hippopotami, T. lyncis, T. manzadiensis, T. vincenti and T. warreni. Toxocara occurs in many definitive host species: canids, felids, civets, mongoose, cattle, raccoons, bats and rodents. In humans, T. canis infections can result in four distinct syndromes: visceral larval migrans, OLM, neuro-toxocariasis and covert toxocariasis. Serological tests supplemented by molecular and imaging techniques provide the basis of diagnosis and may also add to the longitudinal monitoring of treatment. Seroprevalence in humans in developed countries ranges from 3 to 22% and in developing countries from 10 to 92%. Vertical transmission of the parasite in definitive hosts facilitates the earliest potential production of eggs from young animals and provides challenging yet important control opportunities. Climate change and increasing human and companion animal populations have facilitated an expansion in the geographical range of this zoonosis. Behavioural changes coupled with increased urbanization enhance potential transmission, as people and dogs become increasingly crowded together facilitating opportunities for T. canis transmission, and a greater understanding of these factors should be examined to facilitate appropriate and cost-effective control programmes. Anthelminthic used in the elimination of adult parasites from dog or cat intestines can provide an effective control with toxocariasis. Control measures using a one health approach coordinating the expertise of physicians, veterinarians, public health workers, dog owners and aided by legislation facilitates a best practice approach to control.