8 Management and Treatment Options for Human Toxocariasis

Human toxocariasis is a zoonosis caused by infective larvae of Toxocara canis (Beaver, 1956) or Toxocara cati (Nagakura et al., 1990). These ascarids are commonly found in the tissues (larvae) and intestinal tract (adult worms) of dogs and cats, respectively. Infection results from ingestion of embryonated eggs in soil (Glickman and Schantz, 1981) or on contaminated fomites (Vazquez Tsuji et al., 1997). Live larvae can be ingested with raw or undercooked meat, giblets or offal (Nagakura et al., 1989; Stürchler et al., 1990; Fan et al., 2004; Taira et al., 2004). Toxocara infection results in a wide variety of syndromes in humans, although most infections are probably subclinical. Visceral larva migrans (VLM) was first described in 1952, in children with an enlarged liver and hypereosinophilia (Beaver et al., 1952). The typical VLM patient is a child between the ages of 2 and 7 years with a history of geophagia and exposure to puppies in the home. The clinical signs of VLM are usually associated with hepatic and pulmonary larval migration and include abdominal pain, decreased appetite, restlessness, fever, coughing, wheezing, asthma and hepatomegaly (Ehrard and Kernbaum, 1979). Infection is usually characterized by marked and chronic eosinophilia (>2.0 10 cells/l), leukocytosis and hypergammaglobulinaemia. In industrialized countries, VLM is relatively uncommon, and a review of the literature from 1952 to 1979 found only 970 reports (Ehrard and Kernbaum, 1979). Other forms of toxocaral disease were identified in the 1980s by two case–control studies conducted in adults in France (Glickman et al., 1987) and in children in Ireland (Taylor et al., 1988). In French adults, toxocariasis was characterized clinically by weakness, pruritus, rash, difficulty in breathing and abdominal pain. Significant laboratory findings included mild peripheral eosinophilia and increased total serum IgE. This syndrome was termed ‘common toxocariasis’ in adults (Magnaval et al., 1994a). In Ireland, the most frequent clinical findings in children infected with Toxocara larvae included fever, anorexia, headache, abdominal pain, nausea, vomiting, lethargy, sleep and behaviour disorders, pharyngitis, pneumonia, coughing, wheezing, limb pains, cervical adenitis and hepatomegaly. Twenty-seven per cent of patients had high antiToxocara antibody titres, but a normal eosinophil count. This form of the disease in children was coined ‘covert toxocariasis’ (Taylor et al., 1988). Toxocariasis has also been associated with allergy-related syndromes including angioedema (Magnaval and Baixench, 1993), chronic urticaria (Wolfrom et al., 1996), prurigo (Humbert et al., 2000) and reactive arthritis (Bethel, 1981).