Toxocariasis is a zoonotic helminthiasis and one of the most common parasitic infections in humans worldwide. The nematode responsible for this infection, Toxocara canis, is transmitted mainly by dogs [1].
T. canis can follow a direct or indirect life cycle. Adult forms of these parasites parasitize canids and live in the digestive tract of these definitive hosts. Eggs released in the faeces are found in the soil, where they embryonate and become infective. Most often, humans are infected by ingesting embryonated eggs found in nearby soil or on raw vegetables. After ingestion, the eggs hatch and the larvae penetrate the intestinal wall and circulate to the organs of the parasitized individual. Although the larvae do not develop in these organs, they can cause local reactions and mechanical lesions, leading to clinical toxocariasis [2,3,4,5].
The risk of transmission is especially high in tropical regions, where eggs excreted in the stools of definitive hosts remain infective due to hot and humid conditions [6].
While infection with T. canis can lead to severe disease, it is usually asymptomatic and is therefore considered to be underdiagnosed. Four distinct toxocariasis syndromes have been described: a systemic or generalized syndrome comprising common minor/converted toxocariasis and visceral larva migrans; and a compartmentalized syndrome comprising neurotoxocariasis and ocular larva migrans [3, 5, 7].
The most severe, visceral larva migrans, is characterized by respiratory, digestive, and/or cutaneous symptoms and is frequently accompanied by eosinophilia. Cerebral and neurological involvement can also occur: when transverse myelitis is present, diagnosis is difficult and clinical improvement is uncertain despite optimal antiparasitic and anti-inflammatory treatment. Covert toxocariasis, which manifests essentially as recurrent abdominal pain, is also difficult to diagnose [3]. Ocular larva migrans, caused by the entry of T. canis larvae into the host’s eye, is characterized by ocular symptoms. Lastly, neurotoxocariasis consists of neurological symptoms that result from T. canis larvae crossing the blood-brain barrier and invading the central nervous system [8].
Serological monitoring is rarely used in toxocariasis because antibodies can persist for a long time [9]. Serological monitoring is possible but limited to patients receiving antiparasitic treatment (and not those receiving corticosteroid therapy). Furthermore, these serological tests should not be performed too early or too frequently. Serological testing following treatment (> 6–12 months) is useful, provided that the pre-treatment specimen is also repeated at the same time.
Worldwide seroprevalence is estimated at 19.0% according to a recent meta-analysis (95% CI, 16.6–21.4%). There were significant variations by world region: African region (37.7%), Eastern Mediterranean region (8.2%), Southeast Asia (34.1%), Western Pacific (24.2%), Americas (22.8%) and European region (10.5%) [10].
Although T. canis is ubiquitous, its seroprevalence can vary considerably, for example in the same North American region, from 0.6% in a Canadian Inuit community to 30.8% in a population of Mexican children [11].
Seroprevalence with T. canis is especially common in rural and tropical areas [6]. Higher seroprevalence is associated with low income and development index, low latitude, high temperature and humidity, and high rainfall [12]. Certain populations have been shown to be at higher risk of infection: living in a rural area, being young, consuming raw meat, consuming untreated water, having dogs, having a low level of education and living in poverty [11, 13].
Reunion Island is a French overseas territory with a young population and a high level of precariousness. This island of 2512 km² is situated in the Indian Ocean, 700 km east of Madagascar, and characterized by a tropical climate. A study reported in 1994 in this island a T. canis seroprevalence of 93%, confirmed by Western Blot, for the period 1987–1989, on 387 samples from epidemiological surveillance of cysticercosis, and found the infection to be significantly correlated with age and lack of access to drinking water [6]. Given this very high seroprevalence figure, local physicians have found it difficult to distinguish between clinical presentations. Unfortunately, data on T. canis seroprevalence on the island have not been updated since.
Reunion Island is home to a large number of stray dogs, mainly abandoned animals (estimated at 42,000 in 2018) [14]. In recent decades, a number of health measures, especially actions to reduce the number of stray dogs and improvements in sanitary conditions, have been implemented on the island to lower the burden of zoonoses.
The aim of this study was to describe the characteristics of patients who were suspected of toxocariasis and underwent T. canis serology in the local university hospital in 2021.