History of Toxocara and the associated larva migrans.

This review covers the systematics and nomenclature of the Ascaridoid genus toxocara, and more specifically the species Toxocara canis and Toxocara cati. Also discussed is the discovery of the persistence of these larvae in the tissues of paratenic hosts, and the role that other species of this genus might or could play in other such hosts; including those where the life cycle has been described, i.e., Toxocara vitulorum, Toxocara pteropodis, Toxocara mackerrasae, and Toxocara tanuki. Also examined is the work that led to the realization that the larval stage leaving the egg actually being a third rather than a second stage larva. Also discussed on the work showing that the larvae can persist in paratenic host with remarkable longevity without undergoing any morphological change for years and that these larvae can be transmitted from one paratenic host to another by ingestion. People are usually infected by the ingestion of eggs containing third-stage larvae, but infections also occur on occasions from the ingestion of uncooked paratenic hosts.

Toxocara eggs in an 18th century Franciscan from Portugal. The challenge of differentiating between parasitism and chance in Paleoparasitology.

In 2005, an adult male was excavated in the cloister of the former Convent of the Holy Spirit, in the Franciscan Province of Holy Mary of Arrábida, Lisbon district. From the anterior part of the sacrum, a darker organic agglomeration was collected and studied for intestinal parasites. Samples were rehydrated with Lycopodium tablets in a Na3PO4 5% solution for 72h, followed by the swirl technique. Organic material was concentrated at 2500rpm. At least 20 slides of each sample were examined using a light/polarized microscope. A control sample from outside the pelvis revealed no biological remains. A sample collected inside the pelvic girdle was positive for pollen grains, other plant remains and Toxocara eggs, perhaps T. cati (2766 eggs/gram sediment). This finding, although exciting, cannot be explained in a simple way because humans are not definitive hosts for Toxocara species. Ingestion of feces-contaminated food or water, geophagy, or true infection are hypotheses considered in this study, which demonstrates the difficulty of interpreting the presence of animal parasites in human remains. This is the first time Toxocara eggs are found associated with human remains.

Earliest Evidence of Toxocara sp. in a 1.2-Million-Yr-Old Extinct Hyena (Pachycrocuta brevirostris) Coprolite from Northwest Pakistan.

The study of fossil parasites can provide insight into the antiquity of host-parasite relationships and the origins and evolution of these paleoparasites. Here, a coprolite (fossilized feces) from the 1.2-million-yr-old paleontological site of Haro River Quarry in northwestern Pakistan was analyzed for paleoparasites. Micromorphological thin sectioning and Fourier-transform infrared spectrometry (FTIR) analysis confirms the coprolite belonged to a bone-eating carnivore, likely the extinct giant short-faced hyena (Pachycrocuta brevirostris). Parasitological analysis shows the coprolite to be positive for Toxocara sp. To our knowledge, this is the earliest evidence for Toxocara sp. found.

Toxocariasis.

Toxocariasis is one of the most commonly reported zoonotic helminth infections in the world with a higher prevalence in tropical settings and in rural populations. It is caused by the larval stages of the ascarids Toxocara canis, the common roundworm of dogs, and probably also by the larval stages of Toxocara cati, the roundworm of cats. The clinical spectrum of toxocariasis in humans varies from asymptomatic infection to severe organ injury caused by larval migration to the major organs ("visceral larva migrans"). Clinical involvement of the nervous system in visceral larva migrans due to Toxocara is thought to be rare, although in experimental animals the larvae frequently migrate to the brain. The CNS migration leads to a variety of neurological disorders such as meningo-encephalitis, space-occupying lesion, cerebral vasculitis, epilepsy, and myelitis. Several studies have evidenced high seropositivity rates for T. canis among people with epilepsy suggesting that toxocariasis could play a role in the incidence of epilepsy in endemic areas. Diagnosis of neurotoxocariasis is based on the history; blood tests, including differential blood cell count; CSF investigations, including determination of antibodies anti-Toxocara canis; and neuroimaging. Like the visceral manifestations, neurological manifestations of toxocariasis are treated with benzimidazole components.