Toxocara is a good example of a parasite moving from wild canids to their domestic counterparts and then to humans. The first human infection was reported in 1950, and since then it has been reported in almost 100 countries with most cases occurring in France, Austria, India, Japan, Korea, China, USA, and Brazil. In the UK, urban and rural foxes are the primary source of eggs and infections to humans. The human transmission cycle begins when they ingest infectious Toxocara eggs in soil contaminated by dog or cat feces. Other routes are possible, including stroking an infected dog and ingesting eggs that are present on the dog’s fur. Once inside the human intestine, Toxocara larvae hatch but do not undergo further maturation into adult worms; instead, the larvae burrow through the intestinal wall into blood vessels and then migrate to various organs in the body. Infected humans cannot transmit toxocariasis to others because humans do not excrete eggs i.e., they are paratenic hosts. The disease (toxocariasis) caused by migrating T. canis larvae results in two syndromes: visceral larva migrans (affecting lungs, liver, and central nervous system) and ocular larva migrans, where the larvae enter the posterior segment of the eye (Woodhall & Fiore, 2014).
Toxocariasis has a significant socioeconomic impact, particularly on impoverished communities around the world. Over the last few years, toxocariasis has gained an increasing international attention and was listed among the five most neglected parasitic infections according to the US Centers for Disease Control and Prevention (CDC). There is no anti-toxocariasis vaccine and anthelminthic drugs are used to treat infections in dogs and humans for adult worms. However, chemotherapy in humans varies, depending on symptoms and location of larvae (Rostami et al., 2019). Other methods used to decrease the risk of ingesting Toxocara eggs include regularly deworming pets, removing pet waste, promoting good hand hygiene and teaching children the dangers of eating soil.
- Chen et al. (2018). Toxocariasis: a silent threat with a progressive public health impact. Infect Dis Poverty. 7: 59.
- Rostami et al. (2019). Human toxocariasis – A look at a neglected disease through an epidemiological ‘prism’. Infect Genet Evol. 74:104002.
- Woodhall & Fiore (2014). Toxocariasis: A Review for Pediatricians. Journal of the Pediatric Infectious Diseases Society, Volume 3, Issue 2.
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