Article Citation: Al-Awadhi, M. A. (2020, October 17). Epidemiology of human toxocariasis: An update. Kuwaiti Journal of Medical Parasitology. https://q8jmp.com/epidemiology-human-toxocariasis/
Toxocariasis is a zoonotic parasitic infection (parasite is transmitted from animals to humans). Toxocara canis and Toxocara cati infect dogs and cats, respectively, and produce eggs in the animal intestines which are then shed through defecation into the environment. Humans contract the infection upon accidental ingestion of Toxocara spp. eggs from the environment (e.g. contaminated soil, especially children in playgrounds) or contaminated food such as unwashed vegetables, or by direct contact with contaminated pet cat and dog fur. Human infection by Toxocara spp. larvae usually remains asymptomatic or manifests as mild symptoms. However, less commonly, the infection can progress to cause ocular toxocariasis (damage to retina or other eye tissue leading to blindness, usually in one eye) or visceral toxocariasis (damage to organs such as the liver or brain). Globally, nearly 1 in 5 people are infected with Toxocara spp. (Rostami et al., 2019).
Due to the ubiquitous nature of Toxocara spp., a PubMed search was performed for updated studies published in the year 2020 related to the epidemiology of human toxocariasis. We found a total of 19 studies which reported the seroprevalence rates of toxocariasis in humans. The average seroprevalence rate of human toxocariasis from 19 published studies was 27.9% and ranged from 1.4% to 92.4%. The highest rates were recorded among pregnant women in Nigeria (92.4%), followed by schoolchildren in Honduras (88.6%) and the general population in Ghana (62.0%). In Iran, 6 studies were reported from which the highest rate (28.6%) was found among multiple sclerosis patients. The seroprevalence of Toxocara spp. infection among patients with eosinophilia was reported in Ecuador (38.0%) and South Korea (22.2%). Among children, seroprevalence rates were reported in 4 studies from Honduras (88.6%), Thailand (58.2%), Mexico (13.8%) and the USA (3.6%).
It is clear from recent studies that African and Southeast Asian countries had the highest prevalence of human toxocariasis, whereas industrialized countries including the USA and European countries showed the lowest seroprevalence rates. It is important to mention that in the USA and most European countries, stray cats and dogs are usually removed from the streets by the authorities and are sheltered until adopted or put down. Such measures probably reduce the parasitic load from soil environments and consequent exposure of humans to Toxocara spp. eggs during outdoor activities. Furthermore, it is a common practice in these countries that pet owners remove and properly dispose of pet feces from the playground and park soil after defecation, which further decreases the prevalence of Toxocara spp. eggs in the environment.
Human toxocariasis epidemiology studies published in 2020 (PubMed).
| Study Group | Country / Region | Seroprevalence Rate | Reference |
| Pregnant women | Nigeria | 92.4% | Ikotun et al., 2020 |
| Schoolchildren | Honduras | 88.6% | Hernández et al., 2020 |
| General population | Ghana | 62.0% | Boyko et al., 2020 |
| Patients | Vietnam | 59.0% | De et al., 2020 |
| Schoolchildren | Thailand | 58.2% | Phasuk et al., 2020 |
| Patients with eosinophilia | Ecuador | 38.0% | Morales-Yánez et al., 2020 |
| Patients with multiple sclerosis | Iran | 28.6% | Khalili et al., 2020 |
| Patients with eosinophilia | South Korea | 22.2% | Song et al., 2020 |
| Pregnant women | Iran | 21.2% | Raissi et al., 2020 |
| General population | Russia | 16.0% | Akhmadishina et al., 2020 |
| General population | Iran | 14.5% | Asadi et al., 2020 |
| Children | Mexico | 13.8% | Ponce-Macotela et al., 2020 |
| General population | Iran | 11.0% | Abbaszadeh Afshar et al., 2020 |
| General population | Iran | 6.5% | Shafiei et al., 2020 |
| Recent immigrants | USA | 6.4% | Herrick et al., 2020 |
| General population | Europe | 6.2% | Strube et al., 2020 |
| Adults | Mexico | 4.7% | Ponce-Macotela et al., 2020 |
| General population | Slovakia | 3.7% | Fecková et al., 2020 |
| Schoolchildren | USA | 3.6% | Bradbury et al., 2020 |
| Nomads | Iran | 1.4% | Arefkhah et al., 2020 |
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