By Siva Bubby, BASIS Scottsdale, Scottsdale, AZ, USA
Ascariasis, characterized by the WHO as one of the most common human parasitic infections, is a neglected tropical disease that has crept its way to international scales (“Water related diseases,” 2001). Since 1974, its global prevalence has increased 300-fold, infecting nearly 1.2 billion people today and claiming 60,000 lives annually (“Ascariasis,” 2020; Shah & Shahidullah, 2018). Although its victims show few to no symptoms, ascariasis has been linked to severe health conditions such as blindness, epilepsy, and cancer (Schluth et al., 2020). As this disease continues to spread, it is imperative to understand its pathology and mitigate its detriment to global health.
The disease’s primary vector is Ascaris lumbricoides, a roundworm transmitted by ingesting contaminated food, water, or soil (“Ascariasis,” 2020). While commonly found in tropical regions or areas with poor sanitation, what facilitates the parasite’s global presence are its resistance to extreme conditions and large number of offspring per reproductive event (Shah & Shahidullah, 2018). A similar parasite, Ascaris suum (pig roundworm), is associated with ascariasis in well-developed countries (Haburchak, 2018); however, according to the CDC, its global prevalence remains unknown. International migration and trade exacerbate both parasites’ infectious capabilities (Kanneganti et al., 2013; Räisänen et al, 1985). With these traits, it is no surprise that these roundworms can pervade continents.
Ascariasis infections typically begin with the host consuming contaminated food or water. The parasite’s eggs quickly hatch in the small intestine and spread throughout the bloodstream into the liver and lungs. While continually growing, the larvae are swallowed again upon arrival at the host’s pharynx. When the parasites return to the small intestine, they will have completely matured, at which point they begin reproducing. Females can lay over 200,000 eggs daily (Haburchak, 2018). After male roundworms fertilize the eggs, the host releases them as feces. In soil, these eggs can survive for nearly a decade and become infective within two weeks (Shah & Shahidullah, 2018). The cycle repeats as more contaminated food or water is consumed.
The Ascaris roundworm population dictates the disease’s spread, but particular risk factors yield insight into its behavior. For example, children are at greater risk of infection than adults (Haburchak, 2018). Ascariasis is also associated with poor socioeconomic conditions (poverty and substandard sanitation) and warmer climates, especially in densely populated regions. While victims are generally asymptomatic, those with higher bodily roundworm concentrations are more likely to experience gastrointestinal damage or abdominal pain as the parasite traverses through the host’s body (“Ascariasis,” 2020; Shah & Shahidullah, 2018). Ascariasis can result in stunted child growth, impaired cognitive development, clogged organ ducts, and death (Else et al., 2020).
As of 2018, ascariasis is present in at least 150 countries. A case distribution from Medscape reveals that 75% of the world's infected population reside in Asia and Oceania, 16.7% are in Africa and the Middle East, and 8.3% are located in South and Central America (Shoff, 2018). These figures offer a holistic understanding of the disease, but each country’s prevalence varies based on its local communities and resources. Moreover, a 2016 study analyzing the global health and economic impacts of hookworm suggests a worldwide productivity loss of roughly $11 billion in 2004 (Bartsch, 2016). Since ascariasis mainly attacks low-resource regions, it is widely understudied and contains little up-to-date statistical information in its epidemiological profile (Schluth et al., 2020).
The WHO’s ascariasis control strategy for endemic regions includes periodic population-wide “deworming” treatments (via medications such as albendazole and mebendazole), increased health education, and improved sanitation to reduce reinfection rates. Regional organizations work with federal governments to implement community interventions through school-based health programs. India’s National Deworming Day in 2016, for instance, was an initiative in which school and healthcare workers provided albendazole to roughly 270 million children (“World’s largest deworming campaign,” 2018). Similarly, deworming campaigns targeting copious schools across Uganda reduced the average prevalence from 60% to 8.8% between 2004 and 2016 (Adriko et al., 2018). By 2030, the WHO aims to “ensure universal access to at least basic sanitation and hygiene” in high-risk areas (“Soil-transmitted helminth infections,” 2020).
Simultaneously, the WHO seeks to increase funding for diagnostics research and personalized treatments. Current Kato-Katz diagnostics analyze fecal matter for parasitic eggs, but their low resolution causes them to inefficiently predict patients’ conditions. Other blood-based and molecular diagnostics exhibit greater predictive accuracy but are limited by low applicability or high costs for individual allocation (Lamberton & Jourdan, 2015). Consequently, several ascariasis victims are left without treatment. The WHO intends to gather funds to support programs for individualized preventative chemotherapy across endemic regions (“Soil-transmitted helminth infections,” 2020).
While there is no silver bullet to eliminate ascariasis, continuous collaboration among governments, researchers, healthcare professionals, and local communities can unveil a solution to one day stop this disease.
References
Adriko, M., Tinkitina, B., Arinaitwe, M., Kabatereine, N. B., Nanyunja, M., & M Tukahebwa, E. (2018). Impact of a national deworming campaign on the prevalence of soil-transmitted helminthiasis in Uganda (2004-2016): Implications for national control programs. PLoS neglected tropical diseases, 12(7), e0006520. https://doi.org/10.1371/journal.pntd.0006520
Ascariasis. (2020, November 23). In CDC. Retrieved February 8, 2021, from https://www.cdc.gov/parasites/ascariasis/
Bartsch, S. M., Hotez, P. J., Asti, L., Zapf, K. M., Bottazzi, M. E., Diemert, D. J., & Lee, B. Y. (2016). The Global Economic and Health Burden of Human Hookworm Infection. PLoS neglected tropical diseases, 10(9), e0004922. https://doi.org/10.1371/journal.pntd.0004922
Else, K.J., Keiser, J., Holland, C.V. et al. Whipworm and roundworm infections. Nat Rev Dis Primers 6, 44 (2020). https://doi.org/10.1038/s41572-020-0171-3
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Kanneganti, K., Makker, J. S., & Remy, P. (2013, June 11). Ascaris lumbricoides: To Expect the Unexpected during a Routine Colonoscopy. Case Reports in Medicine, 2013(2015). https://doi.org/10.1155/2013/579464
Lamberton, P. H. L., & Jourdan, P. M. (2015, October 3). Human Ascariasis: Diagnostics Update. Current Tropical Medicine Reports, 2(2015), 189-200. https://doi.org/10.1007/s40475-015-0064-9
Räisänen, S., Ruuskanen, L., & Nyman, S. (1985). Epidemic Ascariasis—Evidence of Transmission by Imported Vegetables. Scandinavian Journal of Primary Health Care, 3(3), 189-191. doi:10.3109/02813438509013944
Schluth, C., Standley, C., Bansal, S., & Carlson, C. (2020, January 01). Mapping the human helminthiases: Advances and gaps in neglected disease surveillance. Retrieved February 08, 2021, from https://doi.org/10.1101/2020.10.30.20223529
Secretariat, SuSanA. (20 November 2014). Ascaris lumbricoides life cycle [Infographic]. Creative Commons. https://www.flickr.com/photos/23116228@N07/15834812242
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