Transmission and Epidemiology



Transmission

+ Human transmission of Oesophagostomum most likely occurs through fecal-oral routes.

+ Because direct transmission between humans is difficult to document, there is little supporting evidence that the parasite can be transmitted from person to person.

+ An alternative explanation is that transmission occurs primarily between animals, that contaminate the soil with their infected feces, and people who accidentally ingest the larvae in the soil.


Borrowed from Polderman and Anemana. "Human Oesophagostomiasis: A Regional Public Health Problem in Africa." Parasitology Today. 1999. 15:129-139.




Vector

+ Like the other intestinal nematodes, this parasite has no vector. Instead, it has a free-living stage in the soil where eggs hatch and L1 develop into infective L3 parasites.


Reservoirs


+ The specific animal reservoirs harboring Oesophagostomum parasites which infect humans is unknown.

+ However, cattle, sheep, goats, cows, wild pigs, and primates all have been identified as hosts for the parasite.

+ Laboratory experiments have shown that this parasite has a high level of species specificity. it is hypothesized that the most likely reservoir candidates are primates.

+ Humans are an unlikely reservoir. In most cases, the parasite is unable to complete its life cycle since it cannot completely penetrate the intestinal wall. Consequently, eggs are rarely found in the stool of infected people and so the eggs are not passed to the soil.


Epidemiology


The epidemiology of Oesophagostomum in humans is an interesting phenomenon. Clinical cases are primarily localized to northern Togo and Ghana, two countries located in West Africa. As indicated in the map below, Ghana is the country outlined in purple and Togo is the country outlined in green.


Map of West Africa. Ghana is outlined in purple and Togo, adjacent to Ghana, is outlined in green. Map borrowed from The World Fact Book.
http://www.cia.gov/cia/publications/factbook/geos/gh.html

Because the epidemiology of Oesophagostomum bifurcum is so clinically relevant to the people living in these areas, many studies have been carried out in order to elucidate the mode of transmission and the reason why the parasite is located in these specific foci. Below is a brief review of three epidemiological studies on Oesophagostomum bifurcum.

+"Human Oesophagostomum infection in northern Togo and Ghana: epidemiological aspects." By: Krepel et al. Annals of Tropical Medicine and Parasitology.1992. 86:289-300.

A regional survey of O. bifurcum infection was carried out in Togo and Ghana. The parasite was found in 38 of the 43 villages surveyed, with the highest prevalence rates reaching 59% in some small, isolated villages. Infection was found to be positively correlated with hookworm infection; however, the difficulty in distinguishing these parasites may have had some confounding effect. Infection rates were low in children under 3 years of age, beyond that, rates of infection increased dramatically until 10 years of age. Interestingly, females showed higher prevalence of infection (34%)than men (24%). Based on these epidemiological studies, this group was ale to conclude that tribe, profession, or religion had no effect on the prevalence of infection in the different communities surveyed. They explain the association between O. bifurcum infection and Necator americanus infection by suggesting that these two parasites live in a similar type of environment and have a similar life cycle and route of infectivity. This explanation is not satisfying, however, because Necator americanus is distributed throughout the world while O. bifurcum is very localized. The habitats and life cycle of this parasite do not explain its distribution.

+ "Clinical epidemiology and classification of human oesophagostomiasis." By: P.A. Storey et al. Trans R Soc Trop Med Hyg. 2000. 94:177-182.

The study investigated the clinical epidemiology of oesophagostomiasis by observing 156 cases in the Nalerigu hospital between 1996-1998. About 1 patient/week presented with this disease over the course of two years and 1% of all surgeries carried out were related to oesophagostomiasis. 13% of the patients presented with the multinodular form of the disease in which they had several nodules in their small intestine, abdominal pain, diarrhea, and weight loss. The other 87% of the patients presented with the Dapaong, or single, tumor form of the disease that was associated with inflammation in the abdomen, fever, and pain. This study also reported on the improved treatment of this disease that resulted when ultrasounds began to be used for detection and disease assessment, instead of performing invasive surgery. They also note that treatment with Albendazole has decreased the need for surgery.

Introduction
Classification
Life Cycle
Epidemiology
Clinical Manifestations
Diagnosis
Treatment
Links
References

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