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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