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== Transmission ==
Transmission of ''Oesophagostomum'' is believed to be oral-fecal for both humans and animals, largely because percutaneous infection with ''Oesophagostomum'' has never been reported.<ref>Ziem, J.B.  “Controlling human oesophagostomiasis in northern Ghana.” (Doctoral thesis)  Leiden University.  2006. <https://openaccess.leidenuniv.nl/dspace/handle/1887/4917?mode=more>.</ref>  It is unclear whether or not parasite transmission is specifically waterborne, foodborne, or both.  Regardless, introduction of the stage three infective larvae is necessary for human infection.  Much about the biological mechanism of transmission is still unknown, and current knowledge of oral-fecal transmission mechanisms does not explain why Oesophagostomum are mostly localized to Northern Togo and Ghana.  It is possible that there are behavioral factors or unique soil conditions that facilitate larval development and are not found outside the current endemic areas.<ref>Ziem, J.B.  “Controlling human oesophagostomiasis in northern Ghana.” (Doctoral thesis)  Leiden University. 2006. <https://openaccess.leidenuniv.nl/dspace/handle/1887/4917?mode=more>.</ref>
Oesophagostomiasis is generally classified as a zoonotic disease, which is an infectious disease that can be transmitted between animals and humans. This has been called into question recently, as recent research has found that human-to-human transmission is possible.<ref name="Sun, Tsieh 1999"/>
== Reservoir ==
''Oesophagostomum'' are carried predominantly by non-humans, infecting [[cattle]], [[sheep]], [[goat]]s, wild [[pig]]s, and [[primate]]s.  Humans are largely presumed to be an accidental host, as they are not suitable for completion of the ''Oesophagostomum'' development; however, the extreme localization of oesophagostomiasis to northern Togo and Ghana in Africa suggests the possibility that the ''Oesophagostomum'' is increasingly exhibiting preference for human hosts.<ref name="Gasser, R B 2006">Gasser, R B, J M de Gruijter, and A M Polderman. “Insights into the epidemiology and genetic make-up of Oesophagostomum bifurcum from human and non-human primates using molecular tools.” Parasitology 132.Pt 4 (2006): 453-60.</ref>
Until recently it was believed that primates were the main reservoirs of human-infecting ''Oesophagostomum'' in northern Togo and Ghana, as these particular species have a considerable concentration in non-human primate reservoirs.  A 2005 study done by van Lieshout and de Grujiter found that ''O. bifurcum'' in humans from northern Ghana is distinct from the ''O. bifurcum'' found in olive [[baboon]]s and mona [[monkey]]s outside the endemic area.  They used species-specific PCR and microscopy to establish the identification of two separate species of ''O. bifurcum.'' <ref>van Lieshout, Lisette et al. “Oesophagostomum bifurcum in non-human primates is not a potential reservoir for human infection in Ghana.” Tropical Medicine & International Health: TM & IH 10.12 (2005): 1315-20.</ref>  These results are significant, as they necessitate further research to determine the definitive reservoirs of human-infecting ''O. bifurcum''.
== Vector ==
Oesophagostomiasis has no vector.<ref>“GIDEON Infectious Diseases - Diseases.” GIDEON Infectious Disease Database.  5 Feb 2009. <http://web.gideononline.com/web/epidemiology/index.php?gdn_form=ZGlzZWFzZT0xMTY1MA==>.</ref>
== Incubation period ==
The life-cycle of ''Oesophagostomum'' can usually be completed in less than 60 days.<ref>Ziem, J.B.  “Controlling human oesophagostomiasis in northern Ghana.” (Doctoral thesis)  Leiden University.  2006. <https://openaccess.leidenuniv.nl/dspace/handle/1887/4917?mode=more>.</ref> When the eggs are passed into the feces to the outside environment, they hatch into stage one larve.  The stage two larve then molt twice, developing into infective stage three larva in 6–7 days. These stage three larvae can survive extended periods of desiccation by shrinking within their sheaths.<ref name="Polderman, A. M. 1995"/>
== Morphology ==
[[file:Cylinder1.JPG|thumb|Morphology]]
Adult worms of all ''Oesophagostomum spp.'' exhibit a cephalic groove by its proximal gut as well as a visible secretory pore, or stomum, at the same level of the oesophagus19.  Like other nematodes, ''Oesophagostomum spp.'' contain a developed, multi-nucleate digestive tract as well as a reproductive system.  Their developed buccal capsule and club-shaped oesophagus are useful for distinguishing ''Oesophagostomum spp.'' from hookworms.<ref>Elmes, B et al. (1953). Helminthic abscess, a surgical complication of oesophagostomes and hookworms. Annals of Tropical Medicine and Parasitology. 48: 1-7.</ref>
Both sexes of adults have a cephalic inflation and an oral opening lined with both internal and external leaf crowns.<ref name="Ash, Lawrence R 1995"/> Female adults, which have a length range of 6.5–24&nbsp;mm, are generally larger than their male counterparts, with a length range of 6-16.6&nbsp;mm.  Males can be distinguished by their bell-like copulatory bursa, located in the tail, and their paired rodlike spicules.<ref>Ziem, J.B.  “Controlling human oesophagostomiasis in northern Ghana.” (Doctoral thesis)  Leiden University.  2006. <https://openaccess.leidenuniv.nl/dspace/handle/1887/4917?mode=more>.</ref>
Eggs are ovular in shape and range from 50 to 100 micrometres in size; they closely resembles those of hookworms, which renders diagnosis via stool analysis useless in areas co-infected with both ''Oesophagostomum'' and hookworm.<ref>Ziem, J.B. “Controlling human oesophagostomiasis in northern Ghana.” (Doctoral thesis)  Leiden University.  2006. <https://openaccess.leidenuniv.nl/dspace/handle/1887/4917?mode=more>.</ref>
== Life cycle ==
[[file:Life cyc.jpg|thumb|Life cycle]]
For non-human hosts, the life cycle of ''Oesophagostomum''  begins with the passing of eggs in the animal feces.  From there the eggs develop into stage one larvae.  These larvae then spend 6–7 days in the environment developing into stage two and then infectious stage three larvae.<ref>Ziem, J.B. “Controlling human oesophagostomiasis in northern Ghana.” (Doctoral thesis)  Leiden University.  2006. <https://openaccess.leidenuniv.nl/dspace/handle/1887/4917?mode=more>.</ref>  Infection begins with the ingestion of soil contaminated with stage three larvae.  After ingestion the larvae end up in the small intestine, unsheathing and penetrating the intestinal wall to form nodules. The resulting adult worms that remain in the intestinal lumen copulate; the eggs from the female are then deposited in the feces. Females usually lay around 5,000 eggs per day, which is on par with reproductive rates of other nematodes within Strongyloidea.<ref name="Krepel, H P 1992">Krepel, H P, and A M Polderman. “Egg production of Oesophagostomum bifurcum, a locally common parasite of humans in Togo.” The American Journal of Tropical Medicine and Hygiene 46.4 (1992): 469-72.</ref>
For human hosts, the life cycle is very similar to that of ''Oesophagostomum'' in animals.  It begins when an animal reservoir defecates into the soil, leaving feces infested with eggs that develop into rhabitiform larvae.<ref>Ziem, J.B.  “Controlling human oesophagostomiasis in northern Ghana.” (Doctoral thesis)  Leiden University.  2006. <https://openaccess.leidenuniv.nl/dspace/handle/1887/4917?mode=more>.</ref> These larve then develop into stage two and then infectious stage three larvae in the environment over the course of 6–7 days. Human infection occurs when soil or water containing the third-stage larvae is ingested, presumably via contaminated meat obtained from infected livestock or crops with contaminated soil.  Once ingested, the filariform larvae migrate to the submucosa of the small or large intestine, then to the lumen of the colon. The developing worms then penetrate the intestinal tissues, causing nodular lesion formation in the intestines and colon; it is in these nodules that the larvae mature to stage four larvae.<ref name="Gasser, R B 2006"/>  These larvae may then emerge from their nodules and migrate back to the intestinal lumen, where they mature into adults. But many larvae often do not complete development and remain in their colon nodules, as humans are generally unsuitable hosts for ''Oesophagostomum''.  The instances where ''Oesophagostomum'' have completed development in humans seem to be dependent on certain environmental and host factors that have yet to be identified.<ref name="Ziem, J.B. 2006">Ziem, J.B. et al. “Impact of repeated mass treatment on human Oesophagostomum and hookworm infections in northern Ghana.” Tropical Medicine & International Health: TM & IH 11.11 (2006): 1764-72.</ref>


== Diagnostic tests ==
== Diagnostic tests ==

Revision as of 13:52, 5 December 2012

style="background:#Template:Taxobox colour;"|Template:Taxobox name

style="background:#Template:Taxobox colour;" | Scientific classification
Kingdom: Animalia
Phylum: Nematoda
Order: Strongylida
Family: Strongyloidae
Genus: Oesophagostomum
Species: Oesophagostomum aculeatum

Oesophagostomum bifurcum
Oesophagostomum brumpti
Oesophagostomum stephanostomum
Oesophagostomum stephanostomum var thomasi

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Diagnostic tests

A definitive diagnosis of Oesophagostomum infection is traditionally done by demonstrating the presence of the larval or young adult forms in nodules of the intestinal wall via surgical examination of tissue. The larvae usually found in tissues can be 500 nanometers or longer in length.[1] With microscopy, one can identify the larvae based on the presence of somatic musculature divided into four quarters, along with a multinucleated intestine as well as an immature reproductive system.[2]

Laboratory methods are of little use for Oesophagostomum diagnosis. It is virtually impossible to make a diagnosis based on microscopy of stool samples alone, as Oesophagostomum eggs cannot be differentiated from hookworm eggs, which are often found in Oesophagostomum endemic areas.[3] The only way to differentiate between the two species of eggs is to perform coproculture, which allows eggs to develop to their stage three larvae, although this is both time consuming and unreliable.[4] Immunoassay tests like ELISA that monitoring for increases in IgG4 antibodies can indicate tissue invasion by Oesophagostomum.[3]

Recent advances, however, have allowed for less invasive and more accurate methods of diagnosis. The following is a review of three articles detailing the diagnostic use of PCR assays and sonographic imaging. Verweij, Jaco J., Anton M. Polderman, et al. “PCR assay for the specific amplification of Oesophagostomum bifurcum DNA from human faeces.” International Journal for Parasitology 30.2 (2000): 137-142. This study developed a molecular-based approach to diagnosing oesophagostomiasis caused by O. bifurcum in humans. Using genetic markers in ribosomal DNA, the researchers developed PCR assays to selectively amplify O. bifurcum DNA from human fecal samples. These assays achieved sensitivity ratings of 94.6% and specificity of 100%, suggesting that the PCR method could be a viable alternative to the long-standing methods of diagnosis as well as an opportunity to reveal more about the epidemiology of oesophagostomiasis.[5]

Storey, P A, S Anemana, et al. “Ultrasound diagnosis of oesophagostomiasis.” The Brit. J. of Radiol. 73.867 (2000): 328-32.

Sonographic imaging and ultrasound were used to examine two cases of oesophagostomiasis in the Nalerigu hospital in northern Ghana. The technology allowed for the detection of intestinal and abdominal wall modules, as well as their size, type and location in the case of the ultrasound. Multinodular disease was representedby nodular colonic lesions and pseudokidney appearances, while the single-nodular Dapaong tumor had the appearance of an echo-free lumen surrounded by a defined but badly reflective wall. The ability to diagnose oesophagostomiasis via ultrasound can reduce the number of excessive invasive surgeries and put greater emphasis on chemotherapy.[6]

Verweij, Jaco J, Eric A T Brienen, et al. “Simultaneous detection and quantification of Ancylostoma duodenale, Necator americanus and Oesophagostomum bifurcum in fecal samples using multiplex real-time PCR. (2007) Am. J. of Trop. Med. Hygiene 77 (4) 685-690

A multiplex PCR method was developed for simultaneously detection of A. dudodenale, N. americanus and O. bifurcum in human fecal samples. The method was tested on human fecal samples from an area in Ghana where co-infections with all three species are endemic. Results showed that the method was both highly specific and sensitive, attaining 100% specificity and sensitivities of 100%, 86.7%, and 100% for detection of N. americanus, O. bifurcum and A. duodenale respectively. Furthermore, cycle threshold values, which correspond to parasite-specific DNA load, correlated with measured intensity of infection as demonstrated in Kato-Kato smears. This PCR method could potentially elucidate species-specific transmission pathways of hookworm-like infections and improve monitoring of interventions.[7]

Management and therapy

The typical adult therapy for oesophagostomiasis is a single 400 mg dose of albendazole (200 mg for children) or pyrantel pamoate.[8] Albendazole works by binding to the free beta tubulin, which inhibits tubulin polymerization. This results in the inhibition of glucose uptake by the Oesophagostomum. Albendazole and pyrantel pamoate at these doses have cure rates of 85% and 59-82%, respectively.[2] Excision of Oesophagostomum larvae from nodules has been shown to have a curative effect on the patient but is invasive and more resource intensive than chemotherapy.[2]

For oesophagostomiasis with complications, the type of treatment varies depending on the severity of the disease. Usually 200–400 mg of albendazole will be given immediately and continued for up to 5 days in conjunction with 250 mg dosages of amoxicillin.[9] In the case of formation of abscesses or fistulae arising from Dapaong tumors, incision and drainage is performed, followed by a regimen of albendazole and antibiotic treatment.[10]

Epidemiology

Oesophagostomiasis is endemic or potentially endemic to 35 countries; approximately 250,000 are infected worldwide, with 1 million more at risk according to the Gideon Infectious Diseases Database. Most of the cases originate in Africa, specifically in Ghana, Togo, Uganda, Nigeria, Zimbabwe and other nearby countries. A few sporadic cases have been reported in countries in South America and Southeast Asia, including Brazil, Indonesia and Malaysia.[11] The vast majority of clinical cases have been collected from northern Togo and Ghana, in West Africa. 156 cases from the areas alone were collected in a 2000 study; before then, only 116 cases were recorded in the literature.[12] O. bifurcum infection in northern Togo and Ghana is found in virtually every village, with some rural areas exhibiting as much as 90% prevalence.[4]


Prevalence is higher in children between ages 2–10), and females older than 5 years of ages have higher prevalence than males within the same age group. These age demographic and gender discrepancies are not yet sufficiently explained – possible factors include differential exposure to contaminated water and strength of immune response.[4]

A study done by Krepel in 1992 revealed a correlation between infection with O. bifurcum and N. americanus in that individuals living in endemic villages were either coinfected with both parasites or neither.[13] This could be due to cofactors shared by both parasites, including poor hygiene, certain agricultural practices and the dearth of potable water suitable for consumption.

Below is a review of some epidemiological studies on the epidemiology of Oesophagostomum bifurcum in northern Togo and Ghana.

"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. The habitats and life cycle of this parasite do not explain its distribution.[14]

"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.[15]

Public health and prevention strategies/vaccines

Given that infective Oesophagostomum larvae are most likely transmitted via oral-fecal routes, sufficiently cleaning and cooking meat and vegetables, as well as boiling all consumed water or only using potable water would help to complement a mass treatment program. Factors like religion, family size and wealth do not suffice in explaining the unique epidemiology of Oesophagostomum; geographic and geological factors must be explored in more detail.[16]

Since oesophagostomiasis is primarily a regional problem (localized in northern Ghana and Togo, an optimal approach to addressing it requires mobilization of resources within and around the endemic area. One proposed solution is to organize all research and intervention projects at the local level, so as to instill knowledge of the infection in the community, and establish a regional collaboration between Ghana, Togo, and Burkina Faso in order to effectively combat oesophagostomiasis.[17]

There is no vaccine for oesophagostomiasis, although prolonged treatment with albendazole seems to be highly effective in countering the Oesophagostomum threat. In fact, recent research indicates that albendazole treatment may be the best intervention available for eliminating oesophagostomiasis from northern Togo and Ghana; following treatment, prevalence continued to go down even with interruption of the intervention. The following is a review of J. B. Ziem’s study of a mass treatment campaign in northern Ghana, as well as the follow-up conducted with the Lymphatic Filariasis Elimination Program.

Ziem, Juventus B et al. “Impact of repeated mass treatment on human Oesophagostomum and hookworm infections in northern Ghana.” Tropical Medicine & International Health: TM & IH 11.11 (2006): 1764-72.

This was a two year study, with four rounds of albendazole treatment administered to a village in Ghana; the target area and an untreated control area were monitored. In the target area, prevalence went down dramatically from 53.0% to 5.4% in the first year to 0.8% in the second year. Larval counts in stools also went down, as well as hookworm prevalence. In contrast, the control area saw an increase in prevalence from 18.5% to 37%. The results indicate potential for elimination of oesophagostomiasis utilizing similar albendazole-distributing mass treatment programs.[18]

Ziem, J. B. et al. “Annual mass treatment with albendazole might eliminate human oesophagostomiasis from the endemic focus in northern Ghana.” Tropical Medicine & International Health: TM & IH 11.11 (2006): 1759-63.

This follow-up to the original two-year study by J.B. Ziem saw collaboration with the Lymphatic Filariasis Elimination Programme, essentially expanding the scope of the Oesophagostomum Intervention Research Program that Ziem worked under. 11 villages across northeastern Ghana were given albendazole-ivermectin treatment and monitored for changes in prevalence; once again, decreases in both Oesophagostomum and hookworm infections occurred after two years of mass treatment. However, after interrupting mass treatment, Oesophagostomum prevalence continued to decrease even as hookworm prevalence increased again. Human oesophagostomiasis infection thus seems interruptible; even small numbers of persistent Oesophagostomum post-treatment were not sufficient to cause reinfection.[19]

References

  1. ↑ Ziem, J.B. “Controlling human oesophagostomiasis in northern Ghana.” (Doctoral thesis) Leiden University. 2006. <https://openaccess.leidenuniv.nl/dspace/handle/1887/4917?mode=more>.
  2. ↑ 2.0 2.1 2.2
  3. ↑ 3.0 3.1
  4. ↑ 4.0 4.1 4.2
  5. ↑ Verweij, Jaco J., Anton M. Polderman, et al. “PCR assay for the specific amplification of Oesophagostomum bifurcum DNA from human faeces.” Int. J. Parasitol. 30.2 (2000): 137-142.
  6. ↑ Storey, P A, S Anemana, et al. “Ultrasound diagnosis of oesophagostomiasis.” Brit. J. Radiol. 73.867 (2000): 328-32.
  7. ↑ Verweij, Jaco J, Eric A T Brienen, et al. “Simultaneous detection and quantification of Ancylostoma duodenale, Necator americanus and Oesophagostomum bifurcum in fecal samples using multiplex real-time PCR.” Am. J. Trop. Med. and Hygiene 77.4 (2007): 685-690.
  8. ↑ “GIDEON Infectious Diseases - Diseases.” GIDEON Infectious Disease Database. 5 Feb 2009. <http://web.gideononline.com/web/epidemiology/index.php?gdn_form=ZGlzZWFzZT0xMTY1MA==>.
  9. ↑ Ziem, J.B. “Controlling human oesophagostomiasis in northern Ghana.” (Doctoral thesis) Leiden University. 2006. <https://openaccess.leidenuniv.nl/dspace/handle/1887/4917?mode=more>.
  10. ↑ Ziem, J.B. “Controlling human oesophagostomiasis in northern Ghana.” (Doctoral thesis) Leiden University. 2006. <https://openaccess.leidenuniv.nl/dspace/handle/1887/4917?mode=more>.
  11. ↑ “GIDEON Infectious Diseases - Diseases.” GIDEON Infectious Disease Database. 5 Feb 2009. <http://web.gideononline.com/web/epidemiology/index.php?gdn_form=ZGlzZWFzZT0xMTY1MA==>.
  12. ↑ “GIDEON Infectious Diseases - Diseases.” GIDEON Infectious Disease Database. 5 Feb 2009. <http://web.gideononline.com/web/epidemiology/index.php?gdn_form=ZGlzZWFzZT0xMTY1MA==>.
  13. ↑
  14. ↑ "Human Oesophagostomum infection in northern Togo and Ghana: epidemiological aspects." By: Krepel et al. Annals of Tropical Medicine and Parasitology.1992. 86:289-300.
  15. ↑ "Clinical epidemiology and classification of human oesophagostomiasis." By: P.A. Storey et al. Trans R Soc Trop Med Hyg. 2000. 94:177-182.
  16. ↑ Ziem, J.B. “Controlling human oesophagostomiasis in northern Ghana.” (Doctoral thesis) Leiden University. 2006. <https://openaccess.leidenuniv.nl/dspace/handle/1887/4917?mode=more>.
  17. ↑ Polderman, A. M., S. D. Anemana, and V. Asigri. “Human Oesophagostomiasis: A Regional Public Health Problem in Africa.” Parasitology Today 15.4 (1999): 129-130.
  18. ↑
  19. ↑ Ziem, J.B. et al. “Annual mass treatment with albendazole might eliminate human oesophagostomiasis from the endemic focus in northern Ghana.” Tropical Medicine & International Health: TM & IH 11.11 (2006): 1759-63.

Online resources

  • [2] - a free online compendium of all aspects of Oesophagostomum bifurcum biology
  • [3] - Gideon Infectious Disease database entry on oesophagostomiasis
  • [4] - J.B. Ziem’s doctoral thesis on controlling human oesophagostomiasis in northern Togo and Ghana
  • [5] - A.M. Polderman’s review on human oesophagostomiasis

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