Diagnosis of Oesophagostomiasis

Before technological advances were developed, diagnosis of Oesophagostomiasis could only be confirmed by exploratory surgery and identification of the worm as Oesophagostomum spp. Unlike other parasitic diseases, Oesophagostomiasis cannot be diagnosed by eggs in the stool since they are rarely found and when they are found, they cannot be distinguished from hookworm eggs. The following is a review of three recently developed diagnostic techniques that have aided in identifying the presence of the parasite or the disease itself. Diagnosis plays a pivotal role in treating and eventually eliminating a parasitic disease. It is important that advances in diagnostic techniques continue.


Diagnosis of the Parasite


+"Determining the prevalence of Oesophagostomum bifurcum and Necator americanus infections using specific PCR amplification of DNA from faecal samples." Verweij and Pit. Tropical Medicine and International Health. 2001. 6:726-731.

Although identification of eggs in the stool cannot be used to distinguish Necator americanus and Oesophagostomum, the eggs from stool samples can be grown in culture for 7 days and then the parasites in the L3 stage can distinguish the two species (this technique is known as coproculture). This study developed an alternative method of identifying the two parasites from fecal samples. Specifically, they used PCR to amplify DNA from the feces in order to determine the prevalence of each parasite. They compared the specificity of detection by PCR to the prevalence of each parasite as determined by the coproculture assays. O. bifurcum-PCR identified 57 out of 61 samples known to contain O. bifurcum by coproculture. Similarly, N.americanus-PCR identified 136 out 147 samples known to contain N.americanus. In addition, both PCR assays for the two parasites detected DNA is samples that were not identified via the coproculture technique. No O. bifurcum DNA was found in 91 controls from non-endemic areas. Thus, this study concluded that these specific PCR assays were useful in determining the prevalence of N.americanus and O. bifurcum infection.



Agarose gel of PCR samples. The upper gel contains O. bifurcum samples in lanes 2, 3, 4, 6, and 7. No specific product in lanes 1, 5, 8, 9, and 10. The lower gel contains specific N. americanus samples in all lanes except 7 and 10.

+ "Characterization of Oesophagostomum bifurcum and Necator americanus by PCR-RFLP of rDNA." Romstad and Gasser. Journal of Parasitology. 1997. 83:963-966.

This study developed a molecular diagnostic assay to distinguish between Oesophagostomum bifurcum and by using the ribosomal DNA as a genetic marker of each parasite. The rDNA was analyzed by PCR-linked restriction fragment length polymorphism using a variety of restriction enzymes. These restriction fragments showed that there was no difference in band pattern within a species but there was a difference in pattern across species. They were able to conclude that the fragment lengths of the rDNA were valid genetic markers because they distinguished between the two parasites.


Diagnosis of the Disease


+"Ultrasonographic Detection and Assessment of Preclinical Oesophagostomum bifurcum-Induced Colonic Pathology." Storey and Spannbrucker. Clinical Infectious Disease. 2001. 33:166-70.

The goal of this study was to determine if colonic-wall pathology induced by infection in asymptomatic/pre-clinical patients could be determined my ultrasound. 464 people that ranged from highly infected to uninfected as determined by stool samples were examined by ultrasound. 128 asymptomatic people out of 364 people from endemic regions were positive for colon pathology as determined by ultrasound. No colon nodules were seen in people from non-endemic towns. Thus, ultrasound is a potentially useful detection tool to identify pre-clinical Oesophagostomiasis. This has important implications for the prevention and treatment of this disease.

Sample Ultrasound and Stick Drawing



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