Ancylostoma duodenale

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    Ancylostoma duodenale (AD), also known as the Old World Hookworm, is a close relative of Necator americanus (NA), the New World Hookworm.

    NA and AD are the two hookworm species that most commonly infest humans, with NA occupying the lower end of the jejunum and the upper end of the ileum, and AD preferring to reside a little higher in the digestive tract, in the duodenum / jejunum. [1]

    While AD is not currently in use for therapy, it was actually the first helminth ever to be used for a therapeutic purpose.

    It was employed, in rather large numbers - 300-600 AD larvae were given to each patient - in a study commencing in 1939 to treat 25 patients with polycythemia, which causes an abnormally high number of red cells in the blood. The treatment was described as producing results that were "uniformly good and satisfying", with a slow and lasting fall in red blood cell counts that was "harmless to the patient".

    AD was arguably ideal for this particular purpose because it draws a large amount of blood while feeding (reportedly nine times more than NA), but this characteristic might be seen as a disadvantage in most cases of treatment, along with its ability to migrate via breast milk and to cross the placenta to infect a foetus. [2] In very rare cases, AD has caused pancreatitis by entering the hepatopancreatic duct, where it can produce inflammation and, potentially, blockage of the duct. [3]

    While taking larvae by mouth has been found to be ineffective as a means of inoculation in the case of NA, the oral route has been shown to be successful in AD. [4]