Whip it. Population structure and cross-species transmission of Whipworms

Whipworm (photo from WikiMedia commons)

This may be my second worm-related post, but it comes from the PLoS journal that is first in my heart: PLoS Neglected Tropical Diseases. And, as the journal name suggests, it is about a neglected tropical disease: the Whipworm (Trichuris sp.).

Whipworms are one of the most common nematodes that infect humans, with an estimated number of yearly infections that approaches 1 billion. Infection results when a host – human or other – ingests the embryonated Whipworm eggs. It’s at this stage that the infection gets a bit graphic and drifts into the world of Aliens.

Following ingestion, first-stage larva hatch and move through the gastrointestinal tract where they develop in the caecum, molt into adults, and tunnel into the mucosa of the large intestine.

The adult worms remain fixed in the intestine, where females mate with males and then release up to 20,000 eggs per day, which are shed in the feces of the host.
Their fascinating life history aside, Whipworms are a huge public health burden and we need to understand which species infect what hosts in order to develop better and more effective prevention and treatment methods.
In this study, Ghai et al resolved the phylogenetic relationship between Whipworms infecting a primate guild in Kibale National Park in Uganda. Kibale, renowned for its chimpanzee research, is also home to over 9 other species of non-human primate – many of which are known to be infected by Whipworms.
The authors collected fecal samples from hundreds of primates representing nine species that are sympatric in Kibale. With these samples in hand – and while wearing gloves I hope – the authors began their molecular investigation. First, they used microscopy to identify samples that were positive for Whipworm eggs. Next, using these Whipworm-positive samples, the authors designed a nested set of PCR primers to amplify short sequences of rRNA that were then Sanger sequenced. Interestingly, the sequencing revealed results that were hidden to the naked microscope-enhanced eye:

We identified three genetically distinct groups of whipworms that could not be distinguished by microscopic examination of their eggs. One of these groups was found in all nine species of primates examined, including humans.

Overall, their findings demonstrate the value of molecular identification of parasites in combination with more traditional methods.

These findings suggest that some varieties of whipworms are indeed transmissible between humans and non-human primates, which raises concerns for both human health and conservation.

Ghai RR, Simons ND, Chapman CA, Omeja PA, Davies TJ, Ting N & Goldberg TL (2014) Hidden population structure and cross-species transmission of whipworms (Trichuris sp.) in humans and non-human primates in Uganda. R. B. Gasser, ed. PLoS Negl. Trop. Dis. 8, e3256. doi: 10.1371/journal.pntd.0003256

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