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TWiP 31 Letters

Chandler writes:

Hi Dr.'s Racaniello and Despommier,

After listening to your podcast on Onchocerca volvulus I decided to contact you in hopes of enlisting your expertise. I am a PhD student of biology at Northern Arizona University and while my research is in novel antimicrobial gene discovery using halophilic Archaea I am also currently working with Onchocerca lupi. There has recently been an increase in incidence of Onchocerca lupi infections in dogs in the Southwestern United States. My dog, at 2 years of age, began showing symptoms of an eye infection that persisted after several different rounds of antibiotics. After seeking out an ophthalmologist, exploratory surgery was performed and a single nematode found. Almost a year and four surgeries later, his infection is still present. The worms have been coming to the outside surface of his eyes where I see them and pull them out as well as forming several nodules in his eyes. He is given monthly injections of ivermectin and takes doxycycline daily (200mg) in hopes of killing the Wolbachia and rendering the parasites sterile. Between only two vets I have seen in the Phoenix area they have seen nine cases of Onchocerca lupi recently. I am receiving nodules removed from the eyes of my dog as well as parasite samples from California and Utah cases. I am currently sequencing the partial mitochondrial genes from all samples in hopes of comparing the parasites in the U.S. to others published from Central Europe where Onchocerca lupi is endemic. I wish to sequence the entire biome of Onchocerca lupi in hopes of discovering highly conserved unique DNA as a potential treatment target as well as other possible endosymbionts as potential targets. I also would just like to see this information available to others who specialize in parasites. Funding, however, seems very difficult to secure for this parasite.

I have a couple of questions I hope you can answer and if not perhaps you can point me in the direction of someone who can. I have not found any literature on O. lupi that shows these subcutaneous nodules throughout a canines body. The samples I have received have all been found in nodules on the eyes. However, I am finding several 'bumps' on my dog's body and am wondering if these might be nodules or if they are a calcium build up from the high, long-term dose of oral prednisone. Secondly, after recently dissecting a newly formed eye nodule, I found several worms that I believe are calcified ( I have not yet tested to be certain) and several worms that I am not sure if were alive or dead or perhaps unhealthy. Are there ways of testing whether these are healthy/living parasites? Will all dead parasites become calcified? Do you have any ideas why several of the worms have migrated to the outside surface of his eyes?

I feel I had a million questions to ask you and now can only remember these. I did want to point out that recently in areas where this parasite is endemic (Europe) a couple of papers have been published on Onchocerca lupi being zoonotic. These findings are based on molecular analysis. This seems like reason for concern in the United States where it looks like it is also soon to be endemic.

I have included a picture from one of my dog's surgeries of what we are calling a drainage tract. It seems too large to be created for the adult worms to migrate through, could it be for the microfilaria? Have you seen anything like this before? The vets and I are at a loss for what it is, but after having all surrounding tissue removed several months later another one formed. Thank you for taking the time to read my ridiculously long email and any information you can give me is greatly appreciated.


Tommy writes:

Hi Vincent and Dick,

Loving the podcast, and I'm glad that you guys finally got around to the wonderfully peculiar and complex trematodes! Having worked with various different species of trematodes for the last few years, I am
glad to finally hear them make an appearance on TWiP. When you were discussing schistosome cercariae penetrating their host, I was reminded of some videos I filmed over a year ago which can be found here:


There, you will find the video of some cercariae of a fluke call Curtuteria australis (which I wrote a post about for the Parasite of the Day blog: http://dailyparasite.blogspot.com/2010/01/january-15-curtuteria-australis.html)
penetrating the foot of its second intermediate host, a bivalve called Austrovenus stutchburyi.

Back on the subject of the schistosomes, some recent research indicate that schistosomes can get "divorced":

Beltran, S., Boissier, J. (2010) Male-biased sex ratio: why and what consequences for the genus Schistosoma? Trends in Parasitology 26: 63-69.

Beltran, S., Cézilly, F., Boissier, J. (2008) Genetic dissimilarity between mates, but not male heterozygosity, influences divorce in schistosomes. PLoS ONE 3(10): e3328.

Beltran, S., Cézilly, F., Boissier, J. (2009) Adult sex ratio affects divorce rate in the monogamous endoparasite Schistosoma mansoni. Behavioral Ecology and Sociobiology 63: 1363-1368.

Steinauer, M.L. (2010) The sex lives of parasites: investigating the mating system and mechanisms of sexual selection of the human pathogen Schistosoma mansoni. International Journal for Parasitology 39: 1157-1163. (interesting supplementary video for this paper)

Also on the subject of trematodes in general, it is true that the majority of them have a snail first intermediate host, but there is a handful of families (e.g: gymnophallid, fellodistomatid, bucephalid, etc) which have bivalve first intermediate host. Finally there are a few very odd species which use polychaetes of all things as first
intermediate hosts (e.g: Cardicola forsteri), however such examples are very rare. So generally speaking all digenean/trematodes have *mollusc* first intermediate hosts, and the majority of them have snail first intermediate hosts.

Keep up the good work, the podcast is always informative and I look forward to more fluke talk!


Kenton writes:

Are there hieroglyphics indicating schistosomiasis was a recognized disease in ancient Egypt?

Thank you. I enjoy listening to your podcasts on TWiP.



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