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Population genetic studies in the parasitic nematode Onchocerca ochengi

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Hildebrandt,  J       
Parasitic Nematode Group, Department Integrative Evolutionary Biology, Max Planck Institute for Developmental Biology, Max Planck Society;
Department Integrative Evolutionary Biology, Max Planck Institute for Developmental Biology, Max Planck Society;

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Hildebrandt, J. (2014). Population genetic studies in the parasitic nematode Onchocerca ochengi. PhD Thesis, Eberhard-Karls-Universität, Tübingen, Germany.


Cite as: https://hdl.handle.net/21.11116/0000-000E-7866-9
Abstract
The filarial nematode Onchocerca ochengi is a nodule forming parasite of cattle and very closely related to the human parasite Onchocerca volvulus, the causative agent of river blindness. Both species are endemic in tropical and subtropical parts of Africa and share the same vectors which are blackflies of the Simulium damnosum complex. It is technically and ethically easier to study the basic biology of a pathogen in an animal model, likein this case the bovine parasite O. ochengithan in humans. To get better insights in the population structure and reproductive behavior of O. ochengi, the studies in this thesis make use of nuclear and mitochondrial molecular genetic markers. First I established methods for genotyping individual O. ochengi adults, embryos and microfilariae at single copy loci and I identified regions containing single nucleotide polymorphisms that could serve as molecular markers. I used these markers and method to determine parent offspring relationships. I showed that females often produce offspring from multiple males simultaneously. Most of the time, but not always, these putative fathers were still found in the nodules at the time their progeny was ready to hatch. This indicates that males, although they can leave nodules, tend to stay with a particular female for extended periods of time. I was able to assign a large fraction of microfilariae isolated from a skin sample to their parents and thereby show that different females contribute variably to the pool of skin microfilariae. Furthermore I showed that cattle is the vertebrate host of Onchocerca sp. „Siisa‟, a form of Onchocercapreviously described only in the vector O. sp. „Siisa‟ had been separated from other species of Onchocerca based on (only maternally inherited) mitochondrial DNA sequences. Using the bi-parentally inherited nuclear markers, I showed that O. sp. „Siisa‟ interbreeds freely with O. ochengiand therefore belongs to this species.