9 research outputs found
Genetic Selection of Low Fertile Onchocerca volvulus by Ivermectin Treatment
Onchocerca volvulus is the causative agent of onchocerciasis, or
“river blindness”. Ivermectin has been used for mass
treatment of onchocerciasis for up to 18 years, and recently there have been
reports of poor parasitological responses to the drug and evidence of drug
resistance. Drug resistance has a genetic basis. In this study, genetic changes
in β-tubulin, a gene associated with ivermectin
resistance in nematodes, were seen in parasites obtained from the patients
exposed to repeated ivermectin treatment compared with parasites obtained from
the same patients before any exposure to ivermectin. Furthermore, the extent of
the genetic changes was dependent on the level of ivermectin treatment exposure.
This genetic selection was associated with a lower reproductive rate in the
female parasites. The data indicates that this genetic selection is for a
population of O. volvulus that is more tolerant to ivermectin.
This selection could have implications for the development of ivermectin
resistance in O. volvulus and for the ongoing onchocerciasis
control programmes. Monitoring for the possible development and spread of
ivermectin resistance, as part of the control programmes, should be implemented
so that any foci of resistant parasites can be treated by alternative control
measures
Vaccination against helminth parasite infections
Helminth parasites infect over one fourth of the human population and are highly prevalent in livestock worldwide. In model systems, parasites are strongly immunomodulatory, but the immune system can be driven to expel them by prior vaccination. However, no vaccines are currently available for human use. Recent advances in vaccination with recombinant helminth antigens have been successful against cestode infections of livestock and new vaccines are being tested against nematode parasites of animals. Numerous vaccine antigens are being defined for a wide range of helminth parasite species, but greater understanding is needed to define the mechanisms of vaccine-induced immunity, to lay a rational platform for new vaccines and their optimal design. With human trials underway for hookworm and schistosomiasis vaccines, a greater integration between veterinary and human studies will highlight the common molecular and mechanistic pathways, and accelerate progress towards reducing the global health burden of helminth infection