Association of BoLA DRB3 and DQA1 alleles with susceptibility to Neospora caninum and reproductive outcome in Quebec Holstein cattle.

The BoLA DRB3 and DQA1 genes are part of the major histocompatibility complex (MHC) class II in cattle. These genes are highly polymorphic and have been associated with resistance to several diseases, such as mastitis, Bovine Leukemia Virus (BLV) and dermatophilis. Sequenced based typing of these genes has been carried out extensively from blood samples; however it is often impractical or expensive to obtain such samples. Repositories of well-characterized serum from cattle are readily available in many veterinary research facilities. This paper reports a retrospective analysis of BoLA class II genotypes of cattle obtained from stored serum samples from Holstein cattle from Québec dairy farms, which were obtained as part of a previous study on bovine neosporosis. It was possible to genotype 56 cattle with known infection status for Neospora caninum. We identified 14 different DRB3 and 10 different DQA1 alleles in this population. The allele frequency distribution was consistent with previously studied cattle populations, and alleles known to be associated with BLV and mastitis were present. No association was found between allele frequency distribution of DRB3 or DQA genes and infection with N. caninum. However, an association of allele DRB3*1001 and allele DRB3*2703 with resistance and susceptibility to pregnancy loss, irrespective of infection status, was identified.

An analysis of genetic diversity and inbreeding in Wuchereria bancrofti: implications for the spread and detection of drug resistance.

Estimates of genetic diversity in helminth infections of humans often have to rely on genotyping (immature) parasite transmission stages instead of adult worms. Here we analyse the results of one such study investigating a single polymorphic locus (a change at position 200 of the beta-tubulin gene) in microfilariae of the lymphatic filarial parasite Wuchereria bancrofti. The presence of this genetic change has been implicated in benzimidazole resistance in parasitic nematodes of farmed ruminants. Microfilariae were obtained from patients of three West African villages, two of which were sampled prior to the introduction of mass drug administration. An individual-based stochastic model was developed showing that a wide range of allele frequencies in the adult worm populations could have generated the observed microfilarial genetic diversity. This suggests that appropriate theoretical null models are required in order to interpret studies that genotype transmission stages. Wright's hierarchical F-statistic was used to investigate the population structure in W. bancrofti microfilariae and showed significant deficiency of heterozygotes compared to the Hardy-Weinberg equilibrium; this may be partially caused by a high degree of parasite genetic differentiation between hosts. Studies seeking to quantify accurately the genetic diversity of helminth populations by analysing transmission stages should increase their sample size to account for the variability in allele frequency between different parasite life-stages. Helminth genetic differentiation between hosts and non-random mating will also increase the number of hosts (and the number of samples per host) that need to be genotyped, and could enhance the rate of spread of anthelmintic resistance.

Detection of benzimidazole resistance-associated mutations in the filarial nematode Wuchereria bancrofti and evidence for selection by albendazole and ivermectin combination treatment.

The Global Program to Eliminate Lymphatic Filariasis has been implemented to reduce human microfilaremia to levels low enough to break the transmission of the disease by using single annual doses of albendazole in combination with diethylcarbamazine or ivermectin. Many veterinary helminth parasites have developed resistance against both albendazole and ivermectin. Resistance to albendazole in veterinary nematodes is known to be caused by either of two single amino acid substitutions from phenylalanine to tyrosine in parasite beta-tubulin at position 167 or 200. We have developed assays capable of detecting these single nucleotide polymorphisms (SNPs) in Wuchereria bancrofti, and have applied them to microfilaria obtained from patients in Ghana and Burkina Faso. One of the SNPs was found in worms from untreated populations in both locations. Worms from treated patients had significantly higher frequencies of these mutations. These findings indicate that a beta-tubulin allele associated with benzimidazole resistance is being selected in these populations.

The impact of selective oviposition and infection with Plagiorchis elegans on Aedes aegypti pre-imago population dynamics at optimal food availability.

Progressive changes in the attraction of waters harboring pre-imago populations of Aedes aegypti exposed to different levels of the entomopathogenic digenean Plagiorchis elegans to ovipositing conspecific females were assessed under conditions of optimal food availability. The impact of ovipositional preference and parasitic infection on population structure and development was investigated. Probabilities that larvae progress from one stage to the next or die within 24 h were calculated for all life stages. Exposure to P. elegans cercariae did not significantly affect the attractiveness of larval-holding waters. Ovipositional preference increased significantly with growing bio-mass of the larval population, with the event of pupation and, in some cases, with late instar mortality. Exposure to various levels of the parasite significantly increased mortality of all instars, but most of the damage caused by the parasite occurred in the form of increased pupal mortality and decreased adult emergence. Exposure to the parasite significantly reduced the number of adults produced yet did not impair larval development. Thus, larval recruitment into environments containing P. elegans remains high, the structure of larval populations remains relatively normal, but few adults are produced.