Epsilon Open Archive

Abstract

Haemonchus contortus is a blood-sucking nematode of the abomasum in small ruminants. It is responsible for extensive losses and huge animal welfare problems globally. This thesis is based on four publications with the overall aim to characterize H. contortus from Sweden, and includes both genotypic and phenotypic aspects of this parasite. This nematode has by tradition been considered a tropical parasite due to the climatic requirements for its preparasitic lifestages. Its development and survival is dependent on temperature and humidity, and the window of opportunity to complete its life cycle in Sweden is limited. The species status of Haemonchus in Sweden was investigated by comparing the genetic differences in the internal transcribed spacers (ITS-1 and ITS-2) of the ribosomal DNA (rDNA) in worms from Sweden and Kenya. As no fixed differences were found between these isolates they are considered to be distinct populations of the same species, H. contortus. The population structure of H. contortus at a global level was studied by analysing the genetic variability using both amplified fragment length polymorphism (AFLP) and nad4 sequences of the mitochondrial genome. The results show that both the genetic variation and the genetic structure were high between the different isolates, and that populations from each continent mostly formed monophyletic groups in the phylogenetic analysis. The thesis also includes experimental infection studies performed with both fresh and cold- treated infective larvae of either Kenyan or Swedish origin. These investigations covered a range of phenotypic traits, to search for any potential adaptations the parasite might have in order to survive Sweden’s cold temperate climate. In addition, several studies were performed on the development and long-term survival of the parasite in climatic chambers, as well as studies on the overwinter survival of H. contortus on pastures in Sweden. The results show that this parasite can survive winters on pastures. However, the survival capacity was very low and is of limited significance in the transmission between grazing-seasons. Taken together, the results presented in this thesis indicate that H. contortus has a large phenotypic plasticity rather than having undergone any evolutionary adaptation.