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Evolutionary Biology of Parasitism
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2023
Eric S. Loker, Bruce V. Hofkin
For parasites with complex life cycles, the genes that optimize fitness in one host may not optimize fitness in another obligate host in the life cycle. In the tick-borne apicomplexan parasite Theileria parva that causes East Coast fever in cattle in Africa, passage of the parasite through ticks results in a dramatic alteration in genetic composition of the parasite, as does passage through cattle. The parasite is continually being shaped by selection imposed by two very different host environments and immune systems. As another example, in Schistosoma mansoni, deliberate selection to optimize fitness in the snail intermediate host resulted in an inverse relationship with the parasite’s fitness in the definitive host (Figure 7.9). Exposing such genetically based constraints has important implications for interpreting the epidemiology of parasites with complex life cycles. Under natural situations, the alternating demands regularly imposed by selection acting in very different host species and in free-living environments likely results in an integrated overall optimization of deployment of genetic resources by the parasite, one very much shaped by the properties of the particular host species involved. Once again, unique aspects of the biology of the particular parasite–host system in question can strongly influence the microevolutionary process, often in distinctive ways that defy generalization.
Biology and Distribution of Ticks of Medical Importance
Published in Jürg Meier, Julian White, Handbook of: Clinical Toxicology of Animal Venoms and Poisons, 2017
André Aeschlimann, Thierry A. Freyvogel
Several tick species contribute to the survival of pathogen populations in susceptible hosts by combining transstadial with transovarian transmission (Figure 6). Transovarian transmission is not possible for all pathogens; no transovarian transmission has been observed with either Theileria or Acanthocheilonema. Where it does occur, it may may take place through several consecutive tick generations. In this case the tick population simultaneously assumes the role of both vector and reservoir. How effective this is depends on the pathogens concerned. Transmission of rickettsiae is 100% transovarian, and of B. duttoni 40%. For B. burgdorferi, however, this route accounts for only 3 - 6% of transmission, and for encephalitis viruses only for 0.1%. Such figures provide some indication as to how relevant transovarian transmission may be under given epidemiological circumstances.
The Role Of Vaccines For The Control Of Human Parasitic Diseases
Published in F. Y. Liew, Vaccination Strategies of Tropical Diseases, 2017
In the veterinary field a major effort is being made to develop vaccines for the control of Theileria, the organism causing East Coast Fever in Africa and some field trials have shown promise either by immunization by infection combined with treatment or by using attenuated or heterologous organisms. Other protozoa of veterinary importance where vaccine studies have been carried out include coccidial infections in poultry but none of these studies are of immediate relevance to the development of vaccine for the control of human protozoal disease.
How relevant are in vitro culture models for study of tick-pathogen interactions?
Published in Pathogens and Global Health, 2021
Cristiano Salata, Sara Moutailler, Houssam Attoui, Erich Zweygarth, Lygia Decker, Lesley Bell-Sakyi
The theilerioses are tick-borne diseases of ruminants caused by obligate intracellular protozoa of the genus Theileria, which are responsible for immense losses in domestic livestock. Although these organisms are of great importance in the veterinary field, cultivation in tick cell lines has not been reported. Maturation in vitro of Theileria parva in backless tick explants was compared with that in cultured excised salivary glands derived from already-infected ticks [58]. Backless tick explants and excised salivary glands showed similar numbers of infected acini per infected tick when cultured at 36°C, possibly due to the high temperature [170]. However, after 12 days at 28°C, backless tick explants showed 20–30 times as many infected acini per infected tick as excised salivary glands.
Functional genetic evaluation of DNA house-cleaning enzymes in the malaria parasite: dUTPase and Ap4AH are essential in Plasmodium berghei but ITPase and NDH are dispensable
Published in Expert Opinion on Therapeutic Targets, 2019
Hirdesh Kumar, Jessica Kehrer, Mirko Singer, Miriam Reinig, Jorge M. Santos, Gunnar R. Mair, Friedrich Frischknecht
P. berghei and P. falciparum belong to the Apicomplexa phylum which includes parasites of humans and livestock. They include Toxoplasma gondii which causes infections in immunocompromised individuals, Cryptosporidium (causing cryptosporidiosis), Theileria (theileriosis and East Coast fever in cattle) and Eimeria (coccidiosis in poultry). Using BLASTP we explored the repertoire of house-cleaning enzymes in these related protozoans using P. berghei as query sequences. Nucleotide sanitation enzymes are present in the three apicomplexan lineages Piroplasmida, Hemosporida, and Coccidia. Specifically dUTPase, ITPase and Ap4AH were conserved across the two Plasmodium species, Toxoplasma gondii, Eimeria spp., Theileria annulata, and Cryptosporidium spp; NDH on the other hand was only found in Plasmodium and Theileria (Table 2; Supplementary Figures 10–13).
Tick transmission of toxoplasmosis
Published in Expert Review of Anti-infective Therapy, 2019
Ticks have been found to harbor hundreds of known pathogens, and it is widely believed that there are likely more tick-borne organisms, capable of causing human disease, yet to be discovered. Several tick species are currently known to harbor parasites, such as Babesia spp. and Theileria spp. The discovery that T. gondii is an unrecognized tick-borne pathogen helps to explain the widespread prevalence of the parasite and the presence of Toxoplasma in humans and animals without common risk factors, such as eating meat and cat ownership.