THE MOLECULAR MECHANISMS OF TICK PATHOGEN TRANSMISSION

Forgivemore Magunda

Ticks vector numerous diseases important to livestock and humans and are often indispensable to the life cycle and continued existence of these agents. However, little is known about their biology and interactions with the pathogens they transmit. This gap in knowledge limits development of interventions that can be limit tick borne disease burden. Anaplasma marginale establishes infection within Dermacentor spp. for weeks escaping the complex network of vacuolar peptidases responsible for digestion of the tick blood meal. How this prolonged maintenance of infectivity is effected has been unknown. In the first study we used the natural vector Dermacentor andersoni, and demonstrated that A. marginale-infected tick vacuoles (AmVs) concurrently recruit markers of the early (Rab5), recycling (Rab4 and Rab11) and late endosome (Rab7), are maintained near neutral pH, do not fuse with lysosomes, exclude the protease cathepsin L, and engage the endoplasmic reticulum and Golgi for up to 21d post infection. Maintenance of this safe vacuolar niche required active A. marginale protein synthesis; in its absence AmVs mature into acidic, protease-active phagolysosomes. In the second chapter we analysed the transcriptional response to infection by ticks. Pathogens co-evolved with ticks developing mechanisms to subvert tick biological processes to facilitate infection, replication and eventual transmission. we used Ion torrent high throughput RNA sequencing to compare the midgut transcripts of Dermacentor andersoni (Da) male ticks that are unfed to those fed on a blood meal that is either uninfected or infected with Anaplasma marginale (Am) St. Maries strain. Sequencing of tick midgut mRNA yielded 11.7M reads. After De novo assembly the remaining 11 716 transcripts were annotated and analyzed using K-means clustering. Global analysis of all transcripts shows high degree of transcription in response to the blood meal and differential transcription of key gene families between infected and uninfected ticks. Among annotated genes, were genes related to antioxidant process (catalase and cytochrome p450) and the immune system (peritrophin) that reflect response to both the pathogen and oxidative challenge. These findings suggest that specific differential transcription in the midgut in response to pathogens may play a role in tick transmission competency.

THE MOLECULAR MECHANISMS OF TICK PATHOGEN TRANSMISSION

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