Etudiante en Master

Laboratoire d'écologie et évolution des parasites
Institut de biologie
Rue Emile-Argand 11
2000 Neuchâtel

oceane.courbat@unine.ch

Manipulation of the host phenotype by parasites is common (Moore 2002). Indeed, parasites can manipulate behavioural, physiological and morphological traits of their hosts or vectors to increase their transmission and fitness. Manipulation of vertebrate hosts and arthropod vectors is well studied for malaria (De Moraes et al. 2014, Koella et al. 1998, 2002, Lacroix et al. 2005), but not in Lyme borreliosis (LB). The spirochete bacteria that cause LB belong to the Borrelia burgdorferi sensu lato species complex. In Europe, these tick-borne pathogens are transmitted by the sheep tick Ixodes ricinus. The study of this complex of bacteria is important because they can infect humans and cause severe pathology. The purpose of my Master thesis is to test whether Borrelia afzelii manipulates the behaviour of I. ricinus.
A previous study used field-collected I. ricinus nymphs to test whether Borrelia infection influenced their attraction to reservoir host odours. In the present study, I created experimentally infected and uninfected I. ricinus nymphs to better control for a variety of factors such as age and nutritional status that may influence nymphal questing behaviour. Blood-engorged adult female I. ricinus ticks were collected from hunted deer in Nantes, France. Larval I. ricinus ticks hatched in the lab and were allowed to feed on B. afzelii-infected or uninfected laboratory mice. The engorged larval ticks were allowed to moult into nymphs.
I will use behavioural experiments to test whether B. afzelii infection influences questing behaviour of I. ricinus nymphs. I will use the same vertically oriented tick questing arena as Berret and Voordouw (2015). The arena contains eight wooden sticks that can be selected by the questing ticks. Sticks will be scented with the odour of a bank vole or the odour of an empty cage (odours are captured using a piece of medical gauze). Ticks will be given 90 minutes to select a questing perch after which I will collect the ticks and analyse their bacterial load by quantitative PCR. This experiment will allow me to test whether B. afzelii infection influences the motivation of ticks to quest and the attraction of nymphal ticks to rodent odours. If yes, this study will prove that B. afzelii bacteria can manipulate their vector, I. ricinus, to increase their chances to find a host and achieve transmission. This study of how pathogens manipulate their arthropod vectors is important for understanding how we can fight against vector-borne diseases.

References:

Berret J, Voordouw MJ. Lyme disease bacterium does not affect attraction to rodent odour in the tick vector. Parasit Vectors. 2015 Dec;8(1).
De Moraes CM, Stanczyk NM, Betz HS, Pulido H, Sim DG, Read AF, et al. Malaria-induced changes in host odors enhance mosquito attraction. Proc Natl Acad Sci U S A. 2014 Jul 29;111(30):11079–84.
Koella JC, Rieu L, Paul RE. Stage-specific manipulation of a mosquito’s host-seeking behavior by the malaria parasite Plasmodium gallinaceum. Behav Ecol. 2002;13(6):816–820.
Koella JC, Sørensen FL, Anderson RA. The malaria parasite, Plasmodium falciparum, increases the frequency of multiple feeding of its mosquito vector, Anopheles gambiae. Proc R Soc B Biol Sci. 1998 May 7;265(1398):763–8.
Lacroix R, Mukabana WR, Gouagna LC, Koella JC. Malaria Infection Increases Attractiveness of Humans to Mosquitoes. PLOS Biol. 2005 août;3(9):e298.
Moore J. Parasites and the Behavior of Animals. Oxford University Press; 2002. 329 p.