Comparison of the lifetime host-to-tick transmission between two strains of the Lyme disease pathogen Borrelia afzelii

Background: transmission from the vertebrate host to the arthropod vector is a critical step in the life-cycle of any vector-borne pathogen. how the probability of host-to-vector transmission changes over the duration of the infection is an important predictor of pathogen fitness. the lyme disease pathogen borrelia afzelii is transmitted by ixodes ricinus ticks and establishes a chronic infection inside rodent reservoir hosts. the present study compares the temporal pattern of host-to-tick transmission between two strains of b. afzelii. methods: laboratory mice were experimentally infected via tick bite with one of two strains of b. afzelii: a3 and a10. mice were repeatedly infested with pathogen-free larval ixodes ricinus ticks over a period of 4 months. engorged larval ticks moulted into nymphal ticks that were tested for infection with b. afzelii using qpcr. the proportion of infected nymphs was used to characterize the pattern of host-to-tick transmission over time. results: both strains of b. afzelii followed a similar pattern of host-to-tick transmission. transmission decreased from the acute to the chronic phase of the infection by 16.1 and 29.3% for strains a3 and a10,respectively. comparison between strains found no evidence of a trade-off in transmission between the acute and chronic phase of infection. strain a10 had higher lifetime fitness and established a consistently higher spirochete load in nymphal ticks than strain a3. conclusion: quantifying the relationship between host-to-vector transmission and the age of infection in the host is critical for estimating the lifetime fitness of vector-borne pathogens. © 2016 the author(s).