Impact of queen infection on kitten susceptibility to different strains of Bartonella henselae

•Infection of pregnant queens with Bartonella henselae led to birth of Bartonella culture or qPCR negative kittens.•Presence of maternal antibodies could be detected in some of the kittens.•Challenge of young kittens with the same strain used to infect the queen led to low or moderate bacteremia.•Challenge of young kittens with a different strain of the same B. henselae genotype led to high level of bacteremia in the kittens, indicative of a lack of protection from maternal immune response. Domestic cats are the natural reservoir of Bartonella henselae, the agent of cat scratch disease in humans. In kittens, maternal IgG antibodies are detectable within two weeks postpartum, weaning in six to ten weeks postpartum and kittens as young as six to eight weeks old can become bacteremic in a natural environment. The study’s objective was to evaluate if maternal antibodies against a specific B. henselae strain protect kittens from infection with the same strain or a different strain from the same genotype. Three seronegative and Bartonella-free pregnant queens were infected with the same strain of B. henselae genotype II during pregnancy. Kittens from queens #1 and #2 were challenged with the same strain used to infect the queens while kittens from queen #3 were challenged with a different genotype II strain. All queens gave birth to non-bacteremic kittens. After challenge, all kittens from queens infected with the same strain seroconverted, with six out of the seven kittens presenting no to very low levels of transitory bacteremia. Conversely, all four kittens challenged with a different strain developed high bacteremia (average 47,900CFU/mL by blood culture and 146,893bacteria/mL by quantitative PCR). Overall, qPCR and bacterial culture were in good agreement for all kittens (Kappa Cohen’s agreement of 0.78). This study demonstrated that young kittens can easily be infected with a different strain of B. henselae at a very young age, even in the presence of maternal antibodies, underlining the importance of flea control in pregnant queens and young kittens.