Reinfection withAnaplasma phagocytophilumin BALB/c Mice and Cross-Protection between Two Sympatric Isolates

Abstract

Infection with Anaplasma phagocytophilum in white-footed mice results in partial protection against reinfection with the same agent. However, humans and domestic animals may be sequentially exposed to different isolates of the agent circulating in the same or adjacent foci. We investigated whether immune response to a tick-borne infection with A. phagocytophilum provides protection against homologous and heterologous challenges. BALB/c mice were infected with one of the two sympatric isolates of A. phagocytophilum via tick bite and challenged 16 weeks later by Ixodes scapularis nymphs infected with either the same or the alternative isolate. As controls, groups of infected mice were challenged by uninfected ticks to confirm an absence of reactivation of the original infection or groups of naive mice were fed upon by ticks from cohorts used for an infectious challenge. Xenodiagnostic I. scapularis larvae were fed upon each mouse at 14 and 21 days postchallenge (PCH) and tested for the presence of A. phagocytophilum as freshly molted nymphs. Blood samples for quantitative PCR were collected at 7, 14, 21, and 70 days PCH. Serum samples were collected weekly to monitor development of immune response. The proportion of infected animals, levels of bacteremia, and the prevalence of infection in xenodiagnostic ticks were higher in groups of control mice exposed to A. phagocytophilum for the first time than in mice reinfected with either homologous or heterologous isolates. The presence of antibodies against A. phagocytophilum did not protect mice from a challenge with either homologous or heterologous isolates, however the ensuing reinfection was significantly milder and of a shorter duration than the first infection with either isolate.

Reservoir Competency of Goats for the Ap-Variant 1 Strain of Anaplasma phagocytophilum

“…These results demonstrate that the immune response induced by infection with Ap-Variant 1 did not provide protection from a subsequent infection with Ap-ha. This is in agreement with prior studies where sheep and mice were not protected when challenged with heterologous strains of A. phagocytophilum (5,11).…”

Vaccination with an Attenuated Mutant of Ehrlichia chaffeensis Induces Pathogen-Specific CD4+ T Cell Immunity and Protection from Tick-Transmitted Wild-Type Challenge in the Canine Host

“…While this result is disappointing, similar examples of poor protection from heterologous challenge have been previously reported for the rickettsials, including lack of protection between strains of E . ruminantum [ 35 ], of Anaplasma phagocytophilum [ 36 , 37 ] and of E . canis [ 38 , 39 ].…”

Anaplasma phagocytophilum infection in a domestic cat in Finland: Case report

“…In murine experimental studies and in a natural case of human anaplasmosis, previous infection with A. phagocytophilum did not prevent infection. However, the clinical course of the disease can be milder and of shorter duration [ 53 , 54 ].…”