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Title: Tick-Borne Transmission of Two Genetically Distinct Anaplasma marginale Strains following Superinfection of the Mammalian Reservoir Host

item Knowles Jr, Donald

Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2008
Publication Date: 9/2/2008
Citation: Leverich, C.K., Palmer, G.H., Knowles Jr, D.P., Brayton, K.A. 2008. Tick-Borne Transmission of Two Genetically Distinct Anaplasma marginale Strains following Superinfection of the Mammalian Reservoir Host. Infection and Immunity. 76(9):4066-4070.

Interpretive Summary: The movement of agents causing vector-borne diseases in nature is dependent on the ability of the vector to acquire and transmit the agent. Multiple strains of the agents of vector borne diseases are common and are defined by parameters such as ability to cause disease or efficiency of transmission. This works shows that when different strains infect a host they can be acquired and transmitted indicating that vectors (ticks in this case) are capable of acquiring (Anaplasma marginale in this case) multiple strains and transmitting to new hosts. These findings have implications for both epidemiology and vaccine development.

Technical Abstract: Strain superinfection affects the dynamics of epidemiological spread of pathogens through a host population. Superinfection has recently been shown to occur for genetically distinct strains of the tick-borne pathogen Anaplasma marginale that encode distinctly different surface protein variants. Superinfected animals could serve as a reservoir for onward transmission of both strains if the tick vector is capable of acquiring and transmitting both strains. Whether competition among strains during development within the tick vector, which requires sequential invasion and replication events, would limit colonization and subsequent transmission to a single strain is unknown. We tested this hypothesis by acquisition feeding of Dermacentor andersoni ticks on a reservoir host superinfected with the genetically distinct St. Maries and EMF strains. Although the St. Maries strain consistently maintained higher bacteremia levels in mammalian host and the EMF strain had an early advantage in colonization of the tick salivary gland, individual ticks were co-infected and there was successful transmission of both strains. These results indicate that a genetically distinct A. marginale strain capable of superinfecting the mammalian host can subsequently be co-transmitted and become established within the host population despite the presence of an existing established strain.