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United States Department of Agriculture

Agricultural Research Service

Research Project: DETERMINANTS OF ANAPLASMA MARGINALE TRANSMISSION AT THE VECTOR/PATHOGEN INTERFACE

Location: Animal Diseases Research

2007 Annual Report


1a.Objectives (from AD-416)
Our objective in this project is to investigate the factors influencing transmission of Anaplasma marginale by Dermacentor andersoni. We hypothesize that there are interactions between the vector and the pathogen that are determinants of transmission. Our first objective is to set up a field study to examine the relationship between tick vector competence and transmissibility of Anaplasma marginale strains at field sites selected for differences in vector abundance and pathogen strain composition. We will collect ticks annually and determine the susceptibility phenotype of the population at each site by determining the proportion of ticks that are susceptible to midgut infection with A. marginale; midgut susceptibility is a surrogate marker for vector competence. Using a longitudinal survey of a cohort of cattle at each site we will test the hypothesis that some strains of A. marginale are more highly transmissible than others. The first objective will also provide ticks and A. marginale isolates for study in the subsequent objectives. Our next 2 objectives target vector competence of the tick population. First we will attempt to establish if vector competence is a stable genetic characteristic of the tick populations at our field sites by testing the hypotheses that:.
1)the proportion of ticks that are susceptible to midgut infection with A. marginale within each population (i.e. the population susceptibility phenotype) is stable characteristic of the population from one year to the next, and.
2)that there is limited gene flow between populations of D. andersoni. Secondly, we will determine if tick innate immune responses regulate vector competence by testing the hypotheses that.
1)there are differences between tick populations in sequence or expression of tick defensins, and.
2)that these differences correlate with phenotypes which are associated with vector competence for A. marginale. Our final two objectives target A. marginale strain transmissibility. First, we will identify common genetic markers of highly transmissible A. marginale strains collected in our field study, and test the hypothesis that these strains share genetic determinants that are associated with, and are predictive of, more efficient transmission by ticks. We will then identify the outer membrane protein (OMP) structure of these highly transmissible A. marginale strains and test the hypotheses that.
1)highly transmissible A. marginale strains share conserved OMPs, and.
2)that immunization with conserved cross-linked OMPs will induce protection against challenge by heterologous A. marginale strains. By simultaneously approaching studies of the determinates of transmission of A. marginale from the prospective of tick vector competence and from the prospective of strain transmissibility we can begin to define the parameters that influence transmission, including parameters relating to the vector, the pathogen, and to their interaction.


1b.Approach (from AD-416)
Our objective in this project is to investigate the factors influencing transmission of Anaplasma marginale by Dermacentor andersoni. Our first approach is to set up a field study to examine the relationship between tick vector competence and transmissibility of Anaplasma marginale strains at field sites selected for differences in vector abundance and pathogen strain composition. We will collect ticks annually and determine the susceptibility phenotype of the population at each site by determining the proportion of ticks that are susceptible to midgut infection with A. marginale; midgut susceptibility is a surrogate marker for vector competence. Our next approach is to target vector competence of the tick population. We will establish if vector competence is a stable genetic characteristic of the tick populations at our field sites. And secondly, we will determine if tick innate immune responses regulate vector competence by testing if there are differences between tick populations in sequence or expression of tick defensins, and whether these differences correlate with phenotypes which are associated with vector competence for A. marginale. Our final approachs target A. marginale strain transmissibility. First, we will identify common genetic markers of highly transmissible A. marginale strains collected in our field study, and test the hypothesis that these strains share genetic determinants that are associated with, and are predictive of, more efficient transmission by ticks. We will then identify the outer membrane protein (OMP) structure of these highly transmissible A. marginale strains and test the hypotheses that.
1)highly transmissible A. marginale strains share conserved OMPs, and.
2)that immunization with conserved cross-linked OMPs will induce protection against challenge by heterologous A. marginale strains. IBC approved 9-04-06; BSL 1. Formerly 5348-32000-023-00D (12/06).


4.Accomplishments
1) Identification of character of parasite variant selection by transmission of Anaplasma marginale to naïve cattle.

A. marginale causes persistent infection in cattle, resulting in a continuous reservoir for transmission to other cattle leading to economic losses from decreased production and/or death. Scientists in the Animal Disease Research Unit, Pullman, WA discovered that following transmission the simplest form of parasite variants could be selected which apparently have a growth advantage. These data impact vaccine strategies because the data indicate that the complex variants which arise under immune selection are rapidly replaced by simple variants in the absence of adaptive immunity. These data supplement our strategies to develop an effective and safe vaccine against A. marginale, which is endemic in areas of the United States. This accomplishment addresses NP #103, Animal Health, program component #7B, Countermeasure to control and prevent parasitic diseases: Hemoparasitic Diseases.

2) Defining the extent of cross reactivity of major surface protein 5 between A. marginale and A. phagocytophilum

An major surface protein 5 based cELISA was developed by our group and is commercially available and in general use for the detection of cattle infected with A. marginale. Recent data (from another group) suggested that cross reactivity between msp5s of A. marginale and A. phagocytophilum limited the specificity of the current A. marginale cELISA. Scientists in the Animal Disease Research Unit in Pullman, WA in collaboration with the University of Florida showed that serum samples from dogs or humans infected with A. phagocytophilum did not cross react when tested in the commercially available cELISA. These data further defined the specificity of the cELISA for A. marginale and showed that the indirect ELISA format is not appropriate for distinction between A. phagocytophilum and A. marginale infections. This accomplishment addresses NP #103, Animal Health, program component #7B, Countermeasure to control and prevent parasitic diseases: Hemoparasitic Diseases.

3) Identification of the tick salivary gland as a barrier to tick-borne transmission of A. marginale

An understanding of the molecular basis for tick versus non-tick transmissibility of A. marginale strains was investigated. Scientists in the Animal Disease Research Unit, Pullman, WA discovered, in collaboration with Washington State University that in addition to midgut, the tick salivary gland also could become infected with parasite, yet not allow transmission. Research will lead to enhanced understanding of transmissibility of vector-borne diseases and eventually provide a basis for transmission control. This accomplishment addresses NP #103, Animal Health, program component #7B, Countermeasure to control and prevent parasitic diseases: Hemoparasitic Diseases.


5.Significant Activities that Support Special Target Populations
None


6.Technology Transfer

Number of non-peer reviewed presentations and proceedings2

Review Publications
Scoles, G.A., Ueti, M.W., Noh, S.M., Knowles Jr, D.P., Palmer, G.H. 2007. Conservation of Transmission Phenotype of Anaplasma marginale (Rickettsiales: Anaplasmataceae) Strains Among Dermacentor and Rhipicephalus Ticks (Acari: Ixodidae). Journal of Medical Entomology. 44(3):484-491

Ueti, M.W., Reagon, J.O., Knowles Jr, D.P., Scoles, G.A., Shkap, V., Palmer, G.H. 2007. Identification of Midgut and Salivary Glands as Specific and Distinct Barriers to Efficient Tick-Borne Transmission of Anaplasma marginale. Infection and Immunity. 75(6):2959-2964

Strik, N.I., Alleman, A.R., Barbet, A.F., Sorenson, H.L., Wamsley, H.L., Gaschen, F.P., Luckschander, N., Wong, S., Chu, F., Foley, J.E., Bjoersdorff, A., Stuen, S., Knowles Jr, D.P. 2007. Characterization of Anaplasma phagocytophilum Major Surface Protein 5 and the Extent of Its Cross-Reactivity with A. marginale. Journal of Clinical Microbiology. 14(3):262-268

Palmer, G.H., Futse, J.E., Leverich, C.K., Knowles Jr, D.P., Rurangirwa, F.R., Brayton, K.A. 2007. Selection for Simple Major Surface Protein 2 Variants during Anaplasma marginale Transmission to Immunologically Naive Animals. Infection and Immunity. 75(3):1502-1506.

Scoles, G.A., Mcelwain, T.F., Rurangirwa, F.R., Knowles Jr, D.P., Lysyk, T.J. 2006. A Canadian Bison Isolate of Anaplasma marginale (Rickettsiales: Anaplasmataceae) Is Not Transmissible by Dermacentor andersoni (Acari: Ixodidae), Whereas Ticks from Two Canadian D. andersoni Populations Are Competent Vectors of a U.S. Strain. Journal of Medical Entomology. 43(5): 971-975.

Carreno, A.D., Alleman, A.R., Barbet, A.F., Palmer, G.H., Noh, S.M., Johnson, C.M. 2007. In vivo Endothelial Cell Infection by Anaplasma marginale. Veterinary Pathology. 44(1):116-118

Last Modified: 9/2/2014
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