Emergence of Tick-Borne Granulocytic Anaplasmosis Associated with Habitat Type and Forest Change in Northern California

Abstract

An important ecosystem service of intact forests is protection from some emerging infectious diseases. Tick-transmitted disease granulocytic anaplasmosis increasingly occupies second-growth forest. We hypothesized that areas of second growth would have increases in tick and rodent abundance, facilitating emergence of anaplasmosis. We predicted Anaplasma phagocytophilum presence as a function of biocomplexity and forest structure, including vegetation, ticks, and rodents in four sites in California. Significant risk factors for exposure included host species (woodrats with 13% seroprevalence, odds ratio [OR] = 8.3 and chipmunks with 27% seroprevalence, OR = 20.7), and park location (northern parks, OR 25.5–27.7). Exposure to A. phagocytophilum was more likely among chipmunks in redwood sites at one park, but with woodrats and oaks at another. Overall, transects on which small mammals showed greatest A. phagocytophilum exposure had high biodiversity in ticks, rodents, and vegetation, as well as intermediate-sized trees with a high mean and variance in diameter at breast height, findings which suggest that a dilution effect, where increased biodiversity reduces disease risk, does not necessarily apply in this system. Thus, enzootic and potentially emerging anaplasmosis were linked to high biodiversity and mature second-growth forest.

Unique strains of Anaplasma phagocytophilum segregate among diverse questing and non-questing Ixodes tick species in the western United States

“…The complex ecology of A. phagocytophilum in the far-western U.S. features multiple reservoir host species, multiple bacterial strains (Foley et al, 2009b; Rejmanek et al, 2011), and differences in dynamics of hosts and vectors across diverse landscapes (Foley et al, 2009a, 2011). There is also a large diversity of Ixodes tick species.…”

Molecular characterization reveals distinct genospecies of Anaplasma phagocytophilum from diverse North American hosts

“…DNA samples for molecular characterization were obtained from small mammals including chipmunks, dusky-footed woodrats, eastern grey squirrels (Sciurus carolinensis) and western grey squirrels (Sciurus griseus) (Foley et al, 2009a;. DNA from all blood samples was extracted using a Qiagen blood and tissue kit as per the manufacturer's instructions.…”

Anaplasma species of veterinary importance in Japan

“…A. phagocytophilum strains can have different tropism, in which a strain from one animal may not cause disease in another species. Hence, with increasing reports of dissimilar genotypes from different regions of the globe, defining distinct phenotypes and using nomenclature that appropriately clarifies the distinctions are important [74]. It can be implicated that different variants may exist within the same herd, and even simultaneously within the same animal.…”