The geographic limits and life history of the tropical brown dog tick, Rhipicephalus linnaei (Audouin, 1826), in Australia with notes on the spread of Ehrlichia canis.

The tropical brown dog tick, Rhipicephalus linnaei, is a tick of much medical, veterinary, and zoonotic importance. This tick has a nearly world-wide distribution due to its ability to survive and propagate in kennels and houses. Rhipicephalus linnaei is the vector of Ehrlichia canis, the causative agent of canine monocytic ehrlichiosis, an often debilitating disease of canids and, occasionally, humans. To prevent incursion of E. canis into Australia, dogs entering Australia have been required to have a negative immunofluorescence antibody test for E. canis. In May 2020 however, E. canis was detected in Western Australia. The detection of E. canis in Australia prompted disease investigation and concerted surveillance for R. linnaei and E. canis in regions across Australia. These investigations revealed that R. linnaei was established far beyond the previously recognised geographic range limits of this tick. In the present paper, using records from various collections, published data, and data from our network of veterinarian collaborators and colleagues, we update the current geographic range of R. linnaei in Australia. Our analyses revealed that the geographic range of R. linnaei in Australia is much wider than was previously supposed, particularly in Western Australia, and in South Australia. We also map, for the first time, where E. canis has been detected in Australia. Last, we discuss the possible routes of incursion and subsequently the factors which may have aided the spread of E. canis in Australia which led to the establishment of this pathogen in Australia.

Ehrlichia muris in Ixodes cookei Ticks, Northeastern United States, 2016-2017.

Ehrlichia muris is an agent of human ehrlichiosis. To determine its geographic spread in the United States, during 2016-2017, we tested 8,760 ticks from 45 states. A distinct clade of E. muris found in 3 Ixodes cookei ticks from the northeastern United States suggests transmission by these ticks in this region.

The discovery of human granulocytotropic ehrlichiosis.

Human granulocytotropic ehrlichiosis (HGE) is a tick-borne, acute, nonspecific febrile illness that was first described in 1994. At this writing more than 300 cases have been recognized in areas where the presumed tick vector Ixodes scapularis occurs endemically. Ehrlichiosis is a nonspecific influenza-like illness, and associated laboratory alterations are variable. Characteristic morulae (clusters of bacteria in leukocyte cytoplasm) can frequently be found in the cytoplasm of circulating neutrophils after careful inspection of the peripheral blood smear. The diagnosis is confirmed by demonstrating seroconversion to the HGE agent, positive polymerase chain reaction, or growth of the HGE agent in tissue culture. Doxycycline provides rapid and effective treatment.