Duration of tick attachment necessary for transmission of Anaplasma phagocytophilum by Ixodes scapularis (Acari: Ixodidae) nymphs.

This study assessed the duration of tick attachment necessary for a successful transmission of Anaplasma phagocytophilum by an infected I. scapularis nymph. Individual nymphs were placed upon BALB/c mice and allowed to feed for predetermined time intervals of 4 to 72 h. Ticks removed from mice at predetermined intervals were tested by PCR for verification of infection and evaluation of the bacterial load. The success of pathogen transmission to mice was assessed by blood-PCR at 7, 14 and 21 days postinfestation, and IFA at 21 days postinfestation. Anaplasma phagocytophilum infection was documented in 10-30 % of mice, from which ticks were removed within the first 20 h of feeding. However, transmission success was ≥70% if ticks remained attached for 36 h or longer. Notably, none of the PCR-positive mice that were exposed to infected ticks for 4 to 8 h and only half of PCR-positive mice exposed for 24 h developed antibodies within 3 weeks postinfestation. On the other hand, all mice with detectable bacteremia after being infested for 36 h seroconverted. This suggests that although some of the ticks removed prior to 24 h of attachment succeed in injecting a small amount of A. phagocytophilum, this amount is insufficient for stimulating humoral immunity and perhaps for establishing disseminated infection in BALB/c mice. Although A. phagocytophilum may be present in salivary glands of unfed I. scapularis nymphs, the amount of A. phagocytophilum initially contained in saliva appears insufficient to cause sustainable infection in a host. Replication and, maybe, reactivation of the agent for 12-24 h in a feeding tick is required before a mouse can be consistently infected.

Life cycles of seven ixodid tick species (Acari: Ixodidae) under standardized laboratory conditions.

Studies of transmission, maintenance, infectivity, virulence, and pathogenicity of tick-borne agents require the use of large numbers of live laboratory-raised ticks. Colonies of Ixodes scapularis Say, Ixodes pacificus Cooley & Kohls, Amblyomma americanum (L.), Dermacentor occidentalis Marx, Dermacentor variabilis (Say), Hemaphysalis leporispalustris (Packard), and Rhipicephalus sanguineus (Latrielle) have been maintained in our laboratory at the Centers for Disease Control and Prevention for five to 18 continuous generations. New Zealand White rabbits (Oryctolagus cuniculus) are used as hosts for all tick species and developmental stages. Between feedings, ticks are stored in environmental incubators at 22-24 degrees C and 90% RH with a day/night photoperiod of 16:8 (L:D) h. The duration of feeding, molting, preoviposition, and periods of postmolting development were recorded. Here, we describe the life cycles of these common North American tick species under standardized laboratory conditions. At 22-24 degrees C, the minimal time needed for each species to complete one life cycle was as follows: I. scapularis, 204-219 d; I. pacificus, 214-229 d; R. sanguineus, 162-177 d; H. leporispalustris, 209-224 d; D. variabilis, 176-191 d; D. occidentalis, 180-195 d; and A. americanum, 192-211 d.

Infection of a goat with a tick-transmitted Ehrlichia from Georgia, U.S.A., that is closely related to Ehrlichia ruminantium.

We detected a novel tick-transmitted Ehrlichia in a goat following exposure to lone star ticks (Amblyomma americanum) from a park in the metropolitan area of Atlanta, GA, U.S.A. Nineteen days after infestation with field-collected adult ticks, the goat developed a fever of two days duration, which coincided with mild clinical pathologic changes and the presence of DNA from a novel Ehrlichia in peripheral blood. The goat transmitted ehrlichiae to uninfected nymphal A. americanum that fed upon the goat, and the ticks maintained the pathogen transstadially. Five months after exposure, immunosuppression of the goat resulted in transient ehrlichemia with transmission of ehrlichiae to feeding ticks. Sequencing and phylogenetic reconstructions of the 16S rRNA, gltA, map1, map2, and ribonuclease III genes suggest the agent might be a divergent strain of Ehrlichia ruminantium, the agent of heartwater, or a new, closely related species. Convalescent serum from the goat reacted with the MAP-1 protein of E. ruminantium and with whole-cell Ehrlichia chaffeensis antigen. DNA from the novel Ehrlichia was detected in 5/302 field-collected adult A. americanum from the park. Our data suggest that A. americanum is a natural vector and reservoir of this Ehrlichia and that domestic goats can be reservoirs. The geographic range of the agent and its pathogenicity to humans and livestock needs to be evaluated.

Prophylactic use of sustained-release doxycycline blocks tick-transmitted infection by Anaplasma phagocytophilum in a murine model.

A sustained-release formulation of doxycycline hyclate was tested for its ability to block Anaplasma phagocytophilum infection in mice. Mice treated with sustained-release doxycycline showed no splenomegaly and their blood samples were negative by PCR on days 7, 14, and 21. Control mice treated with either oral doxycycline or water had significant splenomegaly and were PCR positive at multiple time points. The sustained-release doxycycline formulation was shown to be efficacious for preventing tick-transmitted A. phagocytophilum infection in a mouse model.