Twenty eight species of Ixodidae have been found on man in South America (21 Amblyomma, 1 Boophilus, 2 Dermacentor, 2 Haemaphysalis, 1 Ixodes and 1 Rhipicephalus species). Most of them are rarely found on man. However, three species frequently parasitize humans in restricted areas of Argentina (A. neumanni reported from 46 localities), Uruguay (A. triste from 21 sites) and Argentina-Brazil (A. parvum from 27 localities). The most widespread ticks are A. cajennense (134 localities in Argentina, Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Suriname and Venezuela), A. ovale (37 localities in Argentina, Brazil, Ecuador, French Guiana, Guyana, Paraguay, Suriname and Venezuela) and A. oblongoguttatum (28 sites in Brazil, Colombia, French Guiana, Guyana, Suriname and Venezuela). Amblyomma aureolatum (18 localities in Argentina, Brazil, French Guiana and Paraguay), A. cajennense, and A. triste are vectors of rickettsioses to man in South America. A better understanding of the respective roles of these and other tick species in transmitting pathogens to humans will require further local investigations. Amblyomma ticks should be the main subjects of these studies followed by species of Boophilus, Dermacentor, Haemaphysalis and Rhipicephalus species. In contrast with North America, Europe and Asia, ticks of the genus Ixodes do not appear to be major players in transmitting diseases to human. Indeed, there is only one record of an Ixodes collected while feeding on man for all South America.

The mitochondrial 16S rRNA gene sequences of the following eight European Metastriata tick species were obtained by direct polymerase-chain-reaction cycle sequencing and silver-staining methods: Rhipicephalus bursa, R. pusillus, R. sanguineus, R. turanicus, Boophilus annulatus, Dermacentor marginatus, Haemaphysalis punctata, and Hyalomma lusitanicum. This mitochondrial gene seems to be a good marker for the establishment of genetic relationships among closely related tick species, but it does not seem to be useful for comparisons of distantly related taxa. The molecular data provide very strong support for the monophyly of the Rhipicephalinae, including Hyalomma spp. However, the genus Rhipicephalus may not be considered a monophyletic group; in all analyses carried out in this study, R. bursa clustered with Boophilus spp. The high percentage of similarity (98.7%) observed between R. sanguineus and R. turanicus sequences would suggest that these species recently diverged within the Rhipicephalus genus. Phylogenetic analyses showed a monophyletic relationship among Amblyomminae taxa. The relationships between Haemaphysalis species and the true placement of this genus within Metastriata could not be resolved.

The causative agent of human granulocytic ehrlichiosis was recently reclassified as Anaplasma phagocytophilum, unifying previously described bacteria that cause disease in humans, horses, dogs, and ruminants. For the characterization of genetic heterogeneity in this species, the homologue of Anaplasma marginale major surface protein 4 gene (msp4) was identified, and the coding region was PCR amplified and sequenced from a variety of sources, including 50 samples from the United States, Germany, Poland, Norway, Italy, and Switzerland and 4 samples of A. phagocytophilum-like organisms obtained from white-tailed deer in the United States. Sequence variation between strains of A. phagocytophilum (90 to 100% identity at the nucleotide level and 92 to 100% similarity at the protein level) was higher than in A. marginale. Phylogenetic analyses of msp4 sequences did not provide phylogeographic information but did differentiate strains of A. phagocytophilum obtained from ruminants from those obtained from humans, dogs, and horses. The sequence analysis of the recently discovered A. phagocytophilum msp2 gene corroborated these results. The results reported here suggest that although A. phagocytophilum-like organisms from white-tailed deer may be closely related to A. phagocytophilum, they could be more diverse. These results suggest that A. phagocytophilum strains from ruminants could share some common characteristics, including reservoirs and pathogenicity, which may be different from strains that infect humans.

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dAnaplasma phagocytophilum causes human granulocytic anaplasmosis. Infection with this zoonotic pathogen affects gene expression in both the vertebrate host and the tick vector, Ixodes scapularis. Here, we identified new genes, including spectrin alpha chain or alpha-fodrin (CG8) and voltage-dependent anion-selective channel or mitochondrial porin (T2), that are involved in A. phagocytophilum infection/multiplication and the tick cell response to infection. The pathogen downregulated the expression of CG8 in tick salivary glands and T2 in both the gut and salivary glands to inhibit apoptosis as a mechanism to subvert host cell defenses and increase infection. In the gut, the tick response to infection through CG8 upregulation was used by the pathogen to increase infection due to the cytoskeleton rearrangement that is required for pathogen infection. These results increase our understanding of the role of tick genes during A. phagocytophilum infection and multiplication and demonstrate that the pathogen uses similar strategies to establish infection in both vertebrate and invertebrate hosts.T icks are ectoparasites of animals and humans and are considered to be the most important arthropod vector of pathogens in some regions (1). Ixodes scapularis Say (Acari: Ixodidae) is an important vector of pathogens that infect and cause disease in humans and domestic animals in the United States. Anaplasma phagocytophilum (Rickettsiales: Anaplasmataceae), the focus of this study, is the causative agent of human, canine, and equine granulocytic anaplasmosis and tick-borne fever of ruminants (2, 3).A. phagocytophilum is an intracellular bacterium that infects vertebrate host neutrophils, where it multiplies within a parasitophorous vacuole, thus evading host defenses while inhibiting apoptosis and promoting cytoskeleton rearrangement for infection and multiplication (4-8). Tick-A. phagocytophilum interactions are not as well characterized as those between pathogen and vertebrate hosts (4). While A. phagocytophilum has been shown to infect I. scapularis gut cells (9) and salivary glands (10), the developmental cycle of this pathogen has not been described in ticks. Tick proteins such as Salp16, subolesin, antifreeze glycoprotein IAFGP, and alpha1-3-fucosyltransferease were differentially regulated and required for A. phagocytophilum infection of I. scapularis (10-20). Activation of heat shock proteins and other stress response proteins in ticks and cultured tick cells in response to A. phagocytophilum infection was also characterized by proteomics and transcriptomics analyses (21).The overall goal of our research is to characterize molecular interactions at the vector-pathogen interface and develop vaccines for the control of tick infestations and pathogen infection/transmission. Our hypothesis is that tick genes differentially expressed in response to pathogen infection would include those involved in pathogen infection, multiplication, and transmission, as well as in the tick protective response to infection. In this researc...