Experimental infection of opossums Didelphis aurita by Rickettsia rickettsii and evaluation of the transmission of the infection to ticks Amblyomma cajennense

The present study evaluated the infection of opossums (Didelphis aurita) by Rickettsia rickettsii and their role as amplifier hosts for horizontal transmission of R. rickettsii to Amblyomma cajennense ticks. Three groups of opossums were evaluated: on day 0, group 1 (G1) was inoculated intraperitoneally with R. rickettsii; group 2 (G2) was infested by R. rickettsii-infected ticks; and group 3 (G3) was the uninfected control group. Opossum rectal temperature was measured daily. Blood samples were collected every 2 to 4 days during 30 days, and used to (1) inoculate guinea pigs intraperitoneally; (2) extract DNA followed by real-time polymerase chain reaction (PCR) targeting the rickettsial gene gltA; (3) study hematology; (4) detect R. rickettsii-reactive antibodies by indirect immunofluorescence assay (IFA). Blood was also collected every 10 days from days 30 to 180, to be tested by serology. Opossums were infested by uninfected A. cajennense larvae and nymphs from days 3 to 15. Engorged ticks were collected and allowed to molt in an incubator. Thereafter, the subsequent flat ticks were allowed to feed on uninfected rabbits, which were tested for seroconversion by IFA. Samples of flat ticks were also tested by real-time PCR. All G1 and G2 opossums became infected by R. rickettsii, as demonstrated by realtime PCR or/and guinea pig inoculation, but they showed no clinical abnormality. Rickettsemia was first detected at days 2 to 8, lasting intermittently till days 1 to 30. Approximately 18% and 5% of the flat ticks previously fed on G1 and G2 opossums, respectively, became infected by R. rickettsii, but only the rabbits infested with G1-derived ticks seroconverted. The study demonstrated that R. rickettsii was capable of infecting opossums without causing illness and developing rickettsemia capable of causing infection in guinea pigs and ticks, although the infection rate in ticks was low.     

Ixodid ticks in the mountainous part of the Crimea]

About a hundred of patients with tick-borne encephalitis (TBE) were recorded over the latest decade in the Crimea, and 60 TBE virus strains were isolated from the ticks collected on the peninsula. The results of studies carried out in 1986-1990 helped define the borders of 4 local natural foci of TBE, study their acarifauna, detect the principal TBE vector--Ixodes ricinus (with a mean virophority of 0.6%), and distinguish two foci with a combination of TBE and Crimean-Congo hemorrhagic fever.     

Characterization of monoclonal antibodies protecting mice against Rickettsia rickettsii

Hybridomas producing monoclonal antibodies to Rickettsia rickettsii were prepared from mice to investigate the function of rickettsial antigens. Of the 31 reactive hybridoma lines thus far tested for immunoglobulin subclasses, 11 belonged to the IgG2A subclass, 9 to the IgG2B subclass, and 7 to the IgG3 subclass; four did not react with any of the isotyping sera. Five of the antibodies recognized epitopes present on molecules that were presumed to be polysaccharide and heterogeneous in molecular weight. Twenty monoclonal antibodies reacted with a 170,000-dalton antigen, and six precipitated both the 133,000- and 32,000-dalton polypeptides. Only those antibodies to the 170,000- and 133,000-dalton antigens protected mice from challenge with R. rickettsii. Antibodies to these same antigens were detected in sera from patients convalescing from Rocky Mountain spotted fever. All monoclonal antibodies reacted with antigens apparently located on the rickettsial surface. The protective activity of these antibodies was not correlated with their reactivity in complement fixation, enzyme-linked immunosorbent assay, and immunofluorescence tests.     

Infection of human vascular endothelial cells by Rickettsia rickettsii

Rocky Mountain spotted fever is caused by Rickettsia rickettsii, an obligate intracellular bacterial parasite. The organism primarily attacks endothelial cells and occasionally attacks smooth-muscle cells of small blood vessels. An effective means of examining host-parasite interaction in Rocky Mountain spotted fever would be to use an in vitro model system with a host-cell type that is similar in structure and function to the putative target cell in human infections. Because human umbilical-vein endothelial cells in culture retain many, if not all, of their characteristic properties in vivo and because they also share many properties of capillary endothelium, the use of this endothelial cell system is appropriate in the study of the interaction between R rickettsii and the cell that is principally parasitized in humans. Uptake by umbilical-vein endothelial-cell cultures of R rickettsii is dose dependent. The organism replicates in both the nucleus and cytoplasm of infected cells and exhibits early cell-to-cell spread without detectable host-cell injury.     

Absence of Rickettsia rickettsii and Occurrence of Other Spotted Fever Group Rickettsiae in Ticks from Tennessee

Rocky Mountain spotted fever (RMSF) is the most common tick-borne illness in Tennessee. Little is known about the occurrence of R. rickettsii, the causative agent, in ticks in Tennessee. To better understand the prevalence and distribution of rickettsial agents in ticks, we tested 1,265 Amblyomma, Dermacentor, and Ixodes adult and nymphal ticks. Additionally, we tested 231 Amblyomma americanum larvae. Ticks were collected from 49 counties from humans, wild animals, domestic canines, and flannel drags. Spotted fever group rickettsiae (SFGR) DNA was detected by polymerase chain reaction (PCR) in 32% of adult and nymphal ticks. A total minimum infection rate of 85.63 was found in larval pools tested. Three rickettsial species, Rickettsia montana, Rickettsia amblyommii, and Rickettsia cooleyi were identified by molecular analysis. Rickettsia rickettsii was not detected. This study suggests that some RMSF cases reported in Tennessee may be caused by cross-reactivity with other SFGR antigenically related to R. rickettsii.     

Ixodid ticks on domestic animals in Samut Prakan Province,Thailand

The prevalence of tick-harboring domestic animals, tick density, and the species of ticks were studied throughout the year 2000, in Muang Samut Prakan, Bang Phli and Phra Pradaeng districts of Samut Prakan Province. The animals examined were Canis lupus familiaris (450), Bos indicus (cross-bred) (189), Bos taurus (30), Bubalus bubalis (171) and Sus scrofa domestica (450). The total number of collected ticks was 1,491. The pigs did not harbor ticks. The stages of ticks collected were larvae, nymphs and adults. The prevalence rates of tick-harboring were 46% (Canis lupus familiaris), 42.86% (Bos indicus, cross-bred), 33.33% (Bos taurus) and 9.35% (Bubalus bubalis). The tick densities were 2.22 (Bos indicus, cross-bred), 2.16 (Canis lupus familiaris), 1.16 (Bos taurus) and 0.36 (Bubalus bubalis). Only 2 species of ixodid ticks, Boophilus microplus and Rhipicephalus sanguineus, were found. R. sanguineus was the dominant species of tick. The percentage of R. sanguineus was 65.2% and B. microplus was 34.8%. In Muang district, R. sanguineus was the dominant species in C. lupus familiaris; in Bang Phli district, B. microplus was the dominant species in Bos indicus (cross-bred). The density of B. microplus was high in the summer season; the density of R. sanguineus was high in the winter season. The number of ticks depended on the geographic location, animal host and season.     

法国野猪中Rickettsia raoultii的流行

目的调查和鉴定法国野猪身上Rickettsiaraoultii的流行情况以及野猪作为贮存宿主所起的作用。方法收集法国2007年9月到11）1的野猪身上的边缘革蜱163只。应用柠檬酸合成酶基因和外膜蛋白基因进行实时定量PCR、普通PCR技术及序列分析方法检测立克次体。结果113只（69．3％）边缘革蜱立克次检测阳性。进一步鉴定为斑点热的两类病原,其中R．raoultii占57．5％（存在于65只蜱中）和R．slovaca占42．5％（存在于48只蜱中）。结论证明R．raoultii是野猪身上边缘革蜱的主要病原,边缘革蜱中感染率较高。应警惕野猪对立克次体的传播作用。     

Molecular survey of tick-borne pathogens in Ixodid ticks collected from hunted wild animals in Tuscany,Italy

Objective: To determine the prevalence of zoonotic tick-borne bacteria in feeding ticks removed from hunted wild animals. Methods: PCR was executed on DNA extracted from 77 tick pools to detect Anaplasma phagocytophilum, Bartonella spp., Borrelia burgdorferi sensu lato, Coxiella burnetii and Rickettsia spp. Results: A total of 432 ticks were collected: 30(6.94%) Haemaphysalis punctata, 72(16.7%) Dermacentor marginatus and 330(76.38%) Ixodes ricinus. For each animal one or two pools of 3 ticks of the same species was constituted. Seventy-seven tick pools were examined by PCR: 58(75.32%) resulted infected and among them 14(18.18%) showed co-infections. In particular, 29(37.66%) pools were positive for Bartonella spp., 23(29.87%) for Anaplasma phagocytophilum, 16(20.78%) for Rickettsia spp., and 5(6.49%) for Borrelia burgdorferi s.l. All samples were negative for Coxiella burnetii. Conclusions: The results demonstrate the presence of several zoonotic tick-borne pathogens in the studied area, and underline the risk of exposure to infections for hunters not only during the outdoor activity, but also when they manipulate hunted animals infested by infected ticks.     

Molecular detection of Anaplasma phagocytophilum in Ixodid ticks in Hebei Province, China

A total of 3696 Ixodid ticks, collected from Hebei Province, China, were examined by a nested polymerase chain reaction for the presence of Anaplasma phagocytophilum. Forty-three (15.4%) of 280 pools tested, including 39 (14.6%) of 267 Haemaphysalis longicornis and four (30.8%) of 13 Dermacentor nuttalli, were positive, but no significant difference was found between D. nuttalli and H. longicornis (p>0.05). Sequence and phylogenetic analyses of 16S rRNA gene indicated that A. phagocytophilum in China is genetically diverse. To our knowledge, this is the first evidence of A. phagocytophilum in ticks from Hebei Province, China, and the first documentation of Anaplasma infection in D. nuttalli.     

Detection of Rickettsia parkeri and Candidatus Rickettsia andeanae in Amblyomma maculatum Gulf Coast ticks collected from humans in the United States

Rickettsia parkeri, a spotted fever group (SFG) rickettsia recently found to be pathogenic to humans, causes an eschar-associated febrile illness. The R. parkeri rickettsiosis, Tidewater spotted fever, has been misdiagnosed as Rocky Mountain spotted fever due to serologic cross reactivity and the lack of specific diagnostic methods. Candidatus Rickettsia andeanae, also a SFG rickettsia, is a recently described agent of unknown pathogenicity originally identified in ticks collected from domestic animals during a fever outbreak investigation in northern Peru. Among 37 Amblyomma maculatum (collected from humans (n=35) and questing (n=2)) obtained from the southern United States during 2000-2009, nine and four A. maculatum nucleic acid preparations were found positive for R. parkeri and Candidatus R. andeanae, respectively, by newly developed genus- and species-specific quantitative real-time polymerase chain reaction assays. In addition Rickettsia felis was found in two A. maculatum nucleic acid preparations.