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Lambs were inoculated with Ehrlichia phagocytophila infected blood at the age of either two or six weeks. The temperature response and degree of parasitaemia were both most pronounced in the lambs inoculated at six weeks old. The half-life of antibodies to E phagocytophila was estimated to be 17.5 days. Lambs inoculated with tick-borne fever (TBF) had lower liveweights in the autumn than TBF-free controls.
Cytoecetes phagocytophila, a neutrophilic rickettsia which parasitizes sheep and cattle, was propagated transiently at 37 degrees C in cultures of heparinized whole blood of sheep supplemented with Medium 199 containing HEPES buffer. Significant increases in the number of infected cells and the number of rickettsias per infected cell were observed within 24 h. Back-passage into sheep produced typical tick-borne fever.
In May 1998, the Oregon Health Division received a report from a local physician that nine persons developed annular skin lesions accompanied by influenza-like symptoms within 8 days of leaving southern Africa. All nine persons were members of a 34-person group from Oregon that traveled to Swaziland in April 1998 to participate in a 3-week humanitarian construction project. This report describes two cases of African tick-bite fever (ATBF) diagnosed in this group and underscores the importance of pretravel counseling about vectorborne illnesses and post-travel recognition of imported rickettsial diseases.
Four groups of lambs aged 1 week, 4 weeks, 1/2 year and 1 year old respectively were inoculated with Ehrlichia phagocytophila infected blood. Clinical signs, temperature reactions, haematological changes and parasitaemia were more moderate in lambs inoculated with E. phagocytophila at the age of 1 week than those recorded in the older animals. The clinical response to tick-borne fever (TBF) appears to be more severe with increasing age of the lambs. The lymphocyte reactivity to mitogens was reduced in the TBF infected lambs, and was most pronounced in lambs in the 3 older age groups.
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Almost 100% of 52 cattle tested from the southern areas of Zimbabwe were found to have antibodies reactive with Rickettsia conorii compared with less than 30% of 120 cattle from the north. Steers artificially infected with R. conorii isolated from Amblyomma hebraeum were found to show no hematological or biochemical signs of disease but did seroconvert. Clinical signs of infection were restricted to regional lymphadenopathy and dermal erythema, edema, and tenderness at the inoculation site. Rickettsemia was detectable for at least 32 days postinfection. Our findings indicate that cattle could be involved in the transmission of rickettsias by A. hebraeum and may serve as a reservoir of human tick-bite fever in southern Africa.
The genomes of spotted fever group rickettsiae isolated in different geographical areas of Israel (two from ticks and four from humans, obtained over a span of 20 years) were studied by polymerase chain reaction (PCR) and restriction endonuclease fragment length polymorphism (RFLP) analysis. The human isolates were obtained from patients suffering from rickettsial disease of different degrees of severity. The PCR products obtained with five pairs of oligonucleotide primers (two primer sets derived from the 190-kDa polypeptide gene and three from the 120-kDa polypeptide gene) and cleaved with restriction endonucleases were used to study the Israeli isolates and reference Rickettsia conorii isolates. Subtle differences between the PCR-RFLP patterns of Israeli isolates and the two R. conorii reference strains (Moroccan and no. 7) were seen when the PCR products derived from the 190-kDa gene-derived primer sets were digested. All of the Israeli isolates were identical by RFLP analysis using all of the primer sets. This study showed that the Israeli spotted fever group isolates (from both ticks and humans) were genetically homogeneous by the criteria used in this study, despite the time and location differences in their original isolation, and different as a group from R. conorii.
The therapeutic efficacy and pharmacokinetics of oxytetracycline (10 mg kg-1), ampicillin (20 mg kg-1) and a combination (TSS) of trimethoprim (20 mg kg-1), sulphadimidine (50 mg kg-1) and sulphamethylphenazole (50 mg kg-1) were investigated in normal dwarf goats and in those infected with Ehrlichia phagocytophila. Goats given oxytetracycline or TSS intravenously showed improvement, whereas ampicillin was ineffective. The infected goats had significantly prolonged elimination half-life values for sulphadimidine and oxytetracycline. The disposition kinetics of ampicillin and sulphamethylphenazole showed no marked differences between the healthy and infected animals. The tick-borne fever model used in the present study can be of value in testing the therapeutic efficacy and pharmacokinetics of chemotherapeutic agents in rickettsial infections.
West African tick-borne relapsing fever is an endemic disease due to Borrelia crocidurae. The tick Alectorobius sonrai is the only known vector of this bacterium. Several species of rodents and insectivores may be reservoir for this spirochete. The geographic distribution of Borrelia crocidurae is not well known. The zone where the presence of the vector has been recorded is situated in Sahelian regions, from Mauritania and northern Senegal up to Chad. In Senegal, it has been shown that the persistence of drought is responsible for a considerable spread of tick-borne relapsing fever to the south. Few epidemiological data are available about West African tick-borne relapsing fever. In Senegal, epidemiological investigations indicate that Borrelia crocidurae is a major cause of morbidity (annual incidence rate of 5.1%). The relapsing nature of tick-borne borreliosis depends on Borrelia's antigenic variability. Except relapsing febrile episodes, this illness presents no pathognomonic signs. Borrelia crocidurae relapsing fever is generally benignant but neurologic or ocular complications can occur. The diagnosis of tick-borne relapsing fever is made by demonstrating the presence of Borrelia in peripheral blood in thick smear, by intraperitoneal inoculation of mice or more recently with quantitative buffy coat method (QBC test). The best treatment for relapsing fever is tetracycline or doxycycline. When tetracyclines are contraindicated, the alternative is erythromycin. In neurologic complications, the effective treatment is intravenous penicillin G or ceftriaxone. West African tick-borne relapsing fever must be systematically mentioned in case of fever in a patient returning from the endemic area.
A total of 1,523 adult Ixodes ricinus ticks were collected from regions where bovine ehrlichiosis is endemic and were examined for Ehrlichia phagocytophila via PCR. Of the ticks from cattle with ehrlichiosis, the ticks from healthy cattle, and the free-living ticks, 26.5% (18 of 68), 4.4% (35 of 802), and 0.8% (5 of 653), respectively, were positive.
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Argasid ticks collected in the site near Mvumi Hospital, Dodoma, Tanzania, were subjected to flagellin gene-based nested polymerase chain reaction (PCR) amplification for examination of borrelial infections. Eight of 13 ticks gave a strong 350-bp signal; three had a weak signal at the same size, and the rest were negative. Sequence determination of eight of the positive samples resulted in three types of flagellin gene sequences. The first type of sequence (shown by three individuals) was identical to that of Borrelia duttonii strain Ly. The second type of sequence from PCR products from four individual ticks had only one base substitution without amino acid alteration in deduced protein sequence. The third type of sequence was different from that of any other Old World relapsing fever borreliae, and the tick was thought to be infected with an unknown Borrelia species. Ticks were also examined to determine the nucleotide sequence of the mitochondrial 16S rRNA gene. The partial sequence of approximately 470 bases was aligned for comparison with previously published sequences to identify the species. The sequences of 13 individual ticks were all identical, and the sequence similarity analysis revealed the ticks should be classified as members of the Ornithodoros porcinus species. The PCR method described in this report appears to be a reliable tool for the detection of borreliae and epidemiological study of tick-borne relapsing fever.
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From 1989 to 1992, a longitudinal study of the relationships between different tick species and domestic ungulates in the transmission and amplification of Crimean-Congo hemorrhagic fever (CCHF) virus was undertaken in the Bandia area in Senegal where the presence of the virus had been reported previously. An epizootic occurred in 1991-1992 and 22 strains of CCHF virus were isolated from Hyalomma marginatum rufipes Koch, Amblyomma variegatum (F.), Rhipicephalus guilhoni Morel & Vassiliades, and R. evertsi evertsi Neumann ticks collected from cattle and goats. No human cases were reported. Transmission of CCHF virus in the area involves a complicated pattern including many tick species and hosts. Amplicons of the S fragment (536 bp) of the CCHF genome of 12 isolates from the study were obtained by polymerase chain reaction and analyzed by restriction-length fragment polymorphism. Three different genotypes of CCHF virus were identified and present during the epizootic. One genotype was recovered from A. variegatum, R. guilhoni, and R. e. evertsi and 2 genotypes were isolated from H. m. rufipes.
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