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PubMed1995

Effects of Dermacentor andersoni (Acari: Ixodidae) salivary gland extracts on Bos indicus and B. taurus lymphocytes and macrophages: in vitro cytokine elaboration and lymphocyte blastogenesis.

Cattle and laboratory animal species-acquired resistance to tick infestation has an immunological basis involving antigen presenting cells, B-lymphocytes, T-lymphocytes, and cytokines. Tick infestation has been shown to impair guinea pig antibody responses to a thymic-dependent antigen and in vitro responsiveness of lymphocytes to T-cell mitogens. Tick salivary gland extracts inhibited in vitro proliferative responses of normal murine lymphocytes to the T-cell mitogen concanavalin A (Con A) and enhanced reactivity of normal B-lymphocytes to the mitogen E. coli lipopolysaccharide (LPS). Salivary gland extracts collected daily during engorgement were shown to inhibit normal murine macrophage elaboration of interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF) as well as murine T-lymphocyte production of interleukin-2 (IL-2) and interferon-gamma (IFN-G). Peripheral blood mononuclear cells collected from purebred Bos indicus and B. taurus were significantly inhibited in their in vitro responses to Con A by salivary gland extracts prepared daily from female Dermacentor andersoni stiles during the course of engorgement. Percentage of suppression of Con A responsiveness was similar for both B. indicus and B. taurus cells. The overall responsiveness of B. indicus derived T cells is significantly greater than that of similar cells from B. taurus, when mean counts per minute of methyl-tritiated-thymidine incorporation were compared for both groups. Cells of B. indicus origin were 34.5% more reactive. In vitro responsiveness of the same cell populations to LPS were significantly enhanced by the presence of tick salivary gland extracts. B. indicus lymphocyte reactivity to LPS was significantly greater (42.9%) than that of similar B. taurus cells in the absence of salivary gland extracts. B. indicus and B. taurus macrophage elaboration of IL-1 were suppressed in a similar manner by tick salivary gland extracts prepared on days 5-9 of engorgement. B. indicus macrophages produced more IL-1 than similar cells of B. taurus origin either in the presence (45.6%) or absence (43.0%) of LPS. Macrophages derived from both genetic backgrounds were significantly suppressed in their LPS induced production of TNF in the presence of tick salivary gland extracts collected on days 0-9 of engorgement. B. indicus might be able to develop more vigorous immune responses to foreign immunogens presented to the animal during tick feeding.

Animals↗
PubMed1995

Evaluation of Ixodes scapularis, Amblyomma americanum, and Dermacentor variabilis (Acari: Ixodidae) from Georgia as vectors of a Florida strain of the Lyme disease spirochete, Borrelia burgdorferi.

The ability of three common tick species from Georgia to maintain and transmit the causative agent of Lyme disease, Borrelia burgdorferi, was compared under laboratory conditions. A B. burgdorferi cotton rat isolate (MI-6) from Florida was selected as a strain from the south, and the SH2-82 isolate from New York was used as a positive control. Amblyomma americanum (L.) and Dermacentor variabilis (Say) did not transmit the MI-6 isolate from inoculated hamsters to naive laboratory mice, and nymphal ticks did not maintain this isolate transstadially. Ixodes scapularis Say transmitted both isolates to laboratory mice. There was a significant difference in the percentage of transmission of the two isolates. I. scapularis also transmitted the MI-6 isolate to two of three cotton rats. This study adds support to the premise that I. scapularis is probably the main tick vector of B. burgdorferi in the southeastern United States.

Animals↗
PubMed1996

Developmental studies of Anaplasma marginale (Rickettsiales:Anaplasmataceae) in male Dermacentor andersoni (Acari:Ixodidae) infected as adults by using nonradioactive in situ hybridization and microscopy.

The development of Anaplasma marginale Theiler was studied in ticks using a nonradioactive in situ hybridization method developed in our laboratory. Male Rocky Mountain wood ticks, Dermacentor andersoni Stiles, were infected intrastadially by allowing them to feed for 7 d on an infected calf (acquisition feeding). The ticks were then removed and held in a humidity chamber for 5 d before being fed on a 2nd susceptible call for 10 d (transmission feeding). Two groups of 10 ticks were collected daily during the 22-d experiment. In one group one-half of each tick was processed and embedded in paraffin and in the other group one-half of each tick was embedded in LR White for in situ hybridization. The companion tick halves from each group were fixed and embedded in Dow Epoxy Resin resin for routine light and electron microscopy. As detected by in situ hybridization on LR White- and paraffin-embedded sections and by microscopy, initial infection of A. marginale in ticks occurred in gut tissues either on the 7th d of acquisition feeding or the 1st d of the held period and infection persisted throughout transmission feeding. The highest number of ticks with gut infection was observed on the 5th d of transmission feeding. Salivary glands became infected with A. marginale on the 1st day of transmission feeding and remained infected throughout the transmission feeding period. Peak infection was observed on day 4 of transmission feeding. After the beginning of transmission feeding, A. marginale infection was also observed in interstitial, reproductive, skeletal muscle, fat body, and Malpighian tubule tissues. Although A. marginale infection of ticks clearly originates in midgut epithelial cells, many tissues eventually become infected during transmission feeding, resulting in a generalized infection. The infection of multiple tissues may contribute to the ability of A. marginale infection to persist in intrastadially infected male ticks.

Anaplasma↗
PubMed1997

Vector competence of Ixodes scapularis, I. spinipalpis, and Dermacentor andersoni (Acari:Ixodidae) in transmitting Borrelia burgdorferi, the etiologic agent of Lyme disease.

This report describes the vector competence of 3 ixodid tick species, Ixodes scapularis (Say), I. spinipalpis (Nuttall), and Dermacentor andersoni (Stiles), for Borrelia burgdorferi in Colorado. The study was based on preliminary field work performed in 6 Colorado counties, where rodents and ticks were collected and assayed for the presence of B. burgdorferi. Four of the 6 counties produced 52 rodent and 39 I. spinipalpis isolates of B. burgdorferi. Two B. burgdorferi isolates were tested under laboratory conditions and found to be infective to Imperial Cancer Research Fund (ICRF) outbred mice. The 1st, a low-passage strain originating from New York (B-31, passage 6) was used as a control, and the 2nd was isolated from ear tissue of a Neotoma mexicana (Baird) (Mexican wood rat) that was trapped in Colorado. Larvae of I. scapularis, I. spinipalpis. and D. andersoni were fed on infected mice and cultured in Barbour-Stoner-Kelly media to assay for infection at 1, 2, 3, and 4 wk after repletion. The infection rates in replete larvae. were 75, 69, and 8.5%, respectively, whereas transstadial nymphal infection rates were 80, 75, and 0%, respectively. Both I. scapularis and I. spinipalpis were shown to be competent vectors that acquired the infection from the host reservoir mice and subsequently transmitted it to naive mice. Given that I. scapularis are not found in Colorado, I. spinipalpis are restricted to the nests and burrows of rodents, and because of the semiarid environment in Colorado, the risk of human contact with B. burgdorferi appears to be low.

Animals↗
PubMed1998

Control of bacterial infections in the hard tick Dermacentor variabilis (Acari: Ixodidae): evidence for the existence of antimicrobial proteins in tick hemolymph.

The ability of hard ticks to prevent infection by bacteria was investigated. During a 72-h period, virtually all Dermacentor variabilis females survived inoculation with Bacillus subtilis, Escherichia coli, and Staphyloccocus aureus but few survived infection with Pseudomonas aeruginosa. The hemocyte population increased to peak abundance at 48 h to approximately 6 times that of the uninfected controls. In contrast, the soluble hemolymph protein content decreased inversely as the hemocytes increased. D. variabilis hemolymph was found to be constitutively antimicrobial (i.e., hemolymph from bacteria-naive individuals inhibited bacterial growth). Infection with various bacterial species enhanced this innate capability. When hemolymph fractions separated by high-pressure liquid chromatography were tested for their ability to inhibit microbial growth, activity against the gram-positive bacterium, B. subtilis, was found in 2 polar fractions. Antimicrobial activity was lost when the fractions were incubated with protease. The least polar fraction contained 1 major protein, M(r) 14.5 kDa, that comigrated with human lysozyme. This protein, tentatively identified as tick lysozyme, was abundant in bacteria-naive ticks but increased greatly (43%) following challenge with B. subtilis. The identity of the other, more polar protein is unknown. Studies to characterize these antimicrobial proteins are planned.

Animals↗
PubMed1998

Characterization of an immunosuppressant protein from Dermacentor andersoni (Acari: Ixodidae) salivary glands.

A 36-kDa soluble protein was found in the salivary glands of female Dermacentor andersoni (Stiles) ticks that suppressed the in vitro proliferative response of murine splenocytes to concanavalin A (Con A). Incubating the purified protein with splenocytes reduced the incorporation of thymidine into the DNA of proliferating T-lymphocytes by more than 90% compared with cells exposed to Con A and buffer alone. The N-terminal amino acid sequence of the immunosuppressant protein was determined to be NH2-Leu-His-Lys-Ala(Asp)-Lys-Ile-Val-Lys-Leu-Thr -Glu-Glu-Ala -Arg-Lys-Tyr-Val-Gly-Arg-Xxx-Xxx-Thr-Thr-Ala-Leu-Gly-. Although the sequence exhibited a modest degree of similarity with a segment of immunoglobulin-binding protein found in several species of mammals, the mode of action of the immunosuppressant protein is unknown. This protein may play an important role in suppressing the host's acquisition of resistance to ticks.

Amino Acid Sequence↗
PubMed1998

Dermacentor hunteri (Acari: Ixodidae): seasonal variation in questing adults and on-host juvenile stages, and host associations and feeding behavior of larvae and nymphs.

Dermacentor hunteri Bishopp is the only completely desert adapted tick in the Nearctic realm, and chiefly parasitizes desert bighorn sheep (Ovis canadensis Shaw) as an adult. The remainder of its life history has been unknown. We conducted field investigations in the Sonoran desert of the temporal and spatial variation of adult host-seeking ticks and of the host associations of juvenile ticks. Additionally, the feeding success of juvenile ticks was assessed in the laboratory. Adult ticks were found in significant numbers only in plateau and rocky slopes habitats, chiefly during the period from January to June. Questing adults were not found in July and August, and they were present in small numbers from September through December. Juvenile stages were found only on desert woodrats, Neotoma lepida Thomas (larvae and nymphs), and cactus mice, Peromyscus eremicus Baird (larvae only), in March, May, and early June. In the laboratory; both larvae and nymphs fed on N. lepida, but only larvae fed on P. maniculatus bairdii (Wagner). We concluded that the life history of D. hunteri may be constrained by the co-distribution of desert bighorn, desert woodrats, and perhaps cactus mice; and that adults oversummer either on desert bighorn or sequestered in favorable microclimates off the host.

Animals↗
PubMed1999

Comparative vector competence of Dermacentor variabilis and Ixodes scapularis (Acari: Ixodidae) for the agent of human granulocytic ehrlichiosis.

Vector competence of Ixodes scapularis Say and Dermacentor variabilis Say for the agent of human granulocytic ehrlichiosis (HGE) was compared. Five white-footed mice, Peromyscus leucopus Rafinesque, were inoculated intra-peritoneally with blood from a mouse infected with the agent of HGE. Approximately 100 I. scapularis and D. variabilis larvae were placed on each mouse and allowed to feed to repletion. Fed larvae were collected, separated according to species and allowed to molt to nymphs. Twenty-six per cent of I. scapularis (34/131) and 11% of D. variabilis (11/96) tested positive for the agent of HGE by polymerase chain reaction (PCR) after molting to nymphs. Positive I. scapularis nymphs transmitted the agent of HGE to P. leucopus mice in 5 of 5 trials. In contrast, the positive D. variabilis nymphs did not transmit the agent of agent of HGE in any of 6 trials. In a 2nd experiment, 3 P. leucopus mice were infested with I. scapularis nymphs that were infected with the agent of HGE. All 3 mice became infected with the agent of HGE and approximately 300 D. variabilis larvae were placed on each mouse and allowed to feed to repletion. Larvae were collected and allowed to molt to nymphs as before. Approximately 8% (5/60) of the nymphs became positive for the agent of HGE as determined by PCR. Twenty-five of these nymphs were then placed on each of 9 P. leucopus mice and allowed to feed to repletion. Evidence of transmission was not observed in any of 9 mice exposed to D. variabilis nymphs. These results demonstrate that although I. scapularis is a competent vector of the agent of the HGF, D. variabilis is not.

Anaplasmataceae↗
PubMed1999

Patterns of infestation by adult Dermacentor variabilis (Acari: Ixodidae) in a mark-recapture study of raccoons (Mammalia: Carnivora) and Virginia opossums (Mammalia: Didelphimorphia) in Tennessee.

A mark-recapture study of raccoons (Procyon lotor L.) and Virginia opossums (Didelphis virginiana Kerr) was conducted from February 1991 through April 1994 to determine host interactions with adult Dermacentor variabilis Say. We captured 1,293 raccoons and Virginia opossums during the 3-yr study (140 individual raccoons and 160 individual Virginia opossums) with 1,895 adult D. variabilis collected. Raccoons had a significantly higher mean intensity and higher prevalence of adult ticks than Virginia opossums (Mann-Whitney Z = 6.15, chi 2 = 51.9, P < 0.001). Mean intensity follows Margolis et al. (1982) as being the mean number of parasite species per infected host. Prevalence follows Margolis et al. (1982) as being the number of individuals of the host species infected with a parasite species divided by the number of hosts examined. The time required for a higher prevalence and mean intensity of ticks to occur on raccoons than Virginia opossums was < 7 d. No significant differences occurred between the mean intensity or prevalence of D. variabilis between sexes or among age classes of raccoons. Significant differences in prevalence and mean intensity of ticks occurred between sexes and among age classes of Virginia opposums. Infestation increased by 0.64 ticks per day on Virginia opossums and 1.77/d on raccoons during the first 7 d. The base host finding rate (ticks per host per day) of adult D. variabilis on Virginia opossums was 0.064 and 0.053 on raccoons. Tick interactions with hosts are quantified and may reflect behavioral differences between sexes and among age groups intraspecifically, and host preferences of adult D. variabilis interspecifically.

Animals↗
PubMed1999

Dermacentor hunteri (Acari: Ixodidae): an experimental vector of Anaplasma marginale and A. ovis (Rickettsiales: Anaplasmataceae) to calves and sheep.

The experimental vector competence of laboratory-reared Dermacentor hunteri Bishopp for Anaplasma marginale Theiler and Anaplasma ovis Lestoquard was evaluated by delayed transfer of male ticks from infected to susceptible Holstein calves and from infected to susceptible domestic sheep, respectively. After feeding for 4 or 5 d on rickettsemic acquisition hosts, the ticks were held off the host at 26 degrees C, approximately 93% RH, and a photoperiod of 14:10 (L:D) h for 7 or 8 d, then test fed for 5 or 7 d. Additionally, ticks test-fed for 5 d on 2 susceptible calves were removed, held off the host for 7 d, and test-fed for 5 d on a 3rd susceptible calf to test the tick's ability to transmit A. marginale by delayed serial transfer. Tick transmission of A. marginale to 3 test calves and A. ovis to 3 test sheep was demonstrated by blood smear and indirect immunofluorescence serology. These data indicate that males of D. hunteri, a tick commonly found on desert bighorn, Ovis canadensis Shaw, in the southwestern United States and northern Mexico, may be competent natural vectors of these organisms present in desert bighorn populations.

Anaplasma↗
PubMed2005

Prefeeding Dermacentor andersoni (Acari: Ixodidae) on cattle with prior tick exposure may inhibit detection of tick paralysis by using hamster bioassay.

The effect of prefeeding Dermacentor andersoni Stiles on naive and previously challenged cattle before conducting virulence assays by using hamsters was examined. In an initial observational trial, ticks prefed on a previously challenged heifer did not cause paralysis after transfer to hamsters, whereas ticks from the same lot that were prefed on a naive heifer did cause paralysis. Subsequent paired trails were conducted to simultaneously compare paralysis after feeding on naive and previously challenged heifers. In the first trial, prefeeding ticks on a previously challenged heifer did not result in loss of virulence. In a second trial, ticks fed on a previously challenged heifer had greatly diminished virulence after transfer to hamsters. This also occurred in a third trial after the previously challenged animal had two prior exposures to virulent D. andersoni. Weight gains of ticks that did not cause paralysis after transfer to hamsters were higher after feeding on previously challenged cattle, indicating that loss of virulence was not due to failure of ticks to reattach and feed. Ticks gained little weight on paralyzed hamsters due to the reduced time spent feeding on hamsters when paralysis occurred. Results indicate that assaying ticks for virulence requires prefeeding on naive hosts. If these are not available, rabbits, a resistant host, can be used for prefeeding ticks.

Animals↗
PubMed2005

Capillary tube feeding system for studying tick-pathogen interactions of Dermacentor variabilis (Acari: Ixodidae) and Anaplasma marginale (Rickettsiales: Anaplasmataceae).

A capillary tube feeding (CTF) system was adapted for studying the interaction between Dermacentor variabilis (Say) and the rickettsial cattle pathogen Anaplasma marginale Theiler. A. marginale undergoes a complex developmental cycle in ticks that begins in midguts and ends by transmission from salivary glands. In this CTF system, male D. variabilis were fed A. marginale-infected blood or cultured tick cells. Ticks that fed on highly rickettsemic calves developed midgut and salivary gland infections as detected by PCR, whereas ticks that were fed from capillary tubes on the same blood developed only midgut infections. An unexpected result of capillary tube feeding was that antibodies against the A. marginale adhesin, major surface protein la, enhanced midgut infections and caused cell culture-derived A. marginale to infect midguts. Another unexpected result was the infection of the midguts of the nonvector tick Amblyomma americanum (L.), after capillary tube feeding on infected bovine blood. The gut cell response of ticks to A. marginale, as determined from SDS-polyacrylamide gel electrophoresis protein profiles, did not differ when ticks were fed infected or uninfected cells from capillary tubes. Selected protein bands, as identified by tryptic digestion-mass spectrometry, contained mostly proteins of bovine origin, including bovine albumin, undigested alpha- and beta-chain hemoglobin and hemoglobin fragments. Although infection of ticks by A. marginale CTF system was not the same as infection by feeding on cattle, the results obtained demonstrated the potential use of this system for identifying aspects of pathogen-vector interactions that are not readily recognized in naturally feeding ticks.

Adhesins, Bacterial↗
PubMed2005

'Candidatus Borrelia texasensis', from the American dog tick Dermacentor variabilis.

TXW-1, a Borrelia strain isolated in March 1998 from an adult male Dermacentor variabilis tick feeding on a coyote from Webb county, Texas, USA, was characterized by using randomly amplified polymorphic DNA (RAPD) analysis, RFLP and sequence analysis of flaB and rrs (16S rRNA gene), DNA-DNA hybridization analysis, SDS-PAGE and Western blotting with mAbs. It shows different banding patterns in RFLP analysis of flaB and forms distinct branches in phylogenetic analysis derived from flaB and rrs genes. It differs from other borreliae based on the banding patterns obtained by RAPD analysis. This strain contains a small, 38-kDa endoflagellar protein. DNA-DNA hybridization experiments revealed that the levels of DNA reassociation between TXW-1 and previously described relapsing fever borreliae were 38.64 % (Borrelia turicatae), 38.40 % (Borrelia parkeri), 7.39 % (Borrelia hermsii) and 18.30 % (Borrelia coriaceae). However, the level of DNA relatedness between B. parkeri and B. turicatae was 78.78 %. Sequence analyses of flaB and rrs genes indicate that the similarities of nucleotide sequences among TXW-1 and B. turicatae or B. parkeri are less than that between B. turicatae and B. parkeri, and that the genetic distances among TXW-1 and B. turicatae or B. parkeri are greater than that between B. turicatae and B. parkeri. TXW-1 lacks an ospC gene. Electron microscope observations showed that this spirochaete had different morphological structures compared to previously described relapsing fever borreliae. All the results obtained from the above-mentioned analyses indicate that TXW-1 is different from other described Borrelia species and that it represents a novel species of Borrelia. We have been unable to revive frozen cultures and so can not meet the requirements of the Bacteriological Code to deposit viable type material at two different culture collections. Therefore we use the Candidatus designation; based on these results, the species 'Candidatus Borrelia texasensis' is proposed.

Animals↗
PubMed2004

Dermacentor-borne necrosis erythema and lymphadenopathy: clinical and epidemiological features of a new tick-borne disease.

This paper describes the epidemiological and clinical features of a tick-borne disease differing somewhat from other tick-borne diseases found previously in Spain. All patients were bitten by Dermacentor marginatus or a large tick. The clinical features include a crustaceous or necrotic lesion at the site of the tick's attachment, surrounded by an erythema (erythema migrans-like) and painful regional lymphadenopathies. The probable aetiological agent is Rickettsia slovaca. Similar cases have been reported in other European countries.

Adult↗
PubMed2006

Differential expression of two glutathione S-transferases identified from the American dog tick, Dermacentor variabilis.

Reciprocal signalling and gene expression play a cardinal role during pathogen-host molecular interactions and are prerequisite to the maintenance of balanced homeostasis. Gene expression repertoire changes during rickettsial infection and glutathione-S-transferases (GSTs) were among the genes found up-regulated in Rickettsia-infected Dermacentor variabilis. GSTs are well known to play an important part in cellular stress responses in the host. We have cloned two full-length GSTs from D. variabilis (DvGST1 and DvGST2). Comparison of these two DvGST molecules with those of other species indicate that DvGST1 is related to the mammalian class theta and insect class delta GSTs, while DvGST2 does not seem to fall in the same family. Northern blotting analyses revealed differential expression patterns, where DvGST1 and DvGST2 transcripts are found in the tick gut, with DvGST2 transcripts also present in the ovaries. Both DvGST transcripts are up-regulated upon tick feeding. Challenge of fed adult ticks with Escherichia coli injection showed decreased transcript amounts compared with ticks injected with phosphate-buffered saline (sham) and naïve ticks.

Amino Acid Sequence↗
PubMed2003

Interactions between rickettsiae and Dermacentor variabilis ticks: analysis of gene expression.

Tick-borne spotted fever group rickettsiae are maintained in nature primarily through transstadial and transovarial transmission in their vector. In the tick, Dermacentor variabilis, the infection of, and persistence within, the ovaries are critical steps in the transmission cycle of rickettsiae from one generation to the next. Although ixodid ticks can experimentally maintain several species of rickettsiae, often only a single species is maintained transovarially. The molecular mechanisms underlying exclusion processes are unknown. In this study, an attempt to identify the molecules that may be involved in rickettsial adhesion to tick cells was carried out. Monoclonal antibodies to mammalian alpha and beta subunits of integrins were used to screen a lambda phage library, constructed from uninfected tick ovarian tissues. Positive plaques for both alpha and beta integrins were identified. For one integrin, beta(3), the plaque was isolated and the insert sequenced. The role of these molecules, identified by library screening, in rickettsial infection and survival are discussed.

Animals↗
PubMed1999

Lethal effect of Rickettsia rickettsii on its tick vector (Dermacentor andersoni).

Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, was lethal for the majority of experimentally and transovarially infected Rocky Mountain wood ticks (Dermacentor andersoni). Overall, 94.1% of nymphs infected as larvae by feeding on rickettsemic guinea pigs died during the molt into adults and 88. 3% of adult female ticks infected as nymphs died prior to feeding. In contrast, only 2.8% of uninfected larvae failed to develop into adults over two generations. Infected female ticks incubated at 4 degreesC had a lower mortality (80.9%) than did those held at 21 degreesC (96.8%). Rickettsiae were vertically transmitted to 39.0% of offspring, and significantly fewer larvae developed from infected ticks. The lethal effect of R. rickettsii may explain the low prevalence of infected ticks in nature and affect its enzootic maintenance.

Animals↗
PubMed2001

Isolation of a spotted fever group Rickettsia, Rickettsia peacockii, in a Rocky Mountain wood tick, Dermacentor andersoni, cell line.

An embryonic cell line (DAE100) of the Rocky Mountain wood tick, Dermacentor andersoni, was observed by microscopy to be chronically infected with a rickettsialike organism. The organism was identified as a spotted fever group (SFG) rickettsia by PCR amplification and sequencing of portions of the 16S rRNA, citrate synthase, Rickettsia genus-specific 17-kDa antigen, and SFG-specific 190-kDa outer membrane protein A (rOmpA) genes. Sequence analysis of a partial rompA gene PCR fragment and indirect fluorescent antibody data for rOmpA and rOmpB indicated that this rickettsia was a strain (DaE100R) of Rickettsia peacockii, an SFG species presumed to be avirulent for both ticks and mammals. R. peacockii was successfully maintained in a continuous culture of DAE100 cells without apparent adverse effects on the host cells. Establishing cell lines from embryonic tissues of ticks offers an alternative technique for isolation of rickettsiae that are transovarially transmitted.

Animals↗