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1.
Newly replete nymphal Dermacentor andersoni (principals) were percutaneously exposed to Anaplasma marginale by injection of either intact or lysed infected bovine erythrocytes. Control nymphs were fed on calves with anaplasmosis. The subsequently molted adults were examined for infection by light microscopy, and companion ticks were tested for infectivity by allowing them to feed on susceptible calves. When they fed as adults, both control ticks and percutaneously inoculated principals transmitted A marginale to susceptible calves. Prepatent periods in calves varied according to the method by which nymphs were infected. Colonies of A marginale were found in all ticks that acquired infection by feeding, but colonies were not observed in any ticks exposed percutaneously. The possible developmental cycle of A marginale in artificially infected ticks is discussed.  相似文献   

2.
Laboratory-reared Dermacentor andersoni ticks experimentally infected as nymphs with Anaplasma marginale were allowed to feed as adults from 1 to 9 days on susceptible, splenectomized calves to determine when, during feeding, the hematozoan was transmitted from ticks to cattle. In experiment 1, ticks were allowed to feed on calves for 1, 2, 3, 4, 5, or 6 days and anaplasmosis did not result. The same calves were used for experiment 2, and ticks were allowed to feed for 1, 3, 6, 7, 8, or 9 days and anaplasmosis occurred in all calves on which ticks fed for greater than or equal to 6 days. In 2 trials in experiment 3, ticks were allowed to feed on calves for 1 to 9 days. Anaplasmosis developed only in calves on which ticks fed for 7, 8, or 9 days. The prepatent periods shortened with longer tick feeding, and linear regression analysis of combined prepatent periods of both trials of experiment 3 indicated a significant (P = 0.05) slope with an estimated daily decrease of 7.75 days from day 7 to 9 of feeding. There was no apparent correlation between length of tick feeding and severity of clinical signs in those calves that developed anaplasmosis. Seemingly, A marginale can be transmitted to cattle by adult D andersoni ticks no earlier than the 6th or 7th day of feeding.  相似文献   

3.
In Anaplasma marginale transmission studies conducted on the high semi-arid range of eastern Oregon during the 1974 and 1975 vector season, A marginale-susceptible calves (principals) were maintained on 2 raised tick-proof platforms. Anaplasmosis-susceptible control calves of approximately the same age and latent-infected cows grazed the area surrounding the platforms. One latent-infected steer spent the entire 1975 vector season on a platform with the principals. The 28 principals did not develop anaplasmosis, whereas 15 of 30 (50%) controls became infected. The disease was not transmitted from the latent-infected cattle to the principals exposed only to flying hematophagous insects, whereas 50% of the controls exposed to the Rocky Mountain wood tick Dermacentor andersoni) = (venustus) developed the disease. Dermacentor andersoni appears to be the principal vector on this range.  相似文献   

4.
Evaluation of jackrabbits as nonruminant hosts for Anaplasma marginale   总被引：1，自引：0，他引：1  
Two black-tailed jackrabbits (Lepus californicus), 1 splenectomized and 1 intact, were inoculated with 0.2 ml of a 1:5 dilution of a Florida Anaplasma marginale stabilate. Five months later, both hares were inoculated with 1 ml of whole blood from a calf with acute anaplasmosis. Neither hare developed any signs of clinical anaplasmosis. Pooled blood (7 ml) from these jackrabbits which was inoculated into 2 Anaplasma-susceptible, splenectomized calves failed to induce hematologic or serologic signs of anaplasmosis for at least 90 days. Two susceptible, splenectomized calves were inoculated with 35 ml of pooled whole blood from 9 wild-collected black-tailed jackrabbits from a known anaplasmosis enzootic area. Both steers remained free of anaplasmosis signs for 90 days.  相似文献   

5.
Hemolymph was collected from adult Dermacentor andersoni Stiles that had been infected with Anaplasma marginale Theiler as nymphs. Before hemolymph was collected, the adult ticks were either incubated and unfed at 37 C for 2.5 days or fed for 6 days on sheep. Hemolymph collected from groups of 100 ticks was inoculated into susceptible splenectomized calves. Smears of hemolymph from the same groups of ticks were prepared for examination by fluorescent antibody technique. Hemolymph from incubated ticks caused anaplasmosis in 2 of 4 trials, and hemolymph from feeding ticks caused anaplasmosis in 4 of 4 trials. Moderately fluorescing bodies were demonstrated in some hemocytes from incubated ticks, whereas hemocytes from feeding ticks contained numerous clusters of brightly fluorescing bodies. Fluorescing bodies were not observed in hemocytes from control ticks.  相似文献   

6.
Canadian cattle are free of bovine anaplasmosis, with the exception of 4 isolated incursions since 1968, which were eradicated. It is not known why the disease has not become established in regions of Canada adjacent to the United States where it is endemic. To assess the vector competence of wild-caught ticks in cattle-rearing regions, Dermacentor variabilis and D. andersoni were collected in western Canada and fed on calves experimentally infected with Anaplasma marginale (St. Maries strain). The 2 tick species were equally competent in transmitting A. marginale to splenectomized calves, all 15 tick-exposed calves becoming infected. The prepatent periods in 13 calves ranged from 18 to 26 d and did not vary in relation to the numbers of ticks fed or the duration of transmission feedings. The unusually long prepatent periods in 2 calves (45 and 55 d) were probably due to concomitant Eperythrozoon infection. This study clearly demonstrated that tick species present in western Canada are competent vectors of bovine anaplasmosis. Potential barriers, including climate, must be considered in developing strategies to prevent A. marginale from becoming established in anaplasmosis-free regions.  相似文献   

7.
The development and transmission of Anaplasma marginale was studied in Dermacentor andersoni males. Laboratory-reared male D andersoni were allowed to feed for 7 days on a calf with ascending A marginale parasitemia. The ticks were then held in a humidity chamber for 7 days before being placed on 2 susceptible calves. Anaplasmosis developed in the calves after incubation periods of 24 and 26 days. Gut and salivary glands were collected from ticks on each day of the 23-day experiment and examined with light and electron microscopy. Colonies of A marginale were first observed in midgut epithelial cells on the sixth day of feeding on infected calves, with the highest density of colonies found in gut cells while ticks were between feeding periods. The first colonies contained 1 large dense organism that subsequently gave rise to many reticulated organisms. Initially, these smaller organisms were electron-lucent and then became electron-dense. On the fifth day after ticks were transferred to susceptible calves for feeding, A marginale colonies were found in muscle cells on the hemocoel side of the gut basement membrane. A final site for development of A marginale was the salivary glands. Colonies were first seen in acinar cells on the first day that ticks fed on susceptible calves, with the highest percentage of infected host cells observed on days 7 to 9 of that feeding. Organisms within these colonies were initially electron-lucent, but became electron-dense.  相似文献   

8.
Sixteen cattle serotest-negative for anaplasmosis with either no previous exposure (2 animals) or cleared 8 months earlier of their carrier state by chemotherapy (14 animals) were each exposed to Anaplasma marginale. Anaplasma serotest titers were determined by complement-fixation and rapid card agglutination tests conducted during a 63-day trial period. Serologic reactions indicated that all cattle (both groups) were converted to seropositive by the 21st day after exposure. Fluctuations in PCV were seen in the 2 groups between days 21 and 35. However, parasitemia levels were detectable only in the 2 previously unexposed control cattle. Three splenectomized calves, given 10 ml of blood from 3 of the former carrier cattle 14 days after the latter were reexposed, developed severe clinical and hematologic signs of anaplasmosis and seroconverted from negative to positive on both serologic tests. The need to acquire a better understanding of immunity in anaplasmosis is discussed.  相似文献   

9.
Bovine anaplasmosis, caused by Anaplasma marginale, is a vector-borne disease that is enzootic in many parts of the USA. Although Dermacentor andersoni, a major vector of A. marginale, occurs in Canada, the Canadian cattle herds are currently considered free of bovine anaplasmosis. There have been two outbreaks of the disease in the province of Saskatchewan, but these have been linked to the importation of infected animals. However, the distribution of bovine anaplasmosis may alter with range expansion of the vectors. The aim of the present study was to use molecular techniques to determine if Anaplasma were present in D. andersoni at a locality near its northeastern distributional limit in Saskatchewan. Nested PCR analyses of the bacterial 16S rRNA gene were conducted on the total genomic DNA of 105 individual ticks. Single strand conformation polymorphism analysis and DNA sequencing of the 11 PCR-positive amplicons revealed the presence of three species of bacteria, none of which have been previously reported in D. andersoni. Although no ticks were infected with A. marginale, a novel genotype of A. bovis was detected in eight individuals. This discovery represents the first report of A. bovis in Canada. The potential implications of this finding with respect to animal health and anaplasmosis surveillance in Canada are discussed. The other two bacterial species detected were genetically similar to "Candidatus Midichloria mitochondrii" and Ignatzschineria larvae, the latter of which has been associated with human disease in Europe. Further investigations are needed to determine the prevalence, reservoir hosts, and pathogenicity of the Canadian genotype of A. bovis.  相似文献   

10.
Treatment of adult Anaplasma carrier cows, with long-acting oxytetracycline at dosage levels generally successful in eliminating infection, was unsuccessful when the treatment was preceded or accompanied by a 2nd exposure to A marginale on days 0, 7, or 14 before treatment. Noninfected calves exposed to A marginale 7 days before a similar treatment developed anaplasmosis and became carriers of infection.  相似文献   

11.
Infectivity of three Anaplasma marginale isolates for Dermacentor andersoni   总被引：1，自引：0，他引：1  
Three isolates of Anaplasma marginale--Virginia (VAM), Illinois (IAM), and Florida (FAM)--were compared for infectivity for Dermacentor andersoni. The isolates were selected, in part, because of a tail-like appendage that has been demonstrated in the VAM and IAM, but not in the FAM. Ticks were exposed to the isolates as nymphs either naturally by feeding on a calf with anaplasmosis or artificially by percutaneous inoculation with infected bovine erythrocytes. They were examined for infectivity after molting to the adult stage by determining their capability to transmit the disease to susceptible calves and by demonstrating colonies in tick gut sections. Only those ticks exposed to the VAM proved to be infected with A marginale; ticks naturally exposed and those artificially infected with this isolate transmitted the disease to susceptible calves. Colonies of A marginale were observed only in gut tissues of ticks naturally infected with VAM. The IAM (appendage present) and FAM (appendage absent) could not be found in ticks exposed by either method, indicating that factors other than the presence of inclusion appendages may be involved in infection of ticks by A marginale.  相似文献   

12.
The cattle rickettsia Anaplasma marginale is distributed worldwide and is transmitted by about 20 tick species, but only Rhipicephalus simus, a strictly African tick species, has been shown to transmit the vaccine strain of A. centrale. The aim of the present study was to examine transmission of field strains of A. marginale and of the vaccine strain of A. centrale by three tick species -Hyalomma excavatum, Rhipicephalus sanguineus and Rhipicephalus (Boophilus) annulatus - to susceptible calves. Two genetically distinct Israeli field strains of A. marginale, tailed and non-tailed (AmIsT and AmIsNT, respectively), were efficiently transmitted by R. sanguineus, whereas H. excavatum transmitted only the tailed isolate, and R. (Boophilus) annulatus did not transmit A. marginale. None of the three tick species transmitted A. centrale. By means of msp1a primers in PCR assays, amplicons of similar sizes were obtained from either A. marginale-infected calves that were used for acquisition feeding, from R. sanguineus fed on the infected calves, or from calves to which anaplasmosis had been successfully transmitted by these ticks. Although an A. centrale-specific fragment was amplified from salivary glands of R. sanguineus, no transmission to susceptible cattle occurred during 3 months of observation, and anaplasmosis was not induced in splenectomized calves that were subinoculated with blood from calves on which R. sanguineus had fed.  相似文献   

13.
Transstadial and transovarial transmission of Anaplasma marginale by Dermacentor variabilis were attempted with with ticks exposed to the organism once by feeding as larvae or nymphs, and twice by feeding as larvae and nymphs. Typical colonies of A marginale were in gut tissues of adults that were infected as larvae, larvae and nymphs, and as nymphs; repeated exposure of ticks did not appear to result in an increase in the number of colonies in the gut of subsequently molted adults nor did it affect severity of the clinical disease that developed in cattle they fed on. In contrast, colonies of A marginale were not found in the midgut epithelium of unfed nymphs exposed as larvae, even though companion nymphs transmitted the parasite, causing severe clinical anaplasmosis in susceptible calves. The organism was not transmitted transovarially by F1 larvae or nymphs from the groups exposed as parent larvae, nymphs, larvae and nymphs, and as adults. Some of the calves fed on by F1 progeny had a few erythrocytic marginale bodies that looked suspiciously like A marginale, as well as postchallenge exposure prepatent periods that were longer than other calves in the transovarial transmission study. Sera from these calves were tested for antibody to A marginale, using a highly sensitive immunoblot technique. Antibodies were not detected in any of the sera.  相似文献   

14.
Infections of the tick-borne ehrlichial pathogen, Anaplasma marginale, in cattle have been controlled, in part, by administration of low doses of tetracycline. Recently, a cell culture system was developed for A. marginale using a tick cell line derived from embryonic Ixodes scapularis. This study was designed to determine the effect of tetracycline on A. marginale propagated in a tick cell culture assay. Various concentrations of tetracycline (0, 0.01, 0.10, 1.0, 5, 10, 20 or 100 microg/ml) were added in medium to cultures 48h after cell monolayers were inoculated with A. marginale. A. marginale growth in the drug treated and control cultures was subsequently evaluated by indirect ELISA at 7 days post-infection (PI) and daily by light and electron microscopy (LM and EM). Infectivity of the culture-derived A. marginale was determined by inoculation of susceptible cattle with treated and untreated control cultures. Tetracycline doses of 5, 10, 20 and 100 microg/ml resulted in significant inhibition of A. marginale growth as determined by ELISA. Morphologic deterioration of Anaplasma, as determined by LM and EM, occurred in cultures treated with the same drug concentrations. A. marginale replication, inhibited in cultures treated on days 2-6 PI with 20 microg/ml tetracycline, was not apparent 96 days after antibiotic removal. Infected cell cultures treated with medium containing 20 microg/ml tetracycline proved to be non-infective when inoculated into susceptible splenectomized calves. All parameters studied herein demonstrated that tetracycline killed A. marginale in cultured tick cells. The Anaplasma-tick cell culture drug assay therefore, would be useful for screening and evaluating novel antibiotics for control of anaplasmosis.  相似文献   

15.
Colonies of Anaplasma marginale in midgut epithelial cells of experimentally infected Dermacentor andersoni were studied in adult ticks 1, 3, and 6 months old. Longevity of the parasite in ticks was assessed by evaluating its infectivity for splenectomized calves; calves were exposed by feeding ticks and by inoculation of tick gut homogenates. Longevity was also evaluated by determining size, type, and density of colonies in male and female ticks. The effect of incubation (2.5 days at 37 C) on colony density was also examined for ticks at each age period. All methods used to assess longevity of A marginale in ticks (tick transmission, calf inoculation, and histologic studies) indicated a decrease of the numbers of organisms in 6-month-old ticks. Furthermore, when tick gut homogenates from 6-month-old nonincubated ticks were not infectious for susceptible calves, incubation of ticks before dissection restored infectivity of homogenates. Colonies of A marginale were detected in gut tissues of 6-month-old ticks that were not infective; therefore, infectivity of ticks could not be confirmed merely by presence of A marginale colonies.  相似文献   

16.
Anaplasmosis is a hemolytic disease of cattle caused by the ehrlichial tick-borne pathogen Anaplasma marginale. Killed vaccines used for control of anaplasmosis in the US used antigen harvested from infected bovine erythrocytes which was often contaminated with bovine cells and other pathogens. In this study, we performed an initial cattle trial to test A. marginale harvested from tick cell culture as an immunogen for cattle. Eleven yearling Holstein cattle were immunized with the cell culture-derived A. marginale and 11 cattle were non-immunized contact controls. Each vaccine dose contained approximately 2 x 10(10) A. marginale in an oil-based adjuvant. Two immunizations were administered subcutaneously 4 weeks apart and the cattle were challenge-exposed 10 weeks after the second immunization with A. marginale infected blood. Maximum antibody levels as determined by an A. marginale specific competitive ELISA were observed 2 weeks after the last immunization. Antibody responses against major surface proteins (MSPs) 1a and 1beta1 were also characterized and immunized cattle demonstrated a preferential recognition for MSP1beta1. Cattle immunized with the cell culture-derived A. marginale had a significantly lower percent reduction in the packed cell volume (P<0.05) after challenge exposure as compared with the controls and did not display clinical anaplasmosis. The cell culture-derived A. marginale shows promise for use as antigen in development of a new killed vaccine for anaplasmosis.  相似文献   

17.
The development of Anaplasma marginale in midgut epithelial cells was studied in feeding, transmitting adult Dermacentor andersoni ticks. Laboratory-reared ticks experimentally infected as nymphs were allowed to feed from 1 to 9 days on susceptible calves. Gut tissues from ticks were collected on each day they fed (total, 9 days) and were processed for light and transmission electron microscopy. Colonies of A marginale were abundant during the first 6 days of feeding, after which numbers decreased. Colonies were adherent to the basement membrane of gut cells early during feeding, with resultant flattening of the colonies. Colonies also were seen in muscle cells on the hemocoel side of the basement membrane. Morphologic features of A marginale within muscle cells varied and were similar to those observed in gut cells. In addition, however, a large reticulated form in the colonies was observed in muscle cells and appeared to give rise to small particles by budding. Development of A marginale in muscle cells appears to represent an intermediate site of development between those in gut and in salivary glands.  相似文献   

18.
The protective effect and anti-Anaplasma complement-fixing and agglutinating antibody responses induced in yearling steers by vaccination with an inactivated Anaplasma marginale vaccine were evaluated by challenge exposure. Eleven 12- to 14-month-old Hereford X Angus steers were randomly allotted into 6 principals and 5 controls. The principals were injected IM with 5 ml of vaccine on days 0 and 21. On day 70, the 11 steers were challenge exposed by IV inoculation of A marginale-infected blood. After a prolonged prepatent period, the vaccinated steers developed a significantly (P less than 0.01) lower A marginale parasitemia (8.0%) than did the nonvaccinated controls (26.3%). The persistence of a greater than or equal to 0.5% parasitemia was significantly (P less than 0.025) reduced from 34 days in the control to 21 days in the vaccinated group. The percentage reduction in PCV was significantly (P less than 0.025) less in the vaccinated group (34%) as compared with the controls (57%). Complement-fixing and agglutinating antibody responses induced by vaccination did not persist for more than 21 days after the 2nd vaccine injection and did not interfere with positive seroconversion resulting from challenge exposure.  相似文献   

19.
Bovine anaplasmosis, caused by Anaplasma marginale, the intraerythrocytic rickettsia, is controlled by vaccination with live Anaplasma marginale ss centrale (A. centrale), a subspecies of relatively low pathogenicity. We have experimentally demonstrated that an animal primarily infected with A. marginale, or with the related vaccine subspecies A. centrale can be infected with the heterologous subspecies, and carries both bacteria. The co-infection was detected in experimentally cross-infected calves for up to 3 months after the last inoculation with the heterologous subspecies. The occurrence of characteristic cyclic rickettsemia of A. centrale and A. marginale was observed by examination of Giemsa-stained blood smears, or by the presence of specific rickettsial DNA confirmed in PCR assays based on specific msp1a and msp4 for A. marginale, and on specifically designed msp3 and msp4 primers for A. centrale. Sequence analysis of msp4-specific fragments for each subspecies revealed the presence of dual infection in both calves on days 30 and 60 after cross-inoculation with the heterologous Anaplasma subspecies. The experimental cross-infection of calves clearly demonstrated that the concept of "infection exclusion" does not apply to Anaplasma infection in cattle; as there was no infection exclusion of A. marginale in A. centrale-infected cattle, and vice versa. The present results confirmed our previous findings that cattle grazing in an anaplasmosis-endemic field were subject to concomitant infection with both the vaccine A. centrale and the field A. marginale strains.  相似文献   

20.
Anaplasma marginale was experimentally transmitted from cattle to bison and back to cattle. Of the 2 splenectomized and 1 intact American bison calves (Bison bison) inoculated with a North Texas A marginale stabilate, 1 splenectomized and 1 intact bison exhibited clinical signs of anaplasmosis. Active parasitemias in these bison were observed along with positive reactions in the rapid card agglutination and complement fixation tests. Blood from the infected bison produced disease in splenectomized bovine calves. Screening tests for anti-Anaplasma antibodies in 178 blood samples collected from adult bison from the National Bison Range, Montana, revealed 1 rapid card agglutination test-positive sample, and 110 negative, 40 suspect, and 28 positive (15.7%) complement fixation test samples.  相似文献   

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