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PubMed1996

Anaplasma marginale: effect of challenge of cattle with varying doses of infected erythrocytes.

Three groups, each of 6 Hereford cattle, were infected by the i.v. inoculation of 10(10), 10(8) or 10(6) Anaplasma marginale-infected erythrocytes. The mean time taken to reach a 1% parasitaemia was 7.3, 13.9 and 19.9 days in the 10(10), 10(8)and 10(6) infection dose groups, respectively. The rates of increase in parasitaemias during the exponential phase of parasite multiplication were similar for the 3 groups (doubling time 0.9 days). The exponential increase of the parasitaemia in the 10(10) dose group extended to a higher level or 10(6) dose groups (to approximately 10% compared with 3%). The mean maximum parasitaemia attained in the 10(10), 10(8), and 10(6) infection dose groups was 23.7, 14.7 and 8.7%, respectively> The time taken to reach the treatment criterion (packed cell volume decrease to 15% or lower) from a 1% parasitaemia was similar for the 3 groups. These results showed that the pathological outcome (anaemia) of anaplasmosis were similar over the 10,000-fold infective dose range tested.

Anaplasma↗
PubMed1997

The prevalence of serum antibodies to tick-borne infections in cattle in smallholder dairy farms in Murang'a District, Kenya; a cross-sectional study.

The most important tick-borne disease of cattle in eastern, central and southern Africa is East Coast fever (ECF) caused by Theileria parva and transmitted by the tick Rhipicephalus appendiculatus. Other less-important tick-borne diseases in cattle are benign theileriosis caused by Theileria mutans, babesiosis caused by Babesia bigemina, anaplasmosis caused by Anaplasma marginale and cowdriosis caused by Cowdria ruminatum. In Murang's District, Central Province of Kenya, five agroecological zones (AEZs) are defined according to climate, altitude and agricultural activities. A cross-sectional serological study was conducted on 750 smallholder dairy farms in Murang's District, selected in a stratified random sampling method. The farms had a total of 362 calves. One hundred and fifty farms were studied from three administrative sublocations in each of the five AEZs. Prevalence of serum antibodies to three tick-borne parasites, that is T. parva, T. mutans and B. bigemina, were determined using the enzyme-linked immunosorbent assay (ELISA) technique. Antibody prevalence values differed across the AEZs. The ranges of means for the prevalences were: T. parva (18-72%), T. mutans (1.5-28%) and B. bigemina (12-49%). The above results serve as indicators of the possible existence of endemic stability in some AEZs for some parasites.

Anaplasma↗
PubMed1998

Effect of controlling natural field-tick infestation on the growth of N'Dama and Gobra zebu cattle in the Gambia.

The effect of tick infestations on liveweight gain (LWG) was assessed by comparison of weight changes in flumethrin-treated N'Dama and Gobra zebu cattle (16-20 months old) with respective control groups submitted to natural tick challenge over 1 year. Flumethrin was applied monthly, fortnightly or weekly. Preventive treatments against anaplasmosis, babesiosis and trypanosomosis were given. Mortality rate was recorded and post-mortem examinations carried out. In both treated and control animals, significantly fewer Hyalomma spp. and Amblyomma variegatum were found on N'Dama than on Gobra zebu cattle. Both breeds are equally susceptible to Rhipicephalus senegalensis infestation. Total annual tick burdens did not cause significant differences in LWG between acaricide-treated and control cattle in either breeds. LWG was also not affected during or after the annual peak of tick infestation (composed mainly by A. variegatum and R. senegalensis). Equally-high mortality (35%), due to unidentified causes, was recorded in acaricide-treated and control Gobra cattle; mortality in N'Dama cattle was 7.5%. In both breeds, about the 90% of mortality occurred at the end of the dry season. Breed differences in tick burden confirm previous results. If tick-borne infections do not influence LWG or mortality, then it is concluded that intensive tick control is not justifiable in Gambian livestock.

Anaplasmosis↗
PubMed2000

Identification and characterization of corpuscular, soluble and secreted antigens of a Venezuelan isolate of Anaplasma marginale.

Anaplasma marginale is the etiological agent of anaplasmosis, a tick-transmitted disease with an important economic impact that affects cattle throughout the world. Although, North American isolates of A. marginale and their antigens have been extensively studied, relatively little information is available on the antigenic composition of South American isolates. The characterization of diverse geographical isolates of A. marginale will result in a thorough antigenic profile and may lead to the identification of additional diagnostic and immunoprophylactic tools. Short-term cultures of a Venezuelan isolate (Ta) of A. marginale were maintained for up to 13 days in vitro. During that period, the A. marginale remained viable and were propagated in the bovine erythrocyte culture system. During the initial days of culture, cell division and reinvasion were evidenced by a significant rise in parasitemia up to a 50%. A. marginale antigens were identified by metabolic labeling with (35S) methionine, followed by fractionation and immunoprecipitation with homologous and heterologous bovine sera. This yielded a complete antigenic set for the Ta isolate of A. marginale, including soluble, secreted and corpuscular polypeptide antigens. Fifteen immunodominant polypeptides were recognized by the bovine sera in the soluble and corpuscular fractions with relative molecular weights of 200, 150, 100-110, 86, 60, 50, 47, 40, 37, 33, 31, 25, 23, 19 and 16kDa. Seven polypeptides were present in the exoantigen fraction. The 31 and 19kDa antigens were recognized by the ANAR76A1 and ANAF16C1 monoclonal antibodies, respectively which are specific for MSP-4 and MSP-5 from North American isolates of A. marginale. Metabolic labeling with (14C) glucosamine prior to immunoprecipitation with bovine sera allowed the identification of glycoprotein antigens of 200, 100-150, 60, 55, 50, 45-43, 37, 33, 31, 22, 19 and 16kDa in the soluble fraction.

Anaplasma↗
PubMed2002

Effect of tetracycline on development of Anaplasma marginale in cultured Ixodes scapularis cells.

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.

Anaplasma↗
PubMed1997

Increased resistance to Anaplasma marginale infection in cattle chronically infected with Theileria buffeli (syn. T. orientalis).

Calves chronically infected with the benign haemoprotozoan parasite Theileria buffeli (syn. T. orientalis) and T. buffeli-free calves were experimentally infected with virulent Anaplasma marginale. The daily mean maximum parasitaemia in the T. buffeli-carrier calves was lower and delayed relative to that of the Theileria-free calves. Anaemia was less marked in the Theileria infected calves, although this difference was not statistically significant. The susceptibility of Theileria-carrier and Theileria-free older cattle to virulent A. marginale infection was also investigated. The mean maximum parasitaemia observed in the Theileria-infected cattle was significantly lower than that of the Theileria-free cattle and the time to maximum parasitaemia was increased significantly in the Theileria-infected relative to the Theileria-free cattle. Of the Theileria-carrier cattle, 33% exhibited maximum parasitaemias of less than 0.1% infected erythrocytes and no clinical anaemia as a result of A. marginale infection. In contrast, the lowest maximum parasitaemia observed in the Theileria-free cattle was 7%. The percentage of cattle requiring treatment to prevent mortality due to anaemia was 50% and 91% in the Theileria-infected and Theileria-free cattle respectively. For the duration of increasing A. marginale parasitaemia, the level of Theileria in carrier cattle was significantly depressed or undetectable. Following the resolution of peak A. marginale parasitaemia, the level of Theileria parasites increased rapidly to become significantly higher than that prior to infection and then decreased gradually to a level similar to that prior to infection. The mechanism of the increased resistance to A. marginale infection conferred by T. buffeli-carrier state is unknown, but is likely to involve non-specific cell-mediated immunity, as no serological cross-reactivity exists between these two highly divergent parasite species. The susceptibility of relatively mature cattle to clinical anaplasmosis under field conditions is likely to be significantly affected by the widespread distribution and common occurrence of T. buffeli throughout the range of A. marginale in Australia, Africa and southeast Asia.

Anaplasma↗
PubMed1998

Characterization of Anaplasma isolates from eland (Taurotragus oryx). Pathogenicity in cattle and sheep and DNA profiles analysis.

Two eland Anaplasma isolates, AnapE1, from Kenya, and AnapE2, from South Africa were characterised. Their characterization was based on their pathogenicity to intact and splenectomized cattle and sheep and also their DNA profiles. Their DNA profiles were analysed and compared to Anaplasma marginale, A. ovis and A. centrale after endonuclease restrictions and probing with Anaplasma DNA probes, AC5-12 and AC-1. The results of the pathogenicity trials showed AnapE1 to be similar to A. ovis and AnapE2 an isolate of A. marginale. On DNA profiles, AnapE1 was close to A. ovis, with differences that occur even in same Anaplasma species isolates from different locations. On the other hand, AnapE2, resembled one of the A. marginale isolates known to occur in South Africa. The DNA profiles correlated well with the pathogenicity results. It is concluded that elands are carriers of both A. marginale and A. ovis parasites and are therefore important reservoirs that need attention in epidemiology of anaplasmosis.

Anaplasma↗
PubMed2002

Conservation of major surface protein 1 genes of Anaplasma marginale during cyclic transmission between ticks and cattle.

Bovine anaplasmosis is a rickettsial disease of world-wide economic importance caused by Anaplasma marginale. Several major surface proteins with conserved gene sequences have been examined as potential candidates for vaccines and/or diagnostic assays. Major surface protein 1 (MSP1) is composed of polypeptides MSP1a and MSP1b. MSP1a is expressed from the single copy gene msp1 alpha and MSP1b is expressed by members of the msp1 beta multigene family. In order to determine if the msp1 genes are conserved, primers specific for msp1 alpha, msp1 beta(1), and msp1 beta(2) genes were synthesized and used to amplify msp1 sequences of A. marginale from tick cell cultures, from cattle during acute and chronic infections and from salivary glands of Dermacentor variabilis. Protein sequences of MSP1a, MSP1b(1) and MSP1b(2) were conserved during the life cycle of the parasite. No amino acid changes were observed in MSP1a. However, small variations were observed in the MSP1b(1) and MSP1b(2) protein sequences, which could be attributed to recombination, selection for sub-populations of A. marginale in the vertebrate host and/or PCR errors. Several isolate-specific sequences were also observed. Based on the information obtained in this study, the MSP1 protein appears to be fairly well conserved and a potential vaccine candidate.

Amino Acid Sequence↗
PubMed2005

Serological survey of Babesia bovis and Anaplasma marginale in cattle in Tete Province, Mozambique.

A serological survey of bovine babesiosis and anaplasmosis in communal cattle was conducted in the northwestern province of Tete, Mozambique. Blood was collected from cattle ranging from 4 to 15 months old from randomly selected farms from six districts. Thirty-nine per cent of all 478 calves tested in Tete Province were seropositive to the ELISA for Babesia bovis antibodies and 63% of all calves were seropositive in the card agglutination test for Anaplasma marginale. Seroprevalence of B. bovis ranged from 22.8% in Tete City District to 48.1% in Angonia District. For A. marginale, it ranged from 34.4% in Angonia District to 87.3% in Moatize District. The dominant factor affecting seroprevalence for both haemoparasites was district and there was a trend for higher intensity of tick control to be associated with a higher seroprevalence of B. bovis and a lower seroprevalence of A. marginale. The obvious differences were the low prevalence of B. bovis in Tete City Council District and the low prevalence of A. marginale in Angonia District. The levels of exposure to B. bovis seen in our study are well below any that could be considered to be consistent with endemic stability, yet they are sufficiently high to ensure that clinical disease would be a risk. The seroprevalence of A. marginale, however, suggests that endemic stability with respect to this disease could exist in districts other than Angonia. There was no strong and consistent relationship between the intensity of control and the likelihood of seropositivity to either of the diseases.

Agglutination Tests↗
PubMed2003

Conservation of a gene conversion mechanism in two distantly related paralogues of Anaplasma marginale.

Anaplasmataceae, the causative agents of anaplasmosis and ehrlichiosis, persist in the bloodstream of their mammalian hosts, allowing acquisition and transmission by tick vectors. Anaplasma marginale establishes persistent infection characterized by sequential cycles of rickettsaemia in which new antigenic variants emerge. The two most immunodominant outer membrane proteins, MSP2 and MSP3, are paralogues, each encoded by a distinct family of related genes. This study demonstrates that, although the two gene families have diverged substantially, each has maintained a similar mechanism to generate structurally and antigenically polymorphic surface antigens. Like MSP2, MSP3 is expressed from a single locus in which variation of the expressed msp3 gene is generated by recombination using msp3 pseudogenes. Each of the msp3 pseudogenes encodes a unique central variable region (CVR) flanked by conserved 5' and 3' regions. Changes in the CVR of the expressed msp3, concomitant with invariance of the pseudogenes, indicate that expression site variation is generated using gene conversion. A. marginale thus maintains two large, separate systems within its small genome to generate antigenic variation of its surface proteins, while analogous structural elements indicate a common mechanism.

Acute Disease↗
PubMedDate not supplied

Tick- and flea-borne rickettsial emerging zoonoses.

Between 1984 and 2004, nine more species or subspecies of spotted fever rickettsiae were identified as emerging agents of tick-borne rickettsioses throughout the world. Six of these species had first been isolated from ticks and later found to be pathogenic to humans. The most recent example is Rickettsia parkeri, recognized as a human pathogen more than 60 years after its initial isolation from ticks. A new spotted fever rickettsia, R. felis was also found to be associated with fleas and to be a human pathogen. Similarly, bacteria within the family Anaplasmataceae have been considered to be of veterinary importance only, yet three species have been implicated in human diseases in recent years, including Ehrlichia chaffeensis, the agent of human monocytic ehrlichiosis, Anaplasma phagocytophilum, the agent of human anaplasmosis (formerly known as "human granulocytic ehrlichiosis agent", E. equi and E. phagocytophila), and finally Ehrlichia ewingii, which causes granulocytic ehrlichiosis in humans. We present here an overview of the various tick- and flea-borne rickettsial zoonoses described in the last 20 years, focusing on the ecological, epidemiological and clinical aspects.

Anaplasmosis↗
PubMed1992

Development of Anaplasma ovis (Rickettsiales: Anaplasmataceae) in male Dermacentor andersoni (Acari: Ixodidae) transferred from infected to susceptible sheep.

The development of Anaplasma ovis was studied in Dermacentor andersoni males transferred from infected to susceptible sheep. Laboratory-reared male D. andersoni were allowed to feed for 6 d on a sheep with ascending A. ovis parasitemia. The ticks were removed and held at room temperature in a humidity chamber for 6 d, after which they were allowed to feed on five susceptible sheep for 1, 3, 5, 7, or 9 d. Gut and salivary glands were collected from ticks during the 21-d experiment and examined with light and electron microscopy. Anaplasmosis developed in all susceptible sheep. Colonies of A. ovis were first observed in midgut epithelial cells on the 3rd d ticks fed on the infected sheep, and infection persisted in gut cells throughout the experiment. The first colonies contained one large organism that subsequently gave rise to many reticulated ones, which became electron dense over time. After ticks were transferred to susceptible sheep and began the second feeding, individual A. ovis organisms were found from days 3-9 in muscle cells on the hemocoel side of the gut basement membrane. However, colonies did not develop in these cells, and the host cells did not hypertrophy as did cells similarly infected with A. marginale. A final site of development of A. ovis was in salivary glands. Individual organisms were first seen in acinar cells on the first day that ticks fed on the second calves, and salivary gland infections persisted throughout the 9-d feeding period. Colonies of A. ovis developed in salivary gland acinar cells and organisms within these colonies were initially electron lucent but became electron dense. Multiple colonies often were observed within salivary gland cells and often contained organisms in various stages of development.

Anaplasma↗
PubMed1992

Persistence of Anaplasma marginale (Rickettsiales: Anaplasmataceae) in male Dermacentor andersoni (Acari: Ixodidae) transferred successively from infected to susceptible calves.

The persistence of Anaplasma marginale Theiler in male Dermacentor andersoni Stiles ticks exposed to the organism as adults was studied as the ticks were successively transferred to five susceptible calves. All calves fed upon by these ticks rapidly developed clinical anaplasmosis; incubation periods of infection ranged from 19 to 26 d and did not change significantly with successive feedings. Development of A. marginale in tick midgut and salivary glands was followed daily during tick feeding (total, 35 d) with light microscopy and DNA hybridization. With microscopy, A. marginale colonies persisted in midgut cells throughout the experiment. Large colonies were observed in gut muscle cells on days 8 through 35 and were the predominant infected cell type during this part of feeding. Colonies were seen in salivary gland acini from day 2 throughout the 35-d experiment. The DNA probe confirmed the presence of Anaplasma DNA in midgut and salivary glands throughout the experiment. Quantitative estimates of infection intensity in tissues of individual ticks approximated 10(7) initial body equivalents, confirming heavy infections. A marginale in midgut tissues decreased with feeding time, whereas the estimated number of organisms in salivary glands remained constant. These data demonstrate that D. andersoni males are efficient vectors of A. marginale and may be potential reservoirs of infection for ruminants for extended periods.

Anaplasma↗
PubMed1996

Establishment of the tick (Acari:Ixodidae)-borne cattle pathogen Anaplasma marginale (Rickettsiales:Anaplasmataceae) in tick cell culture.

Anaplasma marginale is a tick-borne rickettsia that causes bovine anaplasmosis worldwide. Despite its importance, A. marginale has thus far not been established in a continuous culture system. We have propagated A. marginale continuously for the 1st time in a tick cell line derived from the black-legged tick, Ixodes scapularis Say, using infected bovine blood as the inoculum. Erythrocytic stages invaded the tick cells and multiplied in membrane-lined vacuoles to form colonies typical of those observed in naturally infected ticks as demonstrated by light and electron microscopy. The rickettsiae have been passaged serially for 3 yr and have been cryopreserved in liquid nitrogen. Antigens present in A. marginale from tick cell culture were recognized by bovine immune serum against the blood stages of A. marginale. A. marginale grown in this tick cell line was infective for calves, and male ticks fed on the calves transmitted A. marginale to a susceptible calf. The ability to culture A. marginale removes a major impediment to the study of Anaplasma biology in vitro, and will enhance development of vaccines and diagnostic tests.

Anaplasma↗
PubMed2006

Flow cytometric evaluation of selected antimicrobial efficacy for clearance of Anaplasma marginale in short-term erythrocyte cultures.

The tick-borne rickettsia, Anaplasma marginale, causes the economically important cattle disease anaplasmosis. Once infected, cattle remain lifelong carriers. Herein, we used flow cytometry to test the efficacy of three antimicrobials; oxytetracycline, imidocarb and enrofloxacin against Virginia (VGN) or Oklahoma (OK) A. marginale isolates in short-term erythrocyte cultures. Parasite viability was assessed using the vital dye hydroethidine (HE), which is detectable when living organisms convert HE to ethidium bromide. Viability of A. marginale in selected cultures was determined by subinoculation into susceptible calves. Data were analyzed by MANOVA, Tukey-Kramer honest significant difference and Wilcoxon rank sum tests. Receiver operating characteristic (ROC) analysis was used to correlate results with culture infectivity. Enrofloxacin inhibited A. marginale in a dose dependent manner. Surprisingly, higher concentrations of imidocarb were less effective than lower concentrations against A. marginale with significant differences (P < 0.05) observed between the two isolates. Oxytetracycline was the least active drug tested. Cultures infected with the OK isolate exposed to 4.0 microg/mL enrofloxacin and those of the VGN and OK isolates exposed to 1.0 microg/mL imidocarb were sterilized. This is the first in vitro study demonstrating the efficacy of enrofloxacin against A. marginale. Furthermore, these data indicate that flow cytometry is a useful assay for screening antimicrobials against A. marginale.

Anaplasma marginale↗
PubMed1998

The development of a semi-automated latex agglutination test for the detection of antibodies to Anaplasma marginale using a cell culture-derived antigen.

Serologic diagnosis of anaplasmosis is currently done by the complement-fixation, ELISA, and card agglutination tests. These tests have utilized A. marginale harvested from bovine erythrocytes as antigen which is often contaminated with erythrocyte stroma. We are currently testing A. marginale propagated in a Ixodes scapularis cell line as antigen for serologic tests. In this study, we report the use of the cell culture-derived A. marginale as antigen for development of a rapid, semi-automated latex agglutination test. Diluted serum and latex (polystyrene microspheres), sensitized with cell culture-derived A. marginale proteins, were dispensed into 96-well microtiter plates. An initial reading of light transmission was recorded by a computer-interfaced scanning autoreader. After 30 minutes, the plates were mixed and read a second time, recording the delta % light transmittance. The sensitized latex microspheres (latex) agglutinated in the presence of A. marginale antibodies, thus producing an increase in light transmittance. In preliminary tests, 724/977 of the sera were positive for A. marginale antibodies with an apparent agreement of 83.3% when compared with the complement-fixation test. Sensitization and sera dilution buffers were shown to have a marked effect on the sensitivity and specificity of this assay. Results will be presented on the optimization of buffers and the testing of sera from experimentally and field-infected cattle.

Anaplasma↗
PubMed2000

Culture-derived parasites in vaccination of cattle against tick-borne diseases.

The major economically important tick-borne diseases of cattle are theileriosis, babesiosis, anaplasmosis, and cowdriosis. Culture-derived attenuated schizonts of Theileria annulata have proved to be safe for all types of cattle and they protect against tick-borne theileriosis. T. parva was also successfully grown in vitro; however, inoculation of cattle with allogeneic schizont-infected cells resulted in rejection and destruction of the parasites together with the host cells. The number of schizont-infected cells needed for immunization is greater than for T. annulata theileriosis. Culture-propagated Babesia bovis and B. bigemina were used for large scale vaccination in the field. An avirulent population of Babesia spp. was obtained by in vitro cloning; inoculation of cattle did not induce clinical babesiosis, but produced specific antibodies. Culture-derived exoantigens of Babesia spp. proved to be completely safe for cattle, however, they conferred less protection than live parasites. Cell-cultured Cowdria ruminantium was highly infective for susceptible animals but, attenuated in vitro, could offer a potential source for vaccination. Anaplasma marginale, successfully grown in tick cell culture, may be developed for vaccines. Factors that should be considered in the developing of vaccines against tick-borne diseases include: the protective immune response to the pathogenic parasite developmental stages, virulence, immunological strain differences, and antigenic variations in cattle and in culture.

Anaplasmosis↗
PubMed2000

An in vivo model to investigate lymphocyte-mediated immunity during acute hemoparasitic infections. Use of a monoclonal antibody to selectively deplete CD4+ T lymphocytes from thymectomized calves.

Thymectomized calves were selectively depleted of CD4+ T lymphocytes with a monoclonal antibody (mAb) specific for the bovine CD4 monomer (ILA-11). Calves were treated with high loading doses of ILA-11 during the first week of the study then treated with subsequent lower maintenance doses. Depletion of CD4+ T lymphocytes was assessed weekly by flow cytometric analysis of PBMC and mononuclear cells from lymph node and spleen biopsies. Treatment with high doses of ILA-11 resulted in rapid and marked depletion of CD4+ T lymphocytes from the peripheral blood, peripheral lymph nodes, and spleen. Although CD4+ T lymphocytes slowly returned to the peripheral blood, peripheral lymph nodes, and spleen by day 21 post-treatment, the numbers of CD4+ T lymphocytes in depleted calves remained below pre-depletion levels for the duration of the study. CD4+ T lymphocytes failed to be effectively depleted from a non-thymectomized calf treated with the mAb ILA-11. Development of a T lymphocyte depletion model in thymectomized calves will permit testing of the hypothesis that CD4+ T lymphocytes and IFN-gamma are required in cattle for control of acute anaplasmosis. In subsequent planned studies, thymectomized calves depleted of CD4+ T lymphocytes will be experimentally infected with A. marginale and parameters of disease compared between depleted and non-depleted calves.

Anaplasmosis↗