Relationship between burden of infection in ungulate populations and wildlife/livestock interfaces.

In southern African transfrontier conservation areas (TFCAs), people, livestock and wildlife share space and resources in semi-arid landscapes. One consequence of the coexistence of wild and domestic herbivores is the risk of pathogen transmission. This risk threatens local livelihoods relying on animal production, public health in the case of zoonoses, national economies in the context of transboundary animal diseases, and the success of integrated conservation and development initiatives. The level of interaction between sympatric wild and domestic hosts, defining different wildlife/livestock interfaces, characterizes opportunities of pathogen transmission between host populations. Exploring the relationship between infection burden and different types of wildlife/domestic interfaces is therefore necessary to manage the sanitary risk in animal populations through control options adapted to these multi-host systems. Here, we assessed the infection burdens of sympatric domestic cattle (Bos taurus/Bos indicus) and African buffalo (Syncerus caffer) at an unfenced interface and compared the infection burdens of cattle populations at different wildlife/livestock interfaces in the Great Limpopo TFCA. Patterns of infection in ungulate populations varied between wild and domestic hosts and between cattle populations at different wildlife/livestock interfaces. Foot-and-mouth disease, Rift Valley fever and theileriosis infections were detected in buffalo and cattle at unfenced interfaces; bovine tuberculosis was only present in buffalo; and brucellosis and lumpy skin disease only in cattle. At unfenced interfaces, cattle populations presented significantly higher Theileria parva and brucellosis prevalence. We hypothesize that cattle populations at wildlife/livestock interfaces face an increased risk of infection compared to those isolated from wildlife, and that the type of interface could influence the diversity and quantity of pathogens shared. Additional host behavioural and molecular epidemiological studies need to be conducted to support this hypothesis. If it is confirmed, the management of wildlife/livestock interfaces will need to be considered through the prism of livestock and public health.

A survey of ectoparasites, cestodes and management of free-range indigenous chickens in rural Zimbabwe.

A survey of ectoparasites, cestodes and husbandry aspects of indigenous free-range chickens was carried out in selected districts from the highveld and lowveld of rural Zimbabwe. The survey recorded infection with 4 species from the order Phthiraptera (lice), 1 species from the order Siphonaptera (fleas), 6 species from the order Acarina (ticks and mites) and 9 species of cestodes. Among the ectoparasites, the most prevalent was Menacanthus stramineus (87.7%) followed by Echidinophaga gallinacea (71.9%). Chickens in the Mazowe district had the highest number of ectoparasites species (10 of 11) followed by Goromonzi district (9 of 11) both these districts are situated in the highveld of Zimbabwe. The most prevalent cestode species was Raillietina tetragona (84.4%), followed by Raillietina echinobothrida (32.2%). Chickens in the Goromonzi district had the highest number of cestode species (7 of 9), followed by Mazowe district (one subgenus and 5 of 9). In all the districts sampled the main purpose of keeping free-range chickens was for meat for the household, with few households using the birds as a source of income. The majority of households kept their birds extensively with barely any appropriate housing, and supplementary feeding was only occasionally practised.

Ixodid ticks infesting domestic goats in communal land areas of Zimbabwe.

The purpose of this study was to determine the species spectrum of ticks infesting goats owned by resource-limited farmers in the state-owned communal land areas of Zimbabwe. Ticks were collected from goats at a single locality within each of 5 communal land areas, and a total of 14 ixodid tick species was recovered. The most numerous tick was Rhipicephalus evertsi evertsi, which was present in all areas at each sampling, and a Rhipicephalus sp. (near R. punctatus), which was most abundant on goats in the central regions of Zimbabwe during the March rainy season. Amblyomma hebraeum was present on goats in all areas sampled. In the eastern central region its distribution overlapped that of Amblyomma variegatum, while in the northwest it overlapped those of both Amblyomma marmoreum and A. variegatum. Hyalomma truncatum was present at all localities, whereas only a single Hyalomma rufipes was recovered. Rhipicephalus appendiculatus was collected from goats in the moist, slightly cooler regions, while the few Rhipicephalus zambeziensis recovered were present in the hotter, drier regions. Species recorded in lower numbers were Rhipicephalus (Boophilus) decoloratus, Rhipicephalus lunulatus, Rhipicephalus simus, Rhipicephalus tricuspis and Rhipicephalus turanicus. Attachment in the inter-digital space of adult A. hebreaum and H. truncatum was sometimes associated with lameness.

Seroprevalence of Toxoplasma gondii infection in domestic pigs reared under different management systems in Zimbabwe.

Serum samples from 474 domestic pigs (Sus scrofa) from Zimbabwe were tested for anti-Toxoplasma gondii IgG antibodies using the indirect fluorescent antibody test. The results showed that T. gondii infection is widespread in Zimbabwean pigs. Seroprevalence was lowest in fattening pigs from large and small-scale commercial farms that practise good hygiene (19.75% of 238) and highest in backyard scavenging pigs (35.71% of 70). Only 11.7% (11) of the 127 positive samples had titres of > or = 1:400 and nine (81.82%) of these 11 originated from pigs reared under poor hygienic conditions. A prevalence of 3.51% was found in the same group of fattening pigs using an indirect IgG enzyme-linked immunosorbent assay at the single serum dilution of 1:400. The serosurvey shows the importance of modern intensive husbandry systems in reducing the prevalences of T. gondii infection in domestic pigs.

Preliminary characterisation of Toxoplasma gondii isolates from Zimbabwe, with stage-specific monoclonal antibodies.

Cell-culture-derived clones of eight Toxoplasma gondii isolates from Zimbabwe were characterised in IFAT with a panel of five monoclonal antibodies (mAb). Each clone had been established from a single murine brain cyst. The antibodies were bradyzoite-specific (4.3), tachyzoite-specific (4.25, 5.1 and anti-P(30)), or tachyzoite- and bradyzoite-specific (5.15). Their strong reactivity with the bradyzoite-specific mAb 4.3 and their weaker reactivity with the tachyzoite-specific 4.25, 5.1 and anti-P(30) indicated that all the isolates are probably of genetic type II. Each of the isolates reacted in the IFAT in a similar way to the Danish reference strain of T. gondii, SSI-119.

Seroprevalence of Toxoplasma gondii in farm-reared ostriches and wild game species from Zimbabwe.

One hundred and seventy one serum samples from 10 game species from Zimbabwe were tested for IgG antibodies to Toxoplasma gondii infection using the modified agglutination test (MAT). Significantly higher seroprevalences were found in the felidae (Panthera leo) (92% of 26), bovidae (Tragelaphus species) (55.9% of 34) and farm-reared struthionidae (Struthio camelus) (48% of 50) compared to the other groups tested. Among the bovidae, the nyala (Tragelaphus angasii) had the highest seroprevalence of 90% (9/10). Anti-Toxoplasma antibody prevalences in browsers [greater kudu (Tragelaphus strepsiceros) (20% of 10), giraffe (Giraffa camelopardalis) (10% of 10) and elephant (Loxodonta africana) (10% of 20)] were generally in the lower range. No antibodies were detected in the wild African suidae [warthog (Phacochoerus africanus) and bushpig (Potamochoerus larvatus)]. Attempts to isolate T. gondii from the heart muscles of seropositve ostriches by subinoculation in BALB/c mice were unsuccessful.

Seroprevalence of Toxoplasma gondii infection in goats and sheep in Zimbabwe.

Seroprevalence rates of Toxoplasma gondii anti-antibodies in adult goats and sheep from different parts of Zimbabwe were determined. A total of 225 (67.9%) of the 335 serum samples tested were positive for anti-T. gondii IgG antibodies with the indirect fluorescent antibody test. There were differences in antibody seroprevalences among communal land goats from the different agro-ecological zones (Natural regions llb and III: 80 and 96.7%, respectively; Natural region IV: 65.9%; Natural region V: 45%; and Natural region III had a significantly higher seroprevalence than IV and V. The highest seroprevalences found in Natural regions II b and Ill are likely to be linked to the existence of more households and hence the possibility of a higher concentration of domestic cats that increases the chances of environmental contamination with their faeces harbouring T. gondii oocysts. The seroprevalence rate in sheep from a large commercial farm (10%) was significantly lower than that of sheep reared under the communal grazing system (80%). Overall, significantly higher proportions of seropositive animals had antibody titres of 1:50 (34.2% of 225) and 1:100 (44% of 225) as compared to the 9.8% and 12% with antibody titres of 1:200 and > or =1:400, respectively.

Detection of antibodies to the Ehrlichia ruminantium MAP1-B antigen in goat sera from three communal land areas of Zimbabwe by an indirect enzyme-linked immunosorbent assay.

A total of 1,286 caprine serum samples collected from three communal land areas in Zimbabwe from March 1999 to February 2000 were tested for Ehrlichia ruminantium antibodies using the indirect MAP1-B enzyme-linked immunosorbent assay. Of the 480 samples tested from Mudzi, a non-heartwater area, 425 (89.4 %) were positive. In the heartwater endemic areas, of the 441 samples 352 (79.4 %) from Gwanda and 300 of the 365 samples (83.2 %) from Bikita tested positive. The seroprevalence in the Bikita and Gwanda (approaching 90 %) is consistent with reports in related serological surveys that puts the seroprevalence of E. ruminantium in goats from endemic areas of Zimbabwe at 90 %. However, the high seroprevalence in the non-heartwater area of Mudzi is unexpected and can be a result of the presence of a serologically cross-reacting organism, which has to be isolated and characterized. The results need to be confirmed by alternative tests, based on molecular diagnostic tools. There were no significant differences in seroprevalence between the three sampling areas as there were between the three sampling periods. The highest corresponded with the period January to February (peak tick activity) and the lowest with the period July to September (minimal tick activity).

Interleukin-6, C-reactive protein, and expression of human leukocyte antigen-DR on peripheral blood mononuclear cells in patients after laparoscopic vs. conventional bowel resection: a randomized study.

PURPOSE: The aim of the study was to investigate the effect of surgical trauma in terms of approach (laparoscopic vs. conventional surgery) and extent of bowel resection (ileocolic resection vs. colectomy) on interleukin-6 level, C-reactive protein level, and expression of human leukocyte antigen-DR on peripheral blood mononuclear cells. Second, the length of the incision was correlated with the inflammatory response. METHODS: Thirty-four patients were analyzed as part of a randomized trial comparing laparoscopically assisted vs. open bowel resection for Crohn's disease, ulcerative colitis, and familial adenomatous polyposis. C-reactive protein levels and expression of human leukocyte antigen-DR on peripheral blood mononuclear cells were measured preoperatively and one day after surgery. Interleukin-6 was measured preoperatively and on Days 1 and 7 postoperatively. RESULTS: Four of the 34 patients were excluded because of blood transfusion after surgery. One day postoperatively, the interleukin-6 level peaked significantly within the laparoscopic and conventional group. There was no significant difference between the conventional and laparoscopic groups at Day 1 postoperatively. At Day 7 postoperatively, interleukin-6 levels were similar in both groups and returned to baseline levels. There was a higher C-reactive protein level in the conventional group one day after surgery than in the laparoscopic group, although the difference was not significant. Preoperative and postoperative human leukocyte antigen-DR expression on monocytes and postoperative percentage of lymphocytes expressing human leukocyte antigen-DR did not differ between the conventional and laparoscopic groups. No differences in immune response with respect to the measured parameters were noticed in patients with a large or small bowel resection segment or in patients with a small (8 cm) incision. CONCLUSIONS: These data suggest that surgical trauma did not significantly affect the immune status of patients with respect to the measured parameters in terms of either the approach or the extent of bowel resection.

Buffalo-associated Theileria parva: the risk to cattle of buffalo translocation into the Highveld of Zimbabwe.

There has been an increase in the introduction of game animals, including African buffaloes, into the Highveld of Zimbabwe to establish private game reserves on condition that they are confined in separate and secured paddocks. Owing to shortages of pastures cattle were grazed in buffalo-grazed paddocks resulting in outbreaks of buffalo-derived theileriosis. This paper reports the results of epidemiological observations carried out on two game reserves to assess the risk of buffalo translocation. The infection rate with Theileria parasites in ticks collected from buffalo-grazed pastures was high and produced fatal theileriosis in susceptible cattle. Similarly, adult R. appendiculatus ticks artificially fed as nymphs on the buffaloes produced fatal infections in susceptible cattle. Theileria parva (Boleni), the vaccine used to immunize cattle against theileriosis, and a buffalo-derived T. parva stabilate (BV-1) were inoculated in naïve buffaloes to study the Theileria carrier-state in these animals. The two buffaloes that had received the Boleni stabilate showed no clinical theileriosis reaction; however, the ticks derived from them produced a subclinical reaction in one susceptible calf. The buffalo which had received stabilate BV-1 developed fever, high schizont parasitosis for 10 days and 15% piroplasms parasitemia. R. appendiculatus ticks fed as nymphs on this buffalo produced fatal theileriosis reaction in a susceptible calf.

Ecto-, endo- and haemoparasites in free-range chickens in the Goromonzi District in Zimbabwe.

A cross-sectional study determined the prevalence of ecto-, endo- and haemoparasites in free-range chickens from the Goromonzi District, Zimbabwe. Fifty young and 50 adult birds were selected randomly. All chickens harboured ecto- and endoparasites, and 32% were infected with haemoparasites. Eight different ectoparasites were identified; the more prevalent ones had the following prevalences (young, %; adult, %): Argas persicus (6; 14), Cnemidocoptes mutans (6; 32), Echidnophaga gallinacea (72; 74), Goniocotes gallinae (0; 22), Menacanthus stramenius (90; 88) and Menopon gallinea (24; 66). The prevalences of C. mutans, G. gallinae and M. gallinae were higher in adults compared to young chickens. The mean (+/-S.D.) number of helminth species per chicken was 6.7+/-2.0 for young chickens and 6.4+/-2.0 for adult chickens with a range of 1-10 for young chickens and a range of 1-11 for adult chickens. The most prevalent nematodes identified were (with prevalence in % for young/adult birds): Allodapa suctoria (76; 72), Ascaridia galli (48; 24), Gongylonema ingluvicola (28; 56), Heterakis gallinarum (64; 62) and Tetrameres americana (70; 62). For cestodes the prevalences were: Amoebotaenia cuneata (60; 68), Hymenolepis spp. (62; 80), Raillietina echinobothrida (66; 34), Raillietina tetragona (94; 100) and Skrjabinia cesticillus (50; 76). The young chickens had higher prevalences of A. galli and R. echinobothrida compared to adults, but lower prevalence of G. ingluvicola and S. cesticillus. Eimeria spp. oocysts were isolated in 36% of 47 investigated samples. The prevalence was 47% for young chickens and 18% for adult chickens. Prevalences (in %) of haemoparasites in young and adult chickens were: Aegyptinella pullorum (7; 6), Leucocytozoon sabrazesi (3; 1), Plasmodium gallinaceum (8; 6) and Trypanosoma avium (2; 3).

Dichotomal role of inhibition of p38 MAPK with SB 203580 in experimental colitis.

BACKGROUND: Crohn's disease is characterised by a chronic relapsing inflammation of the bowel in which proinflammatory cytokines play an important perpetuating role. Mitogen activated protein kinase p38 (p38 MAPK) has been established as a major regulator of the inflammatory response, especially with regard to production of proinflammatory cytokines, but its role in inflammatory bowel disease is unexplored. In this paper we describe the effects of a specific p38 MAPK inhibitor, SB 203580, in trinitrobenzene sulphonic acid (TNBS) induced colitis in mice. RESULTS: SB 203580 had a dichotomal effect in TNBS mice. Weight loss of TNBS mice treated with SB 203580 was significantly worse and colon weight on sacrifice was significantly increased in MAPK inhibitor treated TNBS mice (229.2 mg and 289.1 mg, respectively). However, the total number of cells in the caudal lymph node decreased to 188.8 x 10(4) cells in SB 203580 treated TNBS mice compared with 334 x 10(4) cells in vehicle treated mice. CD3/CD28 double stimulated caudal lymph node cells of SB 203580 treated mice showed decreased interferon gamma production but increased tumour necrosis factor alpha production. The concentration of interleukin 12p70 in colon homogenates was significantly decreased in SB 203580 treated mice whereas concentrations of interleukin 12p40, tumour necrosis factor alpha, and interleukin 10 were similar in vehicle and SB 203580 treated TNBS mice. CONCLUSION: Our results reveal a dichotomy in p38 MAPK action during experimental colitis.

Infliximab treatment induces apoptosis of lamina propria T lymphocytes in Crohn's disease.

BACKGROUND AND AIMS: Treatment with infliximab induces remission in about 70% of patients with steroid refractory Crohn's disease. Because Crohn's disease is considered to be mediated by uncontrolled activation of mucosal T lymphocytes, we hypothesised that infliximab could induce apoptosis of T lymphocytes. METHODS: Induction of apoptosis in vivo was studied in 10 patients with therapy refractory Crohn's disease. In vitro, resting or stimulated Jurkat T cells were incubated with infliximab. RESULTS: Infusion of infliximab (5 mg/kg) in steroid refractory patients with Crohn's disease induced a clinical response in 9/10 patients but did not influence expression of activation markers, homing receptors, memory cells, Fas expression, or Bax/Bcl-2 expression on peripheral blood T lymphocytes. In contrast, a significant increase in CD3 and TUNEL positive cells within colonic biopsies was detected 24 hours after infusion of infliximab, suggesting that infliximab stimulates apoptosis of activated T lymphocytes but not of resting T cells. To test this hypothesis, the effects of infliximab on Jurkat T cells were investigated. We observed that infliximab induced apoptosis and an increase in the Bax/Bcl-2 ratio of CD3/CD28 stimulated Jurkat T cells but not of unstimulated Jurkat cells. CONCLUSIONS: Our data indicate that infliximab treatment causes a rapid and specific increase in apoptosis of T lymphocytes in the gut mucosa. These findings may explain the rapid and sustained therapeutic effects of infliximab in Crohn's disease.

Blockade of endogenous IL-18 ameliorates TNBS-induced colitis by decreasing local TNF-alpha production in mice.

BACKGROUND & AIMS: Interleukin (IL) 18 has proinflammatory effects. IL-18 plays a pivotal role in Th1 responses, but its proinflammatory activities extend beyond Th1 cells, including macrophages and production of tumor necrosis factor (TNF) alpha and IL-1beta. IL-18 is up-regulated in colonic specimens of patients with Crohn's disease. The goal of this study was to evaluate the role of IL-18. METHODS: Activity of IL-18 was neutralized using recombinant human IL-18 binding protein isoform a (rhIL-18BPa) in trinitrobenzene sulfonic acid (TNBS)-induced colitis. RESULTS: Mice treated daily with rhIL-18BPa (8 mg/kg) had significant reductions in clinical score, body weight loss, and colon weight increase compared with saline-treated mice. Histologic analysis showed that rhIL-18BPa-treated mice developed only mild colitis without signs of ulceration, with a mean total score of 9.8 +/- 1.3 points compared with 15.9 +/- 1.1 points observed in saline-treated mice with colitis. Analysis of cytokine levels in colon homogenates showed a significant decrease in TNF-alpha, IL-6, and IL-1beta after rhIL-18BPa treatment but no effect on interferon gamma. The therapeutic potential of rhIL-18BPa treatment was confirmed in TNBS mice that were treated only on days 8 and 9 after the start of the experiment. In these mice, significant reductions in total colitis score and colon weight were also observed. CONCLUSIONS: These findings show that inhibition of rhIL-18BPa bioactivity, via rhIL-18BPa, may be beneficial for the treatment of IBD.

Chemokine receptor CXCR3 expression in inflammatory bowel disease.

CD4+ T lymphocytes in the lamina propria (LP) of the gut play a central role in the immune response in inflammatory bowel disease (IBD). CXCR3 is a chemokine receptor expressed on activated T lymphocytes, and a key component for the recruitment of T helper (Th1) effector cells to the site of inflammation. To determine if CXCR3 is involved in localization of T cells to the gut in IBD patients, we investigated the expression of CXCR3 on CD4+ T lymphocytes in the LP and in the submucosa of resection specimens from 51 IBD patients and 15 control patients. Positive cells were microscopically scored using a semiquantitative analysis on a five-point scale. We found that CD4+ T cells, CXCR3+ cells, and CD4+CXCR3+ T cells in the LP were slightly increased in both IBD groups compared with control non-IBD specimens. In addition, CD4+ and CXCR3+ cells in the submucosa were significant increased in the CD group compared with the control group. CD4+ and CXCR3+ expression was not statistically different between CD and UC. Flow cytometry was used to analyze the percentage of CXCR3+ cells within the CD4+ T-cell population isolated from biopsy specimens and peripheral blood from IBD patients and control patients. There was no difference in the percentage of CD4+CXCR3+ cells between the different groups in the gut as well as in the circulation. These results suggest that CD4+CXCR3+ T cells migrate to the normal and inflamed intestinal mucosa, indicating a role in maintaining normal gut homeostasis. The selective expression of CXCR3+ cells in the submucosa of CD patients might also indicate that these cells play a role in inflammation.

Development of chronic colitis is dependent on the cytokine MIF.

The cytokine macrophage-migration inhibitory factor (MIF) is secreted by a number of cell types upon induction by lipopolysaccharide (LPS). Because colitis is dependent on interplay between the mucosal immune system and intestinal bacteria, we investigated the role of MIF in experimental colitis. MIF-deficient mice failed to develop disease, but reconstitution of MIF-deficient mice with wild-type innate immune cells restored colitis. In addition, established colitis could be treated with anti-MIF immunoglobulins. Thus, murine colitis is dependent on continuous MIF production by the innate immune system. Because we found increased plasma MIF concentrations in patients with Crohn's disease, these data suggested that MIF is a new target for intervention in Crohn's disease.

IC14, an anti-CD14 antibody, inhibits endotoxin-mediated symptoms and inflammatory responses in humans.

CD14 is a receptor for cell wall components of Gram-negative and Gram-positive bacteria that has been implicated in the initiation of the inflammatory response to sepsis. To determine the role of CD14 in LPS-induced effects in humans, 16 healthy subjects received an i.v. injection of LPS (4 ng/kg) preceded (-2 h) by i.v. IC14, a recombinant chimeric mAb against human CD14, at a dose of 1 mg/kg over 1 h, or placebo. In subjects receiving IC14, saturation of CD14 on circulating monocytes and granulocytes was >90% at the time of LPS injection. IC14 attenuated LPS-induced clinical symptoms and strongly inhibited LPS-induced proinflammatory cytokine release, while only delaying the release of the anti-inflammatory cytokines soluble TNF receptor type I and IL-1 receptor antagonist. IC14 also inhibited leukocyte activation, but more modestly reduced endothelial cell activation and the acute phase protein response. The capacity of circulating monocytes and granulocytes to phagocytose Escherichia coli was only marginally reduced after infusion of IC14. These data provide the first proof of principle that blockade of CD14 is associated with reduced LPS responsiveness in humans in vivo.

p38 mitogen-activated protein kinase inhibition increases cytokine release by macrophages in vitro and during infection in vivo.

p38 mitogen-activated protein kinase (MAPK) has been suggested as a mediator of cytokine release and is currently being targeted for anti-inflammatory therapy. However, experimental data are contradictory and lack sufficient affirmation in vivo. We tested the effect of p38 MAPK inhibition in several cell types and in different murine models of infectious disease. We observed that most cell types react to p38 MAPK inhibition with diminished cytokine release, but that this treatment induced increased cytokine release in macrophages. Furthermore, we observed increased cytokine production in mouse models of pneumococcal pneumonia and tuberculosis accompanied by severely reduced bacterial clearance. This apparent inefficacy of p38 MAPK inhibition in reducing cytokine release in infectious disease, as well as its immune-compromising action, suggest that targeting p38 MAPK may not be a suitable anti-cytokine strategy in patients with such disease or at risk for infection.

A survey of parasitic nematode infections of chickens in rural Zimbabwe.

A survey to determine the nematode species in rural chickens reared extensively was carried out in six districts of Zimbabwe. Two-hundred-and-seventy chickens were randomly collected from the districts and processed for helminth recovery. One genus and 10 species were identified from the gastrointestinal tract but no parasites were found in the respiratory tract and eyes. Skrjabinocerca sp., Capillaria obsignata, Capillaria contorta and Trichostrongylus tenuis are new records in Zimbabwe. Allodapa brumpti and Tetrameres americana were the most common species with a prevalence of 64.8% and 64.1%, respectively.

Epidemiological observations of Zimbabwean theileriosis: disease incidence and pathogenicity in susceptible cattle during Rhipicephalus appendiculatus nymphal and adult seasonal activity.

Fifty-nine Hereford cattle susceptible to tick-borne diseases were used as tracer animals to assess the tick challenge and pathogenicity of Theileria parva under field conditions in Zimbabwe. They were moved periodically in groups of five to three commercial farms (one group consisted of four) during seasons of Rhipicephalus appendiculatus nymphal and adult activity. All tracer cattle were herded together with the farm cattle but were not dipped. The nymphal tick counts were high on two of the farms (up to 2000 per animal) but were very low on the third farm (less than ten per animal). On the three farms, 19 out of 24 (76%) tracers had patent Theileria schizonts. There was a range of clinical manifestations of theileriosis with acute and fatal infections occurring on one farm. The adult R. appendiculatus infestations during the wet season numbered 120-800 per animal on the three farms. The disease transmitted by the adults was very pathogenic on the three farms; 30 out of 35 (86%) had severe theileriosis infections. Cattle, which survived the nymphal diseases challenge, showed various degrees of immunity to subsequent T. parva challenge transmitted by adult ticks. Therefore, 13 out of 18 (72%) of these cattle had a second disease episode and the case fatality rate on the three farms was 46%. The factors which determined the epidemiological status of Theileria challenge on the farms, such as the farming systems and presence of wild animals, are discussed.