Age resistance to Theileria parva bovis infection in calves

Data collected in the Zimbabwean province of Mashonaland-West, in the period 1980-1988, showed that mortality in calves owing to Theileria parva bovis infection (January disease) was significantly lower in animals younger than 7 months than in older cattle. Groups of seven Holstein-Friesian calves from non-immune dams aged approximately 1, 4, 7, 10 and 13 months were infected with a Theileria parva bovis tick-derived stabilate. The dose chosen was lethal for 40% of the calves in the trial. Mortality was highest in the 4-month age group. The reactions in the 7-, 10- and 13-month age groups became progressively milder. The reactions in the 1-month old calves were the least marked, being very mild. The age-related resistance in the youngest calves, as can be concluded from our results, is only of short duration and cannot explain the lower incidence of January disease observed in calves in the field.     

Kinetics of infection with Theileria parva (East Coast fever) in the central lymph of cattle

During the course of a lethal infection with Theileria parva in susceptible cattle, the dissemination of the parasite was examined in central lymph efferent from superficial lymph nodes in the thoracic duct. From the regional node, lymphocytes containing macroschizonts of T. parva were detected in efferent lymph 8 days after challenge where their appearance coincided with a dramatic increase in the output of lymphoblasts. The number of infected cells reached a maximum around Day 14, when 60-65% of efferent lymphocytes were parasitized. A severe reduction in the total cell output occurred after Day 14, at the time when widespread lymphocytosis was observed in the parent lymph node. A similar pattern of cellular kinetics was observed in the thoracic duct and in lymph efferent from lymph nodes distant from the site of challenge, although in the latter, the parasitosis reached only 10% of total cells. There was no selective depletion of parasitized cells from central lymph during the third week of infection, although the comparative parasitosis between lymph and lymph node cells indicated that infected cells entered central lymph less readily during this period. Macroschizonts appeared in cultures of lymphatic lymphocytes sampled between 5-9 days after challenge. These results, together with the failure of ablation of the regional lymph node 2, 3 or 5 days after challenge to delay the onset of the disease, indicated that dissemination of the infection from the site of challenge occurred within the first 2-3 days after the inoculation T. parva.     

Endemic stability for Theileria parva infections in Ankole calves of the Ankole ranching scheme, Uganda

A population-based study was carried out on the Ankole ranching scheme in south-west Uganda with the aim of determining the endemic status of Theileria parva infections. For this purpose, the age-related sero-prevalence of T. parva and the specific calf mortality associated with the parasite were assessed. Blood samples were collected from 931 Ankole calves of up to 12 months of age from 81 randomly selected herds. The relationship between rainfall pattern and whole-body Rhipicephalus appendiculatus counts was determined. The influence of tick control practices on East Coast fever-related calf mortality, and sero-positivity were also determined. A significant (r2 = 0.76, P = 0.000) association between R. appendiculatus counts and rainfall was observed. There was no significant (P > 0.05) association between theileriosis-related calf mortality, sero-positivity and the different tick control practices. Antibody prevalence based on the PIM ELISA was above 70% among calves of 6 months of age in 96% in all the herds. Theileria parva-related calf mortality determined by repeated herd visits and farm records ranged between 0 % and 5.4 %. It was concluded that endemic stability for theileriosis, caused by T. parva, existed in the study area, and that the risk of the occurrence of economically important outbreaks of East Coast fever in indigenous cattle was regarded as minimal under the prevailing conditions.     

Fatal cases of Theileria annulata infection in calves in Portugal associated with neoplastic-like lymphoid cell proliferation

This study was carried out to investigate fifteen cases of acute lethal infection of calves (≤ 4 months of age) by the protozoan parasite Theileria (T.) annulata in the south of Portugal. Calves developed multifocal to coalescent nodular skin lesions, similar to multicentric malignant lymphoma. Infestation with ticks (genus Hyalomma) was intense. Theileria was seen in blood and lymph node smears, and T. annulata infection was confirmed by isolation of schizont-transformed cells and sequencing of hypervariable region 4 of the 18S rRNA gene. At necropsy, hemorrhagic nodules or nodules with a hemorrhagic halo were seen, particularly in the skin, subcutaneous tissue, skeletal and cardiac muscles, pharynx, trachea and intestinal serosa. Histologically, nodules were formed by large, round, lymphoblastoid neoplastic-like cells. Immunohistochemistry (IHC) identified these cells as mostly CD3 positive T lymphocytes and MAC387 positive macrophages. A marker for B lymphocytes (CD79αcy) labeled very few cells. T. annulata infected cells in these nodules were also identified by IHC through the use of two monoclonal antibodies (1C7 and 1C12) which are diagnostic for the parasite. It was concluded that the pathological changes observed in the different organs and tissues were caused by proliferation of schizont-infected macrophages, which subsequently stimulate a severe uncontrolled proliferation of uninfected T lymphocytes.     

Occurrence of Theileria parva infection in cattle on a farm in the Ladysmith district, KwaZulu-Natal, South Africa

Theileria parva causes widespread morbidity and mortality in cattle in endemic regions. An outbreak of theileriosis occurred on a farm near Ladysmith in KwaZulu-Natal, South Africa, which is not a declared Corridor disease-infected area. A survey of Red Brangus cattle from all age groups and areas of the farm was performed. Transmission of the parasite from infected animals on the farm to susceptible animals by tick transmission and tick-stabilate injection, was attempted. The survey indicated high numbers of animals with antibody titres to T. parva but only 6 infected animals, based on real-time PCR and RLB analysis. The transmission experiments failed to transmit the parasite. The study shows the difficulty in elucidating a source of infection and determining the dynamics of new infections in a herd where multiple possible sources are present and treatment with tetracyclines has taken place.     

Comparative histopathology of the lymph nodes, spleen, liver and kidney in experimental ovine trypanosomosis

The infection of Yankassa rams with three important trypanosome species affecting livestock, namely, Trypanosoma congolense, T. vivax and T. bruceiproduced both acute and chronic fatal conditions. Chronic infections were induced in the three infections by the application of subcurative doses of diaminazene aceturate (Berenil). Pathological changes in the infected animals included splenomegaly and hepatomegaly which were more pronounced in acute than in chronic T. congolense infection. However, these changes were more severe in chronic than in acute T. vivax infection. While splenomegaly was more pronounced in chronic T. bruceiinfection than in acute, hepatomegaly and lymphadenopathy were more severe in acute than in the chronic condition. The increases in size of the spleen, lymph nodes and liver were associated with congestion, increases in cell density related to increased immunological reactions in the spleen and lymph nodes as well as increase in numbers, size and activity of the phagocytic cells in these organs.     

Distribution of T and B cells in thymus, blood and lymph nodes of the cat.

The proportions of T and B cells in the thymus, blood and lymph nodes were estimated in cats from three months to three years of age. T cells were identified by formation of E rosettes with guinea-pig red blood cells and B cells by the presence of surface immunoglobulin (Ig) as shown by the mixed antiglobulin reaction. Using a double test, it was shown that these methods identify separate, non-overlapping cell populations. The proportions of T cells shown in the thymus ranged from 10-73 per cent, in the blood 5-62 per cent and in the nodes, 5-44 per cent. Cells with surface Ig ranged from 0-10 per cent in the thymus, 26-68 per cent in the blood and 32-18 per cent in the nodes. Two cats with lymphadenopathy had unusually high B cell counts and one cat with depletion of the thymus was deficient in peripheral T cells. Papain treatment reduced or abolished E rosette formation by T cells.     

Haematological and biochemical studies on experimental Theileria annulata infection in crossbred calves

Administration of ground-up tick tissue stabilate (0.75 tick equivalent) by the subcutaneous route to crossbred calves aged 1 week to 1 month led to the development of acute theileriosis. Haematological studies revealed significant progressive decreases in haemoglobin concentration, packed cell volume and red blood cell count, whereas the total leukocyte count showed an initial non-significant leukocytosis followed by a significant leukopenia. Analysis of serum revealed significant increases in levels of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, creatinine kinase and -glutamyltransferase, and in the concentrations of uric acid, blood urea nitrogen and bilirubin. The concentrations of total protein, albumin, glucose, cholesterol and calcium showed non-significant decreases, while phosphorus decreased significantly during the terminal stages of the disease.     

Some preliminary observations on the susceptibility and resistance of different cattle breeds to Theileria parva infection

Theileria parva-na?ve Friesian (Bos taurus), Boran (Bos indicus) and Maasai Zebu steers (B. indicus) were infected with a T. parva sporozoite stabilate dose which had previously been shown to induce an estimated 50% mortality rate in Boran cattle. All the cattle developed patent infections with no significant differences in the length of the prepatent period to development of macroschizonts (P > 0.05) between the three groups. Clinical theileriosis occurred in all eight the Friesians (100%), five out of nine Borans (55.6%) and two out of five Zebus (40%). Three of the Friesians (37.5%), and two of the Borans (22.2%) died of theileriosis. The different cattle types were equally susceptible to the infective dose used as indicated by the length of the prepatent periods, but there was a marked difference in their development of clinical theileriosis. The gradation in resistance to disease confirms the findings of earlier less critical studies and identifies these cattle breeds as suitable for investigations into the mechanisms of resistance to theileriosis.     

Comparative infection rates of Theileria parva lawrencei in salivary glands of Rhipicephalus appendiculatus and Rhipicephalus zambeziensis

Three cattle, which had been experimentally infected with Theileria parva lawrencei and maintained as carriers of the infection, were each infested simultaneously with clean nymphal Rhipicephalus appendiculatus and Rhipicephalus zambeziensis in ear bags on separate ears. After moulting, the ensuing adult ticks were fed on rabbits for 4 days and their salivary glands were examined for infective stages of the parasite. Microscopic examination revealed significantly higher infection rates in the salivary glands of R. zambeziensis than in R. appendiculatus which may indicate an increased vector efficiency of R. zambeziensis for T. p. lawrencei.     

Tick burden and prevalence of Theileria parva infection in Tarime zebu cattle in the lake zone of Tanzania

This study was carried out to assess the distribution, abundance of different tick genera and prevalence of Theileria parva infection in Tarime zebu cattle kept in selected wards of Serengeti and Tarime districts in Mara region. Adult ticks were identified and counted from half body parts of 360 animals which were extensively managed in communal land with natural pastures. Concurrently, blood samples were collected and thereafter DNA extracted and a nested polymerase chain reaction (nPCR) was done using primers specific for p104 gene to detect the presence of T. parva DNA. Ticks were identified into four groups: Amblyomma genus, Boophilus sub-genus of Rhipicephalus genus, other species of Rhipicephalus, and Hyalomma genus. Rhipicephalus genus accounted for 71.8 % of the total ticks, whereas Amblyomma, Boophilus sub-genus of Rhipicephalus genus and Hyalomma constituted 14.1, 14.0 and 0.1 %, respectively. There were more animals (p?p?T. parva was 27.7 % and was higher (p?T. parva did not show any clinical signs of East Coast fever (ECF), suggesting the existence of subclinical infection in Tarime zebu. These results suggest that Tarime cattle can tolerate ECF infection and are likely to serve as potential carriers of T. parva to other less-tolerant cattle breeds in mixed herds. Since Tarime cattle are preferred by most farmers with mixed herds, routine screening for T. parva is highly recommended to minimize introduction of infected cattle into an immunologically naive population.     

Quantitative analyses of lymphoid tissue in the spleen, lymph nodes and Peyer's patches in cynomolgus monkeys

To clarify the morphological characteristics of the cynomolgus monkey immune system, we analyzed quantitative data on their lymphoid organs. Spleens, major lymph nodes and Peyer's patches were sampled from cynomolgus monkeys, and the lymphoid follicle and germinal center areas and percentages of CD3- and CD20-positive areas were calculated. All the organs analyzed showed large interindividual variations in the sizes of lymphoid follicles and germinal centers. Lymphoid follicle in the spleen, submandibular lymph nodes and Peyer's patches showed no marked difference in size. Germinal center size in the mesenteric lymph nodes and Peyer's patches were significantly smaller than those in the spleen. Areas containing T cells were largest in the lymph nodes, while those containing B cells were largest in the spleen and Peyer's patches. The mean size of the splenic lymphoid follicle in cynomolgus monkeys is larger than that in rats and similar to that in humans. Based on the large individual variation and the characteristics of lymphoid organs, it is important to use cynomolgus monkeys in standard toxicity studies. Taking advantage of the characteristics of each species enables reliable evaluation of the immunologic system in standard toxicity studies.     

Epidemiological studies on Theileriosis and the dynamics of Theileria parva infections in Rwanda

An epidemiological analysis based on three country wide surveys was carried out to determine the prevalence of infections with Theileria spp. in Rwanda. In the 1998 dry season, a total of 264 blood samples were submitted to Theileria spp. characterisation using the 18S species-specific PCR-RFLP assay. The same samples together with 634 samples (317 samples/season) collected during the 2002 dry season and the 2003 wet season were further analysed using the p104 Theileria parva specific PCR. The results from the 18S characterisation showed the presence of four Theileria spp., namely T. parva, T. mutans, T. taurotragi and T. velifera in the field. Half of the animals had multiple Theileria spp. infections. T. parva was the most prevalent and a high correlation (94%) was found between the prevalence results using the 18S and the p104 PCR assays. The prevalence of T. parva infections was stable over time and over season but decreased significantly from the high land to the low land areas. This unexpected trend cannot be explained alone by ecology or the dynamics of the tick population in the different zones, many other components such as breed type, tick control practices and grazing system are likely to play a role. Another important finding was the fact that young animals are infected early in life in all regions except in the high land zone indicating the existence of a particular epidemiological situation in this part of the country.     

Effects of experimentally induced Theileria annulata infection on the pharmacokinetics of oxytetracycline in cross-bred calves

The effects of an experimental Theileria annulata infection on the intravenous (10 mg kg-1) pharmacokinetics of oxytetracycline (OTC) were investigated in crossbred calves. The serum concentration-time curve of oxytetracycline before and after the experimental infection was best described by an open two-compartment model. The experimental infection was induced by a subcutaneous administration of ground-up tick supernate (GUTS) equivalent to 30 Hyalomma anatolicum anatolicum ticks infected with Theileria annulata. It produced a definite temperature rise and symptoms of clinical disease in the calves. The haemoglobin, packed cell volume (PCV), white blood cell (WBC) counts and serum Cu, Fe and Zn concentrations decreased after onset of the infection. The distribution and elimination half-lives (t1/2 alpha and t1/2 beta), volume of the central compartment (Vc), AUC0-infinity, AUMC and mean residence time (MRT), were significantly reduced (P < or = 0.05) and the hybrid rate constants K12, Kel, K12/K21 ratio and total body clearance (ClB) of oxytetracycline were significantly (P < or = 0.05) increased after infection. The infection, however, had no effect on the C0, K21, apparent and steady-state volumes of distribution (Vd(area) and Vdss) of the drug. The above changes may necessitate changes in the dosage regimen of oxytetracycline used to treat Theileria infections in cattle under field conditions.     

黄芪多糖对肉鸡脾淋巴细胞转化及信息分子的影响

本实验研究了黄芪多糖对肉鸡脾淋巴细胞转化率及细胞内信息分子 -一氧化氮 (NO)、Ca2 + 及 c AMP、c GMP的影响。发现黄芪多糖能剂量依赖性促进脾淋巴细胞转化率及细胞内 NO、Ca2 + 浓度 ;当作用时间为 2 0 min时 ,4 0 μg/ ml黄芪多糖能增加 c AMP浓度 ,降低 c GMP浓度 (P<0 .0 1) ;而当作用时间为 6 0 m in,对 c AMP和 c GMP浓度无显著影响。以上结果提示 ,黄芪多糖能显著提高脾淋巴细胞免疫功能 ,其作用是通过改变细胞内信息传导实现的。