Prevalence and potential risk factors for amitraz resistance in Boophilus microplus ticks in cattle farms in the State of Yucatan, Mexico

Southern cattle tick, Boophilus microplus, control in the Mexican tropics is based on the application by spray, dip or pour-on of acaricides. In Mexico the first report of ticks resistant to amitraz was reported in 2002. Amitraz resistance affecting the cattle industry of Yucatan State, Mexico, has not been investigated. A cross-sectional study was carried out in order to investigate the possible association between management risk factors and the prevalence of B. microplus ticks resistant to amitraz in Yucatan, Mexico. Ninety-eight cattle farms were randomly selected and a sample of 20–30 engorged B. microplus females was collected from at least 10 cattle from each farm. Collected ticks were taken to the laboratory where the larval progeny were obtained. The modified larval immersion test was used to detect ticks resistant to amitraz. A discriminating dose of 0.0002% amitraz was used. A questionnaire was applied on each collaborating farm. For the statistical analysis a 2 × 2 contingency table was used to identify potential risk factors. The prevalence of farms with B. microplus resistant to amitraz was 19.40%. However, even though tick resistance to amitraz is a present problem there was no evidence that it was associated with the risk factors analyzed in this survey.     

Long-term study of incidence and financial loss due to cattle babesiosis in an Argentinian dairy farm

The incidence and direct financial loss caused by babesiosis were evaluated in 121 Holstein Friesian female cattle that formed eight cohorts (1981–1988) of a dairy farm located approximately 24° 55′S 65° 29′W in Salta, Argentina. Female calves born in 1986 and 1987 (n=32) were vaccinated with a live Babesia vaccine at six months of age.

No cases of babesiosis occurred in the vaccinated cattle. The incidence of babesiosis in the six non-vaccinated cohorts was 23.6% (21/89). Eighteen of the cases were the result of Babesia bovis, one to Babesia bigemina and two to a mixed infection. Two cattle died of B. bovis infection in spite of drug treatment (diaminazene, 3.5 mg kg⁻¹). No disease occurred in cattle younger than seven months or older than 24 months. The number of cases according to age of cattle was: 7–9 months, 5; 10–12 months, 6; 13–24 months, 10.

Financial loss for the six cohorts that suffered clinical cases amounted to US $ 1624.6 (prices in October 1990)—62% were the result of physical losses and 38% to costs of control. A benefit-cost analysis of vaccination was carried out assuming that 95% of the mortality and morbidity losses of the six non-vaccinated cohorts was prevented after a single inculation of a live vaccine (cost of a dose plus administration was US $ 4.2. The benefit-cost ratio was 4:1 for each US dollar expended.     

Epidemiology of theilerioses in the Trans-Mara division, Kenya: Husbandry and disease background and preliminary investigations on theilerioses in calves

All the calves born (116) into 3 Maasai cattle herds in the Trans-Mara Division of Kenya, between August 1978 and October 1979, were recruited into a monthly health study which concentrated on theileriosis. Twenty-two of the calves died before they were 6 months of age, but the mortality only increased to 25% by the time the calves reached 18 months of age. The mean birth weight of calves was 17.5 kg while at 190 days post-birth the mean weight was 53.4 kg. The main causes of mortality were starvation (7.8%), neonatal diarrhoea (2.6%), chronic indigestion (2.6%) and theileriosis (2.6%) due to Theileria parva and T. mutans infections. The calves were infected with ticks from birth (mostly Rhipicephalus appendiculatus and Amblyomma spp.) and the first Theileria schizonts were detected on Day 17 post birth and reached a maximum of 18.4% of calves in the 11th week post-birth. Seasonal peaks of macroschizont incidence occurred in February and July. All calves had patent Theileria piroplasm infections by the time they were 5 months old and 44% had shown patent Theileria macroschizont infections by 6–7 months of age. Generally low parasitosis of Theileria piroplasms and schizonts occurred. Serology using the indirect fluorescent antibody test showed a high proportion of calves received antibodies against T. mutans and T. parva from their dams by way of colostrum. The majority of calves also had active antibody responses against T. mutans and T. parva by the time they were 6 months of age. There was a correlation between the pre-patent period of piroplasms and active antibody responses to T. mutans and between the prepatent period of schizonts and an antibody response to T. parva. Eighteen older calves developed T. velifera infections. “Turning sickness” due to Theileria infection in the brain was detected in older cattle. Other blood parasites such as Trypanosoma vivax, T. congolense, Anaplasma marginale and Babesia bigemina occurred at patent levels at a lower incidence than Theileria spp. and did not cause disease problems in the calves. The calf population was highly resistant to theileriosis since they had a 100% morbidity, but only 2.6% mortality. Theileria infections would appear to have an important effect on the growth of calves but this and many aspects of the epidemiology of theileriosis in the area required more intensive sampling.     

Phylogenetic analysis of Theileria sp. from sika deer, Cervus nippon, in Japan

The 18S rRNA genes of Theileria species detected in sika deer, Cervus nippon centralis in Yamaguchi and Cervus nippon yesoensis in Hokkaido, were analyzed. The percent identities of the nucleotide sequences of Theileria from Cervus nippon centralis and Cervus nippon yesoensis were more than 99%. The percent identities of the Theileria sp. from sika deer and Theileria sergenti, Theileria buffeli and Theileria cervi were 97, 96 and 95%, respectively. Phylogenetic analysis of the gene sequences also revealed that Theileria sp. detected from sika deer comprise a clade that is clearly distinct from the clade comprised of Theileria from cattle.     

Serosurvey of Babesia canis, Babesia gibsoni and Ehrlichia canis in pound dogs in California, USA

The seroprevalence of three canine tick-transmitted parasites, Babesia gibsoni, Babesia canis and Ehrlichia canis, was estimated in selected regions of California. Blood smears and sera were obtained from 971 dogs in seven animal shelters: four in Los Angeles County, one in Yolo County, one in El Dorado County in California and one in Minden, Nevada. Seroprevalence in Los Angeles County shelters were 0–13%, 0–2.6% and 0% for B. canis, B. gibsoni and E. canis, respectively. Seroprevalences of the same three parasites in Yolo County and El Dorado County Shelters were 0% except for a 1% seroprevalence of B. canis in dogs from Yolo County Shelter.

Potential risk factors (breed, age, sex and evidence of ticks on the dogs) for B. canis seropositivity were evaluated. Dogs 3 years of age or older had a significantly higher risk (odds ratio 5.04) of being seropositive to B. canis compared with dogs less than 1 year old. Breed, sex and evidence of ticks were not associated with seropositive reactions to B. canis. Of 29 coyotes captured in Los Angeles County, three (10.3%) were seropositive for B. gibsoni, with titers of 1280 to 2560. This study indicated that dogs in Los Angeles County were at higher risk of being seropositive and potentially infected with canine babesial parasites than dogs in Yolo and El Dorado Counties. Movement of chronically infected dogs from Los Angeles County into other areas could contribute to the spread of these important pathogens.     

国内部分省市肉兔及蜱虫携带土拉杆菌的流行病学调查

本调查旨在探明土拉杆菌在国内部分省份的流行情况。利用本实验室建立的土拉杆菌通用及亚种PCR检测研究方法，对国内肉兔饲养密度比较大的省份和牛羊存栏的部分省市开展了肉兔和蜱虫中土拉杆菌的检测，并对阳性样本进行了土拉杆菌亚种的鉴定和基因测序验证。研究结果表明，肉兔肝脏组织和牛羊携带蜱虫中土拉杆菌DNA检测阳性，其中218份肉兔样本中12份阳性（阳性率5.5%），490份蜱虫样本中15份阳性（阳性率3.1%）；从地区分布来看，山东、河南、四川肉兔病料检测阳性，云南、山东蜱虫阳性率高；PCR检测显示其亚种为F.h，为土拉杆菌毒力较强的亚种。本次调查显示土拉杆菌在肉兔、蜱虫中存在，山东、云南地区存在土拉杆菌病公共卫生安全风险，应引起有关科研院校、医疗单位和政府部门的高度重视。     

Epidemiological Investigation of Francisella tularensis Transmitted by Rabbits and Ticks in Some Provinces of China

The aim of this investigation was to find out the prevalence of Francesella tularensis in some provinces of China. Using the general and subspecies PCR detection method for Francesella tularensis established in our laboratory, PCR detection of Francesella tularensis in rabbits and ticks was carried out in provinces with high-density rabbits feeding and some provinces and cities with sheep and cattle stock. The results showed that DNA detection of Francesella tularensis from rabbit tissues and ticks carried by cattle and sheep was positive. 12 out of 218 rabbit samples were positive (5.5% positive rate), and 15 tick samples were positive (3.1%) of 490 tick samples. In terms of geographical distribution, most of the positive rabbit samples were from Shandong, Henan and Sichuan province, however, ticks collected from Yunnan and Shandong province showed a higher positive rate. PCR detection showed that Francesella tularensis subspecies in this investigation was F.h, which was a subspecies with strong toxicity. This investigation revealed that Francesella tularensis presented in rabbits and ticks, public health and safety risks of Francesella tularensis existed in Shandong and Yunnan province, which should be paid more attention by the relevant scientific research institutions, medical institutions and government departments.     

Prevalence of bovine haemoparasites in Aceh province of Northern Sumatra: Implications for imported cattle

A limited seroepidemiological investigation was conducted in Aceh Province to determine the seroprevalence of Anaplasma marginale and Trypanosoma evansi in indigenous cattle and in groups of Sahiwal cross cattle imported from New Zealand in 1985. The results obtained suggest that these parasites are endemic in the areas surveyed; in local cattle, overall prevalence rates of 82% for A. marginale and 61% for T. evansi were obtained.

Thin blood smears were prepared from 42 anaemic adult cattle and 19 clinically normal calves. Babesia bigemina was detected in 5 blood smears and Theileria orientalis in 51. Sahiwal cattle imported from New Zealand suffered high mortalities during their first year in Aceh and it is suggested that imported naive cattle rapidly become infected with blood parasites.     

Estimates of within-herd incidence rates of Mycobacterium bovis in Canadian cattle and cervids between 1985 and 1994

We analysed the individual-animal data from six of the nine outbreaks of tuberculosis in Canadian cattle and cervids from 1985 to 1994. A “positive/reactor” animal was one which had either a positive culture or a positive or suspicious reaction on a mid-cervical, comparative cervical, or gross or histopathological test for tuberculosis. Individual-animal data were collected only for herds which had one or more positive/reactor animals. Data were collected from the outbreak records in the Regional or District offices of Agriculture and Agri-food Canada’s Animal and Plant Health Directorate. The within-herd spread of Mycobacterium bovis was studied by determining the most-likely date at which the herd was first exposed to M. bovis and the number of reactions which had developed by the time the herd was investigated. The animal-time units at risk in the herd were probably overestimated, resulting in conservative estimates of the within-herd incidence rates. Negative-binomial regression was used to investigate factors which might have influenced the within-herd spread of tuberculosis. Increasing age appeared to be a risk factor for being a positive/reactor animal. When compared to animals 0–12 months old, animals 13–24 months old had an incidence rate ratio (IRR) of 7.6, while animals >24 months old had an IRR of 10.4 (p=0.009). Actual and predicted incidence rates for tuberculosis in mature (>24 months old) animals were calculated. Actual and predicted incidence rates were similar for cervids, within an outbreak. There was more variability between actual and predicted rates in the dairy and beef animals. In the one outbreak (Ontario) where there were positive/reactor cervid, dairy and beef herds, the actual incidence rate for cervids (IR=9.3 cases per 100 animal-years) was almost twice that of dairy cattle (IR=5.0) and three times that of beef cattle (IR=3.1).     

Management factors associated with Babesia bovis seroprevalence in cattle from eastern Yucatán, Mexico.

The effect of management on the seroprevalence of Babesia bovis was studied in 399 Bos indicus cattle 1–2 years old from 92 farms in the eastern Yucatán, México. The management factors studied were: farm-type, production system, herd size, farm size, stocking density, vector control, dipping interval, type of dipping, type of acaricide and cattle introduction to the farm. A cross-sectional study was carried out (2-stage cluster sampling). The number of serum samples was proportionally distributed according to the number of farms in the nine locations of eastern Yucatán, México (399 animals from 92 farms). Antibody activity to B. bovis was tested using an indirect ELISA. The farms with a seroprevalence ≤75% were considered as cases and those with seroprevalence >75% were considered as controls. The variables with p ≤ 0.20 were included in fixed effects logistic regression. The seroprevalence of the zone was 73.8% (66.3–81.3%). The following risk factors were found: Stocking density (<1 head/ha, OR = 4.04, CI (OR) = 1.20–13.62) and dipping interval (>60 days, OR = 5.07 CI (OR) = 1.26–20.48).     

Estimating the distribution and abundance of Rhipicephalus appendiculatus in Africa

The brown ear tick Rhipicephalus appendiculatus is responsible for transmitting the parasite Theileria parva in eastern, central and southern Africa, where it causes East Coast fever, Corridor disease and January disease in cattle. In an effort to assess the impact of these diseases and their control on livestock production in the region, studies are underway to model the factors controlling the distribution of the vector tick. Three recent studies have attempted to quantify and evaluate the variables influencing the distribution of R. appendiculatus, and these are reviewed and discussed in this paper.

The relationship between the distribution of an ecoclimatic index of suitability for the tick, calculated by the model CLIMEX on a 25 km² interpolated climate database for Africa, and of recorded observations of the tick itself, are evaluated. The sensitivity and specificity of the ecoclimatic index were calculated as 70.2–82.6% and 69.4–84.7%, respectively. In addition, addition, satellite-derived mean maximum normalized difference vegetation index (NDVI) for 1987 was assessed as a predictor of R. appendiculatus habitat in eastern Africa, by comparing the distribution of NDVI values in areas in which the presence of the tick has and has not been recorded. Some visual correlation was observed between mean maximum NDVI values of 0.15 or greater and known R. appendiculatus distribution in Kenya. In addition, this range of NDVI values corresponded closely to areas in Ethiopia where the tick does not occur but for which climatic suitability was predicted by CLIMEX. However, these NDVI values should not be considered universal predictors of habitat suitable for R. appendiculatus, and further study of the NDVI with ground truthing of habitat is considered necessary.     

The sensitivity of PCR and serology in different Theileria parva epidemiological situations in Rwanda

Theileria parva is the causative agent of a lethal tick-borne disease of cattle occurring in eastern, central and southern Africa. Variations in the sensitivity of the serological and molecular tests with seasonal vector occurrence and discrepancies between low PCR prevalence and high T. parva vector density are a setback to estimate true prevalences. Therefore, the objectives of the present studies were to evaluate (1) the sensitivity of three serological tests (IFAT, ELISA and SELISA) and one molecular test (PCR) in the diagnosis of chronic T. parva infections in four different agro-ecological zones of Rwanda and (2) the effect of tick challenge and animal's age on the sensitivity of PCR. Blood samples from 635 bovines were collected in four agro-ecological zones of Rwanda. All sera were screened using the IFAT, ELISA, SELISA and PCR. The binary results of the four diagnostic tests were introduced separately for each agro-ecological zone in a Bayesian model to estimate the prevalence of T. parva infections and the sensitivity of the four diagnostic tests. All test specificities were set to 100%. The estimated T. parva prevalence was much higher (83–85%) than estimations based on single diagnostic tests. The estimated sensitivity of serological tests was relatively constant and ranged from 57 to 75% in the various areas. The sensitivity of PCR showed more pronounced variations, ranging from 66% in the low T. parva transmission (high land) zones compared to 24% in the highly vector infested (low land) zones. Calves and adult cattle (n = 194) were also sampled in regularly and irregularly dipped herds in the low land region. The apparent T. parva prevalence detected by PCR was significantly higher in calves than in adult cattle and in herds regularly treated with acaricides, while no significant differences were found with IFAT. The conditional probability that a sample was positive at PCR while it was positive at IFAT was significantly lower in adults. The implication of these findings in the use of diagnostic assays for epidemiological studies is discussed.     

PCR-based detection of Theileria ovis in Rhipicephalus bursa adult ticks

Tick-borne diseases in ruminants are common in tropical and subtropical regions and lead to meat and milk production losses. In this study, polymerase chain reaction (PCR) was used to assess the presence of Theileria ovis in Rhipicephalus bursa ticks. We have demonstrated that the PCR enabled detection of T. ovis in field isolates of R. bursa collected from naturally infested sheep and goats in eastern Turkey. The sampling was done in spring season (between May and June 2004). A total of 420 R. bursa were collected and randomly selected 192 number of them (97 female and 95 male) were dissected. Primers specific for 520 bp fragments small subunit ribosomal RNA (ssu rRNA) gene of T. ovis amplified products from 37 of the 192 (19.27%) samples. The parasite was detected in 17 (17.52%) female and in 20 (21.05%) male ticks. Two T. ovis amplicons from the tick samples were purified and sequenced. The resulting sequences were identical to the nucleotide sequence of the Turkish sheep strain of T. ovis. These results showed that R. bursa might play an important role in the field as a natural vector of T. ovis.     

Effect of agro-ecological zone and grazing system on incidence of East Coast Fever in calves in Mbale and Sironko Districts of Eastern Uganda

Between May 2002 and February 2003 a longitudinal survey was carried out in Mbale and Sironko Districts of Eastern Uganda to determine the influence of agro-ecological zones (AEZ) and grazing systems on tick infestation patterns and incidence of East Coast Fever (ECF) in bovine calves. The study area was stratified into AEZ (lowland, midland and upland) and grazing systems {zero grazing (ZG), restricted-outdoor grazing (ROG) and communal grazing (CG)}, whose strata had previously been shown to influence the prevalence of ECF, babesiosis and anaplasmosis. One hundred and eighty-five smallholder dairy farms with a total of 198 calves of both sexes, between the ages of 1 day and 6 weeks, were purposively selected from the AEZ–grazing system strata. Nine dynamic cohorts (11–51 calves in each) of these calves were examined and sampled monthly. Ticks infesting the calves were counted from one side of the animal body and categorized into the different species, sex and feeding status. Sera were collected at recruitment and monthly thereafter and antibodies against Theileria parva, T. mutans, Babesia bigemina, B. bovis and Anaplasma marginale were measured using ELISA. Tick challenge (total and specific) varied with AEZ and grazing system. The risk of infection with T. parva was higher in the lowland zone compared to the upland zone (hazard ratio (HR) = 2.59; 95% CI: 1.00–6.34). The risk of infection with T. parva was higher in the CG system than the ZG system (HR = 10.00; 95% CI: 3.61–27.92). The incidence risk for sero-conversion, over the 10 months study period, was 62, 16 and 9% in the lowland, midland and upland zones, respectively. Ninety-eight percent of the calves in lowland-CG stratum sero-converted by the age of 6 months, while 56 and 8% did so in the lowland-ROG and the lowland-ZG stratum, respectively. The results of this study show the need to consider farm circumstances and the variation in ECF risk, both spatially and temporally when designing control strategies for ECF.     

四川省甘孜州牦牛梨形虫感染情况的调查

试验旨在调查甘孜藏族自治州（甘孜州）全部18个县（市）牦牛梨形虫的感染情况。2018年6月至11月采集甘孜州18个县（市）临床健康牦牛全血1 381份,采用靶向18S rRNA的巢式PCR进行梨形虫核酸检测,并挑选梨形虫核酸检测阳性样本PCR产物共计124份测序鉴定虫种。结果显示,1 381份牦牛样本中梨形虫核酸阳性样本438份,平均阳性率为31.72%,其中半农半牧业县1 093份牦牛样本中梨形虫核酸阳性样本385份,平均阳性率为35.22%,纯牧业县288份牦牛样本中梨形虫核酸阳性样本53份,平均阳性率为18.40%;124份牦牛梨形虫核酸阳性样本中鉴定出感染的虫种有中华泰勒虫76份、吕氏泰勒虫25份、东方泰勒虫3份、绵羊泰勒虫2份、双芽巴贝斯虫1份和水牛泰勒虫1份,其中中华泰勒虫感染率为61.29%,吕氏泰勒虫感染率为20.16%。本试验结果表明,甘孜州牦牛梨形虫感染率较高,不同地区之间存在差异,优势虫种为中华泰勒虫和吕氏泰勒虫,为甘孜州牦牛梨形虫病防控提供了重要参考。     

Clearance of Theileria sergenti-infected bovine red blood cells in severe combined immune deficiency mice

Clearance of Theileria sergenti-infected bovine red blood cells (Bo-RBCs) from the blood circulation of severe combined immune deficiency (SCID) mice was studied to help understand the mechanisms of anemia developing in cattle infected with T. sergenti. For the clearance test, Bo-RBC samples having 2%, 58%, and 76% parasitemia and, as a control, parasite-free Bo-RBCs were prepared in the Bo-RBC-SCID mouse model. The T. sergenti-infected Bo-RBCs and the uninfected control Bo-RBCs were separately labeled with two, green and red, fluorescent dyes, mixed together, and injected intravenously into SCID mice. The blood samples collected at various time points were observed under a fluorescent microscope, and the numbers of green and red fluorescing RBCs were counted differentially to determine the clearance rates of T. sergenti-infected and uninfected Bo-RBCs. This test clearly demonstrated that the Bo-RBC samples having higher parasitemias were cleared faster from the blood circulation of SCID mice. The results suggest that the intravascular clearance system in SCID mice may have a mechanism by which T. sergenti-parasitized and non-parasitized Bo-RBCs are recognized and cleared differentially.     

Analysis of the IgG antibody response against Paramphistomidae trematoda in naturally infected cattle. Application to serological surveys

The IgG antibody response to Calicophoron daubneyi (Digenea: Paramphistomidae) excretory/secretory antigens was evaluated in naturally infected cattle from Lugo (Galicia, NW Spain) by using an ELISA procedure. Two studies were conducted, first a survey in 524 cattle separated into three groups according to age, G-1 (0–2 years old), G-2 (3–5 years old) and G-3 (>6 years old). In the second study, three groups of cattle were employed: G-I, naturally infected; G-T, naturally infected and treated with oxyclozanide plus levamisole (Nilzan Plus^®); G-C, cattle maintained in a farm where C. daubneyi has never diagnosed. Variations on egg-output and haematic parameters (erythrocytes, haematocrite, leukocytes and lymphocytes) were also analyzed.

The ELISA procedure showed that 61.2% of the cattle in the first study had been exposed to the trematode, but only 10.1% passed eggs in the feces. Age-association with egg-output was shown but not with the IgG values. In the second experiment, the administration of the anthelmintic reduced significantly the IgG kinetic levels and the C. daubneyi-egg-output was suppressed during 12 weeks in the G-T group. The values of red cells, haematocrite, leukocytes and lymphocytes increased significantly in the treated cattle 5 weeks after chemotherapy; however, new reduction after week 5 was recorded, as results of the challenge of these cattle.

This is the first investigation in which evaluation of the IgG humoral response against C. daubneyi in cattle has been carried out. We proved that a notable IgG response in naturally infected cattle is induced, and can be detected by using an ELISA procedure. The IgG antibodies did not increase after challenge infection. Our results proved an important percentage of cattle were exposed to this trematode in the area of study and suitable measures for preventing this relationship must be considered.     

Evaluation of an enzyme-linked immunosorbent assay kit to detect Babesia bovis antibodies in cattle

The sensitivity and specificity of an enzyme-linked immunosorbent assay (ELISA) to detect antibodies; to Babesia bovis was evaluated in 1000 sera from Holstein heifers. Five hundred of them were from cattle naturally or experimentally infected with B. bovis and 500 from uninfected heifers born and raised in a region free of the vector of cattle babesiosis. Additionally, the ELISA was evaluated and compared with an indirect immunofluorescent antibody (IFA) test in 374 heifers inoculated with different kinds of B. bovis antigens in four trials. The cross-reaction was also evaluated in 50 heifers infected with Babesia bigemina and 50 heifers infected with Anaplasma marginale. The mean percentage positivity of negative sera in relation to the ELISA strong positive sera was 8%. The seropositive/seronegative cutoff point was set as twice the mean percentage positivity of negative cattle sera ( = 16%). The sensitivity of the ELISA was 98% with a 95% confidence interval (CI) of 96–99%. The specificity was 95% (CI 93–97%). The agreement was 97% and the kappa value was 0.93. The predictive values of positive and negative results were 95% and 98% respectively. ELISA showed a similar sensitivity to that of the IFA test to detect antibodies to different B. bovis antigens. Its sensitivity ranged from 97.1% to 100% (CI 89–100%), while the sensitivity of the IFA test ranged from 92.8% to 100% (CI 83–100%). ELISA cross-reacted in 8% and 6% of the sera carrying B. bigemina and A. marginale antibodies, respectively, while the IFA showed 4% cross-reaction in each situation. The ELISA evaluated has the advantages of a proper sensitivity, objectivity and capacity to be adapted to test large number of samples in a short period of time. The results indicate that the ELISA is a suitable replacement for the IFA test to detect B. bovis antibodies in cattle sera, especially in epidemiological studies.     

Cattle transfers between herds under paratuberculosis surveillance in The Netherlands are not random

The rate and structure of cattle transfers between 206 Dutch cattle herds with a ‘Mycobacterium avium subsp. paratuberculosis (Map)-free’ status by November 2002, were analyzed over a 3-year period (November 1999–November 2002). Of the 206 ‘Map-free’ herds, 184 were closed herds during the period studied. In total, 280 cattle had been introduced into 22 herds at an average rate of 0.33 animals per year per 100 cattle present in the 206 herds. Assuming a random herd-contact structure, the observed rate of cattle transfers between certified ‘Map-free’ herds was sufficiently low to relax the surveillance scheme to biennial herd examinations by pooled fecal culture of all cattle ≥2 years of age.

The cattle transfers were not randomly distributed over the herds. Forty-four of the 280 cattle originated from 12 other ‘Map-free’ herds. The other 236 cattle did not originate from a ‘Map-free’ herd and were introduced into a herd before it obtained the ‘Map-free’ status. No cattle were introduced into any of the ‘Map-free’ herds from which cattle were transferred to other ‘Map-free’ herds. Thus, continued propagation of the infection by cattle transfers was impossible in the group of herds studied during the study period. Therefore the surveillance scheme may be further relaxed, and may be differentiated regarding the risk herds pose to other herds.     

Exposure of cattle immunized with different stocks of Theileria parva to buffalo-associated Theileria challenge on two game parks in Zimbabwe.

Eight cattle immunized with cattle-derived Theileria parva Boleni stabilate together with six susceptible controls were released in Dombawera Game Park on the Highveld of Zimbabwe. This coincided with Rhipicephalus appendiculatus nymphal activity. The cattle grazed together with African buffaloes (Syncerus caffer) and were not treated against tick infestation. The nymphal tick infestation was high, and seven of the eight immunized cattle and three of the controls had severe and fatal reactions. Subsequently, two stocks of Theileria parva to be tested for their immunizing abilities were prepared-one from adult ticks which were fed as nymphs on one of the sick control animals (Dom 268) and the other from adult ticks collected from pastures grazed by buffaloes (Bv-1). Two groups of cattle were immunized with either the Dom 268-derived strain (eight animals) or the Bv-1-derived strain (four animals). These together with three non-immunized controls, were released in Bally Vaughaun Game Park in the Highveld, where buffaloes are present, during the season of nymphal tick activity. A third group of five cattle, immunized with stabilate Bv-1, and three non-immunized controls were released at the same site during the season of adult tick activity. The nymphal and adult tick infestations of the cattle were large and more than 2000 nymphs and 1000 adult ticks were counted per animal. Cattle were treated with a pyrethroid pour-on preparation to control the tick infestation and screw-worm strike. The immunized cattle in the three groups survived the theileriosis challenge for a period of 18 months, but the non-immunized control cattle suffered a severe and fatal theileriosis 19-23 days after being placed on the pasture.