Effect of different methods of maintenance on the pathogenicity and infectivity of Babesia bigemina for the vector Boophilus microplus

Observations were made on the effects of five different methods of laboratory maintenance on the infectivity and virulence of Babesia bigemina for the tick Boophilus microplus. The original isolate was highly infective and virulent, causing premature death of engorged female ticks and reduced egg production. Maintenance of the strain by syringe passage in unsplenectomised calves at six to 10 week intervals reduced both its infectivity and virulence for ticks. When slow passages were preceded by a series of rapid passages in splenectomised calves, the changes to the strain were less pronounced. The other three procedures, rapid syringe passage in splenectomised calves and tick passage in either splenectomised or intact calves, had no statistically significant effect on the characteristics measured.     

DEVELOPMENT OF A HIGHLY INFECTIVE BABESIA BIGEMINA VACCINE OF REDUCED VIRULENCE

The virulence of a strain of Babesia bigemina was reduced by syringe passaging at 3 to 16-week intervals in a series of 7 calves. The calves were splenectomised 1 to 14 weeks after inoculation to induce the relapse parasitaemias used for passaging. Parasites taken at relapse from the last 3 calves in the series were inoculated into splenectomised calves from which highly parasitised blood for vaccine was obtained.
The vaccine produced mild infections in 32 recipient cattle. When challenged either 5 weeks or 7 months after vaccination, the cattle had substantial immunity to a heterologous strain of B. bigemina .     

甘肃省部分牛羊血液原虫传播媒介的实验研究

利用蜱传播试验,确定了甘肃省一些牛羊血液原虫的媒介和传播方式。甘肃省牛的双芽巴贝斯虫媒介为微小牛蜱。大巴贝斯虫媒介为长角血蜱。瑟氏泰 勒虫媒介为长角血蜱;绵羊无浆体的媒介为草原革蜱。微小牛蜱、长角血蜱可分别传播双芽巴贝斯虫和大巴贝斯虫,传播方式为经卵传递。将采集于甘肃文县牛体上的微小牛蜱和两当县的长角血蜱饱血雌虫孵育而来的次代幼虫分别叮咬除脾牛体后,２头牛各自感染双芽巴贝斯虫或大巴贝斯虫。将采自崇     

Detection of Babesia bigemina in cattle of different genetic groups and in Rhipicephalus (Boophilus) microplus tick

Babesia bigemina infections were investigated in four genetic groups of beef cattle and in Rhipicephalus (Boophilus) microplus engorged female ticks. Blood samples and engorged female ticks were collected from 15 cows and 15 calves from each of the following genetic groups: Nelore, Angus x Nelore, Canchim x Nelore, and Simmental x Nelore. Microscopic examination of blood smears and tick hemolymph revealed that merozoites of B. bigemina (6/60) as well as kinetes of Babesia spp. (9/549) were only detected in samples (blood and ticks, respectively) originated from calves. PCR-based methods using primers for specific detection of B. bigemina revealed 100% infection in both calves and cows, regardless the genetic group. Tick infection was detected by nested-PCR amplifications showing that the frequency of B. bigemina was higher (P<0.01) in female ticks collected from calves (134/549) than in those collected from cows (52/553). The frequency of B. bigemina was similar in ticks collected from animals, either cows or calves, of the four genetic groups (P>0.05).     

A note on the transmission of Babesia bovis (syn B argentina) by the one-host tick, Boophilus microplus.

Boophilus microplus infected with Babesia bovis were transferred artificially from one splenectomised calf to another during each moult in the parasitic life cycle of the tick. Eggs from the engorged female ticks recovered at the end of the cycle were incubated and the resulting larvae used to infest more splenectomised calves. Babesia bovis was transmitted only by the original larvae used at the commencement of the experiment and it was concluded that the protozoan parasite did not persist in an infective form in the ticks beyond the larval stage.     

Pentamidine in chemoimmunisation of cattle againstBabesia bigemina infection

A single dose of 0.5 to 1 mg/kg of Pentamidine led to clinical recovery of splenectomised calves infected with Babesia bigemina. On the other hand as much as 5 mg/kg administered during patency did not destroy the carrier state in intact calves. The fact that the sterilising dose was at least five times as great as that needed for clinical recovery makes Pentamidine a promising agent for chemoimmunisation against B. bigemina infection.     

Overcoming constraints to meeting increased demand for Babesia bigemina vaccine in Australia

Demand for live trivalent tick fever vaccine containing Babesia bovis, Babesia bigemina and Anaplasma centrale produced by the Department of Primary Industries, Queensland, has increased from less than 10,000 doses in 1988 to 500,000 doses in 2001. This paper describes a series of trials aimed at overcoming certain constraints to obtain B. bigemina parasitised erythrocytes (PEs) on a large enough scale from infected splenectomised calves to meet the demand. Passage through a series of splenectomised calves failed to increase the yield per calf but we showed that the dose rate of infected cells could be reduced from the long-time standard of 1x10(7) to 2.5x10(6) without affecting immunogenicity and still leaving a safety margin of at least 50-fold for infectivity. This change quadrupled the potential yield of doses per calf and allowed the DPI to meet the increased demand for B bigemina in vaccine. Due to the high cost and limited availability of suitable, health tested donors, calves previously infected with B. bovis or A. centrale were used to provide B. bigemina organisms but the practice resulted in red cell agglutination in some batches of prepared vaccine. A trial is described where B. bigemina-infected red cells were washed by centrifugation to remove agglutinating antibodies. Washing had no effect on parasite viability and this method is now in routine use in the production of trivalent vaccine.     

PCR-based detection of the transovarial transmission of Uruguayan Babesia bovis and Babesia bigemina vaccine strains

Bovine babesiosis is responsible for serious economic losses in Uruguay. Haemovaccines play an important role in disease prevention, but concern has been raised about their use. It is feared that the attenuated Babesia bovis and Babesia bigemina vaccine strains may be transmitted by the local tick vector Boophilus microplus, and that reversion to virulence could occur. We therefore investigated the possibility that these strains could be transmitted via the transovarial route in ticks using a Babesia species-specific polymerase chain reaction (PCR) assay. DNA was extracted from the developmental stages of the tick vector that had fed on calves immunized with the haemovaccine. It was possible to detect Babesia DNA not only in adult ticks, but also in their eggs and larvae. In addition, it was shown that calves infested with larvae derived from eggs laid by ticks fed on acutely infected calves, were positive for Babesia using PCR. Caution should therefore be shown with the distribution of the haemovaccine in marginal areas. It is still advisable that suitable tick control measures be used to prevent transovarial transmission and the potential risk of attenuated Babesia reverting to virulence.     

Babesia spp. infection in Boophilus microplus engorged females and eggs in Sao Paulo State, Brazil

Babesia spp. infections were investigated in Bos taurus x Bos indicus dairy cows and calves and in Boophilus microplus engorged female ticks and eggs. Blood samples and engorged female ticks were collected from 25 cows and 27 calves. Babesia spp. was detected in ticks by microscopic examination of hemolymph of engorged female and by squashes of egg samples. Cattle infection was investigated in blood thin smears and by DNA amplification methods (PCR and nested PCR), using specific primers for Babesia bovis and Babesia bigemina. Merozoites of B. bovis (3 animals) and B. bigemina (12 animals) were detected exclusively in blood smears of calves. DNA amplification methods revealed that the frequency of B. bigemina infection in calves (92.6%) and in cows (84%) and of B. bovis in calves (85.2%) and in cows (100%) did not differ significantly (P > 0.05). Babesia spp. infection was more frequent in female ticks and eggs collected from calves (P < 0.01) than from cows, especially in those which had patent parasitemia. Hatching rates of B. microplus larvae were assessed according to the origin of engorged females, parasitemia of the vertebrate host, frequency and intensity of infection in engorged female tick, and frequency of egg infection. Hatching rate was lower in samples collected from calves (P < 0.01) than from cows, and in those in which Babesia spp. was detected in egg samples (P < 0.01).     

Morphology and transmission of Theileria recondita (Theileriidae: Sporozoa) isolated from Haemaphysalis punctata from north Wales

Adult Haemaphysalis punctata (Canestrini and Fanzago 1877) collected from an area of rough grazing at Mynydd Mawr, Aberdaron, North Wales, transmitted Theileria recondita (Wales); field-collected nymphs failed to transmit this parasite. Following adult tick infestation, piroplasms were first observed in the blood of splenectomised infested sheep 8 days after tick attachment; the parasitaemia lasted 9 days. The parasite can also be transferred by syringe passage of blood from splenectomised to normal sheep and vice versa. Parasitaemias were higher and of longer duration in splenectomised animals. A rise in parasitaemia was detected in a splenectomised ewe after parturition, 19 months following blood-transmitted infection from which it had recovered clinically. The morphometrics of the piroplasms of T. recondita (Wales) were investigated; the rod and the ring forms were the most common. The mean length of the rod form was 2.09 microns and the mean diameter of the ring form was 1.22 micron.     

Attainment of endemic stability to Babesia bigemina in cattle on a South African ranch where non-intensive tick control was applied

The seroprevalence of Babesia bigemina and Babesia bovis antibodies in non-vaccinated cattle was monitored on a South African ranch. The main objective was to assess the endemic stability to bovine babesiosis in cattle maintained under relaxed tick-control measures. Cattle were bled at the age of 7, 8, 10, 17, 20 and 30-120 months and the sera tested for the presence of antibodies using the indirect fluorescent antibody (IFA) test. None of the animals were positive to B. bovis. Seroprevalence of B. bigemina antibodies was 46, 70, 90, 92, 54 and 82% in the various age classes, respectively. Endemic stability was therefore reached by the time the calves were 9 months old. The high seroprevalence of B. bigemina was probably due to the high vector tick population on the ranch, which would have encouraged frequent transmission of B. bigemina. An endemically stable situation to B. bigemina could therefore be achieved merely by adopting a tick-control method that allows a reasonable number of ticks on cattle rather than relying entirely on intensive tick control and vaccination.     

Babesia bigemina: attenuation of an Uzbek isolate for immunization of cattle with live calf- or culture-derived parasites

The virulence of an Uzbek isolate of Babesia bigemina, obtained from infected Boophilus annulatus ticks from an endemic area in Uzbekistan, was attenuated for immunization of cattle with autochthonous calf- or culture-derived parasites in Uzbekistan. After four "slow passages" in vivo the virulence was reduced, as evidenced by the response of calves inoculated with an experimental live frozen vaccine produced from the following passage. The vaccine was safe and protective against homologous virulent challenge under laboratory conditions. The culture-derived experimental vaccine was produced from cultures initiated after 3 passages in vivo followed by 22 passages in vitro. The cultured parasites did not elicit any clinical sign, but inoculated calves seroconverted following vaccination and were protected against the virulent homologous challenge. Both calf- and culture-derived vaccines were safe for cattle grazing in an endemic area in Uzbekistan. Despite the high polymorphism of B. bigemina, as reported from various geographical regions, the Central Asian strain was attenuated similarly to those that form the basis of the existing live B. bigemina vaccines in other parts of the world.     

Longevity of colonies of Anaplasma marginale in midgut epithelial cells of Dermacentor andersoni

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

The inability of a South African Babesia bovis vaccine strain to infect Boophilus microplus

A strain of Babesia bovis that had been attenuated by rapid syringe passage through a series of 23 splenectomized calves was unable to infect its vector Boophilus microplus. An attempt to transmit the attenuated Australian Babesia bigemina G strain with a South African strain of B. microplus was likewise unsuccessful. The epidemiological implication of these observations in terms of babesiosis control is discussed.     

Transmission of Babesia spp by the cattle tick (Boophilus microplus) to cattle treated with injectable or pour-on formulations of ivermectin and moxidectin

OBJECTIVE: To assess the efficacy of ivermectin and moxidectin to prevent transmission of Babesia bovis and Babesia bigemina by Boophilus microplus to cattle under conditions of relatively intense experimental challenge. DESIGN: Naive Bos taurus calves were treated with either pour-on or injectable formulations of either ivermectin or moxidectin and then exposed to larvae of B microplus infected with B bovis or larvae or adults of B microplus infected with B bigemina. One calf was used for each combination of haemoparasite, B microplus life stage, drug and application route. PROCEDURE: Groups of calves were treated with the test drugs in either pour-on or injectable formulation and then infested with B microplus larvae infected with B bovis or B bigemina. B bigemina infected adult male ticks grown on an untreated calf were later transferred to a fourth group of animals. Infections were monitored via peripheral blood smears to determine haemoparasite transmission. RESULTS: Cattle treated with either pour-on or injectable formulations of ivermectin and moxidectin became infected with B bovis after infestation with infected larvae. Similarly, larvae infected with B bigemina survived to the nymphal stage to transmit the haemoparasite to animals treated with each drug preparation. Cattle treated with pour-on formulations of ivermectin and moxidectin then infested with adult male ticks infected with B bigemina did not become infected with B bigemina whereas those treated with the injectable formulations of ivermectin and moxidectin did show a parasitaemia. CONCLUSIONS: Injectable or pour-on formulations of ivermectin and moxidectin do not prevent transmission of Babesia to cattle by B microplus. Use of these drugs can therefore not be recommended as a primary means of protecting susceptible cattle from the risk of Babesia infection.     

THE DURATION OF LATENT INFECTION AND FUNCTIONAL IMMUNITY IN DROUGHTMASTER AND HEREFORD CATTLE FOLLOWING NATURAL INFECTION WITH BABESIA ARGENTINA AND BABESIA BIGEMINA

Tne Droughtmaster and 9 Hereford cattle were born in an enzootic babesiasis area and became naturally infected with Babesia argentina and B.bigemina during a 3 year period. They were then kept free of cattle ticks (Boophilus microplus) for the remainder of the experiment. Annually for the next 3 years their individual infection status with Babesia was determined by sub-inoculation of blood into splenectomised calves. At the end of this period the functional immunity of all cattle was challenged by blood inoculation of heterologous strains of B. argentina and B. bigemina. Infection with B. argentina persisted in all Herefords for 2 years and in 7 for 3 years after they had been freed of B. microplus. The number of Droughtmasters with detectable B. argentina infection progressively declined, and at the end of 3 years only 2 of 10 were still infected. No Herefords were shown to be infected with B. bigemina following 1 year's freedom from B. microplus but latent B. bigemina infection of at least 2 year's duration was demonstrated in one of the Droughtmasters. A marked degree of resistance was apparent in all cattle when they were challenged with an heterologous strain of B. argentina. There were no differences between the response to challenge of the Herefords and Droughtmasters nor between the reactions of cattle which had apparently naturally sterilised B. argentina infection and those which were still infected. The heterologous strain of B. bigemina produced parasitaemia in the majority of animals but only minimal fever and anaemia resulted with no significant differences between the breeds.     

Infectivity and antigenicity of Anaplasma marginale from tick cell culture

The infectivity and immunogenicity of Anaplasma marginale grown in a tick cell culture from embryonic Dermacentor variabilis ticks were assessed in splenectomized and intact calves, respectively. Culture 1 consisted of the cell line inoculated with midguts of adult ticks infected with the Mississippi isolate of A marginale and dissected 5 to 10 days after repletion and detachment from an experimentally infected calf. Cultures 2 and 3 consisted of the cell line inoculated with midguts of ticks infected with the Virginia isolate of the organism. Inoculum for culture 2 was derived from nymphal ticks dissected 5 to 10 days after repletion and detachment from the infected calf; inoculum for culture 3 was midguts from adult ticks that were fed as nymphs, allowed to molt in the laboratory and dissected 21 to 24 days after molting. In trial 1, cultures 1, 2, and 3 were maintained at pH 6.9 and incubated at 28 C; in trial 2, cultures 1 and 3 were maintained at pH 7.4 and incubated at either 28 C or 37 C. Cultures 1, 2, and 3 failed to induce infection when injected IV and SC into 6 calves in 2 separate trials. Pre-challenge sera from these calves reacted with 2 purified Anaplasma antigens in the ELISA, but failed to react in the complement-fixation test. Results of a trial to use cultures 1 and 3 in combination with an oil-in-water adjuvant to immunize intact calves against A marginale were inconclusive. However, pre-challenge sera from immunized calves reacted with the 2 purified Anaplasma initial body antigens in the ELISA but failed to react in the complement-fixation text.(ABSTRACT TRUNCATED AT 250 WORDS)     

IMMUNITY IN CATTLE TO BABESIA BOVIS AFTER SINGLE INFECTIONS WITH PARASITES OF VARIOUS ORIGIN

Sixty calves, 3 to 6 months old, were vaccinated once against Babesia bovis in groups of 10, by the following methods: (a) tick infestation; (b) inoculation of virulent parasites obtained from the tick-infested animals immediately after infection; (c) inoculation of the parasites used in (b) attenuated by passage through splenectomised calves; (d) inoculation of commercially-available, living, attenuated vaccine; (e) inoculation of virulent parasites obtained from the tick-infested animals in (a) one year after infection; (f) inoculation of the parasites used in (e) attenuated by passage. All vaccinated animals were maintained tick-free and were strongly immune to challenge with a heterologous strain of B. bovis approximately 4 years after vaccination. There was no difference in immunogenicity between any of the B. bovis populations.     

甘肃省牛蜱传性血液原虫生物学特性研究及病原的分离

用病原检查法对甘肃省４２个县市的１３１１头牛进行了牛蜱传性血液原虫病的大面积调查,证实该省牛蜱传染性血液原虫的种类为双芽巴贝斯虫,大巴贝斯虫,瑟氏泰勒虫,环形泰勒虫及国边虫等５种病原,