Origin and history to date of the World Association for the Advancement of Veterinary Parasitology (WAAVP) African Foundation.

The origin of the World Association for the Advancement of Veterinary Parasitology (WAAVP) African Foundation is described. The 16th WAAVP Conference held in South Africa in 1997 generated a surplus of ZAR 430 460 (US$ 70 116). This was invested and a foundation established to manage the fund with the intention of using it to the mutual advantage of the WAAVP and African veterinary parasitologists. To date, more than 110 scholarship applications have been screened, and 51 full and partial scholarships awarded to young African veterinary parasitologists to attend subsequent biennial WAAVP Conferences. This investment has grown into a very successful endowment currently valued at US$ 206 553. This article is written in response to many queries across the globe about the origin of this fund and how it has been invested, managed, sustained and utilised.

Live vaccines against bovine babesiosis.

Bovine babesiosis is an important tick-borne disease caused by Babesia bovis, B. bigemina and B. divergens. The first steps taken in the development of an effective vaccination strategy against bovine babesiosis followed the observations that animals, recovered from natural infection with Babesia were strongly protected against subsequent challenge. Further investigation indicated that the use of donor blood from recovered animals to infect recipient animals did not produce the severe form of the disease. The past century has seen a refinement of this original carrier-donor system to one using attenuated less virulent strains with standardized doses of known parasite concentration to ensure reliability. With the implementation of good manufacturing practices further changes were necessary in the production of these vaccines, such as freezing for long-term storage to allow sufficient time for pre-release safety and effectivity testing. Regardless of these improvements the vaccines are not without problems and breakdowns and breakthroughs occur from time to time. Despite considerable research efforts into the development of alternative more consumer friendly vaccines, none is immediately forthcoming and the live attenuated babesiosis vaccines are still used in many countries.

Residual effect of antibabesial drugs on the live redwater blood vaccines.

It has been demonstrated that the attenuated organisms used in the unfrozen South African Babesia bovis and B. bigemina (redwater) vaccines are susceptible for longer periods to the residual effect of the anti-babesial drugs diminazene and imidocarb dipropionate than the virulent field strains. Reports of vaccine failures in some animals vaccinated with the frozen South African redwater vaccines after prophylactic treatment with imidocarb dipropionate have led us to reinvestigate the validity of the recommended prescribed waiting periods. Results indicated that waiting periods before administration of the frozen B. bovis and B. bigemina vaccines in animals that have been treated with diminazene at 3.5 mg/kg live weight, compare favorably with results initially obtained for the unfrozen vaccines at 4 and 8 weeks, respectively. However, the inhibitory effect of imidocarb dipropionate at 3.0 mg/kg live weight on the infectivity of both frozen B. bovis and B. bigemina vaccines is longer than previously anticipated and necessitated changing the minimum waiting periods before administration of these vaccines from 8 to 12 weeks and 16 to 24 weeks, respectively.

Expression of RoTat 1.2 cross-reactive variable antigen type in Trypanosoma evansi and T. equiperdum.

The variable antigen type (VAT) RoTat 1.2 has been cloned from a T. evansi strain, isolated in 1982 from a water buffalo in Indonesia. All T. evansi isolates hitherto tested express this VAT. In a study on the differential diagnosis of T. equiperdum and T. evansi in horses, we investigated serological evidence for the expression of RoTat 1.2 in 11 T. evansi and six T. equiperdum populations originating from Asia, Europe, Africa, and the Americas. Preinfection sera and sera of days 7, 14, 25, and 35 post-infection (p.i.) were analyzed for the presence of antibodies reactive with RoTat 1.2 in immune trypanolysis, ELISA/T. evansi and CATT/T. evansi. Within the duration of the experiment, all rabbits infected with T. evansi became positive in the three serological tests. Five out of six rabbits infected with T. equiperdum also became positive in the three tests. Only one T. equiperdum strain (the OVI strain from South Africa) did not induce the production of antibodies reactive with RoTat 1.2 and thus might not contain or express a VSG that shares epitopes similar to those on the RoTat 1.2 VSG. The data lead to the conclusion that T. equiperdum can express VSGs containing epitopes serologically similar to those in the T. evansi RoTat 1.2 VAT. This explains, in part, why the antibody detection tests based on Ro Tat 1.2 VSG cannot reliably distinguish between the infections caused by T. evansi and those caused by T. equiperdum. There are no data that contradict the possibility that the putative T. equiperdum strains, which express VSGs with epitopes similar to those on RoTat 1.2, are actually T. evansi.

An Anaplasma centrale DNA probe that differentiates between Anaplasma ovis and Anaplasma marginale DNA.

An Anaplasma centrale genomic library was constructed in pUC13. Two clones pAC5 and pAC137 hybridising to A. centrale and A. marginale DNA were isolated from this library. One of these, pAC5, also hybridised to DNA from A. ovis. The total insert of pAC5 was subcloned into pBR322. This subclone, pAC5-12, could detect 1 ng A. centrale, 0.5 ng A. marginale and 3.9 ng A. ovis DNA. The hybridisation pattern obtained with pAC5-12 on digests of A. centrale, A. marginale and A. ovis DNA suggests that this probe detects EcoR1 and Hind111-polymorphisms. Probe pAC5-12 could detect A. ovis DNA in 36% of blood samples tested compared to the 33% detectability obtained with microscopy.

Detection of Babesia equi in infected horses and carrier animals using a DNA probe.

The ability of the Babesia equi repetitive probes, pSE2 and pSB20, to detect parasites in blood from experimentally infected, naturally infected and carrier animals was tested using a spot hybridization assay. The clinical course of the experimentally infected horses was monitored using microscopy, indirect fluorescent antibody tests, packed cell volume, temperature and the probe assay. The probes sensitively monitored the parasite level during the development of the disease and correlated well with the other parameters tested. The sensitivity of the probe assay was superior to that of light microscopy, and a parasitaemia equivalent to less than 0.0025% could be detected. Detection of B. equi DNA was possible in all natural cases tested and 20 of the 119 randomly selected horses were identified as carriers of B. equi parasites. Microscopy could identify parasites in only 8 of these carrier animals. These results show that the probes can detect B. equi parasites in carrier animals and that they are suitable for use in a laboratory-based assay for B. equi.

Isolation of a South African vector-specific strain of Babesia canis.

A South African strain of Babesia canis parasites was isolated and shown to be vector-specific to only one of the two vectors in the region, Haemaphysalis leachi. This tick was found to transmit the parasite in its adult instar. When infected as larvae, the ticks would not transmit in the proceeding nymphal instar. The vector-specific strain was named the 'Thomas strain' after one of the dogs involved in isolating it. A survey revealed a prevalence of > 50% of this strain in four widely separated areas of the country. Rhipicephalus sanguineus, which transmits B. canis vogeli elsewhere, has not been shown to be a vector of the South African strain of B. canis.

The expression of RoTat 1.2 variable surface glycoprotein (VSG) in Trypanosoma evansi and T. equiperdum.

In order to define whether the variable antigenic type RoTat 1.2 is restricted to Trypansoma evansi and could be used as antigen in serological tests to differentiate T. evansi from Trypansoma equiperdum, the appearance of RoTat 1.2-specific antibodies in rabbits, experimentally infected with T. evansi and T. equiperdum, respectively, was analyzed. Ten strains of T. evansi and 11 strains of T. equiperdum originating from Asia, Europe, Africa and Latin America were tested. Rabbit pre-infection sera and sera of days 7, 14, 25, 35 post-infection (p.i.) were analyzed for the presence of antibodies reactive with RoTat 1.2 in immune trypanolysis, ELISA/T. evansi and CATT/T. evansi. Within the duration of the infection (maximum 35 days), all T. evansi as well as 9 out of 11 T. equiperdum infected rabbits became positive in all these tests. The rabbits infected with T. equiperdum OVI (South Africa) and BoTat 1.1 (Morocco) remained negative in the immune trypanolysis test although the latter rabbit became positive in the CATT/T. evansi and ELISA/T. evansi. On the contrary, both rabbits were positive in immune trypanolysis when tested against their respective infecting population. From these data, we conclude that most T. equiperdum strains express isoVATs of RoTat 1.2. This explains, in part, why antibody tests based on T. evansi RoTat 1.2 cannot reliably distinguish between infections caused by T. evansi and those caused by T. equiperdum unless it can be proven that most described T. equiperdum are actually misclassified T. evansi.

Risk factors to tick infestations and their occurrence on horses in the state of São Paulo, Brazil.

From December 1998 to March 1999, 40 stud farms were studied in the state of São Paulo, Brazil. During visits to farms, horses reared under grazing conditions were examined for the presence of ticks. On each farm visit, horse pastures were closely inspected and a questionnaire was given to the farm supervisor with the purpose of gaining information about ecological and management variables (independent variables) that could be associated with the presence and infestation levels of ticks on the farm (dependent variables). Three tick species were found during the study. Anocentor nitens, Amblyomma cajennense and Boophilus microplus were present on horses from 38 (95%), 20 (50%) and four (10%) farms, respectively. All farms that had A. cajennense or B. microplus infestations also had A. nitens infestations. Only one of the four farms with B. microplus infestations on the horses also had A. cajennense infestations. Two farms had all horses free of ticks. There was a strong association between the presence of infestation by B. microplus on horses and the simultaneous use of a grazing area by cattle and horses (P = 0.000). There was no statistical association between any of the independent variables and the presence or infestation level of A. nitens on the horses (P > 0.20). The presence of A. cajennense was statistically associated with the presence of at least one mixed overgrowth pasture in the farm (P = 0.001). A mixed overgrowth pasture means the presence of undesired plants such as bushes and shrubs in the pasture. The presence of high levels of A. cajennense on horses was also associated with the presence of at least one mixed overgrowth pasture in the farm (P = 0.026). The regular use of acaricides was statistically associated with the presence of ticks on the horses (P < 0.05), making this procedure a result of the inefficacy of controlling ticks on the farms. The occurrence of human infestation by ticks was statistically associated with the presence of A. cajennense on the horses (P=0.000). The presence of at least one mixed overgrowth pasture on the farm was associated (P = 0.000) to either higher horse densities and to farms that did not mow all the pastures once a year, indicating that mowing all the pastures at least once a year can be considered a protective factor against the presence of mixed overgrowth pastures on the farm, and consequently, against the presence of A. cajennense on the horses.

Diagnosis of parasitic disease.

Diagnosis of parasitic diseases requires highly sensitive and specific tests. In many cases the identification of parasites concerns their epidemiology and it is important to distinguish between species and subspecies. Conventional techniques including serology and microscopy do not always meet these requirements. The principle of nucleic acid probes is that a specific sequence of the parasite's DNA is isolated and used in a hybridisation assay to identify homologous parasite DNA from infected material. Since DNA normally remains the same during every stage of the parasite's life cycle this technique has many applications. The use of DNA diagnostics in the identification and differentiation of certain animal parasites is discussed.

A possible new piroplasm in lions from the Republic of South Africa.

A small piroplasm was detected in blood smears from lions (Panthera leo) in the Kruger National Park (KNP; Republic of South Africa) during 1991/1992. The parasite was identified provisionally as Babesia felis, but sera from these lions tested negative to B. felis antigen in the indirect immunofluorescent antibody test (IFAT). Blood from an infected lion was subsequently subinoculated into a domestic cat and two leopards in an attempt to identify the parasite. A lion also was infected with B. felis (from a cat). Serum samples collected from these animals were tested against B. felis, the KNP small piroplasm, and Cytauxzoon felis antigen in the IFAT. The serological results indicate that the KNP small piroplasm isolated from the lion is probably a distinct species from B. felis and C. felis.

The transovarial transmission of Babesia caballi by Hyalomma truncatum.

Babesia caballi, isolated from a horse that originated from South West Africa/Namibia, was transmitted transovarially by adult Hyalomma truncatum. B. caballi proved to be highly infective for adult H. truncatum. Forty-five per cent of ticks feeding on a reacting animal with an extremely low parasitaemia became infected. In spite of a low parasitaemia, the ticks were severely affected by the parasite. Seventy per cent of the infected ticks either died during oviposition or after laying only a few eggs. The features of the infection in horses were: a prepatent period of 10 days, very low parasitaemias with low pathogenicity and spontaneous recovery of the infected animals.

The transstadial transmission of Babesia caballi by Rhipicephalus evertsi evertsi.

Rhipicephalus evertsi evertsi larvae were fed on the ears of rabbits. Seven days after larval infestation, unfed, newly moulted nymphae were manually removed to infest a splenectomized donkey showing a patent Babesia caballi infection. Engorged nymphae were collected from the donkey and the ensuing adult ticks were placed on a susceptible horse. The horse contracted a B. caballi infection showing a prepatent period of 19 days after tick infestation. A very low parasitaemia, (highest score 2), which was patent for only 10 days, was recorded. The lowest packed cell volume recorded was 16%.

The fine structure of developmental stages of Babesia caballi in the salivary glands of Hyalomma truncatum.

The development of Babesia caballi in the salivary glands of Hyalomma truncatum was studied at the electron microscopic level. Kinetes were first observed in the salivary glands of ticks on Day 2 of tick feeding and on each subsequent day of feeding until engorgement on Day 8. Sporogony appeared to involve the formation of cytomeres. After continued nuclear division, sporozoites formed when individual rounded nuclei were incorporated into portions of cytoplasm. Sporozoites were first observed on Day 4 of tick feeding and contained typical Babesia spp. organelles with a polar ring and up to 4 rhoptries, spherical bodies, a nucleus, mitochondria, endoplasmic reticulum and micronemes. The infection rate in the ticks was approximately 80%.

An investigation into the clinical pathological changes and serological response in horses experimentally infected with Babesia equi and Babesia caballi.

Serologically negative horses, as determined with the indirect fluorescent antibody test (IFA), were infected with Babesia equi and 60 days later with Babesia caballi. The only clinical signs of disease observed in these animals were a febrile reaction and slight icterus. Haematological changes included a drop in haematocrit and haemoglobin concentration, as well as lowered platelet counts. The serum concentrations of albumin, iron and phosphorus were lowered. Mildly elevated serum bilirubin and fibrinogen concentrations were observed. Antibody titres were determined with the IFA and complement fixation (CF) tests. Antibodies to B. equi were first detected between Days 10-19 and 12-38 with the IFA and CF test, respectively, while the corresponding IFA periods for B. caballi were 6-8 days after infection. The parasitaemia of both B. equi and B. caballi infections never reached the 1% level.

In vitro cultivation of Babesia equi: detection of carrier animals and isolation of parasites.

By means of an in vitro culture technique, 75 samples of horse blood were examined for Babesia equi, a causative agent of equine piroplasmosis. At the time of culture initiation, 15 samples were microscopically positive for B. equi, and this was subsequently confirmed by culture diagnosis. Sixty samples showed no parasites in Giemsa-stained thin blood smears. However, after the culturing process, parasites were found in blood smears of 36 of these samples. The sensitivity of the in vitro culture method was such that 2.5 microliters (1/40 of the usual volume used for the above-mentioned samples) of packed erythrocytes obtained from a carrier horse still yielded positive results after cultivation. Cultures were initiated from blood samples stored for up to 120 h at 8 degrees C in vacuum tubes containing EDTA as anticoagulant. These results show that the in vitro culture method is highly sensitive. It can be used to identify B. equi carrier horses, to evaluate the effects of chemotherapeutic intervention, and to isolate field strains of B. equi for further characterization.

A sero-epidemiological survey of blood parasites in cattle in the north-eastern Free State, South Africa.

A survey to determine the incidence of parasites in cattle (n = 386) was conducted in the north eastern Free State between August 1999 and July 2000. Giemsa-stained blood smears were negative for blood parasites. A total of 94% of the cattle were sero-positive for Babesia bigemina by indirect fluorescent antibody test while 87% were sero-positive for Anaplasma by enzyme-linked immunosorbent assay. The observation of negative blood smears but high incidence of positive serological results for Anaplasma and Babesia for the same group of cattle indicates that this area is endemic for these diseases but with a stable disease situation. All the animals were sero-negative for B. bovis and this is probably because the tick vector (Boophilus microplus) which transmits the disease is not present in the Free State Province. Two tick species belonging to the family ixodidae were found on cattle, namely Boophilus decoloratus and Rhipicephalus evertsi evertsi. In the present study significant differences in seasonal burdens of B. decoloratus occurred, with the highest infestations recorded from February to June. The presence of R. evertsi evertsi throughout the year without any or with small fluctuations in winter months was observed, with a peak from February to May.

The transovarial transmission of Babesia trautmanni by Rhipicephalus simus to domestic pigs.

Rhipicephalus simus was, for the first time, experimentally proven to be a transovarial vector of Babesia trautmanni of domestic pigs. The nymphal and adult progeny of experimentally infected female ticks transmitted the infection to 2 susceptible splenectomized pigs. Features of the infection included a prepatent period of 6-8 days post-tick infestation, a febrile reaction for 3 days and a maximum parasitaemia score of 15 (more than 6 parasites per 300 red blood cells). Other clinical signs in both pigs were mild inappetence and listlessness. Both pigs recovered without any antibabesial therapy.

Chemotherapy of experimental Besnoitia besnoiti infection in rabbits.

Rabbits were infected with a bovine strain of Besnoitia besnoiti parasites derived from VERO cell cultures. Oxytetracycline, given at 30 mg/kg i.m. simultaneously with infection, prevented the development of orchitis. The controls received no treatment. All infected animals showed a transient febrile reaction. It is concluded that oxytetracycline has some therapeutic potential against Besnoitia besnoiti and that rabbits are suitable models for therapeutic trials.

A survey of the incidence and importance of the tick-borne diseases heartwater, redwater and anaplasmosis in the heartwater-endemic regions of South Africa.

In an almost 50% response to a survey questionnaire, farmers in the heartwater-endemic regions of South Africa indicated that they were experiencing losses of 1.3, 0.3 and 0.2% in cattle due to heartwater, redwater and anaplasmosis, respectively. In small stock, the heartwater mortality was 3.8%. Only 35% of cattle farmers and 15% of farmers keeping sheep and goats, vaccinate their animals against heartwater. It would seem that the present vaccine does not control heartwater adequately and, with 9% of farmers claiming poor protection after immunization, it would be difficult to recommend wider use of the heartwater vaccine. Likewise, vaccination against redwater and anaplasmosis on 11.8 and 14.2% of farms, respectively, appears to have had no beneficial effect on the mortality rates of these diseases. Many farmers still believe that very few or no ticks should be seen on cattle. In fact, it would appear that a considerable proportion of farmers find so few ticks on their cattle, that the frequency of acaricidal treatment is in many cases too high. Although there is no correlation between the incidence of heartwater and the intensity of tick control, there is also no serological evidence to support the possibility of an endemically unstable condition. The concept that endemic stability as a means to control heartwater in cattle can be achieved by allowing more ticks on animals, has not yet been established. The overall impression is that farmers do not regard heartwater in cattle as such a serious problem as it is generally believed to be.(ABSTRACT TRUNCATED AT 250 WORDS)