The virulence of four South African field isolates of NAD-dependent Haemophilus paragallinarum and two field isolates of NAD-independent H. paragallinarum has previously been tested in unvaccinated chickens. In this study, the disease profiles caused by the NAD-dependent isolates of H. paragallinarum in vaccinated chickens were studied. It was shown that the clinical signs induced in the vaccinated chickens were substantially less severe than were those in unvaccinated chickens, as was expected. However, due to the high virulence of the serovar C-3 isolates, clinical signs in the vaccinated chickens challenged with this isolate were still detected. These were as severe as those occurring in unvaccinated chickens challenged with serovar B-1 isolates. Although the clinical signs induced in unvaccinated birds challenged with serovar A-1 were more severe than those occurring when vaccinated birds were challenged with serovar C-3, the overall disease profiles were similar. Substantial clinical signs were recorded in vaccinated birds challenged with serovar C-3. This could be interpreted as vaccination failure if the disease profile obtained in unvaccinated birds is not considered. It was found that a high level of protection was provided by this vaccine against challenge by serovar C-3. The high virulence of this serovar resulted in the development of clinical signs in vaccinated birds. These findings could possibly explain the large number of so-called vaccination failures that are reported in South Africa.

The virulence of four South African field isolates of NAD-dependent Haemophilus paragallinarum and two field isolates of NAD-independent H. paragallinarum has previously been tested in unvaccinated chickens. In this study, the disease profiles caused by the NAD-dependent isolates of H. paragallinarum in vaccinated chickens were studied. It was shown that the clinical signs induced in the vaccinated chickens were substantially less severe than were those in unvaccinated chickens, as was expected. However, due to the high virulence of the serovar C-3 isolates, clinical signs in the vaccinated chickens challenged with this isolate were still detected. These were as severe as those occurring in unvaccinated chickens challenged with serovar B-1 isolates. Although the clinical signs induced in unvaccinated birds challenged with serovar A-1 were more severe than those occurring when vaccinated birds were challenged with serovar C-3, the overall disease profiles were similar. Substantial clinical signs were recorded in vaccinated birds challenged with serovar C-3. This could be interpreted as vaccination failure if the disease profile obtained in unvaccinated birds is not considered. It was found that a high level of protection was provided by this vaccine against challenge by serovar C-3. The high virulence of this serovar resulted in the development of clinical signs in vaccinated birds. These findings could possibly explain the large number of so-called vaccination failures that are reported in South Africa.

A survey to determine the prevalence of bovine tuberculosis caused by Mycobacterium bovis and certain other infectious diseases was conducted on 42 free-ranging African buffaloes, (Syncerus caffer) from May to June 1997 in the Queen Elizabeth National Park, Uganda. Using the gamma interferon test, exposure to M. bovis was detected in 21.6 % of the buffaloes. One dead buffalo and an emaciated warthog (Phacochoerus aethiopicus) that was euthanased, were necropsied; both had miliary granulomas from which M. bovis was isolated. None of the buffaloes sampled in Sector A of the park, which has no cattle interface, tested positive for bovine tuberculosis (BTB) exposure. The prevalence and distribution of BTB does not appear to have changed significantly since the 1960s, but this may be due to fluxes in the buffalo population. Serological testing for foot-and-mouth disease (FMD) demonstrated positive exposure of 57.1% of the buffaloes sampled, with types A, O and SAT 1-3, which is the first known report of FMD antibodies to A and O types in free ranging African buffaloes. Foot-and-mouth disease virus types SAT 1 and SAT 3 were isolated from buffalo probang samples. Two percent of the buffaloes had been exposed to brucellosis. None of the buffaloes tested had antibodies to rinderpest, leptospirosis or Q fever.

A survey to determine the prevalence of bovine tuberculosis caused by Mycobacterium bovis and certain other infectious diseases was conducted on 42 free-ranging African buffaloes, (Syncerus caffer) from May to June 1997 in the Queen Elizabeth National Park, Uganda. Using the gamma interferon test, exposure to M. bovis was detected in 21.6 % of the buffaloes. One dead buffalo and an emaciated warthog (Phacochoerus aethiopicus) that was euthanased, were necropsied; both had miliary granulomas from which M. bovis was isolated. None of the buffaloes sampled in Sector A of the park, which has no cattle interface, tested positive for bovine tuberculosis (BTB) exposure. The prevalence and distribution of BTB does not appear to have changed significantly since the 1960s, but this may be due to fluxes in the buffalo population. Serological testing for foot-and-mouth disease (FMD) demonstrated positive exposure of 57.1% of the buffaloes sampled, with types A, O and SAT 1-3, which is the first known report of FMD antibodies to A and O types in free ranging African buffaloes. Foot-and-mouth disease virus types SAT 1 and SAT 3 were isolated from buffalo probang samples. Two percent of the buffaloes had been exposed to brucellosis. None of the buffaloes tested had antibodies to rinderpest, leptospirosis or Q fever.

Aqueous decoctions obtained from the galls of Guiera senegalensis were screened to determine their phytochemical composition and in vitro antiviral activity against fowlpox virus. In addition, we wanted to investigate the toxic effects, if any, of crude extracts in chickens. Steroids as well as cardiac glycosides not previously reported, an alkaloid, polyphenols and saponins were detected in the various fractions of organic solvents used for extracting the decoctions. Antiviral activity was determined by cytopathic effect inhibition assay in primary chicken embryo skin cells. The 50 % inhibitory concentration (EC50) was shown to be 15.6 µg/ml. Toxicity for cells was established by determining the 50 % cytotoxic concentration (CCy50). A value of 90 µg/ml and a selectivity index (CCy50/EC50) of 5.8 were obtained. In vivo studies of toxicity were performed in chickens that were dosed orally with decoctions of several concentrations for 2 weeks and then monitored for 3 months. No significant changes in several blood chemical parameters were obtained, except for a significant decline in SGOT levels in birds dosed with 100 mg/kg. These levels were nevertheless within the accepted normal range. The findings suggest that aqueous decoctions of galls from G. senegalensis are non-toxic for chickens when administered orally, even at a daily dose of 100 mg/kg for 14 days.

Aqueous decoctions obtained from the galls of Guiera senegalensis were screened to determine their phytochemical composition and in vitro antiviral activity against fowlpox virus. In addition, we wanted to investigate the toxic effects, if any, of crude extracts in chickens. Steroids as well as cardiac glycosides not previously reported, an alkaloid, polyphenols and saponins were detected in the various fractions of organic solvents used for extracting the decoctions. Antiviral activity was determined by cytopathic effect inhibition assay in primary chicken embryo skin cells. The 50 % inhibitory concentration (EC50) was shown to be 15.6 g/ml. Toxicity for cells was established by determining the 50 % cytotoxic concentration (CCy50). A value of 90 g/ml and a selectivity index (CCy50/EC50) of 5.8 were obtained. In vivo studies of toxicity were performed in chickens that were dosed orally with decoctions of several concentrations for 2 weeks and then monitored for 3 months. No significant changes in several blood chemical parameters were obtained, except for a significant decline in SGOT levels in birds dosed with 100 mg/kg. These levels were nevertheless within the accepted normal range. The findings suggest that aqueous decoctions of galls from G. senegalensis are non-toxic for chickens when administered orally, even at a daily dose of 100 mg/kg for 14 days.

Theileria parva-naïve 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.

Theileria parva-nave 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.

Two hundred and twenty-five small mammals belonging to 16 species were examined for ticks in Free State, Mpumalanga and Limpopo Provinces, South Africa, and 18 ixodid tick species, of which two could only be identified to genus level, were recovered. Scrub hares, Lepus saxatilis, and Cape hares, Lepus capensis, harboured the largest number of tick species. In Free State Province Namaqua rock mice, Aethomys namaquensis, and four-striped grass mice, Rhabdomys pumilio, were good hosts of the immature stages of Haemaphysalis leachi and Rhipicephalus gertrudae, while in Mpumalanga and Limpopo Provinces red veld rats, Aethomys chrysophilus, Namaqua rock mice and Natal multimammate mice, Mastomys natalensis were good hosts of H. leachi and Rhipicephalus simus. Haemaphysalis leachi was the only tick recovered from animals in all three provinces.

Two hundred and twenty-five small mammals belonging to 16 species were examined for ticks in Free State, Mpumalanga and Limpopo Provinces, South Africa, and 18 ixodid tick species, of which two could only be identified to genus level, were recovered. Scrub hares, Lepus saxatilis, and Cape hares, Lepus capensis, harboured the largest number of tick species. In Free State Province Namaqua rock mice, Aethomys namaquensis, and four-striped grass mice, Rhabdomys pumilio, were good hosts of the immature stages of Haemaphysalis leachi and Rhipicephalus gertrudae, while in Mpumalanga and Limpopo Provinces red veld rats, Aethomys chrysophilus, Namaqua rock mice and Natal multimammate mice, Mastomys natalensis were good hosts of H. leachi and Rhipicephalus simus. Haemaphysalis leachi was the only tick recovered from animals in all three provinces.

Hyalomma anatolicum anatolicum nymphs were collected from two localities in the Sudan: Eddamer in Northern Sudan and Wad-Medani in Central Sudan. They were allowed to moult to adult ticks, which were assessed for Theileria infection in their salivary glands using Feulgen stain. At Eddamer, 49.6 % of 123 ticks examined were infected with Theileria and the mean intensity of infection was 1.3 (i.e. the number of infected acini / number of infected ticks). At Wad-Medani, 8.6 % of 162 ticks were infected and the mean intensity of infection was 7.9. The prevalence of infection was higher in female than in male ticks at both localities. When adult H. a. anatolicum were applied onto two susceptible calves, both animals developed the severe form of theileriosis.

Hyalomma anatolicum anatolicum nymphs were collected from two localities in the Sudan: Eddamer in Northern Sudan and Wad-Medani in Central Sudan. They were allowed to moult to adult ticks, which were assessed for Theileria infection in their salivary glands using Feulgen stain. At Eddamer, 49.6 % of 123 ticks examined were infected with Theileria and the mean intensity of infection was 1.3 (i.e. the number of infected acini / number of infected ticks). At Wad-Medani, 8.6 % of 162 ticks were infected and the mean intensity of infection was 7.9. The prevalence of infection was higher in female than in male ticks at both localities. When adult H. a. anatolicum were applied onto two susceptible calves, both animals developed the severe form of theileriosis.

Studies on the trypanotolerance of Orma Boran X Maasai Zebu (Orma Zebu) crossbred cattle (F1 progeny) and pure-bred Maasai Zebu contemporaries were carried out in Nguruman, south western Kenya. The two groups were monitored from birth for a period of 2 years. The incidence of trypanosomosis, parasitaemia, packed cell volume (PCV), body mass and average daily mass gain were monitored. During the study period, overall trypanosomosis incidence was low (3 %). The crossbred cattle had a higher incidence of infection (61 % vs 39 %). The mean PCV and mean mass gain for the crossbred cattle was higher than that of the Maasai Zebu. The mean calf body mass at weaning (8 months) for the Orma Zebu and Maasai Zebu was 72 kg and 64 kg, respectively, while at 18 months of age their mean body mass was 164 kg and 123 kg, respectively. During the rainy season significant differences in average daily mass gains were noted (P < 0.05). The superior mass gain of the Orma Zebu observed during the rainy season, despite higher infection rates, indicate an enhanced trypanotolerance. Moreover, the better performance of the Orma Zebu is an attribute that could be exploited in the adoption of the trypanotolerance genotype, as a sustainable trypanosomosis control strategy.

Studies on the trypanotolerance of Orma Boran X Maasai Zebu (Orma Zebu) crossbred cattle (F1 progeny) and pure-bred Maasai Zebu contemporaries were carried out in Nguruman, south western Kenya. The two groups were monitored from birth for a period of 2 years. The incidence of trypanosomosis, parasitaemia, packed cell volume (PCV), body mass and average daily mass gain were monitored. During the study period, overall trypanosomosis incidence was low (3 %). The crossbred cattle had a higher incidence of infection (61 % vs 39 %). The mean PCV and mean mass gain for the crossbred cattle was higher than that of the Maasai Zebu. The mean calf body mass at weaning (8 months) for the Orma Zebu and Maasai Zebu was 72 kg and 64 kg, respectively, while at 18 months of age their mean body mass was 164 kg and 123 kg, respectively. During the rainy season significant differences in average daily mass gains were noted (P 0.05). The superior mass gain of the Orma Zebu observed during the rainy season, despite higher infection rates, indicate an enhanced trypanotolerance. Moreover, the better performance of the Orma Zebu is an attribute that could be exploited in the adoption of the trypanotolerance genotype, as a sustainable trypanosomosis control strategy.

The objective of this study was to determine whether Bos taurus cattle differ form Bos indicus in their susceptibility to infection with the Muguga stabilate of Theileria parva and in their resistance to the resultant disease. Ten Friesians (B. taurus), ten improved Borans (B. indicus), ten unimproved Borans (B. indicus) and ten Zebus (B. indicus) born to dams from an East Coast fever (ECF) endemic area were inoculated with an infective dose50 dilution of T. parva Muguga stabilate 147. All the animals except one Friesian and one Zebu developed schizont parasitosis. All the improved Borans, nine of the Friesians, eight of the unimproved Borans and six of the Zebus developed a febrile response. Four of the improved Borans, four of the Friesians and three of the unimproved Borans died of theileriosis. No significant difference (P > 0.05) in the prepatent period occurred between the groups, but the Zebus had a significantly shorter duration of schizont parasitosis (P > 0.05) and took a significantly shorter time to recover (P > 0.05) than the other three groups. There was no significant difference in the two parameters between the other three groups. The study showed that three B. indicus breds and a B. taurus breed are equally susceptible to T. parva infection. However, Zebus born to dams from an ECF endemic area showed a better ability to control the course of disease than cattle from ECF free areas.

The objective of this study was to determine whether Bos taurus cattle differ form Bos indicus in their susceptibility to infection with the Muguga stabilate of Theileria parva and in their resistance to the resultant disease. Ten Friesians (B. taurus), ten improved Borans (B. indicus), ten unimproved Borans (B. indicus) and ten Zebus (B. indicus) born to dams from an East Coast fever (ECF) endemic area were inoculated with an infective dose50 dilution of T. parva Muguga stabilate 147. All the animals except one Friesian and one Zebu developed schizont parasitosis. All the improved Borans, nine of the Friesians, eight of the unimproved Borans and six of the Zebus developed a febrile response. Four of the improved Borans, four of the Friesians and three of the unimproved Borans died of theileriosis. No significant difference (P 0.05) in the prepatent period occurred between the groups, but the Zebus had a significantly shorter duration of schizont parasitosis (P 0.05) and took a significantly shorter time to recover (P 0.05) than the other three groups. There was no significant difference in the two parameters between the other three groups. The study showed that three B. indicus breds and a B. taurus breed are equally susceptible to T. parva infection. However, Zebus born to dams from an ECF endemic area showed a better ability to control the course of disease than cattle from ECF free areas.