The objective of this study was to determine certain aspects of the biology of Rhipicephalus (Boophilus) decoloratus larvae under laboratory and field conditions. Larvae allowed 48 h to select a vertical questing substrate preferred 90 cm rods in length to those of 60 or 30 cm, while in a separate experiment migration from rods 5 cm or 25 cm in length to rods 45 cm in length continued between 48 h and 72 h after larval release. Hatching of the larval progeny of engorged female ticks exposed to ambient field temperatures during the period June to August, occurred synchronously during the third or fourth week of November. With a single exception, larvae that hatched during November and between April and July survived for 38 days or longer, while those that hatched from December to March survived for 31 days or less. Questing larvae were present on vegetation throughout the year, with most being recovered during January and February. Parasitic larvae were present on cattle from October to May with most being collected during January and February.

Six pregnant gilts were purchased from a high health herd and were found to be serologically positive for swine influenza virus (SIV) subtype H3N2. Three of the gilts, at 80 to 82 days of gestation, were experimentally exposed a second time to the same SIV subtype --- H3N2. No clinical signs resulted from the second exposure to SIV and hemagglutination-inhibition (HI) titers for SIV at 4 weeks postexposure were unchanged suggesting that the gilts had not been reinfected. However, the second exposure to SIV affected the number of pigs born alive. Each of the 3 litters from the twice exposed gilts suffered 2 or 3 stillborn piglets per litter. In contrast the 3 matched, sero-positive gilts that were not exposed to SIV (controls) had no stillborn piglets. These differences were statistically significant using a t-test for unequal variances (P = 0.0086). Sera from 2 of the stillborn piglets were negative for HI antibodies and there was no indication from the pigs born alive that the H3N2 virus had crossed the placenta.

The protective efficacy of isometamidium chloride (ISMM) and diminazene aceturate (DIM) against Trypanosoma brucei, Trypanosoma congolense and Trypanosoma vivax infections in cattle under a suppressed tsetse population was assessed in southeast Uganda. A total of 66 and 57 trypanosome-infected cattle were treated with ISMM and DIM, respectively together with 177 trypanosomefree animals not treated were followed for 12 months, checked every 4 weeks. There was no statistical difference in the mean time to infection with any trypanosome species in animals treated with ISMM or DIM. However, the mean time to trypanosome infection was significantly longer for treated animals than controls. The mean time to infection with each of the three trypanosome species differed significantly, with the average time to T. vivax infection the lowest, followed by T. congolense and then T. brucei. The protective efficacy of DIM was as good as that of ISMM; implying curative treatments against trypanosomosis are sufficient for combination with tsetse control. Isometamidium chloride or DIM had the highest impact on T. brucei and T. congolense infections in cattle.

The crude prevalence of antibodies to Babesia bovis infection in cattle was estimated by serology using indirect ELISA during the period January to April, 1999. Sera were obtained from 1 395 dairy cattle (of all ages, sexes and breeds) on smallholder farms, the majority being kept under a zero grazing regime. The crude prevalence of antibodies to Babesia bovis was 6 % for Tanga and 12% for Iringa. The forces of infection based on the age sero-prevalence profile, were estimated at six for Iringa and four for Tanga per 100 cattle years-risk, respectively. Using random effect logistic regression as the analytical method, the factors (variables) of age, source of animals and geographic location were hypothesised to be associated with sero-positivity of Babesia bovis in the two regions.

Lice have been described on goats in commercial farming systems in South Africa but not from flocks on communal grazing. During a longitudinal survey on the causes of goat kid mortality, conducted in Jericho district, North West Province, lice were collected from communally grazed indigenous goats. These lice were prepared for and viewed by scanning electron microscopy, and micromorphological taxonomic details are described. Three species of lice were found in the study area and identified as Bovicola caprae, Bovicola limbatus and Linognathus africanus. Sucking and biting lice were found in ten of the 12 herds of goats examined. Lice were found on both mature goats and kids. Bovicola caprae and L. africanus were the most common biting and sucking lice respectively in all herds examined. Scanning electron microscopy revealed additional features which aided in the identification of the louse species. Photomicrographs were more accurate aids to identification than the line drawings in the literature and facilitated identification using dissecting microscope.

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

White-tailed deer are susceptible to heartwater (Ehrlichia [Cowdria] ruminantium infection) and are likely to suffer high mortality if the disease spreads to the United States. It is vital, therefore, to validate a highly specific and sensitive detection method for E. ruminantium infection that can be reliably used in testing white-tailed deer, which are reservoirs of antigenically or genetically related agents such as Ehrlichia chaffeensis, Anaplasma (Ehrlichia) phagocytophilum (HGE agent) and Ehrlichia ewingii. Recently, a novel but as yet unnamed ehrlichial species, the white-tailed deer ehrlichia (WTDE), has been discovered in deer populations in the United States. Although the significance of WTDE as a pathogen is unknown at present, it can be distinguished from other Ehrlichia spp. based on 16S rRNA gene sequence analysis. In this study it was differentiated from E. ruminantium by the use of the pCS20 PCR assay which has high specificity and sensitivity for the detection of E. ruminantium. This assay did not amplify DNA from the WTDE DNA samples isolated from deer resident in Florida, Georgia and Missouri, but amplified the specific 279 bp fragment from E. ruminantium DNA. The specificity of the pCS20 PCR assay for E. ruminantium was confirmed by Southern hybridization. Similarly, the 16S PCR primers (nested) that amplify a specific 405-412 bp fragment from the WTDE DNA samples, did not amplify any product from E. ruminantium DNA. This result demonstrates that it would be possible to differentiate between E. ruminantium and the novel WTDE agent found in white tailed deer by applying the two respective PCR assays followed by Southern hybridizations. Since the pCS20 PCR assay also does not amplify any DNA products from E. chaffeensis or Ehrlichia canis DNA, it is therefore the method of choice for the detection of E. ruminantium in these deer and other animal hosts.

A paramyxovirus with a thermostability of 60 min (typical of velogenic viruses) and a mean death time of > 90 h (typical of lentogenic viruses) was isolated from layers near Mooi River, South Africa. Our results, based on comparative nucleotide sequence data indicated that the virus is pigeon paramyxovirus 1 (PPMV-1), a variant of Newcastle disease virus. The F0 cleavage site contains a 112RRKKRF117 motif, and the virus had 98 % sequence identity with PPMV-1 strains from the Far East. PPMV-1 was last reported in South Africa during the 1980s, with this being the first report of PPMV-1 isolated from chickens in South Africa.

The region involved in export of the capsule polysaccharides to the cell surface of Haemophilus paragallinarum was cloned and the genetic organisation determined. Degenerate primers designed from sequence alignment of the capsule transport genes of Haemophilus influenzae, Pasteurella multocida and Actinobacillus pleuropneumoniae were used to amplify a 2.6 kb fragment containing a segment of the H. paragallinarum capsule transport gene locus. This fragment was used as a digoxigenin labelled probe to isolate the complete H. paragallinarum capsule transport gene locus from genomic DNA. The sequence of the cloned DNA was determined and analysis revealed the presence of four genes, each showing high homology with known capsule transport genes. The four genes were designated hctA, B, C and D (for H. paragallinarum capsule transport genes) and the predicted products of these genes likely encode an ATP-dependent export system responsible for transport of the capsule polysaccharides to the cell surface, possibly a member of a super family designated ABC (ATP-binding cassette) transporters.

years, but recently there have been reports of prophylaxis failure under natural conditions. In this study, use of the drug for prophylactic purpose against trypanosomosis in small ruminants was investigated. Forty-two sheep and 44 goats were divided into four treatment groups. Groups 1 and 2 were treated with isometamidium chloride (Samorin(R), Rhone Merieux, Lyon, France) at 3-month intervals while groups 3 and 4 were used as controls. All the animals were exposed to natural tsetse challenge and monitored for serum isometamidium levels and anti-trypanosome antibodies. Seven days after drug administration, isometamidium levels were significantly higher in goats 13.7 + 0.07 ng/mℓ than in sheep 6.2 + 0.06 ng/mℓ. However, the elimination half-life in the sheep was 14.2 + 0.92 days and was significantly higher (P > 0.05) than that of the goats 12 + 0.5 days. This study established that isometamidium metabolism differs between sheep and goats and this difference may have important implications in high tsetse challenge areas.