Long-term follow-up of owned, free-roaming dogs in South Africa naturally exposed to Babesia rossi.

Babesia rossi is an important, tick-borne intraerythrocytic protozoan parasite; however, its natural history and epidemiology is poorly understood. Babesia rossi is the most virulent Babesia sp. in domestic dogs and is generally considered to cause severe babesiosis, which is fatal if left untreated. However, subclinical infections and mild disease from B. rossi have been reported, although the clinical progression of these cases was not reported. Therefore, to better understand B. rossi under field conditions, we evaluated its clinical progression and seroprevalence in an owned, free-roaming dog population in Zenzele, South Africa, where the parasite is endemic and prevention is not routine. The entire dog population in Zenzele was monitored intensively at the individual level from March 2008 until April 2014, primarily for a longitudinal study on rabies control. Subsequent evaluation of B. rossi comprised analyses of clinical and laboratory data collected from the Zenzele dog population during the 6 year study period. A substantial proportion (31% (n = 34)) of 109 dogs (randomly selected from every available dog in February/March 2010 older than ~6-8 weeks (n = 246)) tested by Indirect Fluorescent Antibody Test had seroconverted strongly to B. rossi. All 34 dogs were generally consistently healthy adults, determined from regular clinical examinations between March 2008 and April 2014. Blood smear examinations at multiple time points between July 2009 and February 2011 were also undertaken for almost all of these (34) seropositive dogs and all those tested were consistently negative for Babesia spp. Subclinical infections and mild disease were also the main findings for a separate group of 18 dogs positive for Babesia spp. on blood smear examination and confirmed to be infected with B. rossi by Polymerase Chain Reaction - Reverse Line Blot. Almost all of these dogs were positive at only one time point from repeat blood smear examinations between July 2009 and February 2011. We suggest that these observations are consistent with immunity acquired from repeated, low-level exposure to the parasite, generating transient subclinical infections or mild disease. Should this be the case, the use of tick control, particularly in adult dogs in free-roaming populations in B. rossi endemic regions, should be carefully considered.

The effect of orally administered Aloe marlothii leaves on Boophilus decoloratus tick burdens on cattle.

The effect of a decoction of pulverized aloe leaves (Aloe marlothii) mixed with tap water and administered orally through a gastric tube was determined against ticks on cattle. The decoction was administered to six randomly selected calves seven times at 3-day intervals while the remaining calves received an equivalent amount of tap water only. Five hours after first treatment the calves were infested with Boophilus decoloratus larvae hatched from one gram of eggs. Resultant engorged female ticks were collected, counted and weighed daily. Fertility estimates were determined for 30 engorged female ticks collected from each calf in both the treated and control groups of calves. The treatment had no significant effect on total or daily numbers of engorged females collected per group, nor on their biomasses. Fertility estimates showed the treatment group to yield a marginally higher, yet insignificant, egg laying response (ELR) and reproductive estimate (RE).

The possible role of two common three-host ticks, Rhipicephalus appendiculatus and Amblyomma hebraeum, in the transmission of bovine leukosis virus.

The possible role of Rhipicephalus appendiculatus and Amblyomma hebraeum in the mechanical and transstadial transmission of bovine leukosis virus (BLV) was investigated. BLV-free laboratory strains of R. appendiculatus and A. hebraeum nymphal ticks (n = 400) were fed on a BLV-infected and a negative control bovine. At various intervals after engorgement the ticks were homogenised and injected subcutaneously into BLV-negative sheep. Adult R. appendiculatus and A. hebraeum, which had fed as nymphs on the BLV-infected bovine, were then allowed to feed on BLV-negative sheep. A control sheep was also injected intravenously with blood from the infected bovine. Only the control sheep that received blood from the BLV-positive bovine seroconverted 9 months later. All the other surviving sheep remained serologically negative during the 13 months observation period. It is suggested that the nymphal stages of these ticks probably do not play a role in the transstadial transmission of BLV in southern Africa. The significance of these results is discussed.

The clinical pathology of heartwater. II. Studies on cardiac and pulmonary function in 4 calves with experimentally-induced heartwater.

Studies to evaluate cardiac and pulmonary function were undertaken in 4 calves suffering from experimentally-induced heartwater. There was a marked variation in the course of the disease. Three of the calves recovered spontaneously after developing clinical signs. These included a rectal temperature in excess of 40 degrees C, anorexia and listlessness but no neurological signs. The remaining calf died 2 days after developing a fever and neurological signs. In the 3 calves that recovered, a mild hypoxemia developed during the acute stage of the disease. Arterial CO2 tension remained within normal limits, but there was a tendency towards an alkalosis. Increases in pulmonary dead space and fluctuations in venous admixture were observed. The calf that died showed similar mild changes in blood gas parameters, despite the presence of a marked reduction in minute volume, and a lung oedema was demonstrated on post-mortem examination. No marked changes in systolic and diastolic blood pressures and in right cardiac intraventricular pressures were observed. Terminally, however, there were marked decreases in stroke volume and cardiac output. These changes were associated with a sharp increase in heart rate. No primary cardiac pathology was observed on clinical and post-mortem examinations.

An ELISA using an SDS extract of Brucella abortus strain 99 as antigen to detect B. abortus antibodies in cattle sera.

An ELISA was developed using an SDS extract of Brucella abortus as antigen to detect antibodies in cattle sera. The antigen was stable at 4 degrees C for at least 4 years and although it gave optimal results at a 1/4,000 dilution it could detect reactors at a 1/32,000 dilution. Based on comparative CF tests on 430 sera from negative herds and 187 sera from positive herds a reading of 0,07 or less using a 492 nm filter could be considered a negative reaction. The ELISA could be a useful test to supplement the CF test but further evaluation is still required.

The clinical pathology and pathophysiology of heartwater: a review.

This paper reviews the available literature on the clinical pathology and pathophysiology of heartwater and makes comparisons with unpublished results obtained from a recent study in experimentally-induced heartwater in calves. The pathophysiological changes seem to center on an increased capillary permeability the result of which is reflected most noticeably in cardiac and lung function. There is a marked drop in cardiac output in severe cases and some workers have recorded a severe drop in diastolic blood pressure in the advanced stage of the disease. Changes in lung function are variable, depending on the stage of the disease, and may change from a respiratory alkalosis in the early febrile stage to a respiratory acidosis in more advanced cases. The basic cause for the increased capillary permeability is not known. The main clinical pathological changes measured include a progressive anaemia, fluctuations in total and differential white cell count, of which an eosinopenia and a lymphocytosis are the most marked, increases in total bilirubin which coincide with darkening of plasma colour, and a drop in total serum proteins mostly shown in the albumin levels.

Further studies of the clinical pathology of sweating sickness in cattle.

Experimentally-induced cases of sweating sickness in calves were used in an effort to correlate the blood chemistry with some of the known pathological changes. Results showed that the "sweating" associated with necrotic dermatitis did not alter blood electrolyte levels. Laboratory evidence of a disseminated intravascular coagulopathy was found which correlated with the microthrombi described in cases of sweating sickness. A high blood cortisol level was found in one of the animals that died from the disease and could possibly be used as a prognostic indicator in clinical cases. Recommendations are made with regard to the supportive treatment based on the clinical pathological findings.

The efficacy of hyperimmune serum in the treatment of sweating sickness.

Natural and experimental cases of sweating sickness were treated using a hyperimmune serum as specific treatment and hyperimmune serum combined with symptomatic and supportive treatment based on the clinicopathological changes observed in cases of sweating sickness. The treatment regimens were found to be highly effective in pigs and sheep as well as in calves, although recovery in the latter species was slower.