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Epidemiological analyses in time and space were carried out on all animal rabies cases reported in South Africa for the period 1993-2005. Validation of state veterinary records was done by comparing these with data from the 2 diagnostic laboratories mandated to test for animal rabies. A discrepancy between state veterinary records and laboratory results was found and is discussed. The total number of positive rabies cases reported to veterinary services between 1993 and 2005 was 4767. During this period the proportion of domestic animal rabies had increased to 79 % (19 % more than for the period 1980-1994), with 59 % of the total cases being domestic dogs. Of the domestic animal cases 74 % were canine and only 21 % were bovine; when compared to the data from 1985-1994 there was an increase of 6 % of rabies in canine anda3% decrease in bovine cases. A disturbing trend is the increase in the incidence of rabies over the last 16 years in provinces neighbouring KwaZulu-Natal province, where rabies used to be concentrated, and in Limpopo province.

This paper presents an environmental exposure assessment model for estimating chronic intake of vanadium (a transition metal) by cattle farmed extensively in areas contaminated by vanadium pollutants. The exposure model differs from most other models in several ways: (1) it does not rely heavily on extrapolating information from the point source (e.g. stack height, exit velocity, exit diameter) to the point of exposure. (2) It incorporates the physiological constraints of the species exposed. (3) It takes into account oral as well as inhalation exposure. (4) It addresses terrain, by using measurements at the point of exposure. (5) It accounts for existing background concentrations of pollutants and pollutants from multiple sources. (6) It uses a stochastic process with distribution functions to account for variability in the data over time. Environmental inputs into the model included aerial fall-out sample vanadium (n = 566), unwashed grass sample vanadium (n = 342) and soluble soil sample vanadium (n = 342). Physiological cattle inputs were derived from two cohorts of Brahman-cross sentinel cattle (n = 30). The model provided an estimate of the chronic external exposure dose of vanadium for two separate groups of cattle grazing over a 5-year period (1999–2004) immediately adjacent (median dose = 2.14 mg vanadium/kg body weight/day) and 2 km away (median dose = 1.07 mg/kg/day) from a South African vanadium-processing plant, respectively. The final output of the model is a distribution curve of the probable vanadium intake based on the variability within the inputs over the 5-year period of the study. The model is adaptable enough for application to other transition metals and species (including man), and could be used as an alternative to plume-dispersion modelling.

Various potential biomarkers were sampled for vanadium every 3–4 months from Bos indicus beef cattle farmed extensively immediately adjacent (high exposure (HE) group) and two km away (low exposure (LE) group) from a vanadium processing plant, respectively. Vanadium intake (mg vanadium kg1 bwt d1 ) was modelled using environmental and physiological data as inputs. The vanadium intake ranged from 0.57g to 5.44 mg vanadium kg1 bwt d1 in the HE group and 0.41 to 2.61 mg vanadium kg1 bwt d1 in the LE group over a five-year period of monitoring. Samples collected from live sentinel animals over the five-year period included caudal coccygeal vertebrae, tail-switch hair, milk, urine, faeces, rib-bone biopsies and a wide range of blood clinical pathology and haematological parameters. The data was analysed for differences in response between the HE and LE groups. Where differences were found, a linear mixed-effects regression model was fitted to model the relationship between the exposure dose and the response variable. The model included the effects of age, duration of exposure and response, and allowed the prediction of the exposure dose given these inputs. Moreover, forty-two adult cattle were slaughtered over the five years. A wide range of tissue samples, rumen content and whole blood were taken from the cattle at slaughter for vanadium determination. In live animals, a difference in response was found between the HE group and LE group with respect to serum albumin (n = 36), monocyte (n = 36) and thrombocyte (n = 36) counts, and hair (n = 2) and faeces (n = 34) vanadium concentrations. No difference in vanadium concentrations could be shown for urine (n = 36), the traditional occupational health biomarker. Regression models are described for serum albumin, monocyte counts, faeces and hair, which showed the most promise as biomarkers. Average concentrations of vanadium in the tissues of slaughtered cattle ranged from 0.08 to 2.94 mg kg1 (wet-weight basis) and rumen content contained 16.67 mg kg1 . Significant correlations were found between the exposure dose (end-dose) just prior to laughter and the concentrations of vanadium in the coccygeal vertebrae, liver, diaphragm and rib-bone in descending order of magnitude. Other tissues showed poor correlation to the end-dose. Tissue levels of vanadium in healthy cattle include a much wider range than is currently reflected in the literature. The best tissue from slaughter animals for assessing chronic vanadium exposure is probably the liver

The thesis covers a field outbreak investigation into the cause and pathogenesis of "illthrift" on a dairy farm that was due to vanadium exposure, it examines methods of treating vanadium poisoning in cattle using an experimental study, looks at the use of cattle as sentinels for detecting and monitoring vanadium pollution, and examines the public health implications of cattle being farmed in areas of high background vanadium levels. The outbreak investigation found that vanadium poisoning manifested in animals 4 to 18 months old, which showed emaciation, chronic diarrhoea, and in some cases, rhinitis, conjunctivitis and recumbency followed by death. Post-mortem and clinical pathology findings indicated that malabsorption and immunosuppression were the basis of the pathogenesis in affected animals. In the experimental study, CaNa2EDTA appeared to enhance the excretion of vanadium in calves, but there was no proof that the treatment had a protective effect against vanadium exposure. During the sentinel study a stochastic exposure model was developed. The exposure model differs from most other approaches in several ways: 1.It does not rely heavily on extrapolating information from the point source to the point of exposure. 2. It incorporates the physiological constraints of the species exposed. 3. It takes into account oral as well as inhalation exposure and thus can account for intake from contaminated grazing, vegetables and crops grown in the area of pollution. 4. It addresses the common weaknesses in many models of insensitivity to terrain, by using measurements at the point of exposure. 5. It accounts for existing background concentrations of pollutants and pollutants from multiple sources and 6. the stochastic process and use of distribution functions accounts for variability in the data over time, which is usually a problem with long term studies. Having developed and validated the exposure model, an exposure dose was then modelled for different periods that animals were exposed for and this dose was then correlated to a wide range of biomarker responses that were monitored during the trial. In live animals, a difference in response was found between the high exposure group and low exposure group with respect to serum albumin, monocyte and thrombocyte counts, and hair and faeces vanadium concentrations. No difference in vanadium concentrations could be shown for urine, the traditional occupational health biomarker. None of the other potential biomarkers examined proved to be of much value in determining or predicting vanadium exposure in Bos indicus cattle. Regression models are described for serum albumin, monocyte counts, faeces and hair, which showed the most promise as biomarkers. Average concentrations of vanadium in the tissues of slaughtered cattle ranged from 0.08 to 2.94 mg/kg. Significant correlations were found between the exposure dose just prior to slaughter and the concentrations of vanadium in the coccygeal vertebrae, liver, diaphragm and rib-bone in descending order of magnitude. Other tissues showed poor correlation to the end-dose. The study also evaluated the public health risks of consuming meat and milk from cattle originating from areas high in vanadium. Using a stochastic model and lognormal distribution function to look at possible extreme tissue residue values that are likely to occur, it was concluded from current knowledge of toxicity in humans that the tissue and milk residues of vanadium from cattle should pose no health risk to the consumer. The sentinel study proved that cattle could be used in a mining environment to monitor health risks to both cattle and humans, as a risk communication tool for interested parties and as a way of studying the chronic effects of pollutants.