Porcine circovirus-associated disease in weaner pigs in Western Australia.

OBJECTIVE: To report the occurrence and pathology of porcine circovirus type 2 (PCV2)-associated disease (PCVAD) of postweaning pigs in two Australian pig herds. METHODS: Mortality data from two commercial piggeries that experienced higher than normal postweaning illthrift and mortalities were examined. Gross and histopathological examinations were performed on the index cases, and at weekly intervals thereafter for a period of 10 weeks. Specimens were submitted to the laboratory for routine diagnostic testing and for exclusion of porcine reproductive and respiratory syndrome virus (PRRSV). The genomes of two strains of PCV2 isolated during testing were sequenced. RESULTS: Mortality rates in weaned, 5-12-week-old pigs spiked significantly during mid to late 2007. This increase in the mortalities was mainly attributed to salmonella-associated diarrhoea and illthrift. Salmonellosis was diagnosed in 73/110 cases inclusive of both piggeries. Many pigs also had chronic granulomatous lymphadenitis and diffuse histiocytic interstitial pneumonia consistent with PCVAD and associated with varying amounts of PCV2 antigen and inclusion bodies. All samples tested for PRRSV were negative. Sequence analysis of the PCV2 isolates showed strain differences between piggeries. CONCLUSION: This report describes the first outbreaks of PCVAD in growing pigs in Western Australia (WA) and describes lesions not previously seen in this laboratory. It also describes the first isolation of a PCV2 group 1 virus in WA associated with PCVAD. Although the outbreaks of PCVAD occurred with concurrent salmonellosis, the two diseases were unrelated. Neither of the outbreaks met the Australian case definition for the diagnosis of postweaning multisystemic wasting syndrome.

Understanding the molecular epidemiology of the footrot pathogen Dichelobacter nodosus to support control and eradication programs.

The Gram-negative anaerobe Dichelobacter nodosus is the primary etiologic agent of ovine footrot. Few studies of the genetic diversity and epidemiology of D. nodosus have been done, despite the economic cost and welfare implications of the disease. This study examined a large collection of Australian isolates; 735 isolates from footrot-infected sheep from 247 farms in Western Australia (WA) were tested by pulsed-field gel electrophoresis (PFGE), and a subset of 616 isolates was tested by infrequent restriction site PCR (IRS-PCR). The genetic diversity of WA isolates was compared to that of 61 isolates from three other Australian states. WA isolates were genetically diverse, with 181 molecular types resolved by PFGE, resulting in a simple diversity ratio (SDR) of 1:4 and a Simpson's index of discrimination value (D) of 0.98. IRS-PCR resolved 77 molecular types (SDR = 1:8 and D = 0.95). The isolates were grouped into 67 clonal groups by PFGE (SDR = 1:11, D = 0.90) and 36 clonal groups by IRS-PCR (SDR = 1:17, D = 0.87). Despite the high genetic diversity, three common clonal groups predominated in WA and were found in other Australian states. On some farms, molecular type was stable over a number of years, whereas on other farms genetically diverse isolates occurred within a flock of sheep or within a hoof. This study provides a large database from which to appropriately interpret molecular types found in epidemiological investigations and to identify common and unknown types that may compromise footrot eradication or control programs.

The laboratory network in Australia and New Zealand - an evolving system.

This paper discusses the network of government, private and university veterinary laboratories in Australia and New Zealand and how it is adapting and evolving to meet the challenges it faces. It includes the mechanisms for standardisation of procedures, quality assurance, and the role of national reference laboratories hosted by state government laboratories. It also highlights the crisis in supply of veterinary diagnosticians, especially the declining numbers of veterinary pathologists. Recent positive changes include the setting up of the National Animal Health Laboratory Strategy and an initiative to empower State and Territory government laboratories to test for exotic diseases. The ideal outcome for Australia and New Zealand is a laboratory service that remains the gold standard around the world.

Cattle deaths during sea transport from Australia.

OBJECTIVE: To establish the death rate and the causes of death in cattle exported by sea from Australia. PROCEDURE: Cattle deaths on voyages from Australia to all destinations between 1995 and 2000 were analysed retrospectively. On four voyages to the Middle East between December 1998 and April 2001, cattle that died were examined to determine the cause of death. RESULTS: The death rate was 0.24% among 4 million cattle exported, and a greater proportion of deaths occurred on voyages to the Middle East (0.52%, P < 0.05) than to south east Asia (0.13%). The risk of death on voyages to the Middle East was three times greater for cattle exported from southern ports in Australia compared to northern ports. The main causes of death were heat stroke, trauma and respiratory disease. CONCLUSION: Cattle have a low risk of death during sea transport from Australia. The risk of death can be reduced on voyages to the Middle East by preferentially exporting cattle from northern ports, and selecting those with a higher Bos indicus content whenever possible.

Contagious ecthyma in the live sheep export industry.

OBJECTIVE: To investigate control options for contagious ecthyma (scabby mouth) in Australian sheep exported live to the Middle East. DESIGN: Prevalence, vaccination and modelling studies. PROCEDURE: One hundred and forty weaner sheep (less than 1 year old) on each of 106 farms in Western Australia (WA) and 18 farm groups of adult wethers received at a WA commercial feedlot were examined for lesions of scabby mouth. Sheep on a total of 26 farms in 3 States were divided into treatment and control groups for the vaccination study. A simple deterministic compartmental model was developed to establish which parameters had the greater effect on disease prevalence. RESULTS: The proportion of farms with evidence of scabby mouth in weaner sheep was 23.6% and, on those farms with the disease, the overall prevalence was 6.1%. At the feedlot, 4 out of 18 farm groups had 5 or more sheep with lesions on arrival. The overall prevalence in the 4 diseased groups was 5.2%. Sheep vaccinated on farm before trucking to the feedlot had a lower prevalence of scabby mouth at the end of simulated shipping than controls. The main determinant of scabby mouth prevalence was the proportion of sheep immune to the disease. CONCLUSION: A program of vaccination for scabby mouth will reduce the prevalence of disease during live export. However, using current technology it is not possible to deliver shipments of sheep to the Middle East that are guaranteed completely free of scabby mouth.

Epidemiology of salmonellosis in the live sheep export industry.

Salmonellosis in sheep was studied on 7 commercial voyages from Australia to the Middle East and in one animal house study. Faecal excretion of salmonellas was not a good indicator of pathological changes in the gastrointestinal tract. The ratio of the proportion of sheep excreting salmonellas to the proportion with histological lesions of salmonellosis ranged from 1:1 to 23:1. Increasing excretion rates in our studies indicated that most sheep would be exposed to infection, although deaths from salmonellosis were not spatially or temporally clustered as would be expected if challenge alone was a sufficient cause. We considered that inappetence predisposed to death from salmonellosis, and that sheep with inappetence were likely to be randomly distributed aboard ship. In the animal house study, histological lesions of salmonellosis were exclusively in inappetent sheep although almost all sheep excreted salmonellas in faeces. Lesions of salmonellosis were found only in sheep that were seriously ill or had died, which suggested that, under the conditions of lot-feeding and sea transport, most sheep with enteric lesions are likely to die. Lesions were not found in feeding controls. Adrenal gland weights, an indicator of stress duration and severity, were used to examine the temporal sequence of events in the development of salmonellosis. Weights were greater in sheep that died of inanition than in controls, suggesting that inappetent sheep were already stressed for that reason. The presence of enteric lesions of salmonellosis was associated with further increases in adrenal gland weights.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of lesions in ovine salmonellosis.

Four forms of salmonellosis were recognised in feedlots and during transport by sea: septicaemic, and acute, subacute and chronic enteric. The severity and distribution of lesions in the enteric forms varied according to the progression of the pathological process. The acute disease involved the abomasum and small intestine whereas the subacute disease centred on the lower small intestine and upper large intestine. Chronic disease involved considerable mucosal repair in the ileum, caecum and proximal colon. Septicaemic salmonellosis was often accompanied by acute enteritis and occasionally by cholecystitis. S typhimurium was the most frequently encountered serotype.

The duration of lot-feeding of sheep before sea transport.

Adult wethers (n = 750) were lot-fed for 13 days, 8 days or 3 days before a simulated voyage lasting 18 days to examine whether the period of lot-feeding affected the proportion of sheep that ate pelleted feed and their body weight change during simulated shipping. There was no significant difference in the proportion of non-feeders between treatment groups on days 7 and 14 of the voyage. Body weights were not significantly different between the treatment groups on days 14 and 18 of the voyage. Overall body weight loss, from the farm to the end of simulated shipping, was 4.08 kg (+/- 0.28, s.e.m.), 4.58 kg (+/- 0.28) and 4.51 kg (+/- 0.28) in sheep lot-fed for 13 days, 8 days and 3 days, respectively, and was not significantly different between treatments. It was concluded that lot-feeding for 13 days conferred no advantage in body weight or numbers of non-feeders compared with shorter periods in this study.

Use of the enzyme linked immunosorbent assay (ELISA) to detect the IgM and IgG antibody response to Leptospira interrogans Serovar hardjo in pregnant ewes.

Fourteen pregnant ewes were inoculated with Leptospira interrogans serovar hardjo via intramuscular injection or inoculation via the conjunctiva. The serological response to inoculation detected by the microscopic agglutination test was compared to IgM and IgG antibody levels detected by enzyme linked immunosorbent assay. Intramuscular injection produced a better serological response than conjunctival inoculation. The mean IgM response was short lived whereas the IgG antibody response and the MAT persisted for much longer. The IgM antibody levels may be useful as an indicator of recent exposure. Although leptospiruria was not established in any of the animals, 6 of the 14 pregnant ewes failed to rear a healthy lamb.

A cross-sectional study to show Eperythrozoon ovis infection is prevalent in Western Australian sheep farms.

A serological survey and risk factor study was conducted to estimate the prevalence of Eperythrozoon ovis infection in Western Australian weaner sheep, the prevalence of farms with infected sheep, and to identify factors affecting initiation and maintenance of infection on the farm. The study was conducted on 91 farms, purposively chosen from 41 randomly selected regional shires stratified by sheep number and rainfall zones. Twenty sheep were selected systematically from a mixed-sex flock on each farm and tested for serum antibody to E ovis using an enzyme-linked immunosorbent assay. Information on putative risk factors was collected using an interview questionnaire. Antibody to E ovis was detected in 4.5% of sheep on 47% of the farms sampled. The prevalence of E ovis infection in sheep was estimated at the 95% confidence level to be between 3.6 and 5.5%, and the prevalence of farms with infected sheep was estimated to be between 37.5 and 56.5%. Most farms with serological evidence of infection occurred in the Great Southern agricultural region (79.5%), south-east of Perth through to Albany (latitude 32 to 34 degrees S, longitude 116 to 120 degrees E), and in the Northern region (12.8%) surrounding Geraldton (latitude 29 degrees S, longitude 114 degrees E). There were significantly more farms (P less than 0.05) with evidence of infection in the Great Southern region compared to the Central region between Geraldton and Perth, and on farms in the region south compared to north of latitude 32 degrees S. None of the putative risk factors examined in the questionnaire were associated with serological evidence of infection on the farm.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterisation of virulent and benign strains of Bacteroides nodosus.

The extracellular proteases of 395 isolates of B. nodosus from ovine, bovine and caprine foot lesions were classified as either thermostable or thermolabile. Stable protease was associated with one and unstable protease with four distinctive isoenzyme patterns, each pattern differentiated by the relative mobility of paired isoenzymes. Pathogenicity tests on 64 isolates showed a correlation between the production of stable protease and the production of virulent ovine footrot lesions. The mean values for total protease activity, twitching motility and colony diameter were significantly higher for virulent compared to benign isolates, but the range of values overlapped. SDS-PAGE whole-cell electrophoretic profiles of virulent isolates were similar to the profiles of some benign isolates.

Management of inappetant sheep during export by sea.

In the first of 2 experiments, a simulated voyage was conducted to examine the effects of various treatments on bodyweight change and feeding frequency of inappetant sheep at the end of lot-feeding (non-feeders). The treatments, applied during simulated shipping, were: normal quantities of feed and length of troughs; extra trough length; extra feed. Adult Merino wethers (n = 108) were used in each treatment. A voyage to the Middle East was then conducted to establish whether shipboard mortality could be reduced by separating non-feeders (n = 305) from feeders (n = 5,620) late in the feedlot hase and housing the groups separately aboard ship. A control group of non-feeders (n = 215) mixed with feeders (n = 5,732) was used for comparison. Bars (marker bars), containing a coloured dye, were attached to feed troughs to mark sheep that fed. Most non-feeders (82%) began eating when placed in shipping pens in both studies. However, there was no significant difference in percentage of sheep that fed between non-feeders given extra trough length or extra feed compared with non-feeders given standard management at any stage of simulated shipping. There was no significant difference in mean bodyweights between treatment groups on days 1, 8 and 15 of simulated shipping. Differences in bodyweight on d 22 were probably associated with different levels of gut fill. Death rates were not significantly different in separated and control groups (1.1%, 0.9%, P = 0.6) in the voyage of 14 d to the Middle East.(ABSTRACT TRUNCATED AT 250 WORDS)

Pre-embarkation risk factors for sheep deaths during export by sea from Western Australia.

Truck-drivers and previous owners of sheep from 133 farms (lines of sheep) were asked for information on possible risk factors for inappetance during lot-feeding and for shipboard mortality during 5 voyages to the Middle East. There was no consistent association between a number of factors prior to trucking or during trucking to the feedlot and inappetance during lot-feeding or mortality aboard ship. The factors included: whether sheep were bred or purchased by the owner, whether sheep were mixed with sheep from another farm in the previous 2 or 6 months, previous experience of trucking, frequency of yarding, experience of supplementary feeding, age, rainfall zone of the farm of origin, distance trucked, time on the truck and time off feed on arrival at the feedlot. Inappetance during lot-feeding was significantly associated with total deaths aboard ship for individuals and for lines of sheep. Failure to eat late in the feedlot period was also a risk factor for individuals that died with inanition (relative risk = 6.9) or salmonellosis (relative risk = 5.9). In 2 voyages, there was no significant difference in shipboard death rate between groups that were previously lot-fed in sheds or in paddocks. This was despite significantly more non-feeders in the sheds than in the paddocks prior to one voyage. This finding suggested that some nonfeeders commenced eating pellets aboard the ship. Although inappetance in the feedlot was a risk factor for shipboard deaths, there was no difference in shipboard weight change between feedlot non-feeders and feeders in 2 voyages. It was concluded that most non-feeders began eating pelleted feed aboard ship.

An epidemiological study of sheep deaths before and during export by sea from Western Australia.

A study was conducted to record the deaths that occurred during export, and to examine the temporal pattern of pellet feeding in the feedlot and ascertain the variation in mortality between groups of sheep from different farms. Between November 1985 and April 1987, 5 cohorts of sheep were selected on arrival at a feedlot before live export by sea from Western Australia to the Middle East. Each cohort consisted of 4,118 to 9,612 Merino wethers from 15 to 35 farms (lines). There were few deaths during trucking to the feedlot (rate 0.9, range 0.0 to 3.0 per 10,000 sheep) and during lot-feeding (rate 6.2, range 1.2 to 12.2 per 10,000 sheep). Most of the deaths occurred aboard ship (rate 210.7, range 152.7 to 271.5 per 10,000 sheep). The proportion of sheep that ate pelleted feed increased with increasing length of time in the feedlot. By the end of lot-feeding the percentage of sheep that had not eaten pellets was 23.3, 4.4, 1.2, 2.1 and 0.2 in a representative sample of each of the 5 cohorts. It was considered that offering hay throughout lot-feeding was undesirable for the purpose of maximising the number of sheep that ate pellets before loading on the ship. Half of the deaths aboard ship occurred in 25% of 133 lines of sheep in the 5 cohorts. In each cohort the median per cent death rate (and range) per line was 1.3 (0.3 to 11.9), 1.1 (0.0 to 5.7), 1.8 (0.0 to 6.8), 2.3 (0.0 to 14.3) and 0.9 (0.1 to 5.4).(ABSTRACT TRUNCATED AT 250 WORDS)