P. A. Windsor

Australian dingoes are definitive hosts of Neospora caninum.

To provide objective data on the potential role of dingoes (Canis lupus dingo) in the life cycle of Neospora caninum in Australia, the production of N. caninum oocysts by experimentally infected canids was investigated. Three dingo pups raised in captivity and three domestic dogs were fed tissue from calves infected with an Australian isolate of N. caninum, Nc-Nowra. Oocysts of N. caninum, confirmed by species-specific PCR, were shed in low numbers by one dingo pup at 12-14 days p.i. The remaining animals did not shed oocysts. Furthermore, the blood from two out of three dingoes tested positive for DNA of N. caninum using PCR tests at 14 and 28 days p.i. Oocyst shedding from the intestinal tract of a dingo demonstrates that dingoes are definitive hosts of N. caninum and horizontal transmission of N. caninum from dingoes to farm animals and wildlife may occur in Australia.

Evidence for age susceptibility of cattle to Johne's disease.

Calf rearing programs for the control of bovine Johnes disease (BJD) in dairy farms have been widely adopted globally and are based on evidence that the most significant risk factor for developing the disease is exposure of young calves to infectious doses of the causative organism Mycobacterium avium subsp. paratuberculosis (Mptb). Hygienic calf rearing practices aim to break the transmission cycle of Mptb by removing neonatal calves from their dams within 12h of birth and segregating replacement heifers from the herd until they are 12 months of age. But compliance with these interventions is difficult for many producers and delaying the removal of calves from their dams and earlier return of heifers to the herd are common practices. However, would changing these practices increase the risk of animals contracting BJD? Evidence for age susceptibility of calves and young adults to Mptb is reviewed. The experimental studies selected for inclusion in an analysis of the evidence were those designed specifically to address the issue and were confined to examination of 140 cattle in experiments conducted by eight groups of workers between the years 1938 and 2006. Approximately 75% of calves <6 months of age, 50% of those aged between 6 and 12 months, and just less than 20% of cattle >12 months old developed lesions indicative of BJD infection when exposed to any of the tested routes of Mptb infection. No direct evidence was found to support the commonly held view that calf removal from the dam for a maximum period of 12h is preferable to 24h. However the studies did show that if exposure to infection occurs at birth, then the risk of infection progressing to BJD is high, particularly in a highly contaminated environment or if the dam is infected.

Bulldog dwarfism in Dexter cattle is caused by mutations in ACAN

Bulldog dwarfism in Dexter cattle is one of the earliest single-locus disorders described in animals. Affected fetuses display extreme disproportionate dwarfism, reflecting abnormal cartilage development (chondrodysplasia). Typically, they die around the seventh month of gestation, precipitating a natural abortion. Heterozygotes show a milder form of dwarfism, most noticeably having shorter legs. Homozygosity mapping in candidate regions in a small Dexter pedigree suggested aggrecan (ACAN) as the most likely candidate gene. Mutation screening revealed a 4-bp insertion in exon 11 (2266_2267insGGCA) (called BD1 for diagnostic testing) and a second, rarer transition in exon 1 (−198C>T) (called BD2) that cosegregate with the disorder. In chondrocytes from cattle heterozygous for the insertion, mutant mRNA is subject to nonsense-mediated decay, showing only 8% of normal expression. Genotyping in Dexter families throughout the world shows a one-to-one correspondence between genotype and phenotype at this locus. The heterozygous and homozygous-affected Dexter cattle could prove invaluable as a model for human disorders caused by mutations in ACAN.

Impact of topical anaesthesia on pain alleviation and wound healing in lambs after mulesing.

OBJECTIVE To investigate the impact of using the topical anaesthetic preparation Tri-Solfen on pain alleviation and wound healing in lambs undergoing mulesing. DESIGN Three separate trials, placebo controlled and/or randomised, were carried out over a 5 month period on three mobs of between 60 and 263 merino lambs undergoing routine mulesing. PROCEDURE Wound pain was assessed using 10 and 75 g calibrated Von-Frey monofilaments to determine sensitivity to light touch and pain stimulation over a 4 to 8 h period. Pain-related behaviour was documented by trained, blinded observers using a numerical rating scale. Wound healing rates were determined using scaled digital photography and image analysis software to calculate contraction in wound surface area 2 and 4 weeks after mulesing. RESULTS There was rapid (3 min) and prolonged (up to 8 h) wound analgesia as shown by pain response scores (P < or = 0.01), with absent or significantly diminished primary and secondary hyperalgesia (P < or = 0.01) and significant reduction in pain-related behaviour (P < 0.001) in treated versus untreated lambs. In addition there was improved wound healing in the treated lambs (P < or = 0.05). CONCLUSION Tri-Solfen effects rapid and prolonged wound analgesia, reduction in pain-related behaviour and improved wound healing in lambs undergoing routine mulesing, providing effective alleviation of pain associated with routine mulesing in sheep.

Characterization of an outbred pregnant mouse model of Neospora caninum infection.

Fetal loss and vertical transmission of Neospora caninum were evaluated in outbred Quackenbush (Qs) mice with respect to dose of parasites, N. caninum isolate, and route of injection. Mice were infected with NC-Liverpool or NC-SweB1 at day 5 or 8 of pregnancy with doses of 104, 106, or 107 parasites, through either a subcutaneous or intraperitoneal injection. Polymerase chain reaction was used to detect N. caninum in the brains of offspring, and enzyme-linked immunosorbent assay was used to analyze the maternal immune response. Vertical transmission occurred in mice given 106 NC-Liverpool at day 5 during gestation, and a significant (P < 0.05) maternal antibody response was observed in mice infected with NC-Liverpool or NC-SweB1 at days 5 and 8 of gestation. This study shows that outbred Qs mice are a useful model for the study of vertical transmission associated with N. caninum, as they display less clinical disease and pathogenesis than inbred mice and have large litters, which is advantageous when studying maternal transmission.

Assessment of Financial Impact of Foot and Mouth Disease on Smallholder Cattle Farmers in Southern Cambodia

The financial impact of an outbreak of FMD in 2010 on 62 smallholder cattle farmers in four villages in southern Cambodia was investigated by a financial impact survey questionnaire. Financial losses associated with FMD infection were severe with variation depending on whether the animal survived or died or was used for draft. The average post-FMD loss varied from USD 216.32, a 54% reduction from the pre-FMD value because of weight loss and treatment costs, to USD 370.54, a 92% reduction from pre-FMD values if the animal was treated, died and a rental draft replacement was required. Partial budget analysis identified a strongly positive incentive for cattle to be vaccinated biannually for FMD, providing USD 31.48 per animal for each animal owned. However low vaccination rates suggest that farmers are mostly unaware of the need or averse to the practice of vaccinating their cattle for FMD. This may be due to poor understanding of preventative disease strategies such as vaccination, unavailable disposable income for purchase of vaccines, and failure to recognize the full costs that are incurred when the disease occurs. Enhancing smallholder cattle productivity through the introduction of forage growing systems has been suggested as a pathway for alleviating rural poverty in the Mekong region. As our financial analysis identified a net benefit of vaccination for smallholder farmer enterprises in an endemic FMD area in Cambodia, it is considered important that farmer education strategies aimed at improving cattle productivity, also include both access to vaccine and training in preventative disease risk management and biosecurity practices in Cambodia.

The first report of ovine cerebral neosporosis and evaluation of Neospora caninum prevalence in sheep in New South Wales

Presence of Neospora caninum DNA was detected in the brain and spinal cord of an adult Merino sheep suspected of dying with acute non-suppurative meningoencephalitis and mild to moderate non-suppurative myelitis. The most severe neurological lesions were found in the midbrain at the rostral coliculi with moderate to severe multifocal vasculitis and gliosis. As this was the first known occurrence of cerebral disease in sheep in Australia caused by N. caninum, we surveyed sera from five sheep properties in New South Wales (NSW) to obtain information on the likely prevalence of N. caninum infection in NSW sheep flocks. Serology using a commercial indirect enzyme-linked immunosorbent assay (ELISA) revealed no N. caninum antibody-positive sheep (n=184). However an observed prevalence for N. caninum antibodies using a commercially available competitive ELISA was 2.2% (5/232). We conclude that although the diagnosis of fatal ovine cerebral neosporosis is of importance to our surveillance program for transmissible spongiform encephalopathy (TSE) exclusion, sheep in NSW are not commonly infected with N. caninum and this species likely plays only a minor role in the life cycle of this parasite in Australia.

Oocysts and high seroprevalence of Neospora caninum in dogs living in remote Aboriginal communities and wild dogs in Australia

Canines are definitive hosts of Neospora caninum (Apicomplexa). For horizontal transmission from canines to occur, viable oocysts of N. caninum must occur in the environment of susceptible intermediate hosts. Canids in Australia include wild dogs and Aboriginal community dogs. Wild dogs are those dogs that are not dependent on humans for survival and consist of the dingo, feral domestic dog and their hybrid genotypes. Aboriginal community dogs are dependent on humans, domesticated and owned by a family, but are free-roaming and have free access throughout the community. In this study the extent of N. caninum infection was determined in a total of 374 dogs (75 wild dogs and 299 Aboriginal community dogs) using a combination of microscopic, molecular and serological techniques. Oocysts of N. caninum were observed in the faeces of two juvenile Aboriginal community dogs (2/132; 1.5%). To estimate N. caninum prevalence, a new optimised cut-off of 18.5% inhibition for a commercial competitive ELISA was calculated using a two-graph receiver-operating characteristic (TG-ROC) analysis and IFAT as the gold standard resulting in equal sensitivity and specificity of 67.8%. Of the 263 dog sera tested the true prevalence of N. caninum antibodies was 27.0% (95% confidence limit: 10.3-44.1%). The association between the competitive ELISA results in dogs less than 12 month old and older dogs was significant (P=0.042). To our knowledge this is the first large scale parasitological survey of the Aboriginal community dogs and wild dogs from Australia. The high prevalence of N. caninum infection in Aboriginal community dogs illustrates that horizontal transmission of N. caninum is occurring in Australia. These results demonstrated that N. caninum in dogs is widespread, including the semi-arid to arid regions of north-western New South Wales and the Northern Territory. The populations of free-ranging dogs are likely to be important contributors to the sylvatic life cycle of N. caninum.

Identification of a plant isoflavonoid that causes biliary atresia

A plant toxin with a previously uncharacterized chemical structure causes biliary atresia in zebrafish and mammals. Fishing for a toxin Biliary atresia is a childhood disease of unknown etiology, which causes rapid destruction of the biliary tree. Lorent et al. used a naturally occurring outbreak of biliary atresia in Australian lambs to discover that one cause of this disease may be a plant toxin. During a period of drought, the pregnant ewes’ diet included unusual species of plants growing on land that is normally covered by water. The researchers tested extracts from these plants in a zebrafish model and identified a compound that caused biliary atresia–like changes in the fish as well as in mammalian cells. Although these plants are not eaten by humans, the findings suggest that plant toxins may contribute to the development of biliary atresia in people as well. Biliary atresia (BA) is a rapidly progressive and destructive fibrotic disorder of unknown etiology affecting the extrahepatic biliary tree of neonates. Epidemiological studies suggest that an environmental factor, such as a virus or toxin, is the cause of the disease, although none have been definitively established. Several naturally occurring outbreaks of BA in Australian livestock have been associated with the ingestion of unusual plants by pregnant animals during drought conditions. We used a biliary secretion assay in zebrafish to isolate a previously undescribed isoflavonoid, biliatresone, from Dysphania species implicated in a recent BA outbreak. This compound caused selective destruction of the extrahepatic, but not intrahepatic, biliary system of larval zebrafish. A mutation that enhanced biliatresone toxicity mapped to a region of the zebrafish genome that has conserved synteny with an established human BA susceptibility locus. The toxin also caused loss of cilia in neonatal mouse extrahepatic cholangiocytes in culture and disrupted cell polarity and monolayer integrity in cholangiocyte spheroids. Together, these findings provide direct evidence that BA could be initiated by perinatal exposure to an environmental toxin.

Assessment of farmer knowledge of large ruminant health and production in developing village-level biosecurity in northern Lao PDR.

The purpose of this study was to determine baseline knowledge and identify knowledge gaps of farmers on biosecurity, risk of transmission of transboundary diseases and large ruminant health and production in three provinces of northern Laos, Hua Phan (HP), Luang Prabang (LPB) and Xieng Khoung (XK). The survey was conducted in six villages that are project sites for an Australian Centre for International Agricultural Research (ACIAR) project, with two villages located in each of the three provinces. A census survey was conducted by interview with all 238 farmers participating in the ACIAR project, using a structured questionnaire. The interviews were conducted in Lao language and took 1-2 h per farmer. The answers were recorded in Lao and the survey data were translated into English and transcribed into Microsoft Excel, and a linear mixed model in the Genstat statistical analysis package was used to compare quantitative traits between the target provinces. The results showed that the prediction mean of farmer knowledge scores on parasitic disorders, infectious disease, reproduction and nutrition management were significantly different between the target provinces. The prediction mean of farmer knowledge scores on infectious disease questions ranged between 5.11 in HP to 8.54 in XK of 24 marks (P < 0.001). The prediction mean of total knowledge scores was 13.48 in LPB and 19.29 in XK of 42 marks (P < 0.001). The results indicate both the need for and scope required to attain improvements in farmer knowledge of large ruminant health and production. It was concluded that a participatory research and extension programme to address village-level biosecurity and reduce disease risks, plus enhance large ruminant production capabilities of smallholder producers, is a valid and potentially important strategy to address transboundary disease risk and rural poverty in northern Laos.