The effect of paratuberculosis on milk yield--A systematic review and meta-analysis.

Bovine paratuberculosis is a disease characterized by chronic granulomatous enteritis causing protein-losing enteropathy. Adverse effects on animal productivity are key drivers in the attempt to control paratuberculosis at the farm level. Economic models require an accurate estimation of the production effects associated with paratuberculosis. The aim of this study was to conduct a systematic review and meta-analysis to investigate the effect of paratuberculosis on milk production. A total of 20 effect estimates from 15 studies were included in the final meta-analysis. Substantial between-study heterogeneity was observed. Subgroup analysis by case definition and study design was carried out to investigate heterogeneity. The majority of between-study variation was attributed to studies that defined cases on serology. Calculation of a pooled effect estimate was only appropriate for studies that defined cases by organism detection. A reduction in milk yield, corrected for lactation number and herd of origin of 1.87 kg/d, equivalent to 5.9% of yield, was associated with fecal culture or PCR positivity in individual cows.

Mycobacterium avium subspecies paratuberculosis: an insidious problem for the ruminant industry.

Mycobacterium avium subspecies paratuberculosis is considered as one of the most serious problems affecting the world's ruminant industry due to its significant impact on the global economy and the controversial issue that it may be pathogenic for humans. M. avium subspecies paratuberculosis is the causative agent of Johne's disease in animals and might be implicated in cases of human Crohn's disease. We provide an insight into M. avium subspecies paratuberculosis from some bacteriological, clinical, and molecular epidemiological perspectives.

Effect of Johne's disease status on reproduction and culling in dairy cattle.

Among the costs attributed to Mycobacterium avium ssp. paratuberculosis (MAP) infection in dairy cattle, the effects on reproduction and culling are the least documented. To estimate the cost of MAP infections and Johne's disease in a dairy herd, the rates of calving and culling were calculated for cows in each stage of MAP infection relative to uninfected cows. Data from 6 commercial dairy herds, consisting of 2,818 cows with 2,754 calvings and 1,483 cullings, were used for analysis. Every cow in each study herd was tested regularly for MAP, and herds were followed for between 4 and 7 yr. An ordinal categorical variable for Johne's disease status [test-negative, low-positive (low-shedding or ELISA-positive only), or high-shedding] was defined as a time-dependent variable for all cows with at least 1 positive test result or 2 negative test results. A Cox regression model, stratified on herd and controlling for the time-dependent infection variable, was used to analyze time to culling. Nonshedding animals were significantly less likely to be culled in comparison with animals in the low-shedding or ELISA-positive category, and high-shedding animals had nonsignificantly higher culling rates than low-shedding or ELISA-positive animals. Time to calving was analyzed using a proportional rates model, an analog to the Andersen-Gill regression model suitable for recurrent event data, stratifying on herd and weighted to adjust for the dependent censoring caused by the culling effects described above. High-shedding animals had lower calving rates in comparison with low-shedding or ELISA-positive animals, which tended to have higher calving rates than test-negative animals.

Scenario analysis of changes in consumption of dairy products caused by a hypothetical causal link between Mycobacterium avium subspecies paratuberculosis and Crohn's disease.

Johne's disease is an infectious disease of cattle caused by Mycobacterium avium subspecies paratuberculosis (MAP). Crohn's disease (CD) is a human disease of unknown etiology that is characterized by chronic bowel inflammation. No causal link has been scientifically established between MAP and CD, but it is important to understand possible impacts on society should such a causal link be established. The goal of this paper is to analyze the implications and the possible economic impacts that finding such a link would have on milk demand in the dairy industry and to provide a framework for further discussion among stakeholders. Three scenarios were developed based on the effectiveness of possible risk-mitigation strategies. In the first scenario, it was assumed that an effective strategy exists; therefore, a negligible demand decrease in the consumption of dairy products was expected. In the second scenario, it was assumed that new risk mitigation would need to be implemented to minimize the health hazard for humans. In this case, a small milk demand decrease was expected, but larger demand decreases were also possible. The third scenario assumed that no fully effective risk mitigation was available, and this resulted in a considerable demand decrease and a potential reduction in milk supply as a result of regulatory measures. A milk demand reduction of 1 or 5% resulted in a reduction in consumer surplus of $600 million and $2.9 billion, and a reduction in dairy farm income of $270 million and $1.3 billion, respectively. A decrease in milk supply would cause a slight increase in total losses, but would cause the greatest losses to test-positive dairy farms. Given the current scientific knowledge about MAP and CD, we conclude that if a link were established, it is most likely that the first or second scenario would occur. Thus, consumer response and economic consequences to the discovery of such a link are expected to be limited, but could be large if the consumer's perception of risk is large or if risk-mitigation strategies were ineffective.

Direct production losses and treatment costs from bovine viral diarrhoea virus, bovine leukosis virus, Mycobacterium avium subspecies paratuberculosis, and Neospora caninum.

Our purpose was to determine direct production losses (milk loss, premature voluntary culling and reduced slaughter value, mortaliy loss, and abortion and reproductive loss) and treatmetn costs (veterinary services, medication cost, and extra farm labour cost) due to four infectious diseases in the maritime provinces of Canada: bovine viral diarrhoea (BVD), enzootic bovine leukosis (EBL), Johne's Disease (JD), and neosporosis. We used a partial-budget model, and incorporated risk and sensitivity analyses to identify the effects of uncertainty on costs. Total annual costs for an average, infected, 50 cow herd were: JD$ 2472; BVD$ 2421; neosporosis $ 2304; EBL$ 806. The stochastic nature of the proportion of infected herds and prevalence of infection within a herd were used to estimate probability distributions for these ex post costs. For all diseases, these distributions were right skewed. A sensitivity analysis showed the largest effect on costs was due to milk yield effects. For example, changing milk production loss from 0 to 5% for BVD increased the costs for the disease by 266%.

Progress in national control and assurance programs for bovine Johne's disease in Australia.

Cattle strains of Mycobacterium paratuberculosis are known to infect cattle, goats and alpaca in southeastern Australia, where there are also significant numbers of farmed deer. Although sheep strains have recently been identified in some cattle in Australia, epidemiological evidence to date supports the distinction (between bovine Johne's disease (JD), caused by cattle strains in cattle, goats and alpaca, and ovine JD, caused by sheep strains in sheep and goats) for the purposes of control and assurance programs. The National Johne's Disease Control Program is coordinated by the Australian Animal Health Council, working with the livestock industries and with the Commonwealth, state and territory governments. The council also brokers industry and government funding for the program. The National Johne's Disease Market Assurance Program for Cattle was launched in 1996 as the first of a suite of voluntary national market assurance programs (MAPs) to assess and certify herds as negative for JD. By December 1998, over 550 herds had achieved an assessed negative status. A MAP was also launched for alpaca in 1998 and a program for goats should be finalized in early 1999. National standards for state control of JD through zoning, movement controls and procedures in infected and suspect herds have also been developed. The paper covers factors affecting development and implementation, uptake of and improvements to national control and assurance programs for bovine JD in Australia.

Johne's disease: a hidden threat.

Paratuberculosis, which is also known as Johne's disease, is a chronic, progressive enteric disease of ruminants caused by infection with Mycobacterium paratuberculosis. Cattle become infected with M. paratuberculosis as calves but often do not develop clinical signs until 2 to 5 yr of age. The clinical disease is characterized by chronic or intermittent diarrhea, emaciation, and death. Although animals with clinical disease are often culled from the herd, animals with subclinical paratuberculosis may cause economic losses because of reduced milk production and poor reproductive performance. Although the economic impact of paratuberculosis on the national cattle industry has not been determined, it is estimated to exceed $1.5 billion/yr. The diagnosis of subclinical paratuberculosis is difficult. Bacteriologic culture is the most definitive method of diagnosis, but culture is time consuming and labor intensive. Serological assays are not very useful because animals do not develop an antibody response until the clinical stages of disease. Development of assays to measure cell-mediated immunity is critical to accurate detection of paratuberculosis in subclinically infected animals. Although not considered a zoonotic agent, M. paratuberculosis has been identified in intestinal biopsy tissue from patients with Crohn's disease, an inflammatory enteritis in humans. Currently, the potential human health risk is being addressed by research evaluating pasteurization of dairy products in the US.