NEWS

This is the title of an August 15 blog posting by the Beef Cattle Research Council (BCRC) in Canada.  The author uses Johne’s disease as an example about the broader issues of farm biosecurity.

Here is an excerpt:

A well-run herd can introduce and spread Johne’s disease just by buying the wrong animal. Johne’s cannot be prevented by vaccination or effectively treated by antibiotics, and accurately identifying and culling infected animals is very difficult before they get visibly ill. Johne’s disease also can’t be prevented by high herd health, nutritional, grazing, or genetic management. Many beef producers may think they have closed herds, but realistically speaking hardly anyone does. Appropriate biosecurity is the best thing producers can do to help keep Johne’s from entering their herds.

The article goes on to describe the prevalence of Johne’s disease in Canadian beef cattle herds and much more.  So, check it out!

Management decisions to protect calves from infection such as separation of infected cows at calving and discard of calves, milk and colostrum from MAP positive cows, or pasteurization of their milk, are uncommon in seasonal, pastoral New Zealand (NZ) dairy farming. Pasture management is greatly complicated by any increase in the number of groups of grazing cows. The NZ Animal Compounds and Veterinary Medicines act (1987) prohibits the sale of milk for human consumption when that milk is contaminated with drug residues. Consequently, calves are commonly fed on milk from sick cows, those undergoing antimicrobial treatment or excluded from the main herd for other reasons.

Therefore, in NZ, there has been relatively little engagement from dairy farmers in the control of JD unless they have experienced a high clinical prevalence and there is evidence of increasing prevalence of JD especially in the South Island of the country.

Andrew Bates et al., Vetlife Centre for Dairy Excellence, Geraldine, NZ reported in BMC Veterinary Research (Open Access) the results of a single herd study where a high prevalence of clinical JD and MAP infection was reduced over a 4 year period using an annual test and cull approach. The strategy was based on a herd testing protocol using an initial herd screening using serological ELISA coupled with a quantitative fecal PCR (fPCR) test to confirm the status of ELISA-positive animals.

Over the 4 year period a total of 4,358 blood samples were submitted from 2,211 cows and of these 683 were submitted for fPCR. Culling decisions followed a decision tree approach shown below. To aid the removal of animals shedding large numbers of MAP, a priority was made to remove all animals with a high fPCR status, followed by those that were had high ELISA results.

For all age groups considered the apparent seroprevalence of cows testing positive decreased from 26% in 2013–2014, to 2.3% in 2016–2017. The reported proportion of calved cows culled annually from suspected clinical Johne’s disease fell from 5% in the year preceding the control program to 0.4% in the final year of the study.

On this farm, reduction in the prevalence of infection was achieved by reducing the infectious pressure through targeted culling of heavily shedding animals together with limited measures to protect calves at pasture from exposure to Mycobacterium avium subsp. paratuberculosis (MAP).

This study demonstrates that - with a combination of pre-calving diagnostic testing to identify and remove animals that are the major source of infectious spread, coupled with simple management changes to physically separate replacement calves from MAP infected adult cattle - effective reduction in the prevalence of JD is possible for NZ dairy farmers.

Comment: This important study validates that removing the most infectious animals from a herd significantly decreases the prevalence of the infection.  However, it ignores the economic utility of the program, i.e. the cost-benefit of this approach.  If the ELISA was valued at US$5.00 and the fPCR at US$30 (typical costs in U.S. labs), then the cost of this control program, in laboratory testing costs alone, was $42,280.  Most herd owners would question the return on investment without receiving some compensation from the processor buying his/her milk or from a governmental agency concerned with food safety. 

The study recently published in BMC Veterinary Research, which surveyed 48 countries around the world, highlighted the crucial need to secure funding and international support for implementing long-term veterinary control programs against paratuberculosis. BMC publishers asked Emeritus Professor Richard Whittington, who led and formed the network of international experts, more about the disease, how the survey was carried out and the implications of the survey findings. The blog title is: Q&A on Paratuberculosis in livestock: insights to a neglected disease and experts’ recommendations.

Read the BMC blog.

If you missed it, this takes you to the original survey publication.

Research Article

Nathalia M. Correa-Valencia and colleagues reported on the herd-level prevalence of paratuberculosis in Northern Antioquia, Columbia. Their study, titled: Prevalence of Mycobacterium avium subsp. paratuberculosis infection in dairy herds in Northern Antioquia (Colombia) and associated risk factors using environmental sampling, appears in the latest issue of Preventive Veterinary Medicine. In comparison to other countries, the prevalence of paratuberculosis in dairy herds in this region of Columbia is low.  This finding should increase efforts to protect the as yet non-infected herds.

Abstract

This cross-sectional study aimed to determine Mycobacterium avium subsp. paratuberculosis (MAP) herd-level prevalence using a quantitative real-time PCR method (qPCR), performed on environmental samples. Secondly, the study aimed to explore herd-level risk factors associated with the presence of MAP in dairy herds with in-paddock milking facilities of the Northern region of the Province of Antioquia (Colombia). Study herds (n = 292) located in 61 different districts from six municipalities were randomly selected amongst 7,794 dairies registered in the foot-and-mouth disease vaccination records from 2015. The sampling strategy considered a proportional allocation, both at municipality and district level. Participant herds were visited once between June and October 2016 to collect one composite environmental sample and to complete a risk assessment questionnaire. Each composite environmental sample contained material from six different sites of concentration of adult cattle and/or high traffic areas (e.g. areas surrounding waterers and feeders, areas surrounding the current mobile milking-unit places). Identification of MAP was achieved using a duplex qPCR (Bactotype MAP PCR Kit®, Qiagen). A herd was considered as MAP infected if the environmental sample was positive in the qPCR. Information about the general characteristics of the herd, management practices, and knowledge about the disease was collected using the risk-assessment questionnaire. The information on risk factors was analyzed using a multivariable logistic regression model. The apparent herd-level prevalence was 4.1% (12/292; 95% CI: 1.8-6.4). Herds with a history of mixed farming of cattle with other ruminants had higher odds of being MAP infected than herds without (OR = 3.9; 95% CI: 1.2-13.2). Our study demonstrates the MAP prevalence in dairy herds from Antioquia, Colombia and the possible relationship between MAP environmental positivity with the history of mixed farming of cattle with other susceptible ruminants.

This map from Wikipedia shows the location where the study was done.

Comment: Lombard et al. reported results from a survey of U.S. dairy herds using similar surveillance methods (Preventive Veterinary Medicine 108:234-238).  In that NAHMS Dairy 2007 study, the apparent herd-level prevalence of MAP was 70.4% (369/524 had ≥1 culture-positive composite fecal samples out of 6 tested).  Adjusting for the estimated herd sensitivity and herd specificity of the test method, the estimated TRUE herd-level prevalence of paratuberculosis in U.S. dairy herds was 91.0% (95% probability interval, 81.5 to 99.3%).

Research Article – Open Access

Luttikholt et al. from the Department of Small Ruminant Health, GD Animal Health, The Netherlands, reported on the accuracy of an ELISA (IDEXX) used on milk samples from goats in both MAP-vaccinated and non-vaccinated herds. The cut-off for a positive test was based on ROC analysis and set at 25 S/P%. The cut-off recommended by the kit manufacturer for bovine milk samples is ≥30 S/P%. This article appears in the July 2019 issue of Veterinary Sciences.

Abstract

The aims of our study were to calculate the most appropriate cut-off value for milk samples in a serum-validated Mycobacterium avium subsp. paratuberculosis (MAP) ELISA and to analyze MAP ELISA responses in milk samples from vaccinated and non-vaccinated dairy goats in the Netherlands. Analyzed herds were representative for location and herd size of dairy goat herds in the Netherlands. A significantly higher proportion of the analyzed 49 herds were organic as compared with the total Dutch dairy goat population. First, the MAP ELISA was optimized using 992 paired serum and milk samples. At a cut-off of 25 S/P%, the relative sensitivity (Se) was 58.4% (n = 992, 95% CI: 48.8%−67.6%) and relative specificity (Sp) was 98.5% (n = 992, 95% CI: 97.5%−99.2%), as compared to serum ELISA results. The percentage of positively tested herds was 78.2% (n = 49, 95% CI: 63.4%−88.1%). The percentage of positive milk samples per herd (n = 22) was on average 4.6% (median, min, and max of 4.7%, 0.0%, and 10.7%, respectively). Average age of ELISA-positive (3.2 years) and -negative goats (3.2 years) was not different. Significantly more vaccinated goats tested positive (6.7%) as compared with non-vaccinated goats (1.1%). This study shows that a high number of vaccinated and non-vaccinated commercial dairy goat herds in the Netherlands have MAP-ELISA-positive goats.

Comments

Clearly, MAP infections are common in Dutch dairy goat herds (78.1% had 1 or more milk ELISA-positive animals) which somewhat higher than MAP infection prevalence estimates among goat herds in other countries (see the discussion section of the paper and previous news items on this site). MAP vaccination increased the rate of animals testing positive by the milk ELISA but, as the authors acknowledge, this could be because vaccinating herds have a higher infection rate, i.e. the reason they started vaccinating for paratuberculosis.

This study compared an ELISA on milk samples to the same ELISA applied to serum samples as the reference test. Normally the reference test should be a more sensitive assay such as fecal culture or fecal PCR – sometimes called “gold standard” assays.  By using the serum ELISA as a reference test the reported sensitivity of the milk ELISA is somewhat inflated because the serum ELISA sensitivity in goats when compared to fecal culture has been reported as 74.3% using fecal culture as the reference test by traditional sensitivity estimate methods (Salgado et al., 2007) and 63% using Bayesian methods and including fecal culture results (Kostoulas et al, 2006). Thus, if we assume that the serum ELISA reference test in this study detected 68.6% of all truly MAP-infected animals (based on the mean sensitivity reported by two published studies I cited) and the present study found that only 58.4% of the serum ELISA-positive animals were also milk ELISA-positive, one could estimate that true sensitivity of the milk ELISA in goats for detecting MAP infected animals shedding MAP in feces was at most 40% (58.4% x 68.6%). Had the authors used the cut-off recommended for this ELISA when bovine milk samples, the sensitivity estimate would be lower still.

Use of low sensitivity tests works well for herds, regions or countries wanting to demonstrate that MAP is not a big problem and/or to lessen consumer concerns. However, it can misrepresent the true magnitude of the paratuberculosis problem and lead herd owners to under-estimate the significance of MAP infections to the health of their herd.

Research Article

F. Larussi and colleagues from the Experimental Zooprophylactic Institute of Apulia and Basilicata, Foggia, Italy and University of Barri, Italy reported a large study to investigate the prevalence of Johne’s disease in sheep and goat herds and the risk factors associated with being seropositive. This study was published in Small Ruminant Research August 2019.  It used serum samples and the ELISA kit sold by ID-Vet- Innovative Diagnostics, France.

Abstract: Paratuberculosis (PTB) is a well-documented chronic and sometimes fatal infection that affects the small intestine of ruminants both in captive and free-ranging living conditions. Although the infection has been detected on small ruminant farms worldwide, epidemiological and risk factor information regarding Mycobacterium avium subspecies paratuberculosis (MAP) infection on semi-extensive sheep and goat farms is generally still scarce, particularly in the Mediterranean area and in Italy. This paper reports the epidemiological findings and risk factors of the infection on semi-extensive sheep and goat farms in Apulia. It particularly focuses on the involvement of biological, structural and management factors, as well as the farmers’ socioeconomic data as predisposing causes of PTB, and investigates their possible connection with the survivability of the infection.

The true seroprevalence values of MAP on semi-extensive Apulian sheep and goat farms are reported and the risk factors causing the spread of infection analyzed. Data were collected through a two-year survey over the whole regional area, involving 419 farms, 16,903 sheep and 9369 goats. The epidemiological results showed a true seroprevalence of 66.2% for flocks and of 9.7% at the animal level. Analysis of the risk factors showed that the spread of infection occurs via several concomitant biological, managerial, and farmer-related factors.

The survey highlighted the need for urgent and suitable control plans providing guidelines to help Apulian farmers and their veterinarians contain and eliminate the disease, prevent biological risks for animal and humans as well as negative economic effects on the regional livestock sector.

Comment: This is a well-designed and executed study and one of the largest of its kind in sheep and goats. The study’s analysis of risk factors was particularly interesting and useful. The prevalence findings are similar to those of a survey if dairy sheep and dairy goats in Ontario Canada reported in The Canadian Veterinary Journal, February 2016. Unfortunately, neither the Italian study nor the Canadian study are open access article. Science Direct charges a fee of US$35.95 to purchase a PDF of the Italian article.

New thinking on Johne's and Getting the best from your JD review - AHDB Dairy

Dr. Peter Orpin offers a webinar (published June 27, 2019) discussing how veterinarians and farmers can work together effectively to reduce the prevalence of Johne’s disease in their dairy herds using structured risk assessments, farm walks and 100% engagement in Johne's disease control using UK’s National Johne's Management Plan.

During this webinar Dr. Orpin, a veterinary practitioner in Leicestershire and one of the key experts involved in developing the control strategies for Action Johne’s covers:

• a review of the risks of transmissions and new thinking on disease progression within infected herds,
• advice on how we can effectively manage and create a clear plan of action for infected cows and
• how to generate a “green calving line and green calf line” to produce healthy productive low-risk JD replacements.

The control of Johne's Disease is a real challenge but one that can be tackled. The majority of dairy farms in Great Britain are now part of the National Johne's Management Plan and have adopted one of the 6 strategies for dealing with Johne's disease recommended by the Action Group of Johne’s.

You can access this one hour long webinar on You Tube (the first 40 minutes are a presentation  and the remainder is Q&A).

Explanatory note: The UK program adopts the Danish system of classify cows based on ELISA testing of milk samples for antibody to MAP and the color code animals based on the results: “Red” cows are those that tested positive on the last 2 milk ELISAs, “Yellow” cows have fluctuating milk ELISA results, and “Green” cows are consistently negative by milk ELISA. The Red cows are considered in the most advanced stage of Johne’s disease and the most infectious, i.e. highest risk of spreading the infection on the farm.

Comment: The webinar is particularly good at describing why Johne’s disease control programs on dairy farms fail.

Research Article

A Chilean research team has published a study of how chemical treatments of manure and other wastes from dairy cattle, collectively called slurry, affect the viability of MAP as well as other bacterial organisms. The article appears in the Journal of Applied Microbiology and is authored by C. Avilez et al. from the Instituto de Medicina Preventiva Veterinaria, Universidad Austral de Chile, Valdivia, Chile.

Abstract

Aims: A major drawback of using dairy slurry as fertilizer is that it may contains pathogens such as Mycobacterium avium subsp. paratuberculosis (MAP), and it could represent a risk to animal and public health. Thus, the aim of this study was to evaluate the fate of MAP and bacterial communities in dairy slurry after chemical treatments.
Methods and Results: Cattle slurry, naturally contaminated with MAP, was collected from a dairy herd and divided into 32 glass bottles which were assigned to eight different treatments (control, 3.0% CaO, 0.5% NaOH; 0.087%, 0·11% and 0.14% H2SO4; and 1.0 and 2.5% KMnO4). Treated dairy slurry samples were evaluated at 0, 1, 3, 7, 15, 30 and 60‐days following treatment application for viable MAP and dairy slurry pH, and in addition temperature in this material was monitored continuously. Bacterial counts were estimated at each sampling time. A Bayesian zero‐inflated Poisson mixed model was fitted to assess the effect of each treatment on the count of MAP cells. Model results indicated that only the 3.0% CaO treatment had a statistically important negative effect on MAP counts during the study period. For most treatments, MAP was undetectable immediately after chemical treatment but re‐appeared over time, in some replicates at low concentrations. However, in those cases MAP counts were not statistically different than the control treatment. Regarding the fate of the other bacterial populations, the Firmicutes phylum was the dominant population in the un‐treated slurry while Clostridia class members were among the most prevalent bacteria after the application of most
Conclusion: Only 3% CaO treatment had a statistically important negative effect on MAP viability in cattle slurry.
Significance and Impact of the Study: This study provides evidence of MAP partial control in dairy slurry. This information should be considered as a best management practice to reduce MAP and other pathogens for slurry management on dairy farms. chemical treatments.

Comment: Unfortunately, this is not an Open Access publication. As indicated on the Wiley Online Library site, the article can be purchased for $7 for 24 hour access, $16.50 for read-only access, or $42 for the full text and PDF download.

Research Article

J. Smith and S. van Winden from the department of Pathobiology and Population Sciences, Royal Veterinary College, Hertfordshire, UK reported 10-June-2019 in the journal Animals a study on the association of lameness in dairy cattle with a diagnosis of Johne’s disease (JD) based on ELISA testing of milk samples (IDEXX kit).

Findings: JD cows turn lame on average three months earlier and are lame 2.7 times more often than non-JD cows. Further, high-positive cows were 2.8 times more likely to develop lameness after JD diagnosis compared to medium-positive cows (referring to the magnitude of the ELISA result - further evidence of the importance of reporting ELISA results quantitatively). Results of this study suggest that there is a link between JD and lameness and that JD precedes lameness. The underlying mechanisms for this association remain unknown and were not the scope of this study.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Comment: To assess lameness in dairy cattle a scoring system was created and converted to an App by the faculty at the University of Wisconsin, School of Veterinary Medicine, department of Food Animal Production. Read more about the App and scoring system HERE.

REVIEW ARTICLE

An excellent review on MAP in milk and pasteurization was published 11-June-2019 in International Journal of Dairy Technology. The article is titled: Are we closer to understanding why viable cells of Mycobacterium avium subsp. paratuberculosis are still being reported in pasteurised milk? The author is W Michael A Mullan, UK researcher.

Abstract: Mycobacterium avium subsp. paratuberculosis (MAP) continues to be associated with Crohn’s disease. Following work in the 1990s that suggested that statutory pasteurisation of milk (72 °C, 15 s) was insufficient to destroy MAP, the UK Dairy Industry increased the holding time to 25 s. Since then, some plants have increased the lethality of pasteurisation further with a number using 78 °C for 27 s. Despite the increase in lethality, a recent survey of pasteurised milk in England found that 10.3% of pasteurised milk samples tested positive for viable MAP. This article discusses the significance of MAP and why viable MAP might be found in pasteurised milk.

This 13 page review nicely summarizes the state of understanding on MAP and pasteurization providing 7 tables and 66 references. It concludes with 8 possible explanations as to why MAP continues to be found live in retail HTST pasteurized milk. Normally, this is not an Open Access publication. As indicated on the Wiley Online Library site, the article can be purchased for $7 for 24 hour access, $16.50 for read-only access, or $42 for the full text and PDF download.

UPDATE: The publisher has agreed to make the article freely available, i.e. open access, for one month from today, June 18!  Thank you Wiley Online!

Note: Please excuse the use of both the British and American spellings of pasteurization / pasteurization. Just trying to be fair :-)