Johne�s Disease - - Potential New Controls

Dr. Clell V. Bagley, D.V.M.
USU Extension Veterinarian

Included in the previous issue of the Newsletter were two articles on the potential for increased concern about the relationship between Johne�s Disease and Crohn�s Disease in humans. Below are abstracts from two other publications which describe procedures with the potential to aid in control of JD. I think you will find them very interesting.
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1. Johne�s Disease: The Effect of Feeding Monensin to Reduce the Bioburden of Mycobacterium avium subspecies paratuberculosis in Neonatal Calves

Johne�s disease (paratuberculosis) is a chronic, granulomatous infection of the intestinal tract of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP). There is no approved treatment, no known way to eliminate the infection once established, nor is there an effective vaccine for the disease. Johne�s disease (JD) has emerged as an important disease of cattle due to its economic impact and the potential link to human Crohn�s disease. Methods to control the spread and to reduce within herd transmission of Johne�s disease (JD) are being adopted by both dairy and beef herds in many states through implementation of the national Johne�s disease program. Implementation of best management practices (BMP) following a herd risk assessment (RA) designed to reduce the risk of transmission of JD remains the focal point of the national effort to reduce the prevalence of JD in cattle herds today. Initial infection with MAP is generally considered to occur in the neonatal calves. Our laboratory at the University of Pennsylvania-New Bolton Center has successfully induced experimental MAP infection in neonatal calves via oral gavage of MAP on two consecutive days. The current experiment was designed to assess the efficacy of monensin to reduce pass-through fecal shedding and to reduce tissue bacterial load (bioburden) of MAP in calves. Twelve neonatal Holstein heifer calves (one to three days of age) were purchased from a local dairy. The herd had no evidence of clinical Johne�s disease and was considered a low-risk herd with excellent biosecurity measures for newborn calves. Calves were randomly assigned to receive a carrier containing 35 mg monensin (n=6) or placebo (n=6) added to the milk replacer at each twice-a-day feeding upon arrival at the research facility. The trial was conducted as a randomized double blind trial. Both groups of calves were administered two oral doses of viable Mycobacterium avium subspecies paratuberculosis (MAP) on two consecutive days between days seven and nine of the trial or days eight to 11 of age.

Results

There were no significant differences in feed consumption or weight gain between the two groups. Calves fed monensin had fewer culture-positive (55%) fecal samples, fewer total HEYM positive tubes (63%) and less MAP cfu (72%) detected in the manure compared to controls. Furthermore, monensin fed calves had fewer culture-positive tissues (66%), fewer total culture positive HEYM tissue tubes (68%) and lower MAP cfu (87%) in the tissues compared to controls. All MAP isolates from both groups were from tissues within the abdominal cavity. No isolations of MAP were made from liver, hepatic lymph node or kidney tissues of either group of calves.

Significance

Results of this study suggest that monensin effectively reduced tissue colonization with MAP following oral challenge, and also reduced fecal pass-through shedding of the organism. The MAP detected in fecal samples was clearly the result of pass-through and not active shedding from infected mucosal epithelial cells. Presumably, reduced tissue colonization in the short-term model would translate to lower mycobacterial burden and likelihood of shedding MAP in manure and clinical disease in adulthood. In a prior study, monensin was shown to either halt the progression of lesions or reverse the lesions in cattle with clinical signs of Johne�s disease. Taken together, the results of these two studies suggest that monensin may play a useful role both in the prevention of MAP infection in young cattle, and in the treatment of established infection in adults. The amount of monensin (70 mg) administered per day to calves in this study is higher than the amount that would normally be consumed by a neonatal calf in a calf starter. This study was a proof-of-concept study to determine the efficacy of monensin in controlling infection with MAP in the neonatal calf. Additional work to determine efficacy for controlling infection with MAP with normal inclusion rates in a calf starter are indicated. Monensin added to cattle rations at all phases of their life, coupled with stringent implementation of biosecurity management practices at the farm level, offers new hope to help reduce the unyielding spread of this disease among the nation�s cattle herds. The costs are modest compared to many other management tools designed to reduce MAP bioburden within cattle herds. No other management technique evaluated to date has been shown to reduce MAP shed in manure of cattle and to reduce the tissue uptake of MAP to this extent. In these experimental calves, monensin greatly reduced (>60%) both the pass-through fecal shedding and systemic tissue uptake.

AABP Proceedings 38:191-192 (Sep 2005)

2. MAP Super-shedders: Another Factor in the Control of Johne�s Disease

Traditionally, fecal cultures were either positive or negative for growth of Mycobacterium paratuberculosis (MAP). Nearly all culture-positive cattle were judged to be infected, shedding MAP, and thus a threat to spread the disease to susceptible cattle and were culled from the herd as quickly as possible. Over time it was recognized that differences in MAP shedding existed among culture-positive cattle. Cattle were classified as low, moderate or high shedders based on the visible colonies of MAP on the surface of solid media. Rarely did authors provide the estimated MAP colony forming units (cfu) per gram of manure. Additionally, culture methods were not standardized among diagnostic laboratories in the US, which made it difficult to compare results from one laboratory to another.

Over the past five years most laboratories in the US report the number of visible MAP colonies on each tube of HEYM, but rarely enumerate above 50 to 70 colonies per tube. Accounting for sample preparation, 50 colonies on each of four tubes represents an estimated 1,050 colony forming units of MAP per gram of manure. The objective of this study was to determine the range of MAP cfu/gram of manure in cattle classified as heavy shedders.

Fecal samples from cattle classified as high shedders were serially diluted: 1:5, 1:10, 1:50; 1:100, 1:500, 1:1:000, 1:5,000, 1:10,000 and 1:50,000. This initial pilot serial dilution series helped define a closer range to process a larger number of heavy shedders. Fecal samples from more than 200 cattle classified as heavy shedders were cultured with the routine culture methods and serially diluted at 1:100 and 1:1,000. Super-shedders are defined as cattle with fecal samples having more than 10,000 cfu MAP per gram of manure.

Results

The vast majority of heavy shedders would be classified as super-shedders with more than 10,000 cfu MAP per gram of manure. Based on serial dilution of fecal samples, we have demonstrated that some infected cattle not showing clinical signs of Johne�s disease (JD) shed more than 1,000,000 cfu of MAP per gram of manure. The typical range of MAP cfu for cattle showing clinical signs of JD is from 50,000 to 250,000 cfu of MAP per gram of manure.

Significance

Based on this commonly accepted numerical assessment of MAP cfu, high shedders represent the greatest threat to spread the disease, but rarely did anyone appreciate that one heavy shedder could excrete adequate MAP in the environment to be equivalent to a high shedder in composite manure samples, or that one heavy shedder could excrete more MAP cfu than 5,000 low shedder cattle. Super-shedders represent the greatest risk to spread Johne�s disease among herd mates. Some super-shedders could contaminate the environment with more MAP than 160 heavy shedders, more than 2,000 moderate shedders and more than 20,000 low shedders. The frequency of super-shedders among culture positive cattle in infected herds is being investigated at this time. Based on this new dimension of super-shedders, a significant proportion of low shedders are likely to represent �pass-through� and not active true infections. As little as 10 ml of manure (1 x 107 cfu of MAP) from a super-shedder could both infect another calf or heifer and result in the manure of the heifer being culture-positive with several colonies per tube. Previous research from this laboratory has shown that �pass-through� can result when cattle consume manure from cattle with clinical Johne�s disease. The challenge to the Johne�s academic community will be to develop diagnostic methods to detect these super-shedders in a cost efficient manner and eliminate them from the herd prior to massive environmental contamination.

AABP Proceedings 38:193-194 (Sep 2005)

For more information contact Clell Bagley at (435) 797-1882 or clellb@ext.usu.edu. ©