Nevada County Picayune and Gurdon Times Newspaper Archive

Farm And Home News with Rex Dollar

Johne's disease is caused by mycobacterium paratuberculosis, a disease which lives and multiplies primarily in intestinal cells of the ileum and cecum and associated lymph nodes. Infection causes a gradual accumulation of an excess of affected cells which results in a thickening of the intestinal lining and eventually failure to absorb nutrients.

M.paratuberculosis infects cattle, sheep, goats and wild ruminants world wide. Losses due to Johne's range up to $1.5 billion.

Johne's disease is spread primarily by ingestion of the bacteria which is shed in the manure of infected animals, either directly or via contaminated feed and water. The bacteria is easily spread in manure throughout the environment by infected animals and equipment such as bucket loaders, manure spreaders, tires and boots.

The organism survives well in the environment including freezing. It does not tolerate extreme drying or direct sunlight, but the bacteria is usually protected by organic material. As contamination of the facilities and environment increases, so does the chance that animals living in it will become infected. Heavily contaminated soil, pastures, ponds and streams may also be significant sources of infection.

Calves and younger animals are the most susceptible to infection, but infection can occur at any age.

Affected animals typically exhibit weight loss accompanied by severe, intermittent or chronic diarrhea, which is unresponsive to treatment. Appetite remains normal, but animals eventually become emaciated and die or are sold for salvage.

Signs can be severe and progress the full course in a few days, or they can progress slowly over weeks or months. Signs may resolve in some animals to reappear later, often in another period of stress.

Clinical signs rarely develop in cattle less than two years old and occur primarily in two- to six-year old cattle. At any point in time only a small proportion of the infected animals in a herd will show clinical signs. Clinical cases, which often do not represent infection rates as the percent of infected animals with signs, may range from zero percent to as high as 25 percent in severely infected herds. Most infected animals in a herd will be subclinical and appear healthy, often for a long time, which can be months or even years.

The incubation period (time of infection to onset of disease signs) of Johne's disease ranges from one to many years. Conditions of stress associated with suboptimal management or nutrition, hormone shifts, calving, peak lactation or other diseases may trigger the clinical disease.

Fecal culture is the most accurate test and detects the presence of M.paratuberculosis in the manure. Infected animals shed the bacteria during later stages in infection. Serologic tests for Johne's disease are available but are less accurate than fecal culture because they may produce false positive and false negative results.

A commercial DNA probe test for fecal samples, which detects the presence of the genetic material belonging to the M.paratuberculosis bacteria, is available in some laboratories. Results can be obtained in two days. The specificity is 100 percent (no false positives) but the sensitivity (ability to detect infected animals) is quite low.

Control: The key to controlling and eliminating Johne's disease from an infected herd is management.

Identify infected animals or shedders of the bacteria by testing: These animals can be culled or managed and so can their manure. Information from fecal culture or serology is a useful tool.

Cull or isolate shedders and animals with clinical signs of Johne's disease. It is imperative to get them away from others, especially young stock, as they are shedding billions of organisms in their manure.

Protect young stock from contact with manure from mature animals. Separate facilities are ideal. Solid barriers can be used. Empty and clean buffer areas are very effective.

Keep calving areas dry and clean of manure.

Remove calves from the cow and calving area BEFORE the calf can ingest manure.

Prevent manure contamination of feed and water. DO NOT use common equipment to clean manure and load feed. DO NOT walk in feed mangers.

Sanitation - there is no substitute. Remove manure as completely and as often as possible.