Stage III: Clinical Johne's disease. Animals in this stage have advanced infection, 

 and clinical signs are often brought on by stress. CHnical signs at this stage include 

 acute or intermittent diarrhea, weight loss despite a normal appetite, and decreased 

 milk production. Some animals appear to recover but often relapse in the next 

 stressful period. Most of these animals are shedding billions of lohne's-causing 

 organisms, and fecal culture tests give positive results. Many animals are positive 

 on serologic tests as well. Clinical signs may last days to weeks before the animals 

 progress to Stage IV. 



Stage IV: Emaciated animals with fluid diarrhea. This is the terminal stage of the 

 disease in which animals become extremely thin and develop boiilc iaw. Animals 

 culled to slaughter in this stage may not pass inspection tor human consumption due 

 to disseminated infection. 



In the typical herd, for every animal in Stage 1\ , main t)thcr cattle are infected. For 

 every obvious case of Johne's disease (Stage IV) among dair\ cattle on the farm, 1 5 

 to 25 other animals are likcK' infected. The clinical case represents only the "tip of the 

 iceberg" of Johne's infection. 



In other ruminant species, the progression ol the disease ma\' occur nn)rc rapidly 

 with weight loss as the onh \isible sign ot infection. 



Epidemiology 



Johne's disease usualK- enters a herd when healthx- but infected animals (Stage I or 

 II) are introduced. Cattle are most susceptible to the infection in the first year of life. 

 Calves most often become infected by swallowing small amounts of infected manure 

 from the cah'ing environment ov udder of the cow. In addition, caKes can become 

 infected while in the uterus or b)- swallowing bacteria passed in milk and colostrum. 

 Studies have shown that up to 25 percent of calves are infected in utero if the cow is 

 in Stage III ot the disease. Calves ma\ become inlccled by exposure to contaminated 

 manure an\ time in the first year of life (e.g., from manure splatter to calves raised 

 near adult cows). 



Cattle of any age can become infected, though some age resistance does occur. This 

 age resistance can be overcome b\ high doses of bacteria over time from sources such 

 as manure-contaminated teed bunks or water sources. All ruminants are susceptible 

 to Johne's disease. In addition, all infected animals shed the organism through feces, 

 thereby creating a possible route of exposure. 



Diagnosis 



In the live animal, fecal culture is the most accurate diagnostic test. However, on a 

 herd basis only about 40 percent of infected cattle will be disclosed by even the most 

 sensitive fecal culture technique. The sensitivity of fecal culture is low because some 

 infected cattle (Stages I and II ) do not shed the agent in their manure or because 

 some animals shed the agent only intermittently and can be missed at testing time. 



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