DIAGNOSIS OF JOHNE’S DISEASE IN CATTLE
Worldwide, Johne’s disease (JD), caused by Mycobacterium avium subsp. paratuberculosis, is one of the most prevalent and economically important diseases of livestock and other ruminants. However, it is largely unnoticed on the dairy and its symptoms may be unfamiliar to most dairymen. Johne’s disease (JD) was first diagnosed in India in 1913 at Hissar followed by reports of JD throughout the country with incidence ranging from 1.78 to 1.9%. Latest reports reveal an increased seroprevalence of JD ranging from 15% to 78%. Larson et al, (1978) showed that controlled clinical vaccination trial with whole cell bacterin reduces incidence of clinical JD. van Schaik et al, 1996 showed that vaccination is cost-effective due through reducing the culling rate of clinically affected cattle. National Animal Health Monitoring Systems (NAHMS) study, Dairy 2007, shows that 68.1 percent of U.S. dairy operations are infected with Mycobacterium avium subsp. paratuberculosis (MAP) and also suggests that at least one out of every four U.S. dairy operations may have a relatively high percentage of Johne’s-infected cows in their herds. Although most U.S. beef herds are not infected with Johne’s disease, it is estimated that eight out of 100 U.S. herds may be infected with this devastating disease. The estimation of herd in Netherlands was found to be 55% prevalence (Muskens et al 2000) and in Denmark the figure was 47% (Nielsen et al 2000).
Johne’s disease (JD) or paratuberculosis in animals is incurable, chronic wasting and debilitating disease characterized by weight loss and profuse diarrhea. Paratuberculosis is principally a disease of ruminants but MAP can also infect non ruminant animal species (pigs, dogs, horses, cat etc) including free ranging animals (Blue bull, deer, rabbits) and primates (Chiodini et al., 1984). Johne’s disease adversely affects animal productivity leading to huge economic losses and has been recognized as one of the most costly infectious disease of dairy cattle in the world (Hasonova and Pavlik, 2006). The morbidity rates are very high and distributed over a period of time, thus losses in production go unnoticed and have never been estimated in India despite low per animal productivity (Barbaruah and Joshep 2008). Countrywide survey of MAP infection have not been undertaken so far though JD is endemic in domestic livestock (Singh et al. 2008a, Sharma et al. 2008, Kumar et al. 2007). Country at present lacks any commercial indigenous, cost effective and sensitive diagnostic kits. In animals which do not have apparent symptoms of the disease is still important because it may results in decreased milk production, increased culling rates, decreased fertility and increased incidences of mastitis. Apparent clinical signs may not be seen for 2 to 5 years after infection has taken place during calfhood. After infection has taken place but before clinical symptoms are apparent, the infected animal is likely to be shedding bacteria. These bacteria can contaminate the calving and housing areas and infect other animals in the herd. The evidence suggests that Mycobacterium avium subsp. paratuberculosis shed in the milk from dairy cattle may cause Crohn's disease in humans as pasteurization does kill the bacteria. Control and management of Johne's disease are complicated by the lack of a rapid, sensitive diagnostic test for identifying diseased animals before clinical signs develop. However, an age-dependent resistance develops, and cattle over 1 year old when exposed to the organism rarely become chronically infected (Doyle, T. M. 1953). Paratuberculosis is not only chronic but is also currently incurable and often remains in a subclinical state for years (Cousens, 2004). Thus, it is important to diagnose the disease as early as possible to reduce losses and also spread of infection to susceptible animals and humans. The...
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