Control de paratuberculosis: Un programa con un horizonte a 10 años

Ramón Justé¹, Joseba Garrido¹

(1)-NEIKER

In Spain, paratuberculosis (PTB) was first documented in Charolais cattle in Bizkaia (Juste et al., 1983). Currently, it can be considered widely distributed as the latest large slaughterhouse study showed (Vazquez et al., 2014). There are different voluntary control plans based on test-and-cull (T&C) strategies and good management practices carried out by cattle, sheep and goats’ health defense groups, which are subsidized by regional administrations (Whittington et al., 2019). Although cost-benefit analyses (Cho et al., 2012; Juste and Casal, 1993), show that vaccination against PTB is the best way of controlling the disease and, in Spain, it is widely practiced in dairy sheep and goats, its use in cattle has been restricted to a field trial in the Basque Country that has lasted 15 years. In it, we showed that paratuberculosis was associated with a 8% milk production drop, with vaccination reducing overall mortality by 30% in the first two years of life (Juste et al., 2021) and that MAP shedding could be stopped in less than 10 years of annual replacers vaccination or T&C (in preparation). The study showed that ELISA testing was useless, while fecal PCR proved to be a reliable indicator of prevalence.

The program contemplates two strategies: T&C and vaccination. Each farm has to choose one of them and both should be available in officially tuberculosis free (OTF) regions.

For T&C, all animals aged 12 months or more should be submitted to a recognized fecal PCR with killing of positives in less than one month. According to time and results, five categories will be recognized. Unknown: No confirmatory tests have been carried out. PTB1: The herd has been annually tested between 1 and 4 years and all positive animals have been culled. PTB2: The program has been carried out for 5 years and 10 years and all positive animals have been culled. PTB3: The herd has been submitted to annual testing for more than 4 years and no positive results have been found in the last two consecutive years. PTB free: The herd has been submitted to annual testing for more than 5 years and no positive animals have been found in the last three consecutive controls. Farms in status PTB4 can reduce controls to semiannual antibody detection in bulk tank milk or in an annual fecal sample of not less than 10 animals in order to keep that status. Herds in the higher status levels (PTB3 and PTB4) cannot introduce animals from farms at lower levels. Farms with lower status should only buy animals from farms with higher status but can also exchange animals within their own level. These farms can never introduce vaccinated animals.

Only farms with an initial prevalence higher than 5% by any method and where the local animal health authority have assessed its compatibility with the national bovine tuberculosis eradication program are eligible for vaccination. At the start of the program, to estimate the PTB herd prevalence, blood and feces will be sampled. At that moment, all animals to be kept in the farm should be vaccinated. Afterwards, only replacers (not those to be sold for meat or killed before 18 months). Vaccination should be given as soon as possible and always before the first month of life. After vaccination, PTB confirmation of suspected cases will be carried out by fecal PCR and positive animals must be culled as soon as possible. A biannual PCR control of all cows, 3 surfaces and 3 watering points should be carried out to determine overall paratuberculosis situation. Vaccination of replacers should be indefinitely maintained. Vaccinated farms will be classified as follows. PTB vaccinating farm: Farms that have been vaccinating for less 5 years. PTB vaccinating-negative farms: Farms that have been vaccinating for more than 5 years and are negative in fecal and environmental PCR. Vaccination status will be recorded in the individual bovine identification document. Vaccinating farms can exchange animals only with other farms in vaccination but cannot sell for life to herds in T&C. The farm can acquire animals from T&C at any stage that will be vaccinated at entrance. PTB-free farms: Farms that have been negative in 5 or more consecutive years in each of the strategies monitoring.

In regions not officially tuberculosis free only T&C would be allowed except in special cases such as herds of special genetic value with a risk of extinction or in any other situations that the local competent authority deems necessary. Farms within this strategy can only be submitted to comparative cervical (Serrano et al., 2017) testing in the national bovine tuberculosis program and must be very wary of possible cases.

Both strategies allow to completly eliminate shedders in between 6 and 10 yearly cycles of testing and culling or vaccination or both.