Paratuberculosis

Paratuberculosis


A silent disease


Paratuberculosis is a disease that generates great economic and big heath concerns. It is endemic throughout the world and mainly affects both meat and milk industry in cattle, sheep and goat herds.

It is produced by the bacterium Mycobacterium avium subsp. paratuberculosis. It can survive 11 months in soil contaminated with faeces, between 5 months and 9 months in water and 17 months in laboratory conditions. It could have an incubation period of up to 5 years.

This disease occurs silently, with long incubation periods as well as subclinical stage, where the symptoms are not visible but the disease spreads.

Transmission


It is commonly transmitted by ingestion of food, soil and water contaminated by faeces with the bacteria, or through the consumption of milk and colostrum from infected animals because of the faeces in udders. Other transmission pathways such as transplacental have also been associated in almost 40% of animals in the clinical stage.

Cattle and other ruminants less than 6 months of age are the animals with the greatest risk because it is associated with the period of physiological development of the lymphoid tissue of the intestine. Once the bacterium enters the oral route, it is located in the intestine and produces inflammation with cell proliferation causing granulomatous enteritis.

The factors that may be of risk for the introduction and bacterial shedding within the herd are:

  • Introduction of replacement animals without prior sanitary checks, specially from herds with unknown paratuberculosis status.
  • Contact of young animals with faeces of other animals or contaminated soils.
  • Contamination of water sources and food with faeces.
  • Uncontrolled colostrum of suckler animals with faeces in udders.
  • Use of the same equipment for cleaning and feeding animals.
  • Contact of animals under one year with adult animals.

Clinical Signs


Paratuberculosis is mainly a subclinical infection and the onset of clinical signs is determined by different factors such as infective dose, age, stress, immunosuppressive agents, permanence in acidifying soils, and there is a higher risk of transmission in intensive systems of production.

It is a chronic intestinal disease, characterized by diarrhea and progressive weight loss, general weakness, decreased milk production, increased susceptibility to other infectious diseases. In some occasions, reproductive problems such as abortions and infertility can be observed.

Although some animals may not show diarrhea during its productive stage (subclinical infection), the evolution of the typical disease develops during the first or second lactation.

It is important to keep in mind that for one animal with clinical signs there are around 15 to 25 animals in different stages of life that are infected in different stages of the disease, as shown below:

  • Stage I (silent infection): asymptomatic animals that usually do not eliminate the bacteria (10-14 animals).
  • Stage II (subclinical disease): asymptomatic animals that eliminate the bacteria (4-8 animals).
  • Stage III (Clinical disease): Animals with clinical signs that eliminate the bacteria (1-2 animals).
  • Stage IV (Terminal disease): Animals with advanced disease (1 animal).

Due to the high number of animals in subclinical stages, it is possible that fewer cases than actually exist are reported.

Economic losses


Herds positive of Paratuberculosis have an economic loss of almost US $200 - $900 per cow compared to herds negative for this disease. Different economic losses are associated within the production herds such as:

  • Death of animals
  • Decreased production of both milk and meat:
    Studies indicate that seropositive cows can weigh between 30 to 54 kg (70 - 130 lb) less than animals without the disease.
    As for dairy farms, there is a reduction in production of milk more than 700 liters per cow. Milk production in cows with subclinical infection decreases after the second lactation.
  • Increase in diagnostic costs and reduction of the cost of sale of infected animals (30% of market value)
  • Decrease of the productive life of animals: It is reduced to 50% of the normal expectation.
  • Increase in replacement costs together with costs of unproductive period
  • Low feed conversion, which results in decreased production.
  • Prone to susceptibility of other diseases

Control and prevention


The control of Paratuberculosis approach a challenge for farmers and veterinarians. It is of great importance to combine an adequate diagnostic method together with measures of biosecurity and vaccination, in order to control and eradicate the disease in productive herds.

Additionally, the education of producers and sanitary recommendations for the purchase of animals is fundamental within the control programs and also, are low cost measures.

It is important to make a diagnosis prior to replacing animals, and to reduce the risk of contamination with faecal matter by exercising adequate sanitary control of the herd.

Because the disease is subclinical in most animals, its diagnosis is difficult with evaluation of the signs and symptoms. For this stage, PCR and ELISA diagnostic tests are performed; different samples can be grouped to reduce the cost of this diagnostic method. For animals that show clinical signs, bacterial culture of faecal samples can be used, which additionally allows to categorize animals with high, moderate or low infection.

Other measures of biosecurity to take into account are the removal of newborn animals from sources of contamination with faeces from sick animals; provide colostrum from uninfected cows and replace the milk with milk substitute or milk from healthy females; perform a separate management of calves and young animals. Adult animals can share pastures and facilities with young animals from one year of age.

It is also important to wash all equipment, drinking fountains, feeders and floors with pressure water and detergent, and apply disinfectants such as 5% phenol, 5% formalin, calcium hypochlorite 1:50 or sodium hypochlorite in contact for one hour as minimum with the mentioned surfaces and direct sun with a minimum exposure of 100 hours.

Vaccination is a very valuable tool to reduce the risks of microbial contamination of this pathogen and reduce production losses and pathogenic effects, with a prevention approach. Different studies show a general positive effect of vaccination, valued in productive, epidemiological or pathogenic issues.

References


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