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Bacterial Disease - Paratuberuclosis

Synonyms: Johne's disease.

Etiology

It is caused by M.avium subspecies paratuberculosis (Map).

Prevalence of infection

In Western Norway, paratuberculosis is described as endemic in goats, at the same time reported the occurrence of highest sero-prevalence in roe deer and red deer due to distribution of infection between wild and domestic animals.

The disease has been reported from various parts of the world including India.

Predisposing factors

Pregnancy, parturition and lactation are presumptive influencing factors to enhance, the development of the disease in cattle.

Source of infection

Map survives for prolonged periods at low temperature outside the animal host and can remain viable for several months in contaminated water and soil.

CLINICAL SIGNS

Calves are infected as young following ingestion of milk, feed and water contaminated with M.paratuberculosis.

This causal agent is capable of living in animals for years without showing any clinical signs.

Affected cattle normally appears to be healthy and bright looking without causing any changes in their appetite , nevertheless, they exhibit some of the symptoms such as decreased in milk production, loss of body conditions, and diarrhoea in the early stage cachexia and hyporpotenemia which leads to death in the advance stage.

In small ruminants, the course of the disease may vary from rapid to prolonged periods of time and the symptoms are much more similar to cattle, excepting less frequent diarrhea in the former species. Infected animals, during the clinical phase, pass as high as 1010organism/ gram of feces.

Depending on the extensive nature of infection, the disease has been grouped into different stages;

    • » Stage I silent infection; includes both young and adult with no shedding of bacteria.
    • » Stage II - subclinical excretory phase; adult carriers without clinical signs.
    • » Stage III - clinical excretory phase ; animals with characteristic signs
    • » Stage IV - advanced clinical disease.

NECROPSY FINDINGS

Microscopic lesions of JD is predominantly divided into two; Lepromatous and tuberculoid granulomatous lesion.

Diagnosis

Based on clinical signs and necropsy findings

Detection of acid fast bacilli from dung sample, intestinal mucosa and associated lymphnodes in infected animals are the most essential confirmatory diagnostic method of Para tuberculosis.

Isolation of organism by culture. Solid media which includes, the egg based Lowenstein- Jensen medium(LJ) and Herold's egg yolk medium (HEYM).

The culture method was described as 'gold standard'. culture is time consuming, may require up to 3 months for incubation and labor intensive. Fecal culture test is most sensitive and could be used in herd level testing.

Invivo-intradermal test is a very old technique used to measure sensitized T-lymphocytes response to an antigen. It is a field test using 0.1-0.2ml of johnin PPD at caudal fold or the neck. The reactions of the animals are measured from a difference between the initial and the final thickness of the skin. Animal showing skin thickness of above 4mm after 72 hours of injection is considered positive.

There are several methods like Complement Fixation (CFT) Test, Agar Gel Immunodiffusion (AGID) Test and Enzyme Linked Immunosorbent Assay (ELISA), used in the assessment of humoral immune response of paratuberculosis.

In which CFT test has been considered a best screening test for cattle meant for international export.

Molecular diagnosis by DNA probes may be of use in identifying clinically important bacteria. But for the bacteria like M.paratuberculosis, , the use of species specific DNA probe may be essential. To date only IS900, F57 and HspX genes that are specific to this disease have been identified from its genome.

Sample collection

Dung sample, intestinal mucosa and associated lymphnodes in infected animals are the most essential confirmatory diagnostic method of Para tuberculosis.

Differential diagnosis

Tuberculosis.

Parasitic disease.

Salmonellosis.

Colibacillosis

Rota viral enteritis.

TREATMENT

There is no treatment and antibiotics are available to control paratuberculosis.

Temporarily diarrhoea can be controlled by some antibiotics.

Combined use of Streptomycin, Isoniazid and Rifambicin is suggested in some countries.

Prevention

There are two vaccines commercially available used in cattle, sheep and goats against Para tuberculosis in New Zealand; a live attenuated freeze dried vaccine which was Introduced in New Zealand and the killed vaccine has been involved in the practice.

The killed vaccine is found to reduce number of organism excreted, spread of infection, and development of lesion in the body.

In Para tuberculosis, the development of immune mechanism is bipolar in nature. A cellular immune response (CD4+Th1 cells) develops during the earlier period of infection, is the prime response by which the progression of infection is controlled. CMI wanes and simultaneously provoke the humoral response ( CD8+ Th2 cells)at the later stage. As the immune system in calves is not completely developed they are highly susceptible to disease as compared to adult cattle.

Control

The control of paratuberculosis mainly depends on the early diagnosis of disease by sero-surveillance, quarantine of suspected and culling of infected animals, eradication by vaccination and maintenance of hygiene in the farm premises. Generally surveillance relies on serological tests such as CFT and ELISA.

To date, as antibiotics are proved to be ineffective, expensive and time consuming calf hood vaccination is considered another method to curtail the progression of paratuberculosis from subclinical to clinical stage.

However, the long incubation period, resistant nature of the organisms to the external and internal environmental conditions, shedding through feces makes the control of paratuberculosis become difficult.

As young calves are reported to be highly at risk group of age, separation of calves as soon as they were born is recommended in the first place, in order to avoid them from getting infection from dam is the pasteurization of milk.


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