Mycobacterium

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Mycobacterium species (general)

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ACID FAST

Granuloma formation or granulomatous

Crowding / host genetic susceptibility are important factors

M. bovis, M. tuberculosis, agents of “tuberculosis” in animals

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Mycobacterium species Pathogenic Features:

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Lipid rich cell wall provides resistance to host innate defense mechanisms like reactive oxygen and reactive nitrogen (nitric oxide) radicals.

Catalase enzyme inactivates H202 produced by neutrophils and macrophages

Inhibition fusion of phagosome with lysosome

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Granuloma Formation:

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Mycobacteria live inside macrophages

center of the granuloma may contain necrotic debris

functions to contain bacterial spread

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Mycobacterium bovis

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Cattle are natural host

infects humans, swine, primates, cats, dogs, sheep, goats, horse, deer, elk, other wildlife

National Bovine Tuberculosis Eradication program

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Mycobacterium bovis:
Transmission

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respiratory droplets, sputum, milk, feces, urine, vaginal discharge

Crowded / enclosed conditions aid transmission

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M. bovis:
Clinical Disease in Cattle

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Respiratory signs include moist cough, dyspnea

Weight loss. Rarely mastitis. *Maybe no signs.

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M. bovis :
Diagnosis in Cattle

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Caudal fold test: Skin test measuring delayed type hypersensitivity to tuberculin

Alternatively by lesions at necropsy; acid fast bacteria observed microscopically

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M. bovis:
Treatment / Control in Cattle

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Required to slaughter

Herd of origin quarantined

No vaccine

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M. Bovis Clinical Disease:
In the Cat

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highly susceptible.

rarely zoonotic risk.

Anti-TB drugs

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M. Bovis Clinical Disease:
In Swine and Humans

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very susceptible

Serious zoonotic problem (parts of the world where there is not pasturization of milk)

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M. tuberculosis:
Diagnosis/Treatment

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respiratory signs in dog belonging to household in which someone has TB.

Culture definitive

long term anti-TB drugs

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M. tuberculosis

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Humans are reservoir.

Dogs and cats susceptible. Lap animals especially

Generally respiratory disease, but may disseminate

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M. avium Complex (MAC)

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Feces of many domestic and wild birds contain high numbers of MAC bacteria.


*Major problem in livestock is interference with TB skin testing

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MAC Transmission:

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Ingestion

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MAC Clinical Disease:
General

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opportunistic pathogens, immunocompromised state, or high infectious dose favors disease development

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MAC Clinical Disease:
Swine

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causes non-progressive enlargement of lymph nodes of head and neck in young (4-8 week old pigs).

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MAC Clinical Disease:
Birds

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may cause progressive systemic disease with weight loss, weakness, and death

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MAC Clinical Disease:
Cattle

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mesenteric lymph node enlargement

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MAC Clinical Disease:
Sheep, Goats, Horses

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Sheep and goats- resistant. Rare cases of diarrhea.

Horse- resistant. Rare cases of enteritis.

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MAC Clinical Disease:
Dogs and Cats

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Often G.I. signs- weight loss, anorexia, fever, may disseminate.

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MAC Clinical Disease:
Humans

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common in AIDS patients. G.I. disease with diarrhea or disseminated disease.

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MAC Diagnosis / Treatment /Control

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Diagnosis: Biopsy of lesions, culture / PCR.

Treatment: not done in livestock, birds or horses. Antibiotic therapy may be attempted in dogs and cats. Antibiotics in humans.

Control: exclude wild birds from feeding areas

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Mycobacterium avium subsp. paratuberculosis (MAP)

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Causative agent of Johne’s disease (pronounced
“yo-knees” ) of ruminants.

very slow-growing. Takes @ 8 weeks to get colony in lab.

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Transmission of MAP

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Fecal-oral spread.

Animals exposed shortly after birth by ingestion of small amount of manure, or contaminated feed / water or by acquisition of organisms on udder or in milk.

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Pathogenesis of MAP

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1. Ingested by macrophages in Peyers Patches of ileum. Bacteria multiply intracellularly, kills macrophages and spreads to adjacent cells.

2. Large amount of inflammatory cytokines are released.

1. Response results in thickening of intestine and loss of absorptive function

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MAP Clinical Disease :
Johne’s Disease

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Contagious, chronic debilitating enteritis with emaciation of ruminants

Primary site of infection is ileum, ileal lymph nodes.

signs rarely develop before 2 years of age.

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MAP Clinical Disease :
Johne’s Disease Diagnosis

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Diagnosis: DNA based PCR test is sensitive and USDA approved.

Culture of organisms from manure or ileal node definitive, but takes long time (>2 months). Also organisms are shed intermittently, so culture may be negative despite active infection.

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MAP Clinical Disease :
Johne’s Disease Tx and Control

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Eliminate infected animals

Keep closed herd

calves, lambs, kids should be born in clean environment

Avoid manure contamintation in feed and water

voluntary USDA Johne’s Disease Herd Status program for cattle which provides guidance for elimination of Johne’s Disease from herd.