Lecture 24: Mycobacterium species

Salient features of Mycobacterium species

Aerobic, non-spore forming, non-motile, rods

Cytochemically Gram-positive

Acid-fast (ZN-positive) due to high lipid and mycolic acid in their cell walls

Mycobacterium species multiply

intracellularly and cause chronic, granulomatous infections

Major diseases caused by Mycobacterium species include

tuberculosis (TB), Johne’s disease and feline leprosy

M. aviumcomplex main hosts are

most avian species except psittacines

Mycobacterium are ___ to adverse environmental conditions due to their lipid-rich walls

resistant

Mycobacterium are identified by

Acid-fast staining (Ziehl-Neelsen)

Mycobactin is required for growth for

M. avium subsp. paratuberculosis

Recently highly reliable and fast molecular techniques such as PCR and 16s rRNAgene sequencing have been developed to identify

Mycobacterium

Johne’s disease is caused by

M. avium subsp. paratuberculosis (MAP)

Johne’s disease or Paratuberculosis is a worldwide -

chronic, contagious granulomatous enteritis of mainly ruminants

Johne’s disease is characterized in cattle by

persistent diarrhea, progressive weight loss, debilitation, eventually death

With Johne’s disease, M. avium subsp. paratuberculosis is excreted in

large numbers in feces of infected animals and in lower numbers in their colostrum and milk

How is Johne’s infection spread

fecal-oral route

Introduction of Johne’s disease into a non-infected herd is usually through

herd expansion or replacement purchases via subclinically infected carriers

After ingestion and uptake in the Peyer’s patches of the lower small intestine, the organism of Johne’s disease infects

macrophages in the GI tract and associated lymph nodes

In most cases, the organisms (Johne’s disease) multiply and eventually provoke a

chronic granulomatous enteritis that interferes with nutrient uptake and processing, leading to the cachexia typical of advanced infections

Clinical findings of Johne’s disease

Infected animals can appear healthy for months to years

In cattle, weight loss and diarrhea

ventral and intermandibular edema (due to a protein-losing enteropathy)

Clinical findings of Johne’s disease in sheep and goats and other ruminants

maybe diarrhea

milk yield may drop

as many as 50% of animals may be infected subclinically with associated production losses

Johne’s disease causes lesions which include

Thickened and corrugated intestine with enlarged and edematous neighboring lymph nodes

Lesions caused by Johne’s disease cause

Thickened and corrugated intestine with enlarged and edematous neighboring lymph nodes

Intestinal lesions from Johne’s disease may be mild but typically,

distal small-intestinal wall is diffusely thickened

Diagnosis of Johne’s disease

Organism based test - culture, PCR

Antibody based test - ELISA, AGID

Is there a treatment for Johne’s disease?

No satisfactory treatment

How can we prevent Johne’s disease?

Prevent new infection

• keep young away from adult animals

• colostrum from paraTB-free animals only

Remove the source of MAP from the farm