Quick Facts
What is Mycobacterium avium ssp paratuberculosis?
Site of MAP replication
What are macrophages?
Incubation period
What is at least 2 years?
*MAP persists in intestinal macrophages for a very long time. Some animals may show clinical signs at <2 yrs since infection. Animals can shed the bacteria and be clinically normal.
Animals most susceptible to Johne's infection + clinical disease
What are ruminants?
Primary site of infection
What are ileal Peyer's patches?
*Ileal lymph nodes also involved
Pathogenesis
MAP ingested via fecal-oral route -> invade Peyer's patches -> stimulate host immune response -> phagocytosed by macrophages -> replicate in macrophages -> slow, granulomatous inflammation spreads -> small intestinal wall thickening -> enteritis
Treatment protocol
What is no satisfactory treatment?
*Animals would need to be treated for months for clinical resolution, which is highly impractical + cost prohibitive for many producers. Relapse has been observed in studies as well.
Age at transmission
What are kids, lambs, and calves?
*The perinatal period is the most common age of infection. Often, clinical signs do not develop until >2 yrs of age
Clinical picture
What is a "poor-doer"?
*Sheep & goats with Johne's will maintain a good appetite but will have chronic weight loss to the point of emaciation.
Zoonotic potential
What is none?
*Johne's disease only refers to MAP infections in ruminants, but gastroenterologists have noted similarities between Crohn's disease and Johne's disease presentations. However, Crohn's has no known cause or cure
Route of transmission
What is fecal-oral route?
*MAP is shed in feces. Manure contaminated water, milk, or feed are common sources. In later stages of infection, dams may shed MAP directly into milk. MAP can survive in low numbers for up to a year in feces.
Necropsy findings
Diagnostics
What is fecal PCR?
*Culturing samples takes an extremely long time (8 wks). Fecal PCR best in sheep, blood & milk ELISA available in goats (confirm with fecal PCR).
Principles of prevention
What is maintaining a closed herd/only buying replacements from MAP-negative herds?
*Additionally, clean pastures, barns, water & feed troughs are important to prevention. Animals may test positive without any clinical signs, so its important to cull these animals!!
Additional CS
What are bottle jaw and wool break?
*Bottle jaw due to protein losing enteropathy, wool break due to malnutrition.