What is Johne’s disease?
Johne’s disease is caused by a slow growing bacterium called Mycobacterium avium
. The disease is named after a German pathologist that recognized acid fast bacteria
in the small intestine wall of a thin cow with chronic diarrhea. It was first described
in the United States in the 1900s, affecting Pennsylvania dairy cows. Since that
time it has been diagnosed in a variety of livestock and wildlife species including
multiple breeds of cattle (both beef and dairy), bison, small ruminants, camelids,
moose, bighorn sheep, elk, and deer (Bhattarai 2014, Buerglt 2000, Carta 2013).What are the clinical signs?
In cattle, the typical clinical presentation would be an adult animal, eating well
with chronic weight loss and diarrhea. This differs from the presentation in small
ruminants in which weight loss and diarrhea are not consistently found (http://www.ojd.com.au/about-ojd/
). Other wildlife species can also have variable presentations with only poor body
condition or only loose stools (Williams 1979).How do animals become infected?
The majority of animals become infected early in life by ingesting the bacteria that
has been shed in manure. Other possible routes of infection for young animals includes
ingesting it through milk, and occasionally across the placenta while in utero. Once
infected, the bacteria invades the intestinal wall and begins its slow replication
process. Depending on the number of bacteria ingested, clinical signs will develop
in 2 to over 10 years.What diagnostic tests/samples can be used to detect Johne’s disease?
To diagnose Johne’s disease ante-mortem, we can utilize serum samples or fecal samples.
For serum, we utilize the VMRD ELISA
, which will detect antibodies from cattle and small ruminants. Serology assays can
only diagnose exposure, and it typically takes a minimum of two years for antibodies
to develop. Additionally, the serology assay is not very sensitive; so a negative
result must be interpreted with caution. For fecal samples, we utilize a PCR; and
can pool up to 5 samples in one reaction. If the pool is positive, then we can perform
an individual PCR assay. The caveat for fecal PCR is that cattle in the sub-clinical
stage may be intermittent shedders of the bacterium. So a false negative result is
possible. If the clinical signs remain or worsen, then testing a new fecal sample
To diagnose Johne’s disease post-mortem, we can utilize gross and histologic findings
on the small intestine and the mesenteric lymph nodes. On gross examination the small
intestine will be thickened with prominent Peyer’s Patches. The thickened intestinal
wall is due to an increased number of macrophages and lymphocytes present, in response
to the bacteria. These bacteria can be observed throughout the tissue, when acid-fast
stained. In the photo below (johnes.org
), the top image shows mucosal thickening of the ileum in comparison to normal mucosa
in the bottom image.
Does Wyoming have Johne’s disease?
Yes! The percentage of samples that test positive for Johne’s disease has been increasing
over the past few years. These graphs show the percentage of positive cases from 2019,
2020, and 2021. The left graph indicates the percentage of positives by serology testing,
and the right graph indicates the positives by fecal PCR. WSVL has tested an increasing
number of positive samples in both cattle and small ruminants. Keep in mind the 2021
numbers are incomplete, and only are shown through May. Who do I contact if I have more questions?
At WSVL, you can contact Dr. Kerry Sondgeroth
with additional questions about testing strategies and control options at 307-799-9925 References
B Bhattarai, GT Fosgate, JB Osterstock, SC Park, AJ Roussel. 2014. Perceptions of
veterinarians and producers concerning Johne’s disease prevalence and control in US
beef cow-calf operations. BMC Vet Res 10:27
CD Buerglt, AW Layton, PE Ginn, M Taylor, JM King, PL Habecker, E Mauldin, R Whitlock,
C Rossiter, MT Collins. 2000. The Pathology of Spontaneous Paratuberculosis in the
North American Bison (Bison bison). Vet Pathol 37:428-438.
T Carta, J Alvarez, JM Perez de la Lastra, C Gortazar. 2013. Wildlife and paratuberculosis:
A review. Research in Vet Science 94:191-197.
ES Williams, TR Spraker. 1979. Paratuberculosis (Johne’s Disease) in bighorn sheep
and a rocky mountain goat in Colorado. J Wildife Dis 15:221-227