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Molecular and Pathological Diagnosis of Paratuberculosis in Cattle from
Selected Districts in Uganda
Abstract
Paratuberculosis, caused by Mycobacterium avium subsp. paratuberculosis (MAP) is one of the
most important infectious diseases of cattle. No previous study on the occurrence, pathogen
diversity, pathology and diagnosis of the disease has been done in Uganda. This study has been
carried out to fill this gap. The objectives of the study were:- to determine the seroprevalence of
paratuberculosis in pastoral and dairy cattle in selected district in Uganda, to study the gross and
microscopic lesions of chronic granulomatous lesions in slaughtered cattle and determine the
lesion prevalence thereof; to isolate and characterize MAP organisms from sero-positive cattle
and suspected lesions, and; to develop and assess an immunohistochemical method for diagnosis
of paratuberculosis based antibodies against Heat shock protein 70 antibodies. The
seroprevalence of paratuberculosis was determined using a multistage sampling method and
testing with Pourquier ELISA for paratuberculosis. Gross and microscopic examinations were
used to study the lesions and determine their prevalence. Presence of the causative agent in the
lesions was confirmed by Ziehl Nielsen and immunohistochemical methods. MAP was isolated
on Herrold’s egg yolk medium and characterized using analysis of Short sequence repeats (SSR),
mycobacterial interspersed repeat units-variable number tandem repeats (MIRU-VNTR), and
restriction endonuclease analysis of IS1311 sequence. Immunohistochemical method of diagnosis
of paratuberculosis was developed using antibodies to recombinant heat shock protein. The
findings of the study showed that paratuberculosis is present in all the districts of the study; and
in most of the existing breeds. Although the apparent prevalence is low (3.7%), the within herd
prevalence and the herd prevalence are comparable to those in countries where the disease is
considered endemic. Among healthy slaughtered cattle, 4.7% bear lesions of the disease. The
lesions were very diverse ranging from typical descriptions to forms which the current
characterization methods would exclude from descriptions of paratuberculosis. The combination
of the three methods, SSR, MIRU and IS1311 PCR/REA differentiated 21 isolates into 10
distinct strains. Quite unexpectedly, two isolates corresponding to the bison type of MAP and two
others of unclassified pattern were found using IS1311-REA. SSRs also showed that MAP
isolates from Uganda differ from those reported elsewhere. The findings show that anti-hsp70
can be used for immunohistochemical diagnosis of MAP in infected tissue but positive staining
also occurs with avian and bovine tuberculosis. In conclusion, paratuberculosis should now be
considered one of the serious threats to livestock in Uganda and the infection is caused by widely
varying strains. There is need to institute control measures. Information from this study will
provide the basis for the next course of action.