Detection of subclinical paratuberculosis in dairy cattle in Egypt

Abstract

Paratuberculosis (PTB) is a chronic disease affecting ruminants caused by mycobacterium avium subspecies paratuberculosis (MAP), characterized by the iceberg phenomena, as many cases are subclinical and underdiagnosed. An early diagnosis is imperative; however, no reliable single test is available, leading to delayed culling. Furthermore, using more than one test increases the rate of positively diagnosed cases. The current study aimed to detect subclinical PTB in dairy cows in El-Minia governorate, Egypt, using ELISA jointly with the detection of MAP by PCR. The positive cases were also subjected to pathological examination to determine whether lesions were present and their severity. A total of 145 cows of different breeds (Baladi, Mixed, and Holestins) and ages were tested by ELISA and PCR. Our results showed that the positive PTB cases detected by ELISA and PCR were 17.24% and 20%, respectively. Holestins have a significantly higher infection rate 31.70% than Baladi and Mixed breeds. In contrast, the native (Baladi) breed has the lowest infection rate 11.47%. Moreover, PTB is more common in cows aging (age ≥ 1.5- <2.5 is 28.2% and age ≥ 2.5- <3.5 is 22.91%). Among PCR-positive cases, 58.62% showed gross lesions, mainly thickening and folding of the intestinal mucosa and swelling of mesenteric lymph nodes. Histopathologically, 86.20% had chronic granulomatous enterocolitis and lymphadenitis. Furthermore, acid-fast bacilli were observed in 82.75%. Thus, subclinical PTB diagnosis could be more accurately confirmed when multiple diagnostic tools are used together.

Keywords

• iceberg phenomena
• granulomatous enteritis
• johne's disease
• paratuberculosis
• pathology