Pathological, microscopic, and molecular diagnosis of paratuberculosis/John's disease in naturally infected dromedary camel (Camelus dromedarius)

Abstract

Background and aim: Paratuberculosis (PTB) or John's disease is a chronic disease of ruminants impeding the reproduction and productivity of the livestock sector worldwide. Since there is a lack of pathological studies explaining the nature and development of the disease in camels, this study aimed to highlight the anatomopathological changes of PTB in camels, which may help in verifying and validating some diagnostic tests used to detect the etiology of the disease in camel tissues.

Materials and methods: In August 2017, at Alselaa border's Veterinary Clinic of Al Dhafra Region, Western Abu Dhabi, UAE, one imported culled she-camel of 2 years old was subjected to clinical, microscopic, and anatomopathological investigations along with real-time quantitative polymerase chain reaction (q-PCR) to confirm the infection and correlate between clinical signs and pathological lesions of the PTB in dromedary camels.

Results: Clinically, typical clinical signs compliant with the pathognomonic gross and histologic lesions of PTB were seen in naturally infected dromedary camel. As presumptive diagnosis microscopically, acid-fast coccobacillus bacterium clumps were demonstrated in direct fecal smears as well as in scraped mucosal and crushed mesenteric lymph node films, and in histopathological sections prepared from a necropsied animal and stained by Ziehl-Neelsen stain. Free and intracellular acid-fast clump phagosomes were further confirmed as Mycobacterium avium subsp. paratuberculosis by q-PCR.

Conclusion: Clinical signs and pathological lesions of paratuberculosis in a dromedary camel were found to be similar to those of the other susceptible hosts.

Keywords: Mycobacterium; acid-fast bacteria; dromedary camel; paratuberculosis.

Figure-1

Clinical sings of paratuberculosis infected dromedary camel show (a): Emaciation, rough coat and sign of deviated appetite (pica) due to loss of rare nutrients (b): Evidence of diarrhea material stained the hind limbs.

Figure-2

Dromedary camel ileocecal part and cut surface show remarkable diffuse edematous thickening, intestinal folding, and corrugations with some nodular lesions and watery ingesta.

Figure-3

Intestine sections: (a) shows granulomatous enteritis evident on the lamina propria with proliferative mucoid glands (hematoxylin and eosin stain, 20×). (b) Clusters and clumps of acid-fast bacilli in the lamina propria and mucosa (Ziehl-Neelsen, 20×).

Figure-4

Mesenteric lymph nodes cross section shows remarkable swelling, edematous, nodular, and mottled appearance.

Figure-5

(a) Mesenteric lymph node section shows diffuse lepromatous granulomatous aggregation of macrophages, lymphocytes, plasma, and epithelioid cells. Giant cells were poorly noticed (hematoxylin and eosin stain, 20×): (b) Mesenteric lymph node: clusters of acid-fast bacilli (Ziehl-Neelsen, 200×).

Figure-6

The liver was firm in consistency with diffuse mottling and grossly enhanced lobular pattern (accentuation of hepatic lobulation) giving the liver nutmeg appearance. The cut surface was also mottled with accentuation of hepatic lobules. This appearance is indicative of chronic passive congestion of the liver with hepatocellular degeneration and necrosis of the centrilobular hepatocytes as secondary sequelae of chronic enteritis.

Figure-7

Liver section shows diffuse fatty change of hepatocytes (black arrows) in the centrilobular area. Hepatocytes in the portal area show signs of anaplasia structure particularly mitosis (blue arrow), pleomorphism with foaming appearance (yellow arrows) resembled to focal hepatic carcinoma.

Figure-8

Fecal smear stained with Ziehl-Neelsen stain shows clumps of acid-fast coccobacilli bacteria; Mycobacterium avium subsp. paratuberculosis (arrow).

Figure-9

Mesenteric lymph nodes crush smear stained with Ziehl-Neelsen stain shows numerous closely packed acid-fast bacilli (Mycobacterium avium subsp. paratuberculosis) inside the cytoplasm of macrophages and epithelioid cells (arrows).

Figure-10

The amplification curve of specific Mycobacterium avium subsp. paratuberculosis from ileum and lymph node tissues. The control negative with straight line (no amplification) was also shown.