(a) Discuss the etiology, epidemiology, pathogenesis, symptoms, postmortem lesions, diagnosis and control of Foot and Mouth…

(a) Foot and Mouth Disease (FMD)

FMD is a highly contagious, acute febrile vesicular disease of cloven-hoofed animals, caused by the Foot-and-Mouth Disease Virus (FMDV), a non-enveloped, single-stranded RNA virus belonging to the family Picornaviridae and genus Aphthovirus. There are seven major serotypes (O, A, C, Asia 1, SAT 1-3) with numerous antigenic variants, making serotype-specific immunity critical. In India the circulating serotypes are O (dominant), A and Asia 1; serotype C has not been recorded since 1995.

Epidemiology and Pathogenesis: The disease has a global distribution, with India remaining endemic, particularly in northern and central states. The primary host is cattle, but sheep, goats, and pigs are also susceptible. Transmission occurs via direct contact or aerosols; the virus is shed in saliva, milk, urine, and feces. Ruminants can act as long-term carriers, maintaining the virus in the population. Morbidity is high (up to 100%), but mortality in adult cattle is low (<5%), whereas in calves, it can reach 20-50% due to myocarditis.

Pathogenesis involves viremia leading to viral replication in epithelial cells, causing vesicle formation. In calves, viral myocarditis results in necrosis of cardiac muscle fibers.

Clinical Signs and Postmortem Lesions: In adult cattle, the hallmark is the development of vesicles on the tongue, dental pad, gums, interdigital clefts, coronary bands, and teats. These rupture to form erosions and ulcers, causing severe pain, drooling, lameness, and anorexia. In postmortem examination, distinct vesicles and erosions are found on the oral mucosa and hooves. In young calves, "tigroid" or "marbled" myocarditis is a characteristic lesion, where the heart muscle shows alternating bands of necrosis and healthy tissue.

Diagnosis and Control: Diagnosis involves clinical inspection, RT-PCR for viral RNA, and ELISA for serology. Differential diagnosis must rule out Vesicular Stomatitis and Bluetongue. FMD is a WOAH notifiable disease. Control in India follows the National Animal Disease Control Programme (NADCP, 2019, earlier FMD-CP), which aims to control FMD and eradicate it by 2030 and relies on six-monthly mass vaccination of cattle and buffaloes, ring vaccination, and strict biosecurity rather than stamping-out. Movement restrictions of 21 days are enforced in affected zones. Emergency vaccination is deployed using serotype-matched vaccines. Recently, DIVA (Differentiating Infected from Vaccinated Animals) strategies using non-structural protein markers (3ABC) are being explored to allow trade while maintaining control.

(b) Abdominal Cavity in Ox

The abdominal cavity is bounded cranially by the diaphragm, dorsally by the lumbar vertebrae and associated muscles, laterally by the abdominal muscles and ribs, ventrally by the floor muscles, and caudally by the pelvic inlet. Its contents include the rumen, reticulum, omasum, abomasum, liver, spleen, small and large intestines, kidneys, and reproductive organs.

Topographic Division: For clinical purposes, the abdomen is divided into nine regions using two transverse planes (at the level of the last rib and the tuber coxae) and two sagittal planes. The sagittal planes run along the lateral borders of the rectus abdominis muscles (paramedian planes), not the paralumbar fossae. The cranial row comprises the right and left hypochondriac regions with the xiphoid region between them, the middle row the right and left lateral (flank/paralumbar) regions with the umbilical region, and the caudal row the right and left inguinal regions with the pubic region.

Clinical Importance: This topography is vital for surgical and diagnostic procedures. The left paralumbar fossa is the primary site for rumenotomy and rumen cannulation. For abomasal displacement, Left Displaced Abomasum (LDA) is typically corrected via the left flank or a right paramedian approach, whereas Right Displaced Abomasum (RDA) is corrected via the right flank. Accurate regional identification prevents iatrogenic injury and aids in localizing peritonitis or abscesses.

(c) Reasons for Vaccination Failure

Vaccination failure in animals arises from antigenic, host, procedural, and environmental factors.

Antigenic Factors: Mismatch between the vaccine strain and the field strain is a primary cause, especially in FMD where serotypes vary. Inadequate antigen mass or potency also reduces efficacy.

Host-Related Factors: Maternal antibody interference can neutralize vaccine antigens in young animals. Immunocompromised states due to concurrent infections (e.g., BVD, IBR) or genetic non-responder status limit immune response.

Procedural Errors: Cold chain breaches destroy vaccine potency. Improper route of administration, incorrect dosing, or failure to adhere to booster intervals compromise immunity. Adjuvant incompatibility or poor mixing can also lead to failure.

Environmental Factors: Nutritional deficiency, stress, and concurrent parasitic loads suppress the immune system, rendering the vaccine ineffective.