World Veterinarian Quiz 36

§FMD is a highly contagious viral disease of cloven-hoofed species characterized by fever and vesicles and/or ulcer in the mouth and on the muzzle, teats, and feet.

§Synonym :

§Aphthous fever

§Aftosa

§Enzootic apthiae

•FMD virus belongs to the genus Aphthovirus (aphtha = ulcer) in the Picornaviridae family

•Seven serotypes

•Serotype O : India, Asia, Africa, Europe, America

•Serotype A : India, Asia, Africa, Europe, America

•Serotype C : India, Asia, Africa, Europe, America

•Serotype Asia 1 : India, Asia

•Serotype SAT 1 : Africa

•Serotype SAT 2 : Africa

•Serotype SAT 3 : Africa

•Infection with any one serotype does not confer immunity against another

•Epitheliotropic Virus

HOST :- 

•Domesticated and wild  cloven-hoofed animals

•Cattle, pigs, sheep, goats and water buffalo, camel

•Bison, waterbuck, wild b oar, elephant, yak, llama and giraffe

TRANSMISSION

•Contact between susceptible and infected animals

•All secretion and excretion including semen and milk 

•Respiratory aerosols

•Travel long distances

•Proper temperature and humidity

•Direct contact

•Vesicular fluid

•Ingestion of infected animal parts

•Indirect contact via fomites

•Boots, hands, clothing

PATHOGENESIS

•Entry of virus in body → Reach to pharynx and lung →  Virus replication → Go in the blood → Viremia → dissemination to surface epithelium → Infect Langerhans cells → Infect squamous epithelium → Replication in stratum spinosum → degeneration, lysis and necrosis of the cells →  Formation of epidermal vesicles (hallmark of the disease) → coalesce to produce bullae (5-6 cm) → Rapture in 12-14 hours → Ulcer formation → Secondary infection or Regeneration in 2 weeks 

CLINICAL SIGN

•Incubation period: 2 to 14 days

•Fever of up to 106°F (41°C)

•Excessive salivation

•Smacking (opening and closing) of the lips and tongue

•Vesicles and/or ulcer on the tongue, dental pad, gums, lips, and on the coronary band and interdigital cleft of the feet, teats and udder

•Young calves, lambs, kids, and piglets died without showing any vesicles 

MACROSCOPIC PATHOLOGY

•Single or multiple, fluid-filled vesicles or bullae or ulcer from 2 mm to 10 cm in diameter

•Ulcer on the tongue, dental pad, gums, lips, and on the coronary band and interdigital cleft of the feet, teats and udder

•Secondary bacterial infection may be seen

•Young calves, lambs, kids, and piglets died without showing any vesicles due to myocarditis

•“Tiger-heart" : cardiac degeneration and necrosis can cause gray or yellow streaking in the myocardium; known as “tiger heart” lesions   

MICROSCOPIC PATHOLOGY

•Early stages – Balloon degeneration of cells in the middle of the stratum spinosum

•Latter stage: Necrosis, edema fluid containing bits of fibrin accumulates between the cells and separates them.

•Neutrophils infiltration

•Liquefactive necrosis and accumulation of serum and leukocytes produce vesicles

•Ulcer, erosion or suppurative infllamtion

•Heart: Myocardial necrosis