Foot and Mouth Disease - Fiebre Aftosa
by Jeffrey Muser and Suzanne Burnham
Publisher: Texas A&M University, College of Veterinary Medicine
Definition Known around the world as Afta epizotica, Bek-en-klouseer, Fiebre Aftosa, Fievre aphteuse, Maul-und-Klauenseuche, Foot-and-Mouth Disease. Foot-and-mouth disease is a highly contagious viral disease of domestic cloven-hoofed and many wild animals characterized by erosions in the mucosa of the mouth and hooves. This devastating disease is considered to be the most important livestock disease in the world. It is THE most contagious virus disease of animals. It has not occurred in the US since 1929. Worldwide Occurrence of FMD Important factors Short incubation period Release of virus prior to appearance of clinical signs Massive quantities of virus released Foot-and-Mouth Disease Although not very lethal to adult animals it causes serious production losses.
Etiology The virion is non-enveloped small (about 23-25 nm in Diameter) and has icosahedral symmetry. It is composed of a single-stranded RNA genome of about 8 000 nucleotides.
Etiology Foot-and-mouth Disease virus (FMDV) Family Picornaviridae genus Aphthovirus 7 serological types: Type A Type O Type C South African Territories (SAT) 1 South African Territories (SAT) 2 South African Territories (SAT) 3 and Asia 1 Etiology Foot-and-mouth Disease virus (FMDV) Over 60 subtypes Antigenic variation seems to be greatest for Serotype A.
Host Range All cloven-hoofed domestic animals: Cattle and Buffalo Sheep Goats Swine Host Range Most cloven-footed wild animals: Deer Bison Feral hogs Antelope Host Range Water buffalo can be carriers for 5 years Llamas and alpacas are susceptible but of no epidemiological significance Host Range Giraffes Elephants Host Range Armadillos Armadillos are not only susceptible but are capable of transmitting the disease to each other and possibly to other species Host Range Hedgehogs Nutria Capybaras Rats Mice and Guinea pigs can be infected experimentally Host Range Not seen in odd-toed animals such as horses zebras or rhinos
Incubation Incubation period depends on which strain of FMD virus (7 serotypes) dosage and the route of entry. As short as 2-3 days in close contact As long as 10-14 days from windborne infection Experimentally shown to be as short as 18-24 hours Minimum doses of FMD virus to initiate infection Respiratory Oral Route Route Cattle 12 TCID50 1X 106 TCID50 Pigs 20 TCID50 8X 103TCID50 Sheep 10 TCID50 Impalas 1 TCID50
Pathogenesis Most animals acquire virus usually by inhalation Humans and pigs are more susceptible to infection by oral route Excretion of FMD virus can begin up to 14 days BEFORE clinical disease becomes apparent. Pathogenesis Virus replication in respiratory epithelium and lymphoid tissue In domestic ruminants pharynx and dorsal soft palate are predilection site for replication of FMDv Virus persists there for prolonged periods
Replication in lymphoid tissue tonsils mucosa of soft palate Virus can be recovered from retropharyngeal mandibular and parotid lymph nodes in more than 50% of cattle in pre-viremic stage High virus levels may occur in organs and tissues which do not generally develop gross changes including unaffected skin areas Characteristic Blister Formation Epithelial lesions of FMD are initiated by infection of single cells in the stratum spinosum.
Following infection bullae develop by lysis of cell swollen by degeneration and release of intracellular fluid or focal intercellular edema Bullae coalesce and rupture
Development of characteristic vesicular lesions depends on 2 factors: Infection of epithelium Persistent local irritation or friction.
This explains why the mouth feet and teats are predilections sites for blisters in cattle the dorsum of the snout in pigs from snuffling on the knees of warthogs that kneel when feeding