Foot and mouth disease (FMD) is described as a severe and contagious disease in cattle and pigs. This disease is also seen in goats, sheep, and deer . FMD is not considered an anthrozoonotic infection; thereby, infected animals do not transmit the viral infection to humans.
The incubation period of the virus can be as short as 18 hours to as long as 2 weeks in pigs. The clinical signs are more marked and severe in swine and cattle than those found in goats and sheep . After the incubation period, the initial signs of observed among cattle and pigs with FMD is high grade fever up to 41 degrees centigrade (106 F). Vesicular lesions of the mouth, lips, and tongue leads to the incessant salivation of the afflicted animal. The irritating blisters and vesicles of the foot pads make the animal stomp there feet frequently.
Newly born lambs, kids, piglets, and calves may die from FMD virus even without the cutaneous signs, but this is primarily because of myocardial cell damage by the virus. There is a considerable growth retardation in the case of the younger afflicted animals with progressive deterioration in milk production from the teats. The oral vesicles found in the affected species will resolve spontaneously within 7 days from the onset of symptoms. The horns of the foot may be missing among the deer and the cattle population during FMD infection. In a similar way, the deer shed their antler in face of an impending FMD infection in the afflicted animal.
The mouth vesicles found in FMD affliction is hard to distinguish from the common cattle and wine vesicular stomatitis . The need to harvest the vesicular fluid for culture and histopathologic studies is imperative using buffered saline solution. The pH of the solution must be kept to as close to 7.4 pH as possible during the conduction to prevent viral material and antigen from disintegrating. This samples are diluted to 10% concentration and introduced for tissue culture where an enzyme linked immune-absorbent assay (ELISA) is utilized for identification of FMD antigen .
The identification of the viral non-structural proteins (NSP) from the sample distinguishes the actual presence of viral load from cattle and swine that has only been immunized against the disease . The use of rapid diagnostic tests in farm producers is becoming more popular these days for on-farm diagnosis. The application polymerase chain reactions (PCR) in genetics laboratories have also been implored for the accurate diagnosis of the FMD virus .
In most FMD-free countries, livestock identified to have the FMD virus are immediately slaughtered including those animals in direct contacted with the infected animal. The carcasses of these infected species are immediately burned. Animal movement is then limited for the other uninfected and susceptible farm animals in the area. In countries where FMD is endemic, a massive vaccination campaign is usually implemented especially among the dairy producing herds.
The majority of the infected animals does not die with the FMD. However, the disease often leaves them incapable of producing substantial milk and meat as they used to produce before. The morbidity associated from the pain of the blisters and vesicles tends to make the animal host anorexic, depressed, and lame. In general, FMD outbreaks leads to substantial production loss among ranchers and producers that leads to financial difficulties, and alters livestock trade .
The etiologic agent in FMD is identified as an apthovirus from the viral family of Picornaviridae. There are seven immunologic serotypes documented for FMD: The A, O, SAT, C, Asia 1, 1, 2, 3 and serotypes. The virus is susceptible to pH range of 6 to 9, and are immediately deactivated in these adverse environment. The viruses are resistant to lipid solvents like chloroforms and ethers. They may be transmitted to the young calf via the infected milk.
FMD outbreaks have been recently documented in previously FMD-free countries like Taiwan in 1997, and in United Kingdom last 2001. These developing threats have prompted the scientific community to re-examine this growing threat to the population of susceptible livestock. In the past, FMD outbreaks have been observed in all continents except in New Zealand. At present enzootic transmission from cattle to cattle has been observed worldwide except in the regions of Australia and North America.
The apthovirus latches on the mucosae of the pharynx upon transmission . Alternative viral routes of entry include skin cuts and the gastrointestinal tract of the animal . Upon entry the virus is distributed to the body through the lymphatic system where it is seen to replicate in the epithelium of the mouth, muzzle, teats, and feet. The viral load is also noted in body areas with damage like the knees and hocks in swine. Vesicular lesions develop in these epithelium and eventually rupture giving out that characteristic lesions in FMD. The FMD viremia can exist up to 4 to 5 days in the animal host. Cattle, sheep, goat, and swine can remain as FMD carriers for as long as 2 to 3 years from the time of viral contraction .
The control of FMD infections among livestock is relatively difficult because of its endemicity in multiple countries. The active animal migration control is imperative to contain FMD outbreaks. This will include the effective restrictions of livestock meat and derivatives from infected animals. The use of vaccination against FMD among susceptible farm animal has been proven to be the most effective way to prevent the FMD disease.
Foot and mouth disease (FMD) is a highly contagious viral infection of the cloven hoofed species. FMD is characterized by the formation of vesicles in the mouth, muzzle, nipple, and feet. Morbidity in FMD approaches 100% in susceptible species but fatalities are relatively rare except in younger animals.