FOOT AND MOUTH DISEASE

By Shaun Morris, BVSc (Hons), MSc Agric, Octavoscene Pty Ltd

Foot and mouth disease (FMD) is a severe, highly contagious viral disease of livestock that can have significant economic impacts on farming operations affected by this disease. The disease affects cattle, goats, sheep, pigs, and other clovenhoofed rumina nts. The virus is an aphthovirus belonging to the Picornoviridae family. There are seven strains (A, O, C, SAT1, SAT2, SAT3, and Asia1) which are endemic in different countries worldwide. Type C has been eradicated. The South African strains are SAT1, SAT2 and SAT3, with type O ever encroaching on our borders as our neighboring countries face the challenge of the O type.

In a South African setting, the main reservoir for footand-mouth disease virus (FMDV) is the African buffalo (Syncerus caffer) . Buffalo are persistently infected with FMDV, which sits latently in the nasopharynx and oropharynx. There are specific predilection sites which harbor the virus. In a South African setting, transmission of FMD occurs at the wildlife-cattle interface around the Kruger National Park and other national parks, where cattle frequently graze next to buffalo inside the wildlife reserve. The cattle belonging to the rural communities are often led to graze in the national park due to the lack of grazing in the surrounding rural communities. It is this close contact between buffalo and domestic cattle that leads to the frequent outbreaks of FMD in South Africa’s cattle population.

Foot and mouth disease is characterized by pyrexia in the acute phase of the disease process. Blister-like vesicles on the tongue, in the mouth, and between the claws develop shortly after the primary viremia, which eventually progress to erosions and ulcers at the forementioned anatomical sites. The disease has a high morbidity and low mortality with the SAT strains of the disease. With the A, O, C, and Asia1 strains, the mortality rate is significantly higher. The disease causes severe production losses, albeit for a brief period. Feedlot animals’ performance parameters such as dry matter intake (DMI), average daily gain (ADG), and feed conversion ratio (FCR) will be negatively affected; however, animals recover uneventfully 7 to 14 days after clinical signs developed. The development of serum neutralizing antibodies is very rapid following clinical disease and vaccination.

Transmission and spread

FMD is found in all excretions and secretions from infected animals. This disease is highly contagious and can be spread via the following:

• Animals infected with FMDV being introduced into a herd

• Contaminated vehicles (cattle and feed trucks)

• Contaminated clothing

• Persons who have been on an FMD positive farm (The virus can remain viable in a human’s tonsillar crypts for up to two days and infect naïve animals.)

• Swill

If you believe that you have been in contact with a clinical case or suspected clinical case, please isolate yourself for five days as the nucleic acid can remain viable on your clothing for an extended period.

Animals that have recovered from infection may sometimes carry the virus (in other words, become persistently infected) and initiate new outbreaks of the disease.

Clinical signs

The severity of clinical signs will depend on the strain of virus, the viral load, and the host’s immunity. Morbidity can reach 100% in naïve populations. In the case of recent outbreaks in South Africa, the disease was so mild that not all animals developed clinical signs, despite being positive on serological tests. Mortality is low in adult animals but higher in young calves, lambs, kids, and piglets. The incubation period can vary between 2 to 14 days.

Clinical signs can range from mild or inapparent to severe. They are more severe in cattle and intensively reared pigs than in sheep and goats.

The typical clinical sign is the occurrence of vesicles, erosions, and ulcers on the nose, tongue, lips, inside the oral cavity, and in between the claws. Ruptured blisters can result in extreme lameness and reluctance to move or eat. Usually, the ulcers and erosions heal within 7 to 14 days after they develop.

Diagnostic aids and differential diagnosis

There are several diagnostic aids to diagnose FMDV:

1. PCR of vesicular fluid (the gold standard)

2. PCR of tissue around oral erosions

3. Serology (It is imperative to wait 7 to 10 days for animal to seroconvert.)

Differential diagnosis should include:

1. Lumpy skin disease

2. Vesicular stomatitis

3. Bovine popular stomatitis

4. Epizootic hemorrhagic disease

Control

Biosecurity is of the utmost importance. Those people that do not need to be in contact with the cattle must not be in contact with the cattle. There are several products commercially available to disinfect vehicles coming on the facility, and showering has now been implemented on many of the feedlots we consult. We have also established a questionnaire that requires completion prior to feedlot entry.

Movement control is critical! The movement of all cloven-hooved animals must be curtailed and enforced with immediate effect. If you have not stopped the spread within 48 hours, you have lost the battle.

Dr. Shaun Morris is a young, enthusiastic, highly motivated, strictly disciplined individual with a strong work ethic and a passion for his career path in veterinary science. His family are all veterinarians with soon to be a total of five. Honesty, integrity, and most of all humility are driving forces in his life. South Africa poses a unique challenge with respect to veterinary medicine, with the region having a plethora of what would be considered foreign animal diseases in the United States. He works in an industry that contributes greatly to the economy of South Africa and is proud to say that they have a world class feedlot industry being pioneers in many respects.