Foot-and-Mouth Disease (FMD) is one of the most contagious viral diseases affecting cattle and other cloven-hoofed animals. Its rapid spread and economic impact make it a significant concern for farmers, veterinarians, and policymakers worldwide. This blog provides a detailed exploration of FMD in cattle, covering its etiology, host susceptibility, incubation period, clinical signs and symptoms, morbidity and mortality, pathogenesis, postmortem findings, and treatment. Written in clear, accessible language, this article aims to inform and educate while ensuring originality and readability.
Etiology
Foot-and-Mouth Disease is caused by the Foot-and-Mouth Disease Virus (FMDV), a member of the Aphthovirus genus within the Picornaviridae family. FMDV is a small, non-enveloped, single-stranded RNA virus with a high mutation rate, leading to significant genetic diversity. The virus exists in seven distinct serotypes: A, O, C, Asia 1, and Southern African Territories (SAT) 1, 2, and 3. Each serotype has multiple subtypes, complicating vaccine development and disease control.
The virus is highly stable in certain environments, surviving in cold conditions or organic material like manure for weeks. However, it is sensitive to extreme pH levels, heat, and common disinfectants like sodium hydroxide or formalin. Transmission occurs through direct contact with infected animals, aerosols, contaminated equipment, or even fomites (inanimate objects like clothing or vehicles). Humans can act as mechanical vectors, carrying the virus without being infected.
Host Susceptibility
FMD primarily affects cloven-hoofed animals, with cattle being one of the most susceptible species. Other vulnerable hosts include sheep, goats, pigs, buffalo, and wild ruminants like deer and antelope. Cattle are considered “indicator hosts” because they display prominent clinical signs, making outbreaks easier to detect. Young animals, especially calves, are more severely affected due to their underdeveloped immune systems.
While FMDV does not typically infect humans, rare cases of mild human infection have been reported, usually presenting as flu-like symptoms or skin lesions. The virus can also infect non-cloven-hoofed species like hedgehogs or rodents under experimental conditions, but these are not natural hosts. Susceptibility varies by species and strain; for instance, pigs amplify the virus rapidly, while sheep may carry it asymptomatically, complicating control efforts.
Incubation Period
The incubation period for FMD in cattle ranges from 2 to 14 days, with an average of 3 to 5 days. This duration depends on factors like the viral strain, dose of exposure, route of infection, and the animal’s immune status. Aerosol transmission often leads to a shorter incubation period due to rapid viral replication in the respiratory tract. During this phase, infected cattle may shed the virus before clinical signs appear, contributing to silent spread within herds.
Clinical Signs and Symptoms
FMD in cattle presents a range of clinical signs, varying from mild to severe. The hallmark symptoms include:
- Fever: An initial spike in body temperature (up to 104–106°F or 40–41°C) lasting 1–3 days.
- Excessive salivation: Drooling or frothy saliva due to painful oral lesions.
- Lameness: Cattle limp or refuse to stand because of blisters and sores on their feet.
- Vesicles and ulcers: Painful blisters form in the mouth (on the tongue, lips, and gums) and between the hooves. These rupture within 24–48 hours, leaving raw, painful ulcers.
- Reduced milk production: Dairy cows experience a sharp drop in milk yield, sometimes by 50% or more, often before other signs are noticed.
- Weight loss: Due to difficulty eating and drinking caused by oral pain.
- Teat lesions: In dairy cattle, blisters on teats can lead to mastitis or secondary bacterial infections.
Calves may develop myocarditis, a severe condition affecting the heart muscle, leading to sudden death in young animals. In some cases, cattle become carriers, shedding the virus intermittently for months without showing symptoms.
Morbidity and Mortality
FMD is characterized by high morbidity and low mortality in adult cattle. In susceptible herds, morbidity can approach 100%, meaning nearly all animals become infected and show clinical signs. The disease spreads rapidly, especially in confined settings like feedlots or dairies.
Mortality, however, is generally low, ranging from 1–5% in adults. Higher mortality rates (up to 20–50%) occur in young calves due to myocarditis, often called “tiger heart disease” because of characteristic heart lesions. Secondary bacterial infections, such as pneumonia or mastitis, can increase mortality if untreated. Economic losses stem more from reduced productivity, trade restrictions, and control measures than from animal deaths.
Pathogenesis
The pathogenesis of FMD involves a complex interplay between the virus and the host’s immune system. After exposure, FMDV enters through the respiratory tract, oral mucosa, or skin abrasions. The virus initially replicates in epithelial cells, particularly in the pharynx, leading to viremia (virus in the bloodstream) within 1–3 days. This spreads the virus to secondary sites like the mouth, feet, and mammary glands, where it targets stratified squamous epithelium.
Vesicles form due to viral destruction of epithelial cells, causing fluid accumulation and tissue breakdown. Pain and inflammation follow, contributing to lameness and salivation. In young animals, the virus may infect cardiac muscle, causing necrosis and heart failure. The immune response eventually clears the virus in most cases, but some cattle become carriers, with persistent viral replication in the pharynx for up to 3 years. These carriers pose a risk for new outbreaks, though their role in natural transmission is debated.
Postmortem Findings
Postmortem examination of cattle with FMD reveals characteristic lesions, particularly in acute cases. Key findings include:
- Vesicles and ulcers: Blisters and erosions in the mouth (tongue, gums, and palate) and on the feet (interdigital spaces and coronary bands). Older lesions appear as grayish-white areas of necrosis.
- Esophageal and ruminal lesions: Erosions or ulcers in the upper digestive tract, especially in severe cases.
- Myocarditis in calves: The heart shows pale, streaky, or tiger-like stripes (hence “tiger heart”) due to myocardial necrosis. This is most common in animals under 6 months.
- Secondary infections: Evidence of pneumonia, mastitis, or abscesses if bacteria invade lesions.
- Lymphoid tissue changes: Enlarged lymph nodes and spleen, reflecting immune activation.
In carriers, gross lesions may be absent, but viral RNA can be detected in pharyngeal tissues. Histopathology confirms epithelial degeneration, edema, and inflammatory infiltrates in affected areas.
Treatment
There is no specific antiviral treatment for FMD. Management focuses on supportive care and preventing secondary infections. Key approaches include:
- Isolation and quarantine: Infected animals must be separated to limit spread. Strict biosecurity measures, like disinfecting equipment and restricting movement, are critical.
- Wound care: Cleaning and disinfecting mouth and foot lesions to prevent bacterial infections. Topical antiseptics or antibiotics may be used for secondary infections.
- Pain management: Non-steroidal anti-inflammatory drugs (NSAIDs) can reduce fever and discomfort, improving appetite and mobility.
- Supportive nutrition: Soft, palatable feed or intravenous fluids for cattle refusing to eat due to oral pain.
- Vaccination: In endemic areas, vaccines matched to circulating serotypes are used preventively. However, vaccines do not treat active infections and require regular boosters due to short-lived immunity.
In many countries, FMD outbreaks trigger a stamping-out policy, involving culling infected and exposed animals to eradicate the disease. This approach, while effective, is controversial due to ethical and economic concerns. In endemic regions, control relies on vaccination, surveillance, and movement restrictions.
Conclusion
Foot-and-Mouth Disease remains a formidable challenge in cattle production, with its high contagiousness and economic toll. Understanding its etiology, host range, clinical presentation, and management options is essential for farmers and veterinarians. While the disease’s low mortality is a silver lining, its ability to disrupt livelihoods and trade underscores the need for robust prevention and control strategies. By staying informed and vigilant, stakeholders can mitigate the impact of FMD and protect animal health.
