Foot-and-mouth disease: the various routes of transmission taken by the virus

This is a disease that generally provokes strong reactions because its impact on infected herds—and thus on the economy of the livestock sector—can be so significant. One need only look at the out-of-control crisis in South Africa to understand why a better understanding of foot-and-mouth disease is so crucial. The virulence of the foot-and-mouth virus lies in its ability to spread through the air and via direct and indirect contact. A summary notes that this virus is transmitted through multiple vectors: it spreads from animals to equipment, from equipment to humans, from humans to herds, and under certain conditions from one farm to another via the air or orally.  

Seven serotypes, three routes of transmission

The foot-and-mouth disease virus belongs to the Picornaviridae family and comprises seven immunologically distinct serotypes (O, A, Asia1, C, SAT1, SAT2, SAT3). The three main routes of transmission are contact, the air, and contaminated surfaces. The first route is the most common: direct and indirect contact. Infected animals engage in shedding of the virus through saliva and nasal secretions, as well as through urine, feces, milk, etc. In addition, cattle can harbor the virus in the oropharynx even after the acute phase has passed. The second route of transmission is airborne. Pigs play a particular role in spreading the virus via aerosols capable of traveling several kilometers. Wind, humidity, temperature, and viral load all influence the extent of the outbreak. Analyses of major European epizootics in the 20th century have shown that this route can amplify an epizootic, sometimes extending beyond a single livestock area. The third route involves contaminated materials and equipment (vehicles, clothing, buildings, surfaces, feed). The virus can persist long enough on certain surfaces to become infectious again, which underscores the importance of animal health and biosecurity measures (hygiene, airlocks, traceability, movement restrictions, etc.) to prevent its spread.  

“Silent” vectors: feed, milk, water, and carcasses

Foot-and-mouth disease also spreads through lesser-known but highly effective routes. In pigs, transmission via animal feed is a well-documented risk: experimental studies show that distributing contaminated feed can be sufficient to infect animals. In the dairy industry, the impact is also commercial: the virus can survive in raw milk and even, depending on conditions, in pasteurized milk. Water is less frequently identified as a source of contamination during field investigations. However, a quantitative assessment cited in the article suggests that contaminated water poses a risk under certain circumstances, and the virus’s stability in a moist environment depends heavily on temperature and pH: cold water that is close to neutrality promotes its persistence. As for carcasses, they serve as a viral reservoir: an infected dead animal, particularly a pig, can remain contagious for several days if the carcass is not disposed of promptly or properly.  

High environmental persistence

In soil, the virus’s persistence depends on physicochemical properties and external conditions. Shade and moisture are thought to preserve infectivity for longer, meaning that two neighboring plots are not equivalent in terms of risk. Manure, bedding, and organic waste also play a “protective” role: they can maintain a viable virus and contribute to environmental contamination, particularly where these materials are spread or handled without prior disinfection. pH is part of the equation: the foot-and-mouth disease virus is stable around a neutral pH, but it is rapidly inactivated in acidic (pH < 6) or alkaline (pH > 9) environments. This sensitivity provides a scientific basis for inactivation strategies using acidic or basic treatments, and the article also discusses the effectiveness of certain disinfection agents (including formaldehyde) against local isolates. Finally, heat accelerates the inactivation of the virus, while cold prolongs its viability. Thus, winter does not necessarily provide an epidemiological break. This publication has the merit of summarizing current knowledge regarding the spread of the foot-and-mouth disease virus and suggesting areas of focus for strengthening biosecurity. Foot-and-mouth disease is a highly contagious disease because the virus can spread through multiple routes. However, the article does not address a fundamental aspect of prevention: vaccination.