Foot and mouth disease (FMD)
Author: Prof Gavin R Thomson
Licensed under a Creative Commons Attribution license.
Introduction
example those that prevail in sub-Saharan Africa (arid
No non-zoonotic disease (i.e. diseases that do not
climate with low stocking densities), the infection often
affect the health of people) causes as much disruption
spreads slowly and inefficiently. So the mechanisms
to animal production and international trade in
and rate of spread of FMD are highly variable.
commodities and products derived from animals as
FMD. This situation results from historical approaches
and policies that have evolved over many decades.
Consequently countries in sub-Saharan Africa and
other parts of the developing world have difficulty in
exporting animals and animal products to high-value
markets.
Paradoxically,
especially
in
extensive
livestock production systems, FMD usually causes
relatively mild disease in the wide range of domestic
and
free-living
cloven-hoofed
animals
that
are
susceptible to it.
Tongue lesions commence as blanched foci
Salient features of FMD
which develop into vesicles containing serous fluid
Foot and mouth disease is a contagious viral disease
of cloven-hoofed animals. It is a systemic infection that
results in transient fever and loss of appetite with
accompanying weight-loss, drop in milk production and
the development of vesicles ‒ which soon rupture
leaving painful erosions in the mouth, skin-hoof
junction of the feet and teats ‒ that may cause
salivation
and
lameness.
Most
animals
recover
uneventfully from the infection with 10-21 days.
In some circumstances FMD viruses are able to spread
extraordinarily efficiently, including over long distances
on air currents, and infect large numbers of animals
over a wide area in short time periods. For this reason
it is often referred to as the most contagious disease of
mammals. However, in other circumstances, for
Ring lesions on the claw of a bovine that recovered from
FMD showing the separation between the new outgrowing
tissue and the horn of the hoof that were present distal to the
coronet prior to lesion development
Some ruminants may retain the infection in the oropharynx
for
weeks
to
months
following
clinical
Viruses that cause FMD are classified within the genus
recovery. However, so far only African buffalo have
Aphthovirus and comprise a constantly evolving quasi-
been shown to be capable of so-called carrier
species that is divisible into 7 serotypes named A, O,
transmission.
C, Asia 1, SAT1, SAT2 and SAT3. The SAT serotypes
and the 4 others form two distinct sub-groups. The
Prevention and control
currently available evidence indicates that the SAT
Because FMD is a contagious disease, methods of
serotypes evolved in sub-Saharan Africa in association
control are based on prevention of contact between
with African buffalo while the other 4 evolved in
infected and susceptible animal populations and
Eurasia, probably in association with livestock.
exposure of susceptible animals to fomites and other
sources of indirect exposure. Vaccination can also be
In eastern and southern Africa, unlike the rest of the
an effective way of preventing infection from spreading
world, wildlife populations (buffalo primarily) maintain
to susceptible populations but the diversity of the viral
SAT serotypes of FMD virus, i.e. provide a constant
population (i.e. intra-typic variation) and the fact that
reservoir of infection. For that reason the epidemiology
the currently used inactivated vaccines induce only
of FMD is more complicated in these regions and
short-term protection, complicates achievement of the
results in conflict between livestock development and
high levels of herd immunity required to manage FMD
wildlife conservation policies.
effectively in domestic livestock.
Where does FMD occur?
In southern Africa extensive fencing systems have
SAT serotypes are still confined to Africa while the
traditionally been used to prevent contact between
other serotypes occur widely in Africa, Asia, South
infected and FMD-free animal populations. These
America, parts of central/eastern Europe and the
fencing systems sometimes divide ecosystems with
Middle East. Eradication of FMD has been achieved in
unfortunate ecological impacts.
North America, most of Europe, parts of the Pacific Rim
and Oceania. In sub-Saharan Africa, SAT1, SAT2, A
A ‘Progressive Control Pathway for FMD Control’ (sic:
and O serotypes are widely prevalent; infections
so-called PCP-FMD) has been accepted by the OIE
caused by C are currently rare, as is the case for SAT3
(World Organisation for Animal Health) and FAO (Food
except in buffalo populations. Asia 1 infection has
&
never been recorded in Africa.
recommended way forward for the eventual global
Agriculture
Organisation of
the UN)
as
the
eradication of FMD. However, the proposed pathway
What triggers an outbreak of FMD?
creates a significant problem for southern and eastern
Because FMD is contagious the infection is usually
Africa because it takes no account of the wildlife
precipitated by close contact between susceptible and
problem and clashes in approach to rural development
acutely infected animals. Another common method of
between livestock interests and those of effective
spread occurs where scraps of meat from infected
wildlife (bio-diversity) conservation.
animals are fed to pigs through swill-feeding. Pigs
excrete large quantities of virus and especially on large
Find out more
piggeries may become a potent source of infection for
The CPD module on FMD provides a detailed account
other susceptible animals.
of the disease and the viruses that cause it with
emphasis on the way the disease commonly behaves
in southern Africa, i.e. its epidemiology. Detail is
therefore provided on the role of wildlife in the
maintenance and spread of the disease. Other aspects
covered by the module are the pathogenesis of FMD,
its diagnosis and differential diagnosis, including
clinical
signs
and
pathology,
and
methods
for
controlling the disease. The module concludes with a
section on the effect of FMD on trade in animals and
animal products, i.e. the area in which this disease has
its greatest impact.