jonathanmiller@velhurstfarm.co.uk
The US Department of Agriculture says FMD mortality is usually less than 1% although higher death rates have been reported.
The virology chief of the Israel CVO department told me last week that they routinely treat animals with the disease and they usually recover. "Only rarely" do they have to destroy afflicted animals.
This is all rather academic actually as the current outbreak in the UK does of course
come with 100% mortality for sheep that are even suspected of exposure, whether they have
the disease or not. This also applies to Llamas, Alpacas, Bison and pet goats.
Some references:
Info from Fenner and Gibbs, 'veterinary Virology' 2nd edition
(California, 1993)
p409 'in general clinical signs are most severe in cattle and
swine...sheep and goats usually experience subclinical infection.'
p409-411
'cattle: after an incubation period of 2-8 days, there is fever, loss
of appetite, depression, and a market drop in milk production. Within
24 hours, drooling of saliva commences, and vesicles develop on the
tongue and gums...vesicles may also be found in the inter-digital
skin and coronary band of the feet and on the teats. The vesicles
soon rupture, producing large denuded ulcerative lesions. Those on
the tongue often heal within a few days, but those on the feet and
within the nasal cavities often become secondarily infected with
bacteria, resulting in prolonged lameness and a mucopurulent nasal
discharge. In calves up to 6 months, FMD virus can cause death
through myocarditis. The mortality in adult cattle is very low;
however, although the virus does not cross the placenta, cattle may
abort, presumably as a consequence of fever. Also, affected animals
become nonproductive or poorly productive for long periods. They
often eat little for a week after the onset of clinical signs and are
often lame; mastitis and abortion further reduce milk production. In
endemic areas, where cattle may have partial immunity, the disease
may be mild or subclinical.
In swine, lameness is often the first sign...vesicles within
the mouth are usually less prominent that in cattle/
other animals: the clinical disease in sheep, goat, and wild ruminants
is usually milder than in cattle and is characterised by foot lesions
accompanied by lameness.'
p299-301 on elimination/eradication of viral diseases states: 'The
biological characteristics that would render more likely the
elimination or global eradication of viral diseases of livestock are
as follows: 1) no wildlife host, 2) no reservoir or carrier host,
3)lack of recurrent disease and virus shedding, 4) only one or few
stable serotypes and 5) an effective vaccine. No less important is
the level of public concern, for any eradication program requires a
sustained commitment of human and financial resources.....FMD has the
largest constellation of unfavourable features, balanced in the
industrialised countries by the very high level of concern about its
presence or importation.'
It might be possible to argue that the above suggests that not only is FMD
elimination not justified
by the clinical features of the disease (though cattle do obviously
suffer more than other species) but its epidemiological
characteristics suggest that eradication is also incredibly
difficult, and largely driven by public concern rather than being the
obvious response demanded by the behaviour of the virus.
Blood and Radostits, 'Veterinary Medicine (Bailliere Tindall, London
1994) p965 says 'the morbidity rate in outbreaks of FMD in
susceptible animals can rapidly approach 100% but strains of the
virus are limited in their infectivity to particular species.
However, the (mortality) case is generally very low, about 2% in
adults and 20% in young stock.
p967 'FMD is probably the world's most important animal disease, even
though it is rarely fatal. Losses occur in many ways although loss of
production, the expense of eradication and the interference with
movement of livestock and meat between countries are the most
important economic effects.'
p968 on clinical signs again say in cattle that mouth lesions heal in
a week, though lameness can be severe leading to recumbancy and
mastitis develop following teat vesicles. Very rapid loss of condition
and fall in milk yield occur in the acute period. Eating is resumed
in 2-3 days as the lesions heal but period of convalescence may be as
long as 6 months (I presume this means regaining productivity)
But there is a great deal of variation in field virulence and this
can cause problems in diagnosis.
In sheep, goats and pigs the disease is usually mild and is important
mainly because of the danger of transmission to cattle.