Respiratory airborne and genital infections have occurred worldwide in swine and cattle and there is strong evidence that vaginal infection of cattle was regularly sexually transmitted from sows by man.
Aujeszky's disease – infection with Suid
herpesvirus 1 (SuHV1) – is an infection of pigs, which can infect
several other animal species, regularly with a fatal outcome. It has been found
worldwide but is now eradicated in several countries. Denmark is the country,
where Aujeszky's disease has been studied most intensively, and the results
from investigations of cattle have been of greatest importance for
understanding the epidemiology of the infection in swine. Denmark was the first
country to initiate and complete eradication. In this review, important
epidemiological features are recapitulated at the end of each section or
subsection.
In cattle, the infection will most often give rise to an
intense pruritus of a skin area, preferably on the head, chest, or
hindquarters. Anterior localization of pruritus, on the head or chest, was
found to be associated with a respiratory infection, while posterior pruritus
was linked up with a vaginal infection. Pruritus must be considered a phantom
sensation caused by stimulation or damage of the central nervous system
including sensory ganglia. Respiratory infection of cattle is a dead-end
infection and the source of infection is pigs infected by the respiratory
route. Cattle at risk need not necessarily be placed near the infected pigs, as
the virus in animals is determined by ventilators over distances of 10-20 meters,
even from pigs in a neighboring room. Strong evidence was established of the
condition that vaginal infection in cattle had regularly been sexually
transmitted by men.
In swine, the infection was considered to be exclusively
respiratory for decades, but naturally occurring genital infection was
demonstrated in 1981. In herds with outbreaks in cattle characterized by
pruritus on the hindquarters (vaginal infection), respiratory infection of pigs
was never observed but a sow had characteristically been served by a foreign
boar approx. one week earlier. In some such cases investigated, genital
infection was confirmed in sows, which clearly associated cases in cattle with
a posterior localization of pruritus to a concurrent genital infection of
swine. Respiratory infection of pigs was demonstrated late in the history of
the disease.
The observed aggravation of the disease situation in pigs in
Denmark clearly illustrated that SuHV1 can change in degree of pathogenicity
over time. The changes occurred in two steps. In the early 1960s, respiratory
strains developed, which were spread rapidly between herds due to animal
contacts, mainly by trade, and later in the 1970s strains developed, which had
an even higher degree of pathogenicity for cattle and swine. These new strains
were found syncytial in contrast to earlier isolates from traditional
outbreaks. The new respiratory syncytial strains had not been introduced from
abroad as restriction fragment pattern analyses of virus DNA documented that
they possessed special Danish characteristics.
The decisive spread of the respiratory infection among swine
in a ventilated animal house was found to be by air currents over many meters
determined by the ventilation system and not by close animal-to-animal
contacts. During an acute outbreak in a swine herd, considerable amounts of
virus would be blown out into the surroundings by ventilators, exposing other
herds to the risk of infection. Early observations led to the conclusion that
airborne spread between swine herds might occur over several kilometers and
after eradication of the indigenous infection, new infections were introduced
from abroad, which demonstrated that airborne spread of the virus between herds
might take place over even 10 to 30 kilometers. Syncytial strains of SuHV1 have
shown to possess a pronounced tendency to airborne transmission among swine
herds, which implies that if a syncytial strain is first introduced into an
area, it is likely to become the prevailing type in that area within a
relatively short time.
It is a special conclusion from the epidemiological analyses
that the SuHV1 infection, before the development of the respiratory infection,
had been maintained in the first part of the 20th century in many countries as
an unnoticed porcine genital infection.
Author (s) Details
Viggo Bitsch
The State Veterinary Serum Laboratory (National Veterinary Diagnostic and
Research Institute), Denmark and The Danish Dairy Board, Cattle Health
Laboratory, Denmark.
Please see the book here:- https://doi.org/10.9734/bpi/crpbs/v4/2901
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