CHAPTER IX 
CONTROL OF VIRUS DISEASES 
In this brief review of the methods available for the control of virus 
diseases it will be easier to deal with the virus diseases of animals and 
plants separately. This is because the techniques are of necessity rather 
different, so much of the prevention and control of animal virus diseases 
being based on the development of an acquired immunity of a kind 
not existing, so far as we know, in plants. 
Virus Diseases of Animals 
The methods for the control of animal virus diseases are briefly 
discussed under two heads. In the one case the various types of 
inoculations are dealt with, together with other measures applied to 
the host itself. In the other case, possible methods of destroying the 
vectors of viruses are considered and in this process the new insecticides 
may play an important part. 
1. Measures Applied to the Host 
Under the general head of vaccination there are several techniques 
which are briefly discussed. Vaccination can be performed (a) with 
inactivated virus, (b) with active virus, (c) with modified virus, (d) with 
antiserum from a recovered animal, (e) with both active virus and 
antiserum, and (f) with combined active and inactive virus. It had 
for long been considered that inoculation with inactivated virus failed 
to produce immunity but now there is evidence that such inoculation 
is efficacious in some virus diseases. Probably one of the reasons for 
earlier failures was the use of inadequate amounts of inactive virus or 
the destruction of the antigenicity of the virus. We have learned 
already that it is possible to inactivate some viruses without altering 
their serological properties and this can be done by two main methods: 
(1) inactivation by physical agents, such as ultra-violet light, or visible 
light in the presence of methylene blue; (2) inactivation by chemical 
agents such as formaldehyde, phenol, or chloroform. 
Although the application of inactivated virus vaccines is limited, 
some success has been obtained with dog distemper and equine 
encephalomyelitis. The use of formaldehyde for producing the 
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