406 Microbes and You 



Chicken Pox 



This virus disease, known as varicella, produces inckision bodies 

 in the epithehal skin cells, and elementary bodies can be demon- 

 strated in the fluid of the skin vesicles. The virus has not been 

 successfully cultivated in chick embryos. There is some question 

 as to whether "shingles," caused by Herpes zoster, has the same 

 virus etiology as chicken pox. 



IMMUNITY TO VIRUS DISEASES 



The mode of dissemination of viruses is apparently similar to 

 that for many bacteria: direct contact, droplet infection, and in- 

 sects. Some virus diseases, such as yellow fever, are exclusively 

 carried by insect vectors. 



Immunity to virus infections varies from little or none, through 

 moderate immunity for a number of years, to apparent lifetime 

 immunity to still other viruses. In the case of cold sores the virus 

 appears to remain in the tissues and provide an infection immunity. 

 Occasionally the virus becomes aggressive and attacks skin cells, 

 particularly in the region around the lips. 



While most bacterial vaccines are suspensions of dead cells, it 

 is found that viruses inactivated by heat or with chemicals are 

 generally inefl^ective as vaccines. Anv technic which kills the 

 virus appears to alter the antigenicity of the virus protein. 



DIAGNOSTIC PROCEDURES 



A number of technics are available for aiding in the diagnosis 

 of diseases of virus etiology. An experienced person can look for 

 inclusion bodies in the tissues, but since all viruses do not produce 

 these cell inclusions, the absence of inclusion bodies does not 

 necessarily rule out viruses. Elementary bodies can be sought in 

 fluids from affected tissues. Cultivation of the virus in tissue 

 culture or in embryonated eggs can also be tried. 



Some viruses, like those of influenza, have the abilitv to agglu- 

 tinate red blood cells of selected animals. By collecting samples 

 of a patient's blood during the acute and during the convalescent 



