Experimental Studies With the Agent of the Common Cold

Abstract

Nasal washings we''re collected from several cases of common cold infection 24 hrs. after onset of symptoms. The diluent was 2% rabbit serum in saline. Each of 3 specimens was treated with 30,000 U. of penicillin for 5 min. and then inoculated into the chorioallantoic cavity of 7-day-old chick embryos. These embryos were further incubated at 35 [degree]C. Every 4 days the chorioallantoic fluid was collected and pooled from each strain passage. Each strain was passaged blindly every 4 days. Infectivity of the fluid was checked by intranasal inoculation into humans. When inoculated into synthetic medium, visible organisms could not be cultivated from this material. Strain I was negative when the fluid of the 2d passage was inoculated into 2 subjects. Strain II (MP) was infectious for 2 passages, but very mild or no reactions occurred with the later passages when it was inoculated into human subjects. Strain III (Spill) induced symptoms of the common cold after 9, 11, and 12 series of consecutive passages in the chick embryo. The later passages induced much milder symptoms. The diagnosis of cold infection was based on symptoms, negative blood changes, and negative Hirst influenza tests. Six volunteers were inoculated intranasally with chorioallantoic fluid (Spill strain) of the 9th passage in chick embryos. Five developed symptoms of cold. These 5 and 5 new volunteers were inoculated sub-cut. with 2 doses of infectious chorioallantoic fluid, l.ml. per week. One week after the 2d inoculation they were challenged intranasally with Seitz filtrates of nasal washings from naturally acquired cases of cold infection. All subjects immunized with the embryo-propagated cold agent failed to develop cold symptoms; and with the same challenge inoculum, the 2 controls not exposed to the strain both developed marked symptoms. Six controls were inoculated intranasally with normal fluid from 11-day-old embryos, and none developed symptoms of cold infection. This was also true of 5 controls inoculated intranasally with 2% rabbit serum in saline.