Reactions of Monkeys to Experimental Respiratory Infections. ∗ I. Response to Influenza Virus A

Abstract

Most of our current knowledge of experimental influenza has been derived from observations made on small laboratory animals, particularly mice and ferrets. Vieuchange 1 reported certain manifestations of infection in 2 monkeys inoculated with an unfiltered mouse-lung suspension of the “W.S.” strain of virus. Some 2 years ago we began a series of correlated studies-clinical, hematological, bacteriological, and immunological-in normal monkeys inoculated intranasally: (1) with the virus of influenza A, (2) with Streptococcus hemolyticus Group C, and (3) with the virus and streptococcus in various sequences. 2 Similar studies are in progress, utilizing vitamin-deficient monkeys. This communication records the reaction of normal monkeys to the virus alone.

Methods. The PR-8 strain of influenza virus used was maintained by intranasal passage in young adult white mice. The inoculum for the monkeys was prepared as follows : The lungs of infected mice were triturated in 9 volumes of buffered saline; the suspension was filtered through Berkefeld V candles and the filtrate stored at −78°C; after a period of stabilization it was titrated in mice and was retested for maintained virulence from time to time during experimentation.

Young adult monkeys (Macaca mulatta) were held under quarantine during a period of preliminary laboratory tests. After suitable base-line observations were completed the animals were anesthetized with ether and 3 cc of the prepared material (10,000 mouse mld) were dropped into the external nares.

Complete serial blood-cell studies, repeated tests for the presence of virus in nasal and throat washings, and serum-neutralization tests were continued over a period of several weeks.

Results. None of the 7 monkeys thus inoculated intranasally with the influenza virus manifested clinical symptoms of injection. That invasion regularly occurred, however, was proved: (1) by consistent changes in the blood-cell equilibria, (2) by the development of neutralizing antibodies.