INFLUENZA : I. THE HEMAGGLUTINATION AND INFECTIVITY TITRE CURVES OF PR8 INFLUENZA VIRUS CULTIVATED IN EMBRYONATED EGGS AT DIFFERENT TEMPERATURES

Optimization of incubation temperature in embryonated chicken eggs inoculated with H9N2 vaccinal subtype of avian influenza virus

There are little information about growth properties of low pathogenic (LP) avian influenza virus (AIV) in embryonated chicken eggs (ECEs) at different incubation temperatures. Knowledge of this information increases the quantity and quality of antigen in vaccine production process. For this purpose, 10(-5) dilution of AIV (A/Chicken/Iran/99/H9N2) was inoculated (Intra-allantoic) into 400, 11-day old specific pathogen free (SPF) ECEs in the 0.1 mL per ECE rate and incubated in 32, 33, 34, 35, 36, 37.5, 38, 39 ˚C for 72 hr in 65% humidity. Early death embryos in first 24 hr were removed. Amnio-allantoic fluid was withdrawn into the measuring cylinder, and tested for hemagglutination (HA) activity and egg infective dose 50 (EID50). The utilizable ECEs and amnio-allantoic fluid volume was significantly increased in 35 ˚C, (p < 0.05). Significant difference in HA and EID50 titers, were seen only in 39 ˚C group. Therefore, 35°C is an optimum temperature for incubation of inoculated ECEs.

The level of lactic dehydrogenase activity as an indicator of the grwoth of influenza virus in the embryonate egg

The relation, between time and the levels of lactic dehydrogenase activity of chorioallantoic fluids from embryonate eggs infected with the PR8 strain of influenza virus were determined quantitatively. The mean values, based on 10 determinations for each time interval, followed a sigmoid curve, with the greatest rates of change occurring between 48 and 72 hours after the inoculation of virus. The activities of the fluids from infected eggs at the 72nd hour or later were approximately 18 times higher than those from non-infected eggs. Based on the data above, a qualitative test for the presence of infection with influenza virus was developed.

Formation of non-infectious influenza virus in mouse lungs: its dependence upon extensive pulmonary consolidation initiated by the viral inoculum

Formation of non-infectious virus-particles which hemagglutinate red blood cells and react with antibody to fix complement but do not infect the chick embryo or mouse-occurred when large quantities of certain strains of influenza viruses were inoculated intranasally into mice. Dependent upon the agent employed, 10(6.5) to 10(8.5) E.I.D. was essential to elicit this phenomenon. To accomplish this unusual multiplication it was essential to use a strain of virus which effected extensive pulmonary consolidation; strains of virus which did not produce marked lung lesions, even when as much as 10(8.5) E.I.D. was inoculated, did not form non-infectious virus. The development of this viral form was directly dependent upon the extent of cell damage obtained: consolidation of more than 50 per cent of the lung volume was required. The majority of non-infectious particles developed during the initial cycle of viral multiplication, and concurrently with the formation of non-infectious virus there was a corresponding decrease in the number of infectious viral particles. Non-infectious virus could not be propagated on serial passage in mouse lungs: on second lung passage only fully infectious virus was detectable. The formation of the non-infectious viral form was not the result of interference with synthesis of infectious virus by inactivated virus in the inoculum; for inoculation of heated infected allantoic fluid which contained more than 99 per cent of non-infectious virus did not result in the development of new non-infectious virus. Although inoculation of a large quantity of virus resulted in infection which yielded a relatively low titer of infectious and high titer of non-infectious virus, inoculation of a small quantity of the agent resulted in a high yield of infectious virus and no non-infectious that was detectable. In both instances the total quantity of antigenic viral material synthesized in the mouse lungs was the same. These data do not support the hypothesis that the non-infectious virus formed consisted of immature or incomplete viral particles, but suggest instead that non-infectious virus is inactivated virus or some aberrant form of the agent.

The effects on biological materials of freezing and drying by vacuum sublimation. II. Effect on influenza virus

The infectivity titre of influenza virus-infected allantoic fluid was determined after a variety of procedures involving cyclic slow freezing and thawing, freezing at various rates with subsequent storage at different temperatures freezing at various rates with subsequent dehydration at various temperatures, and different degrees of dehydration. All these factors were found to influence the survival rate of the virus particles. Five freeze-thaw cycles resulted in a fall in titre from 10(-8.6) to 10(-0.8) cycles 2, 3, and 4 causing much greater losses than cycles 1 and 5. Rapid cooling to -40 degrees C. or slow cooling to -80 or 190 degrees C. did not cause significant titre loss, but rapid cooling to temperatures above -40 degrees or slow cooling to temperatures above -80 degrees C. caused definite titre loss. Loss of titre on storage occurred only at temperatures above -40deg;C. The effect of lyophilization depends both on the preliminary treatment and on the dehydration temperature. Better conservation of titre was obtained after preliminary cooling to -190 or -80 degrees C. than after preliminary cooling to higher temperatures. The most effective sublimation temperatures were 0 and -80 degrees .; the least effective was +20 degrees C. Titre losses in suspensions sublimated at -10, -30, and -60 degrees C. were in general intermediate. No loss in titre occurred after preliminary cooling to -80 or -190 degrees C. and subsequent dehydration at -80 or 0 degrees C. The degree of dehydration definitely affects the survival of virus on storage at 0 degrees C., but sublimation for 4 hours at 0 degrees C. gave complete protection against titre loss on storage at this temperature. Possible explanations of the observations made are suggested, based on known physiochemical phenomena such as supercooling, vitrification, variations in size and shape of ice crystals with different freezing speeds, differential enzyme inactivation, changes in salt concentration, and changes in energy levels.

The effect of x-radiation on the multiplication of influenza A virus in embryonate eggs

Groups of embryonate eggs were given 250, 500, 750, and 1000 r of x-radiation. 18 hours later, these 4 groups, together with a control group, were injected intra-allantoically with influenza A virus. Radiation at all dosage levels caused significant changes in the infectivity titre curves during the next 90 hours. The most striking alterations were the prolonged incubation period and the uniformly low infectivity titre in the group of eggs given 750 r.