FAMILY CHARONACEAE 



1269 



in the presence of Haemophilus influenzae 

 suis a severe maladj' occurs under both 

 natural and experimental conditions; it 

 involves fever, cough, and prostration; 

 many infected animals die. Lungworms, 

 Metasirongylus elongatus and Choero- 

 strongylus pudendotectus {META- 

 STRONGYLIDAE), from infected 

 swine harbor virus at least 2 years, living 

 nieantime in earthworms, such as Allolo- 

 bophora caliginosa (LUM B RIGID AE), 

 which are eaten eventually by swine. 

 The swine are refractory to viral infection 

 during May, June, July, and August, but 

 the disease may be invoked later by 

 successive intramuscular injections of 

 Haemophilus influenzae suis or other 

 stimuli, such as feeding embryonated 

 Ascaris ova. In infected swine, virus oc- 

 curs in turbinates, tracheal exudates, and 

 lungs; not in spleen, liver, kidnej', 

 mesenteric lymph nodes, brain, blood, or 

 mucosa of colon. Xeutralizingantibodies 

 appear later (7th to 10th day) in the mild 

 filtrate disease than in typical swine in- 

 fluenza, in which they appear about the 

 6th to the 7th day; maximum titer on 

 14th to 27th daj^ Experimentally in 

 mouse, not contagious as in swine and 

 not dependent on the coexistence of a 

 bacterial component ; death of epithelium 

 of respiratory and terminal bronchioles, 

 complete epithelial desquamation, dilata- 

 tion of bronchioles, collapse of alveoli ; in 

 healing, widespread epithelial prolifera- 

 tion. Experimentally in ferret, mod- 

 erate apathy, lack of appetite, pallor of 

 nose, variable catarrhal symptoms; at 

 acute stage of disease, necrosis of respira- 

 torj^ epithelium of nasal mucous mem- 

 brane, with desquamation of superficial 

 cells, exudation into air passages and 

 inflammatory reaction in the submucosa ; 

 repair follows, beginning on the 6th daj* 

 after infection and becoming essentially 

 complete at the end of 1 month; after 

 recovery, the ferret is immune for 3 

 months or more, with subsequent waning 

 of resistance ; subsequent subcutaneous 

 inoculations of virus restore immunity. 



Transmission : Presumably by drop- 

 lets ; for example between cages of ferrets 

 as close as 5 feet apart, even to levels 3 

 feet higher than cage of diseased individ- 

 uals. Experimentally, from washings of 

 human throats to ferret, mouse, chick 

 embryo (by amniotic route and to allan- 

 toic membrane) ; in mice, bj^ contact and 

 by inhalation of fine droplets. 



Serological relationships : Neutralizing 

 antibodies common in human sera from 

 individuals above 10 j'ears of age ; rarer 

 in sera from j'oung children ; strongly ef- 

 fective for homologous, weak for hetero- 

 logous, virus in convalescent sera. Solu- 

 ble complement-fixing antigen of swine 

 strain has components in common with 

 antigens of human strains (PR8 and WS). 

 Complement fixation best 10 to 14 days 

 after onset in man. Inactivating capa- 

 city of nasal secretions proportional to 

 level of neutralizing antibodies in blood. 

 Agglutination of red cells by influenza 

 virus is inhibited quantitatively bj' 

 specific antiserum. 



Immunological relationships: Specific 

 immunization of ferrets, without obvious 

 disease, occurs as a result of intranasal 

 inoculation of egg-passage influenza virus 

 that is not transmissible from ferret to 

 ferret. In mice, immunizing dose is 

 directly proportional to degree of induced 

 immunity; immunity to the strain used 

 in immunization is more effective in gen- 

 eral than that to heterologous isolates of 

 the virus. 



Filterability : Passes Berkefeld V filter. 



Other properties: Particle size esti- 

 mated as 80 to 120 millimicrons by filtra- 

 tion studies; 80 to 99 millimicrons by 

 ultracentrifugation (820° = 724 X IQ-i" 

 cm per sec. per dyne); electron micro- 

 graphs show bean or kidney-shaped 

 particles, or round particles with central 

 dense spot , averaging 77.6 millimicrons in 

 diameter. Inactivated by oleic, linolic 

 and linolenic acids without loss of im- 

 munizing ability. Inactivated by ultra- 

 violet radiation. 



Literature : Andrewes and Glover, 



