Acta path. microbiol. scand. Section B. 79, 123-124, 1971

BRIEF REPORTS RESPIRATORY INFECTION W I T H PARAINFLUENZA 1,

SENDAI VIRUS I N

GNOTOBIOTIC AND CONVENTIONAL MICE

Miklos Degre' and Tore Midtvedt

I t has been established both clinically and by experimental studies that viral infection of the respiratory tract may be followed by secondary bacterial invasion (2 , 5) . While some of the secondary invaders are recognized as pathogenic species, the majority are derived from the normal resident flora of the upper respiratory tract. The pathogenicity of the latter organisms remains poorly defined. The contribution of these bacteria to the infectious process has not been clearly delineated. Recent studies in our laboratory indi- cate that the secondary invadeis of low patho- genicity may participate in the respiratory infec- tion of mice ( 3 ) . The continuous administration of Penicillin-G to mice infected with parainfluenza 1, Sendai virus reduced the mortality and the polymoIphonuclear (PMN) leukocyte accumula- tion in the lungs (1) . The most! likely explanation for the effect of penicillin was :an elimination of the spontaneous bacterial invasion which follows viral inoculation. This report yxtends these studies to germfree (GF) mice in order to define the role of resident flora by ensuring a complete control of the absence of it.

Young albino mice of CD ,1 strain were used. One group, 15 mice, was obtained GF from the Charles River Mouse Farms, Wilmington, Mass. USA, and was kept under germfree conditions as described elsewhere (6). Negative cultures at the termination of the experiment proved that the mice remained bacteria-free. Groups 2 and 3 in- cluded conventionalized mice of the same strain. -411 three groups were inoculated with 108 EID,, parainfluenza 1 virus, Sendai strain, as previously described (2, 6). The GF group and one of the conventionalized groups were givm water to drink, the third group water, containing Penicillin-G,

Received 20.xi.70 from Kaptein W . Wilhelmsen og Frues Bakteriologiske Institutt, University of Oslo, Rikshospitalet, Oslo, Noruiay.

8000 IU per ml. With the average daily water consumption of 5-6 ml, the mice were administered roughly 4 million IU per kg body weight. The serum level of Penicillin was about 1.5 pg per ml determined by tube dilution method. All three groups were observed for 10 days and mortality was recorded daily. At the end of the observation period the survivers were sacrificed, and their lungs were examined for presence of bacteria and for white cell count, by the methods previously described ( 1 ) . The results are summarised in Table 1. I t seems to be clear that the outcome of disease is correlated with the chance of bacterial contamination. A higher proportion of mice died, and they died earlier in the conventional-untreated group where bacterial spreading occurs freely, than in the treated group, and still less in the GF group. I t appears that parainfluenza I virus alone pro- duces a mild infection, even though the virus seems to multiply in the respiratory organs of G F mice. Significant titers were demonstrated in the lung- wash-outs, 10 days after inoculation, by the hem- adsorption method, using Vero cells and 0.05 per cent of guinea pig erythrocytes. The lower sus- ceptibility of GF mice to viral infection is not a general phenomenon (7, 8, 9 ) . Therefore no con- clusion of general validity can be drawn from the present experiment.

The extent of PMN leukocyte accumulation seems to be correlated with the presence of bac- teria (1, 2) . The differences in the present ex- periment are not significant, although there is a clear tendency to obtain increasing proportion of PMN leukocytes with increasing chance of bac- terial contamination.

The present results support the concept, that if the defense mechanisms are weakened one way or another the resident bacterial flora invades the lower parts of respiratory tract and in some cases produces disease. The defense mechanisms might be reduced by f . i. immunosuppressive drugs (9), or as in the present study by virus infection.

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TABLE 1. Mortality, Whi te Cell Accirmulation and Presence of Bacteria in the Lungs of Germfree and Conventional Mice following Inoculation with Parainfluenza 1 Virus

Mortality Survival White cells in the lung PMN Macro- Bacteria

cent per cent

phages in the Total Mean Total per lung days Total z:t

Conventional mice No treatment 12/15 79* 117 7.8OY ND 2 1 t 12 3/3 § Penicillin-G treatment 7/15 46* 137 9.13* ND 1st 18 1 /8

Germfree mice 1/15 7* 147 9.70* 8x10* 13 t 42 0/14

* p < 0.05. t p > 0.05.

ND Notdone. Survivers after 10 days observation.

Summary The presence of resident bacterial flora in the

respiratory tract influences the outcome of infec- tious disease following parainfluenza 1 virus infec- tion, and, to some extent also the leukocyte inva- sion in the lungs.

References: 1. Degrk, M.: Acta path. microbiol. scand. In press.-2. Degrk, M . & Glasgow, L. A , : J. Infect. Dis. 118: 449-462, 1968.-3. Degrd,M.

& Solberg, L. A,: Acta path. microbiol. scand. In press.-4. Dolowy, W. C. & Moldoon, R. L.: Proc. SOC. Exptl. Biol. Bed. 116: 365-371, 1964.-5. Loosli, C . G.: Yale J. Biol. Med. 40: 522-540, 1967/68.-6. Midtvedt, T. & Trippestad, A.: Acta path. microbiol. scand. Sect. B. 78: 1-5, 1970.-, 7. Mirand, E. A. & Grace, J . T . Jr.: Nature 200: 92-93, 1963.-8. Schaffer, J., Parker, R. B., Trex- ler, P. C., Rreidenbach, G. & Walcher, D. N.: Proc. SOC. Expl. Biol. Med. 112: 561-564, 1963.-9. Sharon, N . & Pollard, M.: Bact. Proc. 1970, p. 76.

Actat path. microbiol. scand. Section B. 79, 124-125, 1971

ELIMINATI'ON OF INTERCURRENT DEATH AMONG RABBITS INOCULATED WITH T R E P O N E M A PALLZDUM

H . J . Skovgaard Jensen

A high incidence of early death among rabbits after inoculation with Treponema pallidum (Ni-

Received 28.xii.70 from Laboratory Animal De- partment, Statens Seruminstitut, Copenhugen, Den- mark.

Requests for reprints should be addressed to: H . J . Skovgaard Jensen, V.M.D., Laboratory Ani- mal Department, Statens Seruminstitut, DK 2300 Copenhagen S , Denmark.

124

chols' pathogenic strain) is observed in TPI labo- ratories in Denmark (Jorgensen 1968), Norway (Erichsen 1968), and Sweden (Gudjdnsson & Skog 1968, 1970). This phenomenon seems to have been recognized first in Denmark and later in Nor- way and Sweden, but it has not been reported from other countries.

In Denmark Nichols' strain of T. pallidum (Nichols & Hough 1913) has been maintained in rabbits since 1951. These treponemes were received,