Experimental mixed CNS infections in mice caused by three Ixodes ricinus transmitted Arboviruses

Approximately 12-day-old mice were infected intracerebrally with tick-borne encephalitis (TBE) virus (strain Hypr), Unkuniemi virus (strain By E50) and Tribec virus, as single virus inoculations, coinfections with two or three viruses, and sequential infections with two or three viruses at 24-hour intervals. The effect of mixed infections on mortality, morbidity and average survival time was recorded. The main findings were that: 1. Some mixed infections with TBE and UUK viruses reduced the mortality and acute morbidity significantly as compared to single infections with each virus. The average survival times were lengthened. 2. Mixed infections with TBE and Tribec did not affect the 100% mortality of TBE. 3. Mixed infections with UUK and Tribec seemed to result in a cumulative effect of the two viruses. 4. With triple co-infections (TBE + Tribec + UUK simultaneously), the mortality and acute morbidity rates were reduced significantly as compared to TBE single infections. 5. Some of the mixed infections tended to result in chronic disease among the survivors.