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A swine influenza virus (A/swine/ Taiwan/70) was shown to be antigenically identical with human A2/Hong Kong/68. It readily infected volunteers and stimulated anti-haemagglutinin and antineuraminidase antibodies. These antibodies reacted both with the infecting strain and with A2/Hong Kong/68. Clinical reactions were, however, modified in comparison with those of human A2/Hong Kong/68 or with those of a recent antigenic variant, but the reactions were still more severe than would be acceptable in a live vaccine. In contrast, two other " classical" swine viruses, immunologically distinct from the Hong Kong strain, possessed only low human infectivity. It is suggested that large outbreaks of human influenza may be caused by major variants originating in animals.

The transovarial development of Rickettsia tsutsugamushi in a colony of Leptotrombidium (Leptotrombidium) akamushi , a mite vector of scrub typhus, has been studied over 5 generations. The transovarial infection rate was 98%; the filial infection rate was usually 100%, though lower rates were occasionally observed. These rates may not be valid for all populations of vector mites because they have been estimated for female mites producing only female offspring. Nevertheless, these studies show that transovarial passage of rickettsiae can be highly efficient. By this mechanism, point foci of virtually 100% infected larval mites could be produced. The risk of infection for man exposed to larval mites in such point loci would be extremely high.