In 1978 a severe epidemic of acute CNS diseases occurred in Hungary. Enterovirus type 71 (E71) proved to be the main aetiological agent. This could, however, be established only by special investigations, since the usual laboratory tests proved inefficient for diagnosis of E71 infections.
Attempts to isolate virus in tissue cultures were made on 1952 samples from 686 patients. E71 could only be isolated in cultures of a Vero cell line and even then only after 3 to 6 blind passages. Successful isolations were made from 47 stool samples, 5 throat swabs and 6 CNS samples originating from 44 patients. This represented only 13.6 per cent of the total number of E71 cases diagnosed in the course of studies, thus indicating the poor sensitivity of these tests. Suckling mice were unsuitable for the isolation of E71, although E71 tissue culture isolates proved pathogenic to these animals. Isolates could be identified by neutralization technique only after disaggregation of virions by ether treatment.
Blood samples from 1050 patients were tested for E71 antibodies by a radial plaque neutralization technique and those from 593 patients proved positive. A significant change in antibody level could only be detected in 52 out of 286 patients whose paired sera were available. The limited usefulness of this technique for the detection of current E71 infections was, however, indicated by the fact that 66 per cent of patients positive in virus isolation experiments already had antibodies in the early phase of their illness which remained at a constant level thereafter.
Investigation of 684 blood samples from 511 patients for E71-specific IgM antibodies showed this test to be the most reliable for the detection of current E71 infections. When appropriate blood samples were available, these antibodies could be detected in patients positive in the above mentioned tests, moreover, this method made an aetiological diagnosis possible in 236 cases which otherwise would have remained undetermined.
Infection with E71 was finally confirmed in 323 cases (poliomyelitis-like paralysis, 13; encephalitis, 145; aseptic meningitis, 161; hand, foot and mouth disease, 4).