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annual inoculation drive which has been in progress since 1959 continued to give encouraging results, and it is gratifying to record that there has been a steady decline in the number of cases notified annually; in 1971 only 25 cases were recorded compared with 43 cases in 1970 and 2,087 cases in 1959.
Measles is most prevalent among children under the age of five years and epidemics are characteristically biennial. In Hong Kong during epidemics the disease is usually associated with high mortality due mainly to complicated bronchopneumonia encountered too late for treatment to be effective. A Colony-wide immunisation campaign began in December 1967 and is continuing. The vaccine is now regularly available at government maternal and child health centres. Health education efforts at health centres are continued and parents are informed of the importance of early treatment of the disease. The disease incidence and its mortality have remained satisfactorily low in the past four years. These results were partly due to the immunisation campaign and the continuing health education pro- grammes.
Influenza occurred only sporadically after the appearance of the epidemic in the summer of 1968. Hong Kong has been collabo- rating with the World Health Organisation in its surveillance programme of influenza disease, and epidemiological and laboratory information is transmitted overseas so that early preventive measures may be taken to meet the threat of new epidemics. During the summer months there was an increase in the number of influenza- like cases attending the outpatient clinics. Some strains of A2/Hong Kong/68 and B influenza virus were isolated.
Japanese B encephalitis among humans is encountered occasional- ly in Hong Kong. The disease is transmitted by a mosquito vector and the important species known to transmit the disease is Culex tritaenio-rhynchus. The mosquito generally breeds in abandoned paddy fields, marshy ground, water hyacinth plots, and in irrigation ditches. Such conditions are found in the rural areas of the New Territories and it is here that this particular mosquito vector has been detected. Humans and horses are only incidental hosts to the Japanese encephalitis virus but pigs are considered important reservoirs. In June several horses at the Royal Hong Kong Jockey Club stables at Beas River, New Territories, were found to be in- fected by the virus. The situation was investigated on the spot by health officers and mosquito control measures were stepped up following a mosquito survey, and advice was given to the resident