Japanese encephalitis surveillance in China (Province of Taiwan) during 1968-1971. I. Geographical and seasonal features of case outbreaks

During 1968-1971 Japanese encephalitis (JE) surveillance was conducted with WHO-assisted programs in Taiwan area. Emphasis was placed on: (1) active case-finding by hospital visits; (2) blood collection from every patient at the suitable time; and (3) the enforcement of standard diagnostic criteria on the results of hemagglutination-inhibition tests. Each year, approximately 90% of reported patients were etiologically examined. JE virus etiology was established in 277 (1968), 279 (1969), 269 (1970) and 158 (1971) cases. Despite the apparent concentration of cases in several cities, practically all the cultivated plains and basins were established as potentially endemic for JE. JE outbreak is found to have been clearly associated with season, not only in subtropical but also in tropical Taiwan. Each year it occurred consistently in mid-July in the southernmost county, 2-3 weeks after the peak of rice transplantation and its duration was a few weeks. On the western side of the island, although less consistently, JE outbreak seems to occur one to three weeks later than in the south. Outbreak in eastern Taiwan was a mid-September phenomenon for 3 years. Observed seasonal lag, which was significant between two neighboring localities on same latitude, suggests that paddy water management is more directly related to date of outbreak than local climate. Seasonal characteristics further suggests that the area may be separated into eight ecologic subdivisions. JE-virus transmission to a man during April at temperatures below the average of 20 C was discussed.

Japanese encephalitis surveillance in China (Province of Taiwan) during 1968-1971. II. Age-secific incidence in connection with Japanese encephalitis vaccination program

A baseline age/morbidity pattern for Japanese encephalitis (JE) epidemic in China (Province of Taiwan) in the 1960s was sought in JE surveillance. The pattern is characterized by: (1) high incidence in age groups 2-4 years, (2) moderately high incidence in age groups 5-7 years, (3) negligible incidence in children under 1 year of age as well as in adults, and (4) the variability of relative height of peak incidence co-incident with the JE-epidemic size in situ. Concurrently with surveillance, a JE-vaccination program was implemented by the Government. The children of target age groups received two doses of vaccine each during April. Vigilant supervision was given to the campaign to achieve a high coverage rate with two-dose vaccination and meticulous record-keeping. During 1969-1972, 2-year olds were the exclusive target; 52.2% (1969), 71.5% (1970), 74.5% (1971), and 83.0% (1972) of the target age group were covered. A considerable change from the baseline age/morbidity pattern seen in 1968 occurred during the above period. The comparison of epidemicity-adjusted incidence by year indications that incidence reduction in the 2- and 3-year old children in 1971 were substantial and suggests the possible impact of vaccination. The total JE incidence for the period 1968-1971 appears to be much lower in vaccinated population (23 reported and 8 confirmed/0.9 million) than in unvaccinated population (1,330 reported and 679 confirmed/2.2 million).

The significance of small erythrocytes

Small erythrocytes (mean corpuscular volume less than 80 mu-3 by the Coulter Model S) were found in 222 (2.75%) of 8,086 consecutive patients admitted to a large suburban general hospital. Forty-five (20.3%) of these 222 patients had laboratory findings consistent with thalassemia. Seventy-six (31.2%) were found to be iron deficient. Patients whose hemoglobin values were below 9.0 Gm. per 100 ml. were more likely to be iron deficient. The hemoglobin A2 values were significantly lower in iron-deficient than in non-iron-deficient patients. Although the mean corpuscular volume is much lower and the erythrocyte count is higher in thalassemia than in iron deficiency, hematologic values obtainable from the Counlter S (such as MCV, erythrocyte count, and hemoglobin) alone are not valuable in differentiating thalassemia from iron deficiency.

Experimental transmission of Japanese encephalitis virus by Culex tritaeniorhynchus and C. fuscocephalus

Experimental transmission of Japanese encephalitis virus from swine to baby chicks was accomplished using Culex tritaeniorhynchus and Culex fuscocephalus, two of three mosquito species in Taiwan from which the virus has been recovered in nature. Whereas neither species had become infective by the twelfth day, one of ten C. fuscocephalus and 11 of 51 C. tritaeniorhynchus were infective by the seventeenth day of extrinsic incubation as verified by viraemia in chicks fed upon by potentially infective mosquitoes. The highest transmission rate obtained was 81% for C. tritaeniorhynchus on the twenty-first day of extrinsic incubation.

Anticoagulant activity of heparin in intravenous fluids

The anticoagulant activity of heparin dissolved in intravenous solutions was measured by two different methods of heparin assay. Both procedures showed markedly reduced anticoagulant activity within four hours after the addition of heparin to the solutions. When measured according to the procedure of Yin, heparin in the intravenous solutions fully regained its lost anticoagulant activity after 24 hours at room temperature. When measured by the thrombin time, however, the heparin anticoagulant activity reamained reduced. The source of heparin, from either the lung or intestine, does not explain the reduction in anticoagulant activity. Although its cause is unknown, the erratic behaviour of heparin in intravenous solutions stresses the importance of a laboratory monitor of heparin therapy.

Seasonal infection of Culex mosquitos and swine with Japanese encephalitis virus

A year-round study of the infection rates of JE virus in Culex mosquitos was made during 1970-71 in 2 hamlets in Taoyuan County, China (Province of Taiwan). JE virus was recovered from 5 of 314 pools of C. annulus, and from 1 of 22 pools of C. tritaeniorhynchus; these recoveries occurred during a 14-day period in July 1971. None of the 288 pools of C. p. fatigans, which had been collected between October and April, was positive. In addition, sentinel swine were assessed for antibody and virus. All the pigs became highly immune by 23 July; in each hamlet all the pigs had become infected within 1 week, virus being detected in them for only 1-2 weeks. Virus-positive mosquitos appeared to have obtained their infections at about the time that viraemia was occurring in the sentinel swine. These observations illustrate once again the lower infection rate and shorter duration of virus-positive mosquitos in China (Province of Taiwan) as compared with Japan.

Red cell size as measured by the Coulter model S

The MCV (mean corpuscular volume) was examined by the Coulter model S. It was found that the MCV measured by the Coulter S was larger than the generally accepted range 82 to 92, or 76 to 96 mu(3). The range in 500 healthy individuals was 82.2 to 100.6 mu(3). It was also found that the mean MCV became larger with increasing age. No sex difference was found. The low MCV by manual methods was generally thought to be attributed to less accurate measurement of erythrocyte counts.

Red cell size and age

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The effect of vaccination with a live attenuated strain of Japanese encephalitis virus on stillbirths in swine in Taiwan

Since an excellent candidate strain (M) for live virus vaccination of swine against Japanese encephalitis was developed, a number of large vaccination programmes have been implemented in Japan with the aim of controlling Japanese encephalitis epidemics in man by reducing the population size of nonimmune swine. Encouraging results have been obtained but no studies have been made on the benefits of live-virus vaccination to the industry. In order to determine the effect of vaccination upon the number of stillbirths occurring in the Japanese encephalitis post-emergence season, a total of 74 vaccinated, and subsequently mated, gilts at a large breeding farm in subtropical Taiwan were subjected to follow-up observations in comparison with a control group. The total incidence of litter stillbirths in the vaccinated group (1/74) was significantly lower than that in the control group (21/68). Over 92% of the newborn piglets from the vaccinated gilts were healthy, while 31.6-54.1% of the newborn piglets in the control groups were stillborn. The litter size of vaccinated gilts was larger than that of the control gilts. The vaccine was shown by tests in 22 swine to have an adequate degree of safety. Four weeks after vaccination with either 10(5.6) or 10(8.0) smicLD(50) of virus, all the swine developed an adequate level of antibody. The results indicate that live virus vaccination could benefit the industry in addition to achieving the main aim of controlling Japanese encephalitis viraemia in swine.