Epidemio-entomological survey on malarial vector mosquitoes in Kyongbuk, Korea.

In order to determine population dynamics of Anopheles sinensis, a survey based on average number of female mosquitoes per trap-night was carried out during the period of 5 years from 1987 to 1991. A. sinensis first appeared between the 2nd and 20th April, and were trapped in large number between the 5th and 12th July. The number of trapped mosquitoes began to decrease from mid-August, and a few were collected until mid-November, each year. The average number of A. sinensis in July was 542.6 per trap-night in 1987, but in 1989 increased abruptly to 1,331.4, and then decreased to considerably lower levels, 271.9 in 1990 and 372.1 in 1991. The nocturnal activity of A. sinensis to attack humans was found to become active in the early night, and it was gradually decreasing at mid-night, however, then slightly increasing toward dawn. The immature stage of A. sinensis in the rice paddies was first found in the correlation pattern with peak adult densities in early July. The highest larval density of A. sinensis in the study area was 21,226 x 10(3) in early July 1990. The larval A. sinensis showed high resistance level and resistance ratios against 3 kinds of organo-phosphorous compounds, diazinon, malathion, and fenitrothion, but low resistance against fenthion. The present results indicated that the population density of A. sinensis in Kyongbuk area is decreasing over the five-year from 1987 to 1991.     

Pilot sero-epidemiological survey on Japanese encephalitis in north-western Burma.

A pilot sero-epidemiological survey of Japanese encephalitis was carried out in three areas of north-western Burma applying the hemagglutination-inhibition test. The existence of Japanese encephalitis infection in these areas was confirmed and its incidences in these areas were estimated and compared graphically.     

Temperature-sensitive mutants of Japanese encephalitis virus.

Ten stable temperature-sensitive mutants of Japanese encephalitis virus were isolated after mutagenesis by growth of cloned wild-type virus in the presence of the nucleic acid precursor analogs 5-fluorouracil and 5-azacytidine. Mutants were selected which grew at least 100-fold better at 33 degrees C than at 41 degrees C. The 5-fluorouracil was found to be more effective at inducing temperature-sensitive mutations than was 5-azacytidine. Analysis of the virus-specific RNA and proteins synthesized by each mutant at the nonpermissive temperature was used to determine biochemical phenotypes. The mutants were analyzed for abilities to complement in mixed infections. Although inefficient and sometimes nonreciprocal, complementation occurred at higher levels than previously reported for flavivirus mutants. Interference between mutants in some mixed infections was also observed. Seven complementation groups were defined. Three groups contained mutants incapable of synthesizing virus-specific RNA at the nonpermissive temperature, whereas the remaining complementation groups displayed an RNA+ phenotype. Levels of protein synthesis comparable to that of wild type were observed at the nonpermissive temperature in three groups. Two other groups were represented by mutants which synthesized only low levels of virus-specific proteins at the higher temperature. Mutants in the remaining two groups did not produce detectable levels of proteins under nonpermissive conditions.     

Thermostability of Japanese encephalitis vaccine produced in India.

Different batches of bulk vaccine, final bulk at in-process level, finished freeze-dried and reconstituted Japanese encephalitis vaccine were assayed for their stability at temperatures of 22, 37 and 40 degrees C. After ultrazonal purification of 50 times concentrated brain suspension, JE Bulk vaccine was found to be stable for up to 2 years at 4 degrees C, however, the percentage loss in potency (log 10 N antibody titre) after 2.5 years was 24%. Three-times concentrated final bulk showed rapid deterioration by the fourth week at 37 and 40 degrees C. Freeze-dried JE vaccine maintained at 22 degrees C for 28 weeks did not show perceptible deterioration. At 37 degrees C, the same vaccine started showing deterioration (14%) after 8 weeks whereas at 40 degrees C the loss of potency was 24% after 8 weeks. The freeze-dried vaccine was found to be stable for up to 2 weeks duration at 40 degrees C.     

Historical review and surveillance of Japanese encephalitis, Republic of Korea, 2002–2004

Japanese encephalitis virus (JEV), transmitted by culicine mosquitoes, is endemic throughout much of South‐East Asia, extending to the Korean Peninsula. The zoonotic cycle is from large water birds to culicine mosquitoes, with swine as an amplifying host and man as an incidental host. Culex tritaeniorhynchus, the primary JEV vector in the Republic of Korea, populations peak in late August through to early September when most cases of Japanese encephalitis (JE) are reported. Cx. tritaeniorhynchus were observed near the Demilitarized Zone in each of the years that mosquitoes were assayed for JEV. Each year that vector mosquitoes were assayed for JEV, minimum field infection rates (number of JEV positive mosquites/1000 Cx. tritaeniorhynchus assayed) ranged from 0.31 to 3.27. The epidemiology of JE has been recorded in Korea for more than half a century, from 1949 to 2005. During a major epidemic in 1949, there were 5616 cases and 2729 deaths reported, with levels persisting near epidemic levels of 1000 cases annually thereafter until 1969. Following the introduction and government mandated mass immunization in 1971, JE decreased dramatically. Since 1984, 0–6 cases of JE have been reported each year. However, continued evidence of mosquitoes positive for JEV indicates that JE continues to be a civilian and military health threat to immunocompromised persons in Korea, as well as non‐immune US soldiers, civilians and their family members.     

7起乙型脑炎疫苗异常反应的调查和分析

对１９９３～１９９７年间因接种乙脑疫苗引起的７起异常反应进行了调查和分析，主要是Ⅰ型变态反应（０．３３％～１．６％）和心因性反应（１１．７％～２４．２％）。反应一般发生在第３针以后，有些发生在第６针。症状表现为过敏性休克、紫癜、荨麻疹、血管神经性水肿、气喘等。对变态反应的发生频率、反应机理、处理方法和预防等问题进行了讨论     

Host preference of mosquito vectors of Japanese encephalitis.

The host preference of 4 Culex mosquito species collected in Miaoli and Pingtung counties, Taiwan was studied by capillary precipitin method. Antisera to alum-precipitated sera of man, bovine, swine, rabbit, horse, dog, cat, mouse, chicken, duck, and pigeon were produced in rabbits and reacted with 758 mosquito blood meals among which reactions to one or more antisera. Culex annulus and Culex tritaeniorhynchus summorosus showed a great avidity for pig, and Culex fuscocephala for bovine. Culex pipiens fatigans was ornithophilic. None of 110 C. t. summorosus and 2.4% of 223 C. annulus had fed on man. Among 66 samples of C.p. fatigans tested 10.3% had fed on man, while none of 359 C. fuscocephala did. It seems that the latter does not act as a primary vector of Japanese encephalitis.     

Agglutination of Japanese encephalitis virus with concanavalin A.

Results of experiments have indicated that reduction in biological activities at high concentrations of Japanese encephalitis virus is caused by aggregates of the virus by concanavalin A. The possibility exists that the concanavalin A binding site is different from hemagglutination and antireceptor sites of Japanese encephalitis virus.