Maturation process of Japanese encephalitis virus in cultured mosquito cells in vitro and mouse brain cells in vivo

The maturation process of Japanese encephalitis (JE) virus in C6/36 cells in vitro and in mouse brain cells in vivo was studied by electron microscopy. In the C6/36 cell infection, 500 to 2250 virions per cell were released into the medium during the period of study; yet, no virus budding process was observed at the host cell membranes. JE virions at various maturation stages appeared within the cisternae of rough endoplasmic reticulum (RER) of infected cells at 24 hours p.i.; and, although C6/36 cells did not show a well-developed Golgi apparatus, the virions appeared to be carried to the cell surface within host-cell secretory vesicles for extracellular release as early as 24 hours p.i. The occurrence of a secretory-type intracellular transport of maturing JE virus particles was well recognizable in brain cells of infected mice, in which JE virus particles were found almost exclusively in the cisternae of RER, in the Golgi apparatus, and in various vesicles, including coated vesicles, in the vicinity of the Golgi apparatus. Our previous study of dengue-2 virus morphogenesis and our present study of JE virus morphogenesis differed substantially at various stages of maturation. Possible mechanisms which explain these differences were discussed.

Induction of secondary immune response by reactivated Japanese encephalitis virus in latently infected mice

Development of secondary immune response has been studied following reactivation of latent Japanese encephalitis virus (JEV) infection in mice. The virus could be reactivated in 43% of the latently infected mice at 27 weeks p.i. by treatment with cyclophosphamide. The reactivated virus induced delayed-type hypersensitivity (DTH) and leucocyte migration inhibition (LMI) responses in mice, with peak activity on Day 5 post-reactivation (p.r.). The DTH persisted at low levels for long periods. Humoral immunity measured by haemagglutination-inhibiting antibody showed a four-fold rise in antibody titres. DTH was transferable by immune spleen cells for 5 days p.r. only. It is, therefore, concluded that JEV reactivation generates a quick and short-lived secondary immune response.

Multiplication and distribution of type 2 dengue and Japanese encephalitis viruses in Toxorhynchites splendens after intrathoracic inoculation

The nonhematophagous mosquito Toxorhynchites (Tx.) splendens was found to be the most susceptible to type 2 dengue (D-2) and Japanese encephalitis (JEV) viruses among three hosts examined by virus titration and replication assays. After inoculation with D-2, the number of viral antigen positive cells in the head, thorax and abdomen increased up to day 15 and D-2 reached the maximum titer of 8.4 log10 PFU/g in the head on day 15. Hemocytes were the earliest cell type that could be detected as D-2 antigen positive on day 2. Multiplication of JEV was faster than that of D-2 in the mosquito. The number of JEV antigen positive cells in each part of the mosquito increased up to day 3, JEV reaching the maximum titer of 8.0 log10 PFU/g in the abdomen on day 3. Hemocytes and fat body cells (FBC) could be detected as JEV antigen positive cells on day 1. The time course of D-2 and JEV infection suggested that intrathoracically inoculated viruses were probably initially phagocytosed by hemocytes and/or FBC, and multiplied primarily in their cytoplasm. The infected hemocytes were then transported by the flow of body fluid and viruses were disseminated to other susceptible organs, such as ganglia, salivary glands, etc. The results obtained indicate that the course of infection of D-2 and JEV in Tx. splendens is similar to that in vector mosquitoes. Tx. splendens is therefore very useful for the study of these viruses.

[Chiroptera viruses transmitted or not transmitted by arthropods]

The authors make a review of literature on viruses isolated from chiroptera's tissues. They study especially two of these viruses: a true arbovirus, the Japanese B encephalitis virus and a virus of the same genus but not arthropod-borne, the Rio Bravo virus. They consider successively for each virus: isolations from bats, serosurveys in bat and in man, and experimental studies with these viruses, allowing to estimate the role of chiroptera in the diffusion and the maintenance of some arboviruses. They also report some personal results of serosurveys in bats from Tunisia and Spain.

Oligonucleotide fingerprint analysis on Japanese encephalitis virus strains after passage histories

Genetic variation in Japanese encephalitis (JE) virus strains after various passage histories was examined by oligonucleotide fingerprints of the 42S genome RNA. The results indicated that genome changes occurred during passages of new virus isolates through cell lines or mouse brains, especially at earlier passage level in order to adapt quickly to different hosts. However, the changes were not sufficient to explain strain differences observed among fingerprints of various isolates.

A focus assay method for Japanese encephalitis virus using complement and anti-virus serum

A sensitive, quantitative, short-time, and reproducible focus assay for Japanese encephalitis (JE) virus is described. After 2 or 3 days of incubation, the infected cells were treated with anti-JE virus serum and complement, and subsequently stained with trypan blue; then clear foci were produced. This method made it easy to titrate the infectivities not only of all seven JE virus strains tested but also of West Nile (WN), Murray Valley encephalitis (MVE), and St. Louis encephalitis (SLE) viruses using hyperimmune anti-JE virus serum for the latter. Moreover, even cell lines which hardly formed plaques by the agar overlay method easily produced foci within 2 or 3 days by this method.

Beneficial role of a nonpathogenic orbi-like virus: studies on the interfering effect of M14 virus in mice and mosquitoes infected with Japanese encephalitis virus

M14 virus, isolated from Culex tritaeniorhynchus mosquitoes collected in a Beijing suburb, was identified as a noncytopathogenic orbi-like virus. It was found to interfere with the growth of Japanese encephalitis (JE) virus, a mosquito-borne virus which infects humans, pigs, and horses in much of Asia, including China. JE virus is transmitted by C. tritaeniorhynchus mosquitoes and causes encephalitis in humans and horses and abortion in pigs. Because it had potential as an interfering agent for the biological control of JE, the M14 virus was characterized and its interfering effect was studied in mice and in C. tritaeniorhynchus mosquitoes.

Electron microscopic observation of a newly isolated flavivirus-like virus from field-caught mosquitoes

Of many unidentified virus strains which were isolated from field-caught mosquitoes by using C6/36 cells (a virus-sensitive clone of Aedes albopictus cells), three strains which formed small size plaques (SP virus) in C6/36 cells were investigated by electron microscopy. Although the SP virus strains did not react with antisera against known arboviruses in serological tests, they closely resembled flaviviruses in morphology. However, when they were compared to Japanese encephalitis (JE) virus, several differences in morphogenesis were observed. Proliferating membranous structures and electron-dense amorphous areas involving precursors of the virus were observed only in cells infected with the SP virus strains. Enlarged areas of endoplasmic reticulum containing mature virions were often observed adjacent to these structures. Since the SP virus strains were isolated from wild mosquitoes and multiplied only in mosquito cells, it seems appropriate to classify them as insect viruses which resemble togaviruses morphologically.

Studies on Japanese encephalitis virus infection of reptiles. I. Experimental infection of snakes and lizards

Experimental infection of four species of snakes, Rhabdophis tigrinus tigrinus, Elaphe quadrivirgata, Elaphe climacophora and Agkistrodon halys, and five species of lizards, Takydromus tachydromoides, Eumeces latiscutatus, Eumeces barbouri, Eumeces marginatus oshimensis and Gekko japonicus, with Japanese encephalitis virus (JEV) was carried out. Evidence of JEV multiplication in snakes was not obtained at least under the conditions used in the present study. All lizards except G. japonicus were infected with JEV by ip injection of virus suspension. The minimum infectious dose for a lizard was around 10(3) MLD50/0.05 ml, and this dose was considered to be proportional to the virus dose which is injected into a host by a vector mosquito at a single bite. Temperature dependence of JE virus growth in the lizards was demonstrated. JEV multiplied slower at 20 degrees C than at 26 degrees C, though the peak titers of viremia were equivalent in both groups of lizards kept at 20 degrees C and 26 degrees C. E. latiscutatus developed viremia with ip injection of a partially attenuated strain, Nakayama NIH which could not infect adult mice by peripheral inoculation. T. tachydromoides and E. latiscutatus were also infected by oral feeding of JEV infected mosquitoes. E. latiscutatus was infected by oral feeding of only one infected mosquito.

Studies on Japanese encephalitis virus infection of reptiles. II. Role of lizards on hibernation of Japanese encephalitis virus

A series of experiments on the role of lizards as overwintering hosts of Japanese encephalitis virus (JEV) was carried out. Two species of lizards, T. tachydromoides and E. latiscutatus, 2 species of mosquitoes, Cx. p. fatigans and Cx. p. pallens, and 2 strains of JEV, JaGAr#01 and JaGAr 19461, were used in this study. Firstly transmission of JEV from infected mosquitoes to uninfected lizards and from infected lizards to normal mice by the bite of mosquitoes was demonstrated successfully. Cx. pipiens group mosquitoes were found to feed readily on lizards as compared to Cx. tritaeniorhynchus, the primary vector of JEV in Japan. Secondly simulated hibernation of JEV in lizards was carried out under indoor and outdoor conditions. In the outdoor hibernation, lizards were injected with JEV on October 14, 1968, entered in hibernation on October 19 and were recovered from hibernation on April 10, 1969. Viremias were demonstrated in the lizards for a few weeks in late April. Thirdly JEV isolation and HI antibody detection were attempted from blood samples of field-caught reptiles, 7 species of snakes and 3 species of lizards and among amphibians, 2 species of frogs. HI antibody against JEV was found at a rate of 14.3% from E. latiscutatus and 4.0% from T. tachydromoides, though JEV was not isolated from all the blood samples of these cold-blooded animals. The roles of lizards as overwintering hosts of JEV were discussed.

Japanese encephalitis vaccine (2-8 strain) and parent (SA 14 strain) viruses in Culex tritaeniorhynchus mosquitoes

The Japanese encephalitis vaccine virus (JE 2-8) and its parent virus (JE SA 14) strains were compared for their ability to infect, to replicate in, and to be transmitted by Culex tritaeniorhynchus mosquitoes. Both viruses replicated in the mosquitoes after intrathoracic infection. The JE 2-8 vaccine was transmitted to 1/36 (3%) of suckling mice bitten by intrathoracically infected mosquitoes; however, the parent JE SA 14 strain was transmitted to 46/46 (100%) of the mice bitten. In oral infection trials, only 4/36 (11%) of the Cx. tritaeniorhynchus mosquitoes ingesting the vaccine JE 2-8 strain became infected, whereas 19/19 (100%) of those ingesting the parent JE SA 14 strain became infected. The vaccine JE 2-8 strain did not revert to virulence during passage in mosquitoes.

Chronic infection of HeLa cells with Japanese encephalitis virus. General characteristics of the system

Chronic infection of HeLa cells was induced by an attenuated variant of Japanese encephalitis (JE) virus (HeLa-K3 cell line). The chronic infection was characterized by alternating phases of degeneration and recovery of the cell monolayer. JE virus was regularly released into the medium of chronically infected cell cultures and virus-specific antigen was regularly demonstrated in the cytoplasm of 15--25% of cells. JE virus persisting in HeLa-K3 cells was sensitive to pancreatic ribonuclease and resistant to treatment with 4 M urea. HeLa-K3 cells did not undergo cytological or karyological transformation; they were susceptible to superinfection with heterologous viruses but resistant to reinfection with homologous virus.

Large-scale purification of Japanese encephalitis virus from infected mouse brain for preparation of vaccine

Large volumes of Japanese encephalitis (JE) virus propagated in mouse brain can be easily purified by polyethylene glycol 6,000. By using the polyethylene glycol precipitation method, mouse hemoglobin was almost all separated from the viral suspension, and consequently the total amount of nonviral protein in the viral suspension decreased. The recovery of infectivity was about 100%. The removal of residual polyethylene glycol in the viral suspension was possible without difficulty by means of ethanol precipitation. This method is recommended as an initial step in large-scale purification of Japanese encephalitis virus propagated in mouse brain because it is simple, rapid, and inexpensive.