Japanese encephalitis virus infection in mosquitoes reared from field-collected immatures and in wild-caught males.

Immature stages of mosquitoes collected in JE endemic areas of Karnataka, India between 1985 and 1987 were reared to adults and processed for the detection and isolation of Japanese encephalitis (JE) virus in an attempt to find naturally occurring vertical transmission of the virus. Males collected during 1985-1986 were also processed. A total of 15,785 adults reared from immatures and divided into 445 pools and 1,756 wild-collected males divided into 128 pools were processed using mosquito inoculation and immunofluorescence techniques. JE virus antigen was detected in 9 pools, 4 of which yielded JE virus. These were 2 pools of males and 1 pool of female Culex tritaeniorhynchus and 1 pool of male C. pseudovishnui, suggesting vertical transmission of JE virus in the mosquitoes.

Isolation of Japanese encephalitis virus from mosquitoes collected in Karnataka state, India from 1985 to 1987.

Detection and isolation of Japanese encephalitis (JE) virus using mosquito inoculation and immunofluorescence techniques were attempted from female mosquitoes collected in JE endemic areas of Kolar and Mandya districts of Karnataka state, India, from 1985 to 1987. 65,388 mosquitoes consisting of 19 species in 1541 pools were processed. Of these, 18 pools showed the presence of JE virus antigen. JE virus was isolated from 9 pools, 3 of Culex gelidus, 2 of C. tritaeniorhynchus, and one each of C. quinquefasciatus, C. fuscocephala, C. vishnui and Anopheles peditaeniatus. Isolation of JE virus from C. gelidus, C. fuscocephala, C. quinquefasciatus and An. peditaeniatus is reported for the first time in India.

Absence of viraemia in cattle after experimental infection with Japanese encephalitis virus.

Cow calves were infected with Japanese encephalitis virus (JEV) by parenteral inoculation. One batch was reinfected with JEV, followed by West Nile virus (WNV), while another batch was reinfected directly with WNV. No viraemia due to either JEV or WNV was demonstrated in any of the calves. Culex tritaeniorhynchus mosquitoes fed on 4 of the calves infected with JEV during the first 10 d had no detectable virus, nor did they transmit the virus by bite to susceptible baby chickens. In another experiment, calves did not develop viraemia after infected C. tritaeniorhynchus mosquitoes were allowed to feed on them. Neutralizing and/or haemagglutination-inhibiting antibodies against JEV were demonstrated in 6 of the 11 calves, which explains the high proportion of JE seropositives among cattle in India. All the 5 calves that were infected with WNV subsequent to JEV developed neutralizing and haemagglutination-inhibiting antibodies against WNV also. The study indicates that cattle do not play a role in the maintenance of JEV in nature.

Experimental studies on the vector potential of certain Culex species to West Nile virus.

Experimental studies were carried out to determine the vector potential of four species of mosquitoes to West Nile (WN) virus, viz. Culex tritaeniorhynchus, Cx. vishnui, Cx. bitaeniorhynchus and Cx. univittatus. All the four species of mosquitoes successfully transmitted and supported the growth of WN virus. The study indicated that the four species of mosquitoes could act as potential vectors of WN virus in nature.

Isolation of Japanese encephalitis virus from Culex pseudovishnui Colless, 1957 (Diptera: Culicidae) in Goa.

A strain of Japanese encephalitis virus was isolated from a pool of 54 female C. pseudovishnui Colless, 1957. The mosquitoes were collected in August 1988 during the period of epidemic of JE. This is the first report of isolation of JE virus from mosquitoes in Goa in the western coastal belt of peninsular India. In view of this isolation, C. pseudovishnui acquires greater importance, even though its density and relative prevalence during the current study was found to be far lower than C. tritaeniorhynchus.

Clinical & virological study of dengue fever outbreak in Jalore city, Rajasthan 1985.

An epidemic of acute febrile illness caused by dengue virus occurred in Jalore town, in south-west Rajasthan, in April and May, 1985. Most patients had classical signs and symptoms of dengue fever or had only a mild atypical febrile illness. A few patients had in addition haemorrhagic manifestations/shock or encephalitis. Virological studies (carried out by the National Institute of Virology, Pune) showed that dengue type 3 virus was the main etiological agent. This is the first reported outbreak of dengue in the arid zone in western Rajasthan, that occurred in summer (April-May) in contrast to other parts of India, where such outbreaks are commonly reported after the rains (between August and November).

Entomological investigations during outbreaks of dengue fever in certain villages in Maharashtra state.

Outbreaks of dengue (DEN) fever are reported from 22 villages in five districts in the state of Maharashtra. DEN viral antigen was detected by indirect immunofluorescence test in 34 of 375 female Aedes aegypti mosquitoes collected from 8 villages. DEN types 2 and 3 were identified among the 16 strains that were isolated. None of the 64 male mosquitoes showed the presence of viral antigen; 281 males and 323 females reared from field collected larvae were also found negative. Indoor spraying of DDT in the affected villages produced a drastic reduction in Ae. aegypti catches. No viral antigen was detected in mosquitoes caught subsequent to the spray. With the introduction of water supply through taps, which is often inadequate, people are compelled to store water for domestic purposes, which favours an increase in Ae. aegypti breeding. In view of changing rural ecology associated with the development process, continued surveillance of the spread of Ae. aegypti as well as the diseases borne by this vector are recommended.

First isolation of Japanese encephalitis virus from the mosquito, Culex tritaeniorhynchus Giles, 1901 (Diptera: Culicidae) in Gorakhpur district, Uttar Pradesh.

A strain of Japanese encephalitis (JE) virus has been isolated from a pool of female mosquitoes of C. tritaeniorhynchus, using C. bitaeniorhynchus cell line. This is the first report of JE virus isolation from mosquitoes in Gorakhpur district of Uttar Pradesh, north India.

Dengue in Gujarat state, India during 1988 & 1989.

Following the reports of epidemics of febrile illness from several rural and urban areas of Gujarat state (India) in 1988, epidemiological investigations were carried out and dengue (DEN) virus activity was demonstrated in large cities such as Surat and Rajkot as well as several villages in Sabarkantha district. Two strains of dengue type-2 each were isolated from human sera from Surat city and a village in Sabarkantha district. Six strains of dengue virus were isolated from Aedes aegypti mosquitoes collected at Chotasan village, two of which were confirmed as DEN type-2. Of the 560 patients' sera tested from different areas (including villages and townships), 122 showed evidence of dengue infection and another 236 showed a broader reaction with flaviviruses. Entomological investigations showed a widespread distribution of Ae. aegypti both in urban and rural areas. In the household conditions this mosquito was found to breed predominantly in containers with non-potable water. Amongst these, cement containers manufactured in towns and distributed to the villages seem to play an important role in the spread of this species. In non-residential areas prolific breeding of Ae. aegypti was observed in automobile tyre dumps, and varied types of scrap, in towns and villages. Distribution and relative prevalence of the species were studied in 46 towns and villages, covering the spectrum of rural-urban-continuum. These studies provide an indication regarding the mechanism of the spread of DEN virus through peoples' movement, transport, the process of urbanisation etc.

Experimental studies on the susceptibility of Aedes vittatus to dengue viruses.

Ae. vittatus mosquitoes were infected by oral route and by intrathoracic inoculation with dengue (DEN) viruses and tested for the presence of dengue virus antigen in their head squashes and salivary glands by indirect immunofluorescence. The results indicate that this species was susceptible to all four types of DEN viruses and supported the growth of DEN-2 virus.

Transmission of Kyasanur Forest disease virus by Rhipicephalus haemaphysaloides ticks.

Larvae of Rhipicephalus haemaphysaloides were infected with Kaysanur Forest disease (KFD) virus by feeding on viraemic rodents and reared into next generation larvae. Fed larvae, nymphs, unfed adults, fed adult males, and females after oviposition were found infected, while the larvae were found free from infection. Nymphs and adults transmitted the infection by bite to rodents and rabbits respectively. The virus was also passed through a second rodent-tick cycle. Adult ticks showed a titre of 3.1 to 4.5 dex mouse LD50/0.03 ml, and the virus was also detected 245 days after infection.

Experimental studies on the susceptibility of domestic pigs to West Nile virus followed by Japanese encephalitis virus infection and vice versa.

A study on the susceptibility of domestic pigs to West Nile virus (WNV) and Japanese encephalitis virus (JEV) infection was carried out. One batch of pigs was inoculated with WNV followed by JEV and another batch was inoculated vice versa. The first batch developed low level of viraemia and haemagglutination-inhibition (HI) antibodies to both viruses. There was a booster effect on the already existing WNV antibodies after challenging with JEV. In the second batch the animals developed high level of JE viraemia but did not develop WN viraemia. They developed HI antibodies to both JEV and WNV with low booster effect of WNV infection on JEV antibodies. Fresh batches of pigs were infected through bite of WNV- and JEV-infected Culex vishnui mosquitoes. WNV-infected pigs did not show viraemia, whereas JEV-infected ones developed JE viraemia. The study indicated that pigs were poor hosts for WNV but good ones for JEV. However, WNV antibodies reduced the level of JE viraemia and JEV infection boosted the already existing WNV antibodies.

Susceptibility of four species of mosquitoes to Chandipura virus and its detection by immunofluorescence.

Susceptibility of Culex tritaeniorhynchus, Cx. Bitaeniorhynchus, Cx. quinquefasciatus, and Aedes aegypti to Chandipura (CHP) virus was compared after parental inoculation of the mosquitoes. Virus detection was done by indirect immunofluorescence (IF). CHP antigen in head squashes of all the four species was seen at 24 hr post infection (p.i.). The mosquitoes supported the virus growth and transmission by bite to 2 days old suckling Swiss albino mice. Ae. aegypti which was found the most susceptible mosquito species for CHP virus can be used as a substitute for laboratory mice.

Activity of dengue-2 virus and prevalence of Aedes aegypti in the Chirimiri colliery area, Madhya Pradesh, India.

Repeated outbreaks of a suspected viral fever in Chirimiri colliery area, Madhya Pradesh were reported since 1990. The area consists of an agglomeration of sprawling settlements at varying altitudes of 816 to 890 m and it has partial sylvan cover. During a 1992 outbreak 25 patients' sera were tested, of which 13 showed seropositivity to dengue (DEN) by MAC-ELISA test; DEN-2 was isolated from Aedes aegypti collected from two of the eight settlements of the area. The principal vector, Ae. aegypti, was prevalent in all the settlements studied; Breteau indices (BI) varied between 2.5 and 125.0; adult house indices (AHI) between 0 and 60.0%; Ae. albopictus and Ae. vittatus occurred in considerable numbers; Ae. aegypti bred in more containers with nonpotable water than those with potable water; the breeding of this species was noted in a maximum number of cement tanks while mud pots were predominant among the available containers. Paired comparisons between relative prevalence indices showed significant correlation and regression coefficients. Significant association of Ae. aegypti breeding with the households having tap water supply was noted, the relative risk declining with the people's use of well water either exclusively or in combination with other sources of water supply. It was also collected in the nonresidential areas. The role of ecological factors in the maintenance and spread of Ae. aegypti and dengue in these settlements is discussed.

The 1993 epidemic of dengue fever in Mangalore, Karnataka state, India.

An epidemic of febrile illness with hemorrhagic manifestations occurred in certain parts of Mangalore city, Karnataka state, India, from the last week of July 1993. The epidemic reached its peak by mid-August and then started declining. Sporadic cases, however, continued to occur till early December. About 200 cases were reported covering all age groups and both sexes. The cases presented with pyrexia, myalgia, arthralgia and headache. Palatal petechiae, magenta colored tongue with central coating, maculopapular rash and facial flush were observed as classical signs. The tourniquet test was positive in 12% of the cases. Hemorrhage was observed in the form of epistaxis (2 cases), subconjunctival hemorrhage (2 cases) or purpura (3 cases). There were no deaths which were attributable to the epidemic. Five strains of dengue (DEN-2) virus were recovered from the acute-phase sera. Dengue virus-specific IgM type of antibodies were detected in 29/116 (25%) sera. Breeding of Aedes aegypti was observed in some of the areas where cases had occurred. No virus was isolated from any of the field-caught Ae. aegypti mosquitos.