Since April 2010, a severe outbreak of duck viral infection, with egg drop, feed uptake decline and ovary-oviduct disease, has spread around the major duck-producing regions in China. A new virus, named BYD virus, was isolated in different areas, and a similar disease was reproduced in healthy egg-producing ducks, infecting with the isolated virus. The virus was re-isolated from the affected ducks and replicated well in primary duck embryo fibroblasts and Vero cells, causing the cytopathic effect. The virus was identified as an enveloped positive-stranded RNA virus with a size of approximately 55 nm in diameter. Genomic sequencing of the isolated virus revealed that it is closely related to Tembusu virus (a mosquito-borne Ntaya group flavivirus), with 87–91% nucleotide identity of the partial E (envelope) proteins to that of Tembusu virus and 72% of the entire genome coding sequence with Bagaza virus, the most closely related flavivirus with an entirely sequenced genome. Collectively our systematic studies fulfill Koch's postulates, and therefore, the causative agent of the duck egg drop syndrome occurring in China is a new flavivirus. Flavivirus is an emerging and re-emerging zoonotic pathogen and BYD virus that causes severe egg-drop, could be disastrous for the duck industry. More importantly its public health concerns should also be evaluated, and its epidemiology should be closely watched due to the zoonotic nature of flaviviruses.

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Duck egg-drop syndrome caused by BYD virus, a new Tembusu-related flavivirus.

Japanese encephalitis (JE) virus is a mosquito-borne zoonotic flavivirus that infects a wide range of vertebrate species in an enzootic cycle primarily of large waterfowl birds and swine. Horses and humans are considered bystanders to this enzootic cycle and, once infected, dead-end hosts. JE infection in humans can manifest in a spectrum of disease from asymptomatic infection to a mildly febrile symptomatic illness to a life-threatening disease affecting the central nervous system (CNS). The latter is associated with a high morbidity and mortality as well as long-term neurologic sequelae. The pathogenesis and disease severity of JE is discussed elsewhere in this volume. JE is the most common cause of encephalitis in most of Asia and causes an estimated 35,000 cases of encephalitis annually (Igarashi 1992). By all accounts this is an underestimate of the true disease burden of this virus and evidence suggests that this virus is endemic over a far wider region today than 50 years ago, despite the use of an effective vaccine for humans and animals.

Japanese encephalitis virus: ecology and epidemiology.

Wild populations of nonhuman primates live in regions of sylvatic arbovirus transmission. To assess the status of arbovirus transmission in Bornean forests and the susceptibility of wild orangutans to arboviral infection, blood samples of wild orangutans, semi-captive orangutans, and humans were examined. Samples were tested by plaque reduction neutralization test for antibodies to viruses representing three families (Flaviviridae, Alphaviridae, and Bunyaviridae), including dengue-2, Japanese encephalitis, Zika, Langat, Tembusu, Sindbis, Chikungunya, and Batai viruses. Both wild and semi-captive orangutan groups as well as local human populations showed serologic evidence of arbovirus infection. The presence of neutralizing antibodies among wild orangutans strongly suggests the existence of sylvatic cycles for dengue, Japanese encephalitis, and sindbis viruses in North Borneo. The present study demonstrates that orangutans are susceptible to arboviralinfections in the wild, although the impact of arboviral infections on this endangered ape remain unknown.

Sylvatic transmission of arboviruses among Bornean orangutans.

An infectious disease of ducks caused by a newly emerged Tembusu virus strain in mainland China.

This report updates the 1993 recommendations by CDC's Advisory Committee on Immunization Practices (ACIP) regarding the prevention of Japanese encephalitis (JE) among travelers (CDC. Inactivated Japanese encephalitis virus vaccine: recommendations of the Advisory Committee on Immunization Practices [ACIP]. MMWR 1993;42[No. RR-1]). This report summarizes the epidemiology of JE, describes the two JE vaccines that are licensed in the United States, and provides recommendations for their use among travelers and laboratory workers. JE virus (JEV), a mosquito-borne flavivirus, is the most common vaccine-preventable cause of encephalitis in Asia. JE occurs throughout most of Asia and parts of the western Pacific. Among an estimated 35,000-50,000 annual cases, 20%-30% of patients die, and 30%-50% of survivors have neurologic or psychiatric sequelae. No treatment exists. For most travelers to Asia, the risk for JE is very low but varies on the basis of destination, duration, season, and activities. JE vaccine is recommended for travelers who plan to spend a month or longer in endemic areas during the JEV transmission season and for laboratory workers with a potential for exposure to infectious JEV. JE vaccine should be considered for 1) short-term ( or=1 year traveling to JE-endemic countries. Supplies of this vaccine are limited because production has ceased. In March 2009, an inactivated Vero cell culture-derived vaccine (IXIARO [JE-VC]) was licensed for use in persons aged >or=17 years. JE-MB is the only JE vaccine available for use in children aged 1-16 years, and remaining supplies will be reserved for use in this group.

Japanese encephalitis vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP).

Thirty isolations of Tembusu virus and four of Sindbis virus were obtained from approximately 280 000 mosquitoes collected between October 1968 and February 1970 in Sarawak, particularly from K. Tijirak, a Land Dyak village 19 miles South of Kuching. Twenty-two isolations of Tembusu virus and two of Sindbis virus were from Culex tritaeniorhynchus; two of Tembusu virus and two of Sindbis virus came from Culex gelidus. Tembusu virus was active throughout the year at K. Tijirak, the highest infection rates in C. tritaeniorhynchus being in January-March and May-August, when the C. tritaeniorhynchus population was declining and ageing. These results confirm that C. tritaeniorhynchus is the principal arthopod host of Tembusu virus in Sarawak. Antibody studies suggest that birds, particularly domestic fowl, are probably vertebrate maintenance hosts of Tembusu and Sindbis viruses in Sarawak.

Arbovirus infections in Sarawak, October 1968--February 1970 Tembusu and Sindbis virus isolations from mosquitoes.

55 viruses were isolated from approximately 174,300 mosquitoes collected in 2 areas of Sarawak between November 1968 and December 1969: 36 isolates, of which 4 have been provisionally identified as strains of Japanese encephalitis virus, came from C. tritaeniorhynchus and 7 isolates, of which 1 is a strain of Japanese encephalitis, from C. gelidus. The infection rate with Japanese encephalitis virus in the human population of Kampong Tijirak was estimated to be approximately 6% per annum. In pigs the infection rate was very much higher and was not uniform throughout the year. Pigs appear to become infected more frequently with increasing age and there was a considerable increase in the pig infection rate during the last quarter of the year coincident with the seasonal peak in C. tritaeniorhynchus population. The lower infection rate in man than in pigs is probably attributable to the considerably lower frequency with which man is bitten by C. tritaeniorhynchus. A considerable proportion of wild birds and of village dogs had Japanese encephalitis virus antibody and a few bats and ducks also had antibody. Fowls, geese and rodents do not appear to play a role in the maintenance of the virus.

Japanese encephalitis in Sarawak: virus isolation and serology in a Land Dyak village.

14 strains of Getah virus were isolated from a variety of mosquito species collected in Sarawak between October 1968 and February 1970. Ten strains were isolated from C. tritaeniorhynchus 7 of them at K. Tijirak. Single strains were isolated from C. gelidus, C. pseudovishnui, M. bonneae/dives and Aanopheles species. 6 of the isolates were obtained in October 1968 when Japanese encephalitis, Tembusu and Sindbis viruses were also very active. The available evidence suggest that Getah virus in Sarawak is maintained in a cycle similar to that of Japanese encephalitis virus and involves C. tritaeniorhynchus, C. gelidus and domestic pigs.

Arbovirus infections in Sarawak, October 1968-February 1970: GETAH virus isolations from mosquitoes.

(1974). Arbovirus infections in Sarawak, October 1968—February 1970: Japanese encephalitis virus isolations from mosquitoes. Annals of Tropical Medicine & Parasitology: Vol. 68, No. 4, pp. 393-404.

Arbovirus infections in Sarawak, October 1968--February 1970: Japanese encephalitis virus isolations from mosquitoes.

449 human sera collected in a Land Dyak village were tested for antibodies to 11 arboviruses. Japanese encephalitis and dengue virus antibodies were particularly prevalent. The rates of infection with these viruses were estimated to be 5-2% per annum for Japanese encephalitis, 8-8% for dengue 1 and 4-3% for dengue 2. Chikungunya virus antibodies were quite common with an annual infection rate of the order of 5% per annum. Infections with other Group A and B and Bunyamwera group viruses were generally at a low level.

Sumitra Kamath

Papers

Arbovirus infections in Sarawak, October 1968--February 1970 Tembusu and Sindbis virus isolations from mosquitoes.

Japanese encephalitis in Sarawak: virus isolation and serology in a Land Dyak village.

Arbovirus infections in Sarawak, October 1968-February 1970: GETAH virus isolations from mosquitoes.

Arbovirus infections in Sarawak, October 1968--February 1970: Japanese encephalitis virus isolations from mosquitoes.

Arbovirus infections in Sarawak, October 1968–February 1970: Human serological studies in a Land Dyak Village