Sunday, August 26, 2018

PRO/AH/EDR> Japanese encephalitis - Cambodia: pig reservoirs

JAPANESE ENCEPHALITIS - CAMBODIA: PIG RESERVOIRS
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Date: Thu 23 Aug 2018
Source: PLoS Neglected Tropical Diseases [edited]
<http://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0006644>


Citation
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Di Francesco J, Choeung R, Peng B, et al. Comparison of the dynamics
of Japanese encephalitis virus circulation in sentinel pigs between a
rural and a peri-urban setting in Cambodia. PLoS Negl Trop Dis. 2018
Aug 23;12(8):e0006644.

Abstract
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Japanese encephalitis is mainly considered a rural disease, but there
is growing evidence of a peri-urban and urban transmission in several
countries, including Cambodia. We, therefore, compared the
epidemiologic dynamic of Japanese encephalitis between a rural and a
peri-urban setting in Cambodia. We monitored 2 cohorts of 15 pigs and
determined the force of infection - rate at which seronegative pigs
become positive - in 2 study farms located in a peri-urban and rural
area, respectively. We also studied the mosquito abundance and
diversity in proximity of the pigs, as well as the host densities in
both areas. All the pigs seroconverted before the age of 6 months. The
force of infection was 0.061 per day (95 percent confidence interval =
0.034-0.098) in the peri-urban cohort and 0.069 per day (95 percent
confidence interval = 0.047-0.099) in the rural cohort. Several
differences in the epidemiologic dynamic of Japanese encephalitis
between both study sites were highlighted. The later virus
amplification in the rural cohort may be linked to the later waning of
maternal antibodies, but also to the higher pig density in direct
proximity of the studied pigs, which could have led to a dilution of
mosquito bites at the farm level. The force of infection was almost
identical in both the peri-urban and the rural farms studied, which
shifts the classic epidemiologic cycle of the virus. This study is a
1st step in improving our understanding of Japanese encephalitis virus
ecology in different environments with distinct landscapes, human and
animal densities.

Author summary
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The number of Japanese encephalitis cases has decreased substantially
over the past decades with the implementation of childhood vaccination
programs. Japanese encephalitis virus, however, remains the most
important cause of acute viral encephalitis in Eastern and Southern
Asia, with an estimated 68 000 cases reported annually worldwide. Our
results demonstrate that Japanese encephalitis virus circulates
intensely both in a rural and a peri-urban setting in Cambodia, which
raises important public health concerns as peri-urban areas are
densely populated. These results support the importance of changing
vaccination recommendations for travelers and of not focusing national
immunization programs against Japanese encephalitis solely on rural
areas.

--
Communicated by:
ProMED-mail from HealthMap Alerts
<promed@promedmail.org>

[Although ProMED has posted relative few reports of Japanese
encephalitis (JE) in Cambodia over the years, that country is within
the JE virus endemic area. JE virus is the leading cause of
vaccine-preventable encephalitis in Asia and the western Pacific. In
Southeast Asia, JE virus is maintained in an enzootic cycle involving
the _Culex tritaeniorhynchus_ group of mosquitoes and wild birds.
Ardeid wading birds and pigs are amplifying vertebrate hosts. In
endemic areas, incidence in humans is one-10 per 10 000 population.
Children under 15 years of age are at greatest risk of encephalitis.
For most travelers to Asia, the risk for JE is very low but varies
based on destination, duration of travel, season, and activities.

Inactivated Vero cell culture-derived Japanese encephalitis (JE)
vaccine (manufactured as IXIARO) is the only JE vaccine licensed and
available in the United States. This vaccine was approved in March
2009 for use in people aged 17 years and older and in May 2013 for use
in children 2 months through 16 years of age.

USA CDC JE Vaccine Recommendations:
- JE vaccine is recommended for travelers who plan to spend 1 month or
more in endemic areas during the JE virus transmission season. This
includes long-term travelers, recurrent travelers, or expatriates who
will be based in urban areas but are likely to visit endemic rural or
agricultural areas during a high-risk period of JE virus
transmission.
- Vaccine should also be considered for the following:
1.- Short-term (less than1 month) travelers to endemic areas during
the transmission season, if they plan to travel outside an urban area
and their activities will increase the risk of JE virus exposure.
Examples of higher-risk activities or itineraries include: 1) spending
substantial time outdoors in rural or agricultural areas, especially
during the evening or night; 2) participating in extensive outdoor
activities (such as camping, hiking, trekking, biking, fishing,
hunting, or farming); and 3) staying in accommodations without air
conditioning, screens, or bed nets.
2.- Travelers to an area with an ongoing JE outbreak.
3.- Travelers to endemic areas who are uncertain of specific
destinations, activities, or duration of travel.

JE vaccine is not recommended for short-term travelers whose visits
will be restricted to urban areas or times outside a well-defined JE
virus transmission season.

CDC summaries of JE virus, its epidemiology and available vaccines can
be found on the US CDC website:
<https://www.cdc.gov/japaneseencephalitis/vaccine/index.html>.

The above report indicates that visitors to peri-urban areas that have
pig populations should also consider vaccination if they are going to
be present during the JE virus transmission season. - Mod.TY

HealthMap/ProMED map available at:
Cambodia: <http://healthmap.org/promed/p/145>]

[See Also:
2008
----
Japanese encephalitis - USA ex Viet Nam/Cambodia
http://promedmail.org/post/20080326.1126
1999
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Japanese enceph., suspected - Cambodia (03)
http://promedmail.org/post/19990118.0078
Japanese enceph., suspected - Cambodia (02) 990114100319
Japanese enceph., suspected - Cambodia (Phnom Penh) 990107150802]
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