Published Date: 2012-04-02 08:50:15
Subject: PRO/EDR> Dengue/DHF update 2012 (14)
Archive Number: 20120402.1087547

DENGUE/DHF UPDATE 2012 (14)
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A ProMED-mail post
http://www.promedmail.org
ProMED-mail is a program of the
International Society for Infectious Diseases
http://www.isid.org

In this update:
[1] Vector mosquito feeding
[2] Cases in various countries:
Latin America
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Paraguay (Asunción metropolitan area and Central department)
Paraguay (pediatric cases)
Brazil (Cuiaba, Mato Grosso state)
Brazil (Mato Grosso state)
Brazil (Ribeirao Preto and Sao Paulo state)
Bolivia (national)
Ecuador (national)
Mexico (Tampico, Tamaulipas state and national)
Mexico (Guerrero state)
Asia
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Malaysia (national)

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[1] Vector mosquito feeding
Date: Fri 30 Mar 2012
Source: Mumbai Mirror [edited]
http://www.mumbaimirror.com/article/9/2012033020120330231901354fb6e2c52/Dengue-virus-turns-mosquitoes-hungry.html


Scientists have shown for the 1st time that infection with dengue virus turns on mosquito genes that makes them hungrier and better feeders, and therefore possibly more likely to spread the disease to humans.

Specifically, the researchers from the Johns Hopkins Bloomberg School of Public Health found that dengue virus infection of the mosquito's salivary gland triggered a response that involved genes of the insect's immune system, feeding behaviour and the mosquito's ability to sense odours.

Dengue virus is primarily spread to people by the mosquito _Aedes aegypti_. Over 2.5 billion people live in areas where dengue fever is endemic. The World Health Organization estimates that there are between 50 million and 100 million dengue infections each year.

"Our study shows that the dengue virus infects mosquito organs, the salivary glands, and antennae that are essential for finding and feeding on a human host. This infection induces odorant-binding protein genes, which enable the mosquito to sense odours," George Dimopoulos, senior author of the study, said. "The virus may, therefore, facilitate the mosquito's host-seeking ability, and could-at least theoretically-increase transmission efficiency, although we don't fully understand the relationships between feeding efficiency and virus transmission. In other words, a hungrier mosquito with a better ability to sense food is more likely to spread dengue virus," he said.

For the study, the researchers performed a genome-wide microarray gene expression analysis of dengue-infected mosquitoes. Infection regulated 147 genes with predicted functions in various processes including virus transmission, immunity, blood-feeding, and host-seeking.

Further analysis of infected mosquitoes showed that silencing, or "switching off", 2 odorant-binding protein genes resulted in an overall reduction in the mosquito's blood-acquisition capacity from a single host by increasing the time it took the for mosquito to probe for a meal.

"We have, for the 1st time shown, that a human pathogen can modulate feeding-related genes and behaviour of its vector mosquito, and the impact of this on transmission of disease could be significant," Dimopoulos added.

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Communicated by:
ProMED-mail Rapporteur Mary Marshall

[This report provides some interesting insight into the dengue virus-vector mosquito relationships and their effects on feeding behavior and its relationship to virus transmission. - Mod.TY

Reference and abstract for the original paper
S Sim, JL Ramirez, G Dimopoulos: Dengue Virus Infection of the _Aedes aegypti_ Salivary Gland and Chemosensory Apparatus Induces Genes that Modulate Infection and Blood-Feeding Behavior. PLoS Pathog 8(3): e1002631 http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1002631

Abstract
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The female _Aedes aegypti_ salivary gland plays a pivotal role in bloodmeal acquisition and reproduction, and thereby dengue virus (DENV) transmission. It produces numerous immune factors, as well as immune-modulatory, vasodilatory, and anti-coagulant molecules that facilitate blood-feeding. To assess the impact of DENV infection on salivary gland physiology and function, we performed a comparative genome-wide microarray analysis of the naive and DENV infection-responsive _A. aegypti_ salivary gland transcriptomes. DENV infection resulted in the regulation of 147 transcripts that represented a variety of functional classes, including several that are essential for virus transmission, such as immunity, blood-feeding, and host-seeking. RNAi-mediated gene silencing of 3 DENV infection-responsive genes -- a cathepsin B, a putative cystatin, and a hypothetical ankyrin repeat-containing protein -- significantly modulated DENV replication in the salivary gland. Furthermore, silencing of 2 DENV infection-responsive odorant-binding protein genes (OBPs) resulted in an overall compromise in blood acquisition from a single host by increasing the time for initiation of probing and the probing time before a successful bloodmeal. We also show that DENV established an extensive infection in the mosquito's main olfactory organs, the antennae, which resulted in changes of the transcript abundance of key host-seeking genes. DENV infection, however, did not significantly impact probing initiation or probing times in our laboratory infection system. Here we show for the 1st time that the mosquito salivary gland mounts responses to suppress DENV which, in turn, modulates the expression of chemosensory-related genes that regulate feeding behavior. These reciprocal interactions may have the potential to affect DENV transmission between humans.

Author summary
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Dengue virus (DENV) is transmitted between humans through the bite of infected _Aedes aegypti_ mosquitoes. Since the virus is inoculated in saliva, infection of the mosquito salivary gland is an essential requirement for transmission. In addition, the gland also produces numerous biologically active compounds that facilitate blood-feeding. Despite the salivary gland's crucial role in DENV transmission, very little is known about the host-pathogen interactions, at the molecular level, in this organ. In this study, we characterized the _A. aegypti_ salivary gland response to DENV infection at both the gene expression and functional levels. We found that DENV induced the expression of several gene transcripts whose products modulate virus replication in the salivary gland. Unexpectedly, the virus also induced transcripts of 2 odorant-binding proteins, which we demonstrate to be important for mosquito host-seeking and probing behavior. This is the 1st study to demonstrate that besides affecting cellular processes that modulate virus replication, DENV also has the potential to alter chemosensory processes in ways that may result in increased virus transmission.]

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[2] Cases in various countries:
Latin America:
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- Paraguay (Asunción metropolitan area and Central department). 30 Mar 2012. The Ministry of Health today [30 Mar 2012] reported 2 new dengue fatalities, which brings the number of deaths from this disease to 7, of a total of 2486 confirmed cases. The Ministry stated that from 1 Jan [2012] until today, there are 6475 reports of patients with dengue symptoms of whom 2486 are positive for the disease, 3160 await confirmation, and 829 have been discarded. The Director of the Office of Health Surveillance of the Ministry, Ivan Allende, explained at a press conference that the epidemic is concentrated in Asuncion and the metropolitan area, as well as in the Central department [state equivalent] adjacent to the capital.
http://www.lanueva.com/elmundo/nota/f9fa2b7283/1/118953.html [in Spanish, trans. Mod.TY]

[A HealthMap/ProMED-mail interactive map of Paraguay can be accessed at http://healthmap.org/r/1l5K. - Mod.TY]

- Paraguay (pediatric cases). 28 Mar 2012. Among the pediatric group, individuals less than 18 years of age, 1708 suspected dengue cases have been reported of whom 538 cases (31.5 per cent) are confirmed and 20 per cent required hospitalization. Of those hospitalized, 42 per cent had alarming signs and 3 per cent had serious dengue. Of those hospitalized, it was observed that 13 per cent (14 of 110) reported having had a similar clinical picture previously.
http://www.abc.com.py/edicion-impresa/locales/hay-538-casos-pediatricos---confirmados-de-la-enfermedad-384016.html [in Spanish, trans. Mod.TY]

- Brazil (Cuiaba, Mato Grosso state). 31 Mar 2012. An attempt is being made to contain the dengue epidemic that has hit the [state] capital. Just this year [2012], 2155 cases of the disease have already been confirmed.
http://www.odocumento.com.br/materia.php?id=389284 [in Portuguese, trans Mod.TY]

[A HealthMap/ProMED-mail interactive map showing the location of Cuiaba in Mato Grosso state be accessed at http://healthmap.org/r/1te_. - Mod.TY]

- Brazil (Mato Grosso state). 30 Mar 2012. One month after the arrival of dengue virus type 4 in Mato Grosso, the state is experiencing a real epidemic of the disease. Just in the past week, 2030 new cases were registered. In the 1st 3 months of this year [2012], 9571 cases of the disease were registered, an increase of 117 per cent compared to the same period last year [2011], when 4049 dengue cases were registered.
http://www.circuitomt.com.br/editorias/geral/12996-mt-vive-epidemia-de-dengue-numeros-deste-ano-se-aproximam-do-total-registrado-em-2011.html [in Portuguese, trans Mod.TY]

- Brazil (Ribeirao Preto and Sao Paulo state). 28 Mar 2012. Ribeirao Preto is having a dengue epidemic (45 confirmed cases), but contrasting to the epidemic in 2011 when 29 637 people were infected. The number of dengue cases in Sao Paulo state in the 1st 3 months of this year [2012] declined 91.9 per cent in comparison to the same period last year. This year 966 locally acquired dengue cases were confirmed in the state. In 2010 there were 11 984 confirmed cases.
http://g1.globo.com/sp/ribeirao-preto-franca/noticia/2012/03/ribeirao-preto-vive-surto-de-dengue-afirma-coordenadora-de-vetores.html [in Portuguese, trans Mod.TY]

[A HealthMap/ProMED-mail interactive map showing the location of Ribeirao Preto in Sao Paulo state be accessed at http://healthmap.org/r/1Ao3. - Mod.TY]

- Bolivia (national). 26 Mar 2012. According to data from the Ministry of Health, up to the beginning of this month [March 2012], 2431 dengue cases have been confirmed in the country with 20 reported deaths due to the epidemic. Health authorities report 8416 suspected dengue cases in this epidemiological period. According to Vice Minister Maturano, 55 per cent of the cases are concentrated in Santa Cruz department [state equivalent], 23 per cent in Cochabamba, 11 per cent in La Paz, and 9 per cent in Beni [departments]. Chuquisaca, Tarija, and Pando register less than one per cent.
http://www.opinion.com.bo/opinion/articulos/2012/0326/noticias.php?id=49520 [in Spanish, trans. Mod.TY]

[A HealthMap/ProMED-mail interactive map of Bolivia can be accessed at http://healthmap.org/r/1Ao1. - Mod.TY]

- Ecuador (national). 30 Mar 2012. In Ecuador, the circulation of the 4 dengue virus serotypes is confirmed. In 2011, types 1, 2, and 4 predominated. To date, 2 deaths and 3200 positive cases of the disease have been reported. Guayas and Los Rios have registered the greatest number of infected people.
http://www.eldiario.com.ec/noticias-manabi-ecuador/224689-temen-nuevo-brote-del-dengue/ [in Spanish, trans. Mod.TY]

[A HealthMap/ProMED-mail interactive map of Ecuador can be accessed at http://healthmap.org/r/1jUf. - Mod.TY]

- Mexico (Tampico, Tamaulipas state and national). 30 Mar 2012. In Tampico and Madero, the dengue statistics are 6 probable DHF cases and 6 confirmed cases of classical dengue fever. This year [2012] the numbers of dengue cases, which have generated alarm, are: Yucatan 239 cases, Michoacan 110, Veracruz 105, Nuevo Leon with 96 cases, and Tamaulipas with 10 cases.
http://conexiontotal.mx/2012/03/30/temen-brote-de-dengue-en-el-sur-del-estado/ [in Spanish, trans. Mod.TY]

[The accuracy of the reported 6 suspected DHF cases and just 6 confirmed dengue fever cases is questionable. Either most or all of the cases are not DHF or the number of dengue fever cases is substantially under-reported. A 1:1 DHF to dengue fever ratio is extremely unlikely.

A HealthMap/ProMED-mail interactive map showing the location of Tamaulipas state can be accessed at http://healthmap.org/r/26*g. - Mod.TY]

- Mexico (Guerrero state). 30 Mar 2012. The Guerrero Secretary of Health, Lazaro Mazon Alonso, announced that so far this year [2012] there have been 113 cases of people infected with dengue virus. Compared with the same period last year [2011] there are 20 more cases registered. Acapulco is the region with the most cases of this disease followed by the north region ad the central area.
http://mizamora.net/noticias/64164in Spanish, trans. Mod.TY.

[A dengue outbreak in a city like Acapulco, a significant tourist destination, can discourage tourism with substantial negative economic impacts.

A HealthMap/ProMED-mail interactive map of Guerrero state can be accessed at http://healthmap.org/r/1COe. - Mod.TY]

Asia
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- Malaysia (national). 29 Mar 2012. The number of dengue cases recorded a slight drop from last week [week of 19 Mar 2012] from 477 cases and no deaths compared with 480 cases and one death the previous week. Director General of Health Datuk Seri Dr Hasan Abdul Rahman said though 7 states registered a slight increase compared with the previous week, the overall tally was lower.
http://www.bernama.com/bernama/v6/newsgeneral.php?id=655782

[A HealthMap/ProMED-mail interactive map of Malaysia can be accessed at http://healthmap.org/r/1yAq. - Mod.TY]

See Also