Dengue: An emerging arboviral disease

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DengueAn emerging arboviral disease
Gary G. Clark, Ph.D. Mosquito and Fly Research
Unit CMAVE, ARS, USDA Gainesville, Florida
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My emergence at Balboa Naval Hospital
San Diego, California
First interaction with a Navy physician
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Discussion topics

• Epidemiology of dengue and DHF
• Emergence of dengue in the Americas
• Aedes aegypti and its development
• Adult control methods for Ae. aegypti
• Evaluation of emergency control studies (CDC and
  the military)
• Dengue and the US military

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Dengue virus

• An arbovirus transmitted by mosquitoes
• Four virus serotypes (DEN-1, 2, 3, 4)
  single-stranded RNA
• Family Flaviviridae (WNV, SLE, YF, JE)
• Causes dengue (headache, fever, joint/retrorbital
  pain, rash, bleeding) and dengue hemorrhagic
  fever (DHF)

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Dengue viruses

• Each serotype provides specific lifetime immunity
  and short-term cross-immunity
• All serotypes can cause severe and fatal disease
• Genetic variation within serotypes some appear
  to be more virulent or have greater epidemic
  potential
• Can produce outbreaks/epidemics
• in urban areas

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Transmission of dengue virusby Aedes aegypti
Mosquito refeeds /
Mosquito feeds /
transmits virus
acquires virus
Intrinsic incubation period
Viremia
Viremia
0
5
8
12
16
20
24
28
Days
Human 1
Human 2
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Dengue A global perspective

• Most important arboviral disease of humans 2.5-
  3 billion people (40 of the world) at risk of
  infection
• 10s of millions of cases of dengue and 100s of
  thousands of DHF cases annually
• A leading cause of hospitalization and death
  among children in Asia
• DHF mortality rate averages about 5

Source WHO, 1996
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World distribution of dengue 2006
Areas infested with Aedes aegypti
Areas with Ae. aegypti and recent dengue epidemics
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Dengue/DHF cases reported to the World Health
Organization1955-2005
Ave. annual no. cases
Source WHO, Sep. 2006
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Dengue in the Americas 1980 2006
Year
Source PAHO (Jan. 19, 2007)
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Dengue hemorrhagic fever in the Americas1980
2006
Cases

Year
Source PAHO (Jan. 19, 2007)
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Why has dengue emergedin the Americas?

• Presence of competent mosquito vector
• Large, susceptible human population
• Conditions supporting abundant mosquito
  population
• Frequent introduction of dengue viruses
• Ineffective vector control programs

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Emergence of dengue Socio-economic factors
Population increase
Billion

• Unprecedented population
  increase
• Uncontrolled and unplanned urbanization
• Inadequate environmental conditions

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5
4
3
2
1
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Reinfestation of the Americas by Aedes aegypti
1930s 1970 2006
Source CDC/PAHO
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Emergence of dengueUncontrolled urbanization

• In 1954, 42 of the population of Latin America
  lived in urban areas, increasing to 75 in 1999.
• Informal communities proliferated as a result
  of poverty.
• Scarcity of basic services running water,
  sewage and collection of garbage.
• High population density

Sources Gubler, 1998. PAHO, 1997.
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Emergence of dengue Inadequate environmental
conditions

• Insufficient collection of disposable containers
• Non-biodegradable containers
• Discarded tires

• Insufficient and inadequate water service
• Increased number of pilas and water storage
  containers
• Inadequate water and sewer conditions

Increase in production sites
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Production sites for Aedes aegypti
Buckets and pails
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Production sites for Aedes aegypti
Water storage tanks
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Production sites for Aedes aegypti
Discarded tires
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Emergence of dengue Population movement

• Migrations
• International Tourism

• More than 750 millon people cross frontiers
  annually
• Increase of migration from rural areas to cities
• 1.4 billion international passengers in 1999
• 697 million international tourist arrivals in
  2000.
• 715 million in 2002, an increase of 3.1

Traffic of microorganisms
Source WTO
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Why has dengue emergedin Latin America?

• Reinfestation by Aedes aegypti
• Ineffective mosquito control programs
• Deteriorated public health infrastructure
• Uncontrolled population growth and
• unplanned urbanization
• Increased air travel by humans

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Aedes aegypti
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Aedes aegypti

• Lives in and around human habitations in urban
  areas
• Lays eggs and produces larvae preferentially in
  artificial containers
• Strong preference for human blood primarily a
  daytime feeder and bites several times in her
  life
• Most important vector of dengue viruses in the
  world

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Life cycle of Aedes aegypti
4. Adult
3. Pupae
1. Eggs
2. Larvae
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Personal protection against mosquitoes

• Apply repellent (20-30 DEET) to exposed skin-
  avoid eyes, mouth, and childrens hands
• Spray clothing with repellents with DEET or
  permethrin
• Use treated mosquito netting over bed
• Spray insecticide in room before going to bed,
  follow label instructions
• Wear long-sleeved shirts and long pants

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Dengue vaccine?

• No licensed vaccine at present
• Effective vaccine must be tetravalent
• Field testing of an attenuated tetravalent
  vaccine currently underway
• Effective, safe and affordable vaccine will not
  be available in the immediate future
• Vector control continues to be key to dengue
  prevention

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Vector control methodsBiological and
environmental control

• Biological control
• Largely experimental
• Option place fish in containers to eat larvae
• Environmental control
• Elimination of larval habitats
• Method most likely to be effective in the long
  term

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Spraying to control adult Aedes aegypti

• Thermal fog
• Aerosols Cold fog and ultra low volume (ULV)
• Inside of residences with portable equipment
• From the ground with vehicle-mounted equipment
• Aerial application

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CDC evaluations Emergency control in Puerto
Rico

• Ground ULV applications versus Aedes aegypti
• C-130 (Hercules transporter) with USAF Reserve
  Unit from Columbus, OH
• US Navy (DVECC) with PAU-9 from JAX
• Mosquitoes susceptible to naled (Dibrom 14) and
  insecticide reached the ground but did not
  penetrate houses
• Limited, transitory impact on wild population
• Other projects with US Army in Honduras and
  the Dominican Republic

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Ground ULV application
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Ground ULV application
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Aerial application in San Juan with C-130
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Aerial application in San Juan with PAU-9
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US Navys PAU-9 unit
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Indoor application with thermal fog unit
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Indoor application with portable ULV unit
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Operation Restore Hope Somalia- 1992-1993

• 30,000 troops deployed 530 were studied
• - 289 hospitalized with fever- 129 with
  unspecified illness- 41 with DEN virus and 18
  with anti-dengue ABs 59/129 (46) with DEN
  infections.
• Study of unit in Baardera 9 (44) of 494 with
  dengue infections
• 70 used DEET uniforms, 61 did not use bed nets and only 25
  kept sleeves rolled down at all times
• Poor compliance with PPMs vs. insects

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Operation Uphold DemocracyHaiti- 1995

• 249 with fever- 79 (32) with DEN infection
• - 44/79 participated in survey
• - 73 with mosquito bites daily
• - 50 used repellents
• - 48 did not use a bed net
• 10/14 (71) of Army units did not have deployed,
  functional field sanitation teams
• 31 of soldiers indicated PPMs emphasized some
  but not enough or not at all
• Low unit readiness to perform VC activities
• Command enforcement of PM doctrine is essential
  for dengue prevention

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DHF in Venezuela 1989-1990

• PAHO-Venezuela requested that CDC-San Juan test
  specimens from suspected fatal case (12 year-old
  girl) of DHF from Venezuela
• Dengue etiology was confirmed epidemic was
  spreading from Maracay to Caracas
• Minister of Health sought epidemic response
  recommendation. Discussed results of USAF and
  Navy trials. Aerial control limited impact,
  dangerous, could not recommend aerial control as
  the solution.
• Minister must take action and intended to
  spray using helicopters with booms attached
• With Ministers decision, I changed hats and
  recommended that he seek professional assistance
  such as from the US Navy No aerial spray
  experience in Venezuela.
• Venezuelan Air Force transported DVECC personnel
  and equipment to Venezuela.

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Preparing to spray with Venezuelan helicopter
MMART Preventive Medicine Assists Venezuela
LCDR Mark T. Wooster, MSC, USN Navy Medicine
(Mar-Apr 1991)
Mobile Medical Augmentation Readiness Team
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DHF in Venezuela 1989-1990

• DVECCs equipo de expertos rociadores aereos
• LCDR Mark Wooster
• LT Joseph Conlon
• LT Stanton Cope
• LT David Claborn
• LT Rafael del Vecchio
• U.S. Navy personnel performed 60 aerial spray
  missions (malathion _at_ 3 oz/acre) during 135
  flight hours over Maracay and Caracas.

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Aterriza de emergencia helicóptero de fumigación
(Newspaper report) MARACAY (Especial) Uno de
los helicópteros de la Fuerza Aérea, que
participa en las operaciones de fumigación
contra el dengue, aterrizó de emergencia en el
estacionamiento del centro comercial El
Castaño, de esta ciudad, resultando gravemente
herido el piloto de la unidad, que no fue
identificado por las autoridades. En la
aeronave viajaban dos oficiales LT Joseph
Conlon and LT Stanton Cope de la Marina de los
Estados Unidos, quienes habrian sufrido
lesiones. Tambien iban dos oficiales de la
Fuerza Aérea Venezolana, y tres guardias
nacionales. La aeronave arrancó una linea de
alta tensión y dejo al sector El Castaño sin
electricidad.
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After mission!
Venezuelan helicopter
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• Fortunately, the injuries to the crew and US
  Navy personnel were minor.
• And, some of our expertos developed a new
  feeling for helicopters on the ground.

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I love my choppers!
Private parking space for AFPMB RLO Silver
Spring, Maryland
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u
b
s
CAPT Stanton E. Cope- Dengue fighter
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Take home messages

• Importance of command emphasis for personal
  protection measures
• Critical that you lead by example and use
  repellents
• Be prepared to respond to requests for help in
  dealing with dengue and other VBD in support of
  US military or in humanitarian missions
• There is no magic bullet to solve the emerging
  problem of dengue/DHF
• You are part of unique national/international
  vector control resources challenges and danger
  may accompany your work
• USDA is anxious to support US military in
  protecting deployed personnel and in responding
  to humanitarian missions

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Walter Reed Army Medical Center
PSA
Washington, D.C.
My last interaction with an Army physician