Page 119 - Journal of Special Operations Medicine - Fall 2014

An Ongoing Series

Seroprevalence of Dengue Fever in

US Army Special Operations Forces:
Initial Results and the Way Ahead

Jennifer B. Caci, MS; Jason M. Blaylock, MD; Rafael De La Barrera, MS;
April N. Griggs, MS; Leyi Lin, MD; Richard G. Jarman, PhD;
Stephen J. Thomas, MD; Arthur G. Lyons, PhD, MD

ABSTRACT
The endemicity of dengue fever (DF) and, consequently, findings as they relate to personal risk and operational
sequelae of DF are increasing worldwide. The increases impact is discussed.
are largely a result of widespread international travel
and the increased range of the mosquito vectors. US Keywords: dengue fever, USASOC, dengue hemorrhagic
Army Special Operations Command (USASOC) person- fever, dengue shock syndrome
nel are at an increased risk of exposure to dengue based
on their frequent deployments to and presence in den-
gue endemic areas worldwide. Repeated deployments
to different endemic areas can increase the risk for de- Introduction
veloping the more serious sequelae of dengue: dengue Dengue is a mosquito-borne disease that is an expand-
hemorrhagic fever (DHF) and dengue shock syndrome ing public health problem in tropical and subtropi-
(DSS). Information about the seroprevalence rate of cal regions. It is member of the genus Flavivirus (FV),
dengue in USASOC personnel, in particular, is lacking which includes several small single-stranded positive-
and is critical to assessing the risk, tailoring preventive sense RNA viruses. Dengue infection is caused by four
medicine countermeasures, leveraging field diagnostics, closely related, but antigenically distinct, dengue virus
and maintaining mission capability. In the first part of serotypes (DENV-1, -2, -3, and -4) primarily carried by
a two-part project to assess baseline seroprevalence in an infected Aedes aegypti or Aedes albopictus mosquito.
USASOC units, a random, unit-stratified sample of 500 Infection with a dengue virus is usually asymptomatic,
anonymous serum specimens from personnel assigned but after an incubation period of 4 to 7 days, it can
to the highest-risk units in USASOC were screened for produce a spectrum of clinical illnesses ranging from a
dengue using a microneutralization assay. Of the 500 nonspecific viral syndrome to severe, fatal hemorrhagic
specimens screened, 56 (11.2%) of 500 had neutraliz- disease. Classic DF is characterized by biphasic fever,
ing titers (NT) (MN ≥ 10) against at least one DENV headache, and pain in various parts of the body, as well
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serotype. Subsequent sample titration resulted in 48 as prostration, rash, and lymphadenopathy. Recovery
(85.7%) of 56 of the samples with NT (MN ≥ 10) from DF is usually complete in 7 to 10 days, but pro-
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against at least one dengue serotype for an overall den- longed asthenia can occur. Infection with one dengue
gue exposure rate of 9.6% (48 of 500). The second part serotype provides lifelong immunity to that virus, but
of the ongoing project, started in 2012, was a multi- there is no cross-protective immunity to the other se-
center, serosurveillance project using predeployment rotypes. In fact, it is theorized that immune enhance-
and postdeployment sera collected from USASOC per- ment can occur on exposure to a second heterologous
sonnel deployed to South and Central America, Africa, (similar but not identical) dengue subtype. A preexist-
and Southeast Asia. Preliminary results show a 13.2% ing dengue antibody recognizes the infecting heterolo-
(55 of 414) seropositivity rate. The significance of these gous virus and forms antigen–antibody complexes. This

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