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AN EXAMINATION OF SCENARIOS IN DENGUE FEVER TRANSMISSION WITH CONSIDERATIONS IN VECTOR CONTROL,
BLOOD DONATION, AND HEALTH COMMUNICATIONS IN THE UNITED STATES
by
Eric C. Andes
BS, Biological Sciences and Anthropology University of Pittsburgh, 2012
Submitted to the Graduate Faculty of
Graduate School of Public Health in partial fulfillment
of the requirements for the degree of
Master of Public Health
University of Pittsburgh
2014
UNIVERSITY OF PITTSBURGH
Graduate School of Public Health
This essay was submitted
by
Eric C Andes
onApril 21, 2014
and approved by
Essay Advisor:James Peterson, PhD ______________________________________Associate Professor Environmental and Occupational Health DepartmentGraduate School of Public HealthUniversity of Pittsburgh
Essay Reader:Bruce Pitt, PhD ______________________________________Professor and Chair Environmental and Occupational HealthGraduate School of Public HealthUniversity of Pittsburgh
Essay Reader:Elizabeth M. Felter, DrPH ______________________________________Visiting Assistant Professor Behavioral and Community Health SciencesGraduate School of Public HealthUniversity of Pittsburgh
ii
Copyright © by Eric C. Andes2014
iii
ABSTRACT
iv
Dengue virus (DENV) is a pathogen transferred via mosquito vectors causing dengue
fever (DF). DF is a growing concern for public health officials globally. In particular, DENV is
of major concern because there is no treatment targeting the virus, vaccine development is
problematic, and the number of cases is increasing dramatically. Furthermore, DENV infection
can be asymptomatic and can unwittingly be contracted through transfusion of blood products
from an infected donor. The United States has not yet experienced large scale DENV outbreaks,
but given global climate change it is only a matter of time before dengue becomes of importance
to public health in the United States. Preparation and planning of appropriate communication
strategies, vector management principles, and blood banking practices can allow for the United
States to address different scenarios of DENV transmission. This allows for the mitigation of
risk to communities and the protection of public health.
v
James Peterson, PhD
AN EXAMINATION OF SCENARIOS IN DENGUE FEVER TRANSMISSION WITH CONSIDERATIONS IN VECTOR CONTROL,
BLOOD DONATION, AND HEALTH COMMUNICATIONS IN THE UNITED STATES
Eric C. Andes, MPH
University of Pittsburgh, 2014
TABLE OF CONTENTS
I. INTRODUCTION: WHAT IS DENGUE? …………….………………………………………1
A. THE PATHOGEN …………...………………………………………………………..2
B. THE VECTORS ...……………………………………………………………………..4
C. EMERGING AREAS OF CONCERN ...…………………………..………………….61. Climate Change and Vector Distribution ...…………………………………….62. Vaccine Development ...…………………………..……………………………73. Blood Supply Safety ...……………………………………………………........8
D. SUMMARY……………………………………………………………………………9
II. SCENARIOS FOR DENGUE TRANSMISSION ...…………………………………………10
A. RELEVANT INFORMATION ...……………………………………………….……101. Management of Mosquito Vectors ………….....………………………….…..102. Basics of Risk Communication …....………………………………………….12
B. THE INITIAL OUTBREAK SCENARIO ...………………………………………....151. Environmental Management Focus ...………………………………………...152. Blood Collection Focus ...…………………………………………………..…163. Communication Focus ...……………………………………………………...16
C. THE SEASONAL OUTBREAK SCENARIO ...…………………………………….171. Environmental Management Focus .....……………………………………….182. Blood Collection Focus ….……………………………………………………183. Communication Focus ……..…………………………………………………19
D. THE ENDEMIC SCENARIO ...……………………………………..……………….191. Environmental Management Focus ….……………………………………….202. Blood Collection Focus ….……………………………………………………203. Communication Focus …..……………………………………………………20
III. FUTURE DIRECTIONS: WHAT CAN WE DO BETTER? ………………………….……21
A. BLOOD SAFETY AND DONOR RETENTION ….…………………..……………21
B. COMMUNICATIONS ….……………………………………………………………22
vi
C. VECTOR AND PATHOGEN CONTROL …..………………………………………22
IV. CONCLUSIONS…………………………………………………………………………….23
BIBLIOGRAPHY ……………………………………………………………………………….24
vii
LIST OF FIGURES
Figure 1. Vector life cycle highlighting key events and points of interest of vectortransmission…………………………………..………..……………………….1
I. INTRODUCTION: WHAT IS DENGUE?
Dengue Fever (DF), Dengue Hemorrhagic Fever (DHF), and Dengue Shock Syndrome
(DSS) are a cluster of clinical manifestations that occur as a result of infection by the Dengue
Virus (DENV). DENV infection and spread by mosquito vectors covers a number of critical
points of interest for public health officials. Globally there has been a rapid expansion of the
range of the mosquito vectors and a 30-fold increase in cases of DF. This in large part is due to
increased urbanization, population expansion, and climate change (WHO, 2012). As a blood
borne infection, DF and more serious clinical manifestations, present challenges to blood
banking systems, threatening the safety and security of the available fresh blood supply.
Additionally, elimination of potential blood donors during outbreaks limits the availability of
blood products. This is an issue because 100% donor efficiency is extremely difficult to achieve
for blood collection services even in the United States. (WHO, 2013). Of additional concern to
public health officials is the environmental management of mosquito vectors, as well as health
communications surrounding disease transmission, outbreak progression, and health education to
reduce risk of DENV infection. The factors listed above, as well as others, are important since
the increasing geographical range of vectors and DF introducing the virus to previously
unexposed populations in the United States.
1
A. THE PATHOGEN
The pathogen is the dengue virus (DENV), an arbovirus in Flaviviridae, characterized by
a single strand of RNA, approximately 11 Kb in length, with a lipid envelope containing glycol
proteins unique to specific viral serotype (Guzman et al., 2010). DENV has four identified
serotypes important to human health referred to as DENV1-4 (CDC, 2014). Infection by one
serotype provides life-long immunity to that specific virus, but not to other serotypes.
Additionally, sequential infection by different serotypes is shown to have increased risk for
development of more serious forms of dengue, such as DHF Infection by DENV in many cases
can be asymptomatic, and often can go unnoticed. DF causes flu-like symptoms including fever,
nausea, vomiting, rash, aches, and pains (CDC, 2013). DF can progress to more severe
manifestations such as dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS).
DHF is characterized by the presentation of the same symptoms as DF; additionally, DHF causes
plasma leakage, liver enlargement, and impairs the central nervous system (CNS). Abdominal
pain is a sign of worsening condition and patients may show a hemorrhagic tendency
(Hadinegoro, 2012). In DSS, the most severe form of dengue infection, patients have increased
leakage of plasma, rapid/weak pulse, and hypotension compared to standards for the patient’s
age group (Hadinegoro, 2012). DSS and DHF are more likely to result in mortality while DF
itself usually is over after a recovery period of about 3 weeks (Mayo Clinic, 2012). There is no
treatment available that targets the virus. Current medical practice is palliative emphasizing
maintenance of fluids, and support for other symptoms (WHO, 2012).
2
The transmission cycle for dengue fever (Figure 1.) is a complex interplay of contact
between, mosquito vectors, specifically Ae. aegypti and Ae. albopictus, human populations, and
non-human primate populations. There are two ways for a vector to become infected with
dengue virus. The first is for a vector to feed on a viremic host. When the mosquito feeds, the
virus is picked up through the blood meal, crosses the gut barrier in the mosquito, and eventually
is present in the salivary glands (Lee and Rohani, 2005). The process takes approximately 8-10
days (Mayo Clinic, 2010). Once in the salivary glands the mosquito is then able to transfer
DENV to other hosts during additional feeding events (WHO, 2013).
3
A second method of transmission of the virus is during the vector life cycle. DENV is
able to cross over from infected female mosquitos into their offspring in a form of vertical
transmission in the ovaries (Lee and Rohani, 2005). Although this is a less likely then a
mosquito picking up the virus from a viremic host, it is theorized that vertical transmission
allows for DENV to persist in mosquito populations during less than optimal environmental
conditions for survival (Lee and Rohani, 2005).
B. THE VECTORS
There are two important DENV vectors. a.) Aedes aegypti, the primary vector important
in urban environments; and b.) Aedes albopictus, a secondary vector important in suburban and
rural environments (Becker N. et al., 2010). Both vectors are members of the subgenus
Stegomyia and, are generally smaller in size than other subgenera of mosquitoes. These species
have a dark coloring and distinctive white markings of bands or spots. Typical of transmission
of arboviruses, the feeding habits of the female mosquito are important. Female mosquitoes feed
on the blood of various hosts (humans are the most preferable); and viral pathogens are then
transmitted through the salivary glands during feeding events (Becker et al., 2010).
The typical lifecycle of these vectors (Figure 1, bottom portion) lasts on average 30-40
days in the wild (Brady et al., 2014, Becker et al., 2010, and Mayo Clinic, 2012). The eggs of
Ae. aegypti and Ae. albopictus are laid in artificial water containers although both species may
utilize natural containers if present (Becker et al., 2010). The eggs themselves are resistant to
desiccation. Thereby, allowing them to survive periods of time when water amount is not
optimal for hatching (Becke. et al., 2010). After 1-2 days in the surface of waters containing a
mild amount of organic content, but generally is not very turbid, the eggs hatch into mobile
4
larvae which feed on the organic content (Becker N. et al., 2010). These undergo 4 instar forms
over 4-5 days before forming pupae and entering metamorphosis, which takes approximately 2
days (Becker N. et al., 2010). Adult mosquitos emerge from metamorphosis and within 1-2
days, females will seek a blood meal that is typically a human host (Becker et al., 2010).
Although both vectors have similar life cycles, their distribution varies due to differences
in ability to survive extreme temperatures. Ae. aegypti has an optimal temperature range of 27-
30°C and is unable to survive in temperatures below 10°C. This limits Ae. aegypti to areas that
do not have cold winters. In regions with cold weather, Ae. aegypti occurrence is limited to
warm/wet months (Becker et al., 2010). In general, Ae. aegypti is limited to tropics, sub-tropics,
and warm temperate regions (Becker et al., 2010).
Ae. albopictus differs from Ae. aegypti in that its eggs are able to enter a diapause during
cold temperatures. This adaptation allows for eggs to lay dormant through cold winter
temperatures and hatch upon warming when sufficient water levels are apparent (Becker N. et
al., 2010). Consequently, the geographic range of Ae. albopictus is much larger and brings the
vector into contact with a wider range of human populations. Additionally, Ae. albopictus is less
selective in its host feeding preferences and is known to feed on humans, other mammals, and
avian hosts (Becker N. et al., 2010). Traditionally Ae. albopictus was geographically constrained
to East Asian countries, providing the non-taxonomic name of the Asian tiger mosquito, but with
an increase in global trade ,in particular rubber tires, the species has been able to disseminate
globally. It was first detected in the United States in Houston, Texas in 1985 (Becker N. et al.,
2010) and has reached as far as areas of Northeast United States (ACHD, 2013).
5
C. EMERGING AREAS OF CONCERN
1. Climate Change and Vector Distribution
Climate change and variability are shown to influence mosquito survival and distribution.
This has led to an increase in the spread of pathogens. As a result of range expansion, mosquito
vectors and human populations come into increasing contact for longer periods (Johansson et al.,
2009 and Morin, 2013). Two primary factors that have importance for vector distribution are
temperature and precipitation (Johansson et al., 2009 and Ramasamy, 2012). There are also
secondary climate change effects that can have important impacts on vector distribution such as
changes in flora and fauna, as well as a rise in sea levels (Ramasamy, 2012). There is an
expected increase over the course of the 21st century in temperature, shifts in precipitation, and a
rise in sea levels as oceans warm (Collins et al., 2013)(Church et al., 2013). Additionally, it is
predicted that there will be an increase in extreme warm weather events and a decrease in
extreme cold weather events (Collins et al., 2013).
Unless significant changes are made in anthropogenic sources of climate change, these
factors (especially temperature and precipitation) will continue to influence vector distribution
and disease transmission (Morin, 2013). The survival of adult female Ae. aegypti, and Ae.
albopictus is important in the transmission cycle of DENV. The more that survive the more
vectors that are available to transmit the virus, and the higher potential there is for an outbreak of
DF (Brady et al., 2013). A culmination of experiments was utilized to determine temperature
ranges of both species in laboratory and field settings which indicate increases in temperature
will expand regions with ideal conditions for mosquito survival (Brady s et al., 2013).
Additional modeling of the data showed that Ae. aegypti is able to survive in a wider range of
temperatures but Ae. albopictus is better at overall survival.
6
Precipitation is also an important primary climate factor in dengue transmission.
Although it is unclear what aspect of precipitation is critical to understanding relationships to
transmission of DENV and vector survival (Johansson et al., 2009), an increase in humidity and
moisture in an area would generally accompany an increase in available breeding sites, providing
a more suitable environment for mosquito vectors to reproduce.
Temperature and precipitation also have secondary impacts that can lead to an increase in
the range and distribution of mosquito vectors primarily through the distribution of flora and
fauna, and through a rise in sea levels (Ramasamy, 2012). As climate change progresses and the
water cycle shifts precipitation at higher latitudes is occurring (Collins et al., 2013). This
precipitation change and the accompanied temperature changes allow for local flora and fauna to
change their geographic distribution, typically with species moving to higher latitudes following
the water cycle (Ramasamy, 2012). Changes in flora can provide new breeding grounds for
vectors, while changes in fauna can allow vectors to survive in new regions as the distribution of
potential hosts shift (Ramasamy, 2012).
Climate change may affect sea level (Church et al. 2013). On a global scale this will
create additional environments for the breeding of mosquito vectors, in particular those vectors
that are able to tolerate salinity (Ramasamy, 2012). This allows for vector distribution along
coastal regions to readily occur and disseminates vectors to large populations that live near
coasts especially along the Eastern coast in the United States (Ramasamy, 2012).
2. Vaccination Development
Currently the best methods utilized for managing dengue is vector control. Strategies to
disrupt the transmission cycle include; a.) intervention in life cycle of vectors thereby, preventing
transmission of the pathogen between vectors and susceptible populations; or b.) immunizing
7
populations to DENV. Immunization is unfortunately not a currently viable method of control at
this point in time. Vaccine development is routinely complicated and this is particularly the case
for DENV due to multiple serotypes of dengue (Wan et al., 2013). For a vaccine to effectively
provide immunization it has to protect against all four serotypes of DENV. Without complete
protection a population will be primed for an outbreak that could lead to a high number of DHF
cases and DSS (Wan et al., 2013).
Additionally, the recent discovery of a fifth viral serotype, DENV-5, further complicates
vaccine development (Normile, 2013). The discovery and subsequent investigation of this new
serotype showed that it was responsible for an outbreak of DF in Malaysia in 2007 (Normile,
2013). This serotype is still in a sylvatic cycle (Figure 1.) utilizing macaques as a host and is
only able to cause disease in human populations that exist within close proximity to non-human
primate populations and mosquito vectors (Normile, 2013). If DENV-5 is able to mutate and
sustain a transmission cycle in human populations, vaccine development will be further
complicated (Vasilakis et al., 2011).
3. Blood Supply Safety
DENV infection, particularly in endemic regions, has the ability to be asymptomatic. As
a result, individuals who are infected with the virus will be able to participate in donating blood
even when they are unwittingly carrying an agent that is transferable through transfusion. This
leads to the development of infections from transfusion, and has been documented in Puerto
Rico, Hong Kong, and Singapore (Katz, 2010; Wilder-Smith, 2009, Tambyah et al., 2008; and
American Red Cross, 2014). The safety of the blood supply can be secured by the utilization of
screening of potential donors and blood products. In the United States the blood supply is not
routinely screened for DENV (American Red Cross, 2014 and Katz, 2010). General practice
8
rather, is to screen donors prior to donation. In regards to dengue fever, it is currently the
standard to defer a donor from the process for 120 days after clearing infection by DENV (Katz,
2010). While this is effective to eliminate DENV contamination, it is a very long period of time
to defer a potential donor especially when red blood cells can be collected once every 56 days
(American Red Cross, 214), effectively limiting an individual from being able to donate two to
three units depending on the length of recovery or severity of disease (American Red Cross,
2014 and Katz, 2010). It is recommended that this period be shortened and research be expanded
in understanding the disease process of DENV (Wilder-Smith, 2009 and Katz, 2010). In the case
of recurring outbreaks and endemic levels of disease, the number of donors will begin to
decrease and blood shortages will become an issue for transfusion practices (Montenegro, 2011).
In particular, the demand for platelets will be of special concern as donated platelets are only
viable for transfusion for 5 days making it impossible to have a large supply stored in case of
emergent situations (American Red Cross, 2014 and Montenegro, 2011). As dengue becomes a
larger health concern, the need to develop assays for screening of units is imperative. Costs for
screening may be mitigated if risk is taken into account (Katz, 2010).
D. SUMMARY
DENV, as a result is of major concern to public health. The lack of treatments for the
virus and the spread of vectors will bring new populations into contact with DENV that have not
seen the disease. Additionally, the limitation of fresh blood and blood products, through donor
deferral, allows DENV to impact health systems outside of being an agent of disease. Shortages
will require screening and managerial efforts to meet demand. Fortunately, for unexposed
9
regions (such as the United States) there is time for planning of management strategies/programs
for handling vector distribution and blood collection processes.
II. SCENARIOS FOR DENGUE TRANSMISSION
The issue of DF and how it interacts with populations depends on a complex web of
environmental conditions, presence of the pathogen in vector populations, and prior outbreaks of
DENV in populations. Consideration of the initial, seasonal, and endemic outbreaks are three
important scenarios in developing a strategy. Each scenario has different challenges for the
public health practitioner in environmental control, blood collections, and risk communication
A. RELEVANT INFORMATION
In order to examine the challenges that will be encountered. A working knowledge of
environmental control methods for mosquito vectors will be useful. Additionally, basic
fundaments in risk communication and risk communication theory are necessary in order to
understand communication challenges in each scenario.
1. Management of Mosquito Vectors
The management of mosquito vectors is focused on the disruption of transmission cycles
or the disruption of the vector life cycle. Management of mosquito vectors can be achieved
through biological control, environmental management, chemical control, physical control, and
genetic control (Becker et al., 2010).
Biological control measures utilize other organisms as a means to reduce mosquito
populations to acceptable levels. Predators, microbes, pathogens, and parasites are examples of
10
biological control methods. In general, biological control is complicated by a need to preserve
ecosystem stability, and should be utilized as part of a comprehensive program for vector control
(Becker et al., 2010). Utilizing complete knowledge of the biology of the agent helps to ensure
that biological control programs are successful, and solve the mosquito problem without
disrupting the status quo of the ecosystem (Becker et al., 2010). In order to prevent negative
effects, it is recommended that the promotion of organisms that are already present in an
ecosystem be utilized as antagonists to mosquito populations. This strategy is designed to avoid
the possibility of displacement or introduction of invasive species. Mosquitocidal bacteria are a
useful biological control agent. The toxins contained in these strains of bacteria are consumed
by larvae and are extremely selective in toxicity to mosquitoes making them environmentally
safe (Becker et al., 2010). Additionally, mosquito species are less able to become resistant to
bacterial than chemical control measures (Becker et al., 2010).
Environmental management of mosquito vectors is accomplished through the
modification and manipulation of the vector habitat in order to decrease potential breeding sites
(Becker et al., 2010). In urban environments, construction goals should include a reduction of
potential breeding sites, specifically focusing on preventing accumulation of water in drainage
systems, sewage and water processing systems, and cemeteries (Becker et al., 2010).
Chemical control (insecticides) of mosquito vectors uses four broad categories of
treatments to reduce mosquito populations including: chlorinated hydrocarbons,
organophosphates (OPs), carbamates, and pyrethroids (Becker et al., 2010). Although effective,
many chemicals negatively impact non-target organisms. A prime example is
dichlorodiphenyltrichloroethane (DDT). Coupled with issues of vector resistance and increasing
11
dosage requirements, there have been growing concerns about the efficacy of chemical
treatments, as well as concern for environmental health and toxicity (Becker et al., 2010).
Physical control of mosquito vectors seeks to physically gather and isolate mosquitos and
is not associated with the development of resistance (Becker et al., 2010). Oils, surface films,
bead beds, and traps are all forms of physical control of mosquito vectors. Each method seeks to
isolate and halt the mosquito life cycle and interrupting the chain of transmission (Becker et al.,
2010).
Genetic control of mosquitoes refers to technologies and methods centered on sterile
insect techniques (SIT) or the prevention of infection by pathogens important to human health.
SIT methods of mosquito control seek to cause changes in the mosquito population that interrupt
the mating cycle by preventing viable offspring from developing (Becker et al., 2010). For
example the release of a population of sterile male mosquitoes will effectively prevent viable
eggs from being deposited eliminating the next generation (Becker et al., 2010). Technologies
that exist to prevent pathogen infection seek to cause genetic changes in mosquito populations
that make them resistant to infection by pathogens (Becker et al., 2010). In DF this would mean
introducing genetic changes that lead to a phenotype that prevents DENV from entering female
mosquitoes during their first blood meal (Figure 1).
2. Basics of Risk Communication
There are a number of techniques that can be utilized to control mosquito vectors, but
most importantly methods must be coupled with community participation/education, and with
each other to form integrated control measures (Becker et al., 2010). Many methods of control
require participation by the community to be truly effective and this can only be achieved
through effective health and risk communications between oversight agencies and communities.
12
Risk communication is a basic element of any program involving human health. With
the integration of communities into mosquito vector control programs, it is important to keep in
mind that the general populace and industry/oversight agencies will have different concerns and
perceptions of risk (Sandman, 1993 and Slovic, 1987). It is important that all perceptions of risk
be taken into account and that communication strategies encompass all perceptions in order to
reach the community and create effective vector control programs.
It is useful to consider risk in the contest of hazard and outrage (Sandman, 1993). Hazard
is the technical component of risk. Hazard is what industry and regulatory agencies would
consider as the risk assessment process. For example, hazard would be the chance of developing
cancer when exposed to a defined level of carcinogen. Hazard represents a quantified analysis of
the likelihood of negative impacts to health of a specific agent or activity (Sandman, 1993).
Outrage is the non-technical reaction to a hazard. Unlike hazard it is more difficult to measure,
but it is equally as important as hazard because it plays a large role in determining how to
address a communications problem (Sandman, 1993). Even if hazard is intrinsically low for a
particular agent or activity, the outrage factor can make the regulation and management of the
situation more complex and crucial (Sandman, 1993). In the case of mosquito vectors, it is
important not to just understand the hazards (the chances of contracting DF) but also
understanding the outrage, reactions of communities to regulatory measures and their concerns
over treatment methods, in order to achieve a suitable management strategy.
Outrage is influenced by a number of factors. For example, if an event is voluntary,
natural, familiar, chronic, and well known, then it is likely that the outrage level of a community
is relatively low (Sandman, 1993). Conversely, if an event or agent is of industrial or man-made
13
origins, rare or exotic, catastrophic, unknown, coerced, or forced upon a community, it is likely
that there will be much higher levels of outrage to contend with (Sandman, 1993).
When risk is appropriately examined, and hazard and outrage are determined, it is
possible to begin to look at theoretical underpinnings on how to frame a communication plan.
When examining different scenarios it is important to keep in mind that risk perception will be
changing from scenario to scenario, and thus the Risk Perception Model will be of use. The Risk
Perception Model suggests that examining the perceptions of risk in the community and tailoring
communications to addressing these perceptions is the primary goal of risk communication
(Covello et al., 2001). This is especially important when outrage has become a major barrier in
communications (Sandman, 1993).
Additionally, in different scenarios the level of stress faced by individuals will vary. The
Mental Noise Model addresses situations of high stress, i.e. mental noise (Covello et al., 2001).
Under high mental noise situations it may be difficult to communicate to individuals. This is
large in part due to a diminished capacity to handle information from high levels of stress. As a
result communication messages should be tailored to address the impaired ability of people to
process information (Covello et al., 2001). This is achieved through short messages and
instructions aimed at reducing immediate risks present in the situation (Covello et al., 2001).
The Negative Dominance Model for risk communication suggests that information
associated with negative and positive trains of thought are treated differently and given different
weights by individuals (Covello et al., 2001). Negative messages are typically given closer
attention and should be counterbalanced by a larger number of positive messages (Covello et al,.
2001). This should be given considerable attention when a donor is prevented from giving blood
and blood products to a collection service. Furthermore, the additional weight given to negative
14
messages can be utilized to emphasize actions to take to reduce overall risk of populations.
Message can be tailored to utilize negative statements such as “don’t” or “never” in order to
prevent higher risk actions (Covello et al., 2010).
Finally, establishing trust is imperative for risk communication. The Trust Determination
Model suggests that building trust takes time, and is bolstered by working to present one
communication strategy from a trusted source with transparency and frequent updates as
information becomes available (Covello et al., 2001).
B. THE INITIAL OUTBREAK SCENARIO
The initial outbreak scenario is characterized by a one-time initial outbreak of DENV into
a susceptible population. In this case, vectors most likely are newly established due to favorable
climate for expansion and survival, and likely will not maintain a permanent presence once
conditions are below thresholds for mating and development. A large proportion of the
population does not have immunity since DENV has never been encountered and anyone with
immunity likely has been exposed during travel to other regions.
1. Environmental Management Focus
Since the disease vectors likely are newly introduced, environmental management should
focus on education and dissemination of information on mosquito breeding sites, and feeding
habits. It is likely that elimination of breeding sites on personal property will be enough to
interrupt the life cycle, but the additional use of chemical sprays may be utilized. Long term
management of vectors is not of a concern at this point in time because this is a rare one-time
event that can be handled on an as need basis.
15
2. Blood Collection Focus
Standard operating procedures for collection services should suffice in preventing
introduction of pathogens into the blood supply. Eliminating donors before the donation process
through screening for symptoms, and waiting until infection has cleared in the community should
be effective methods to maintain security of transfusion of products. The 120 day waiting period
for donor deferral will allow the pathogen to be effectively cleared preserving the safety of the
blood supply. If needed it is possible to import units in from neighboring blood system. Regions
not experiencing outbreaks of DF can help to meet the demand for blood and blood products.
3. Communication Focus
Risk in the case of the initial outbreak is governed primarily through the outrage level.
The hazards of infection by DENV are low in this scenario since the likelihood of more serious
forms of DF such as DHF and DSS as there was no prior infection by different viral serotypes.
Additionally, the elimination of viable breeding sites within an individual’s property will most
likely be able to limit contact with mosquito vector preventing disease transmission. The outrage
levels are high in this situation due to this being an exotic and rare event. The disease process to
the community will be relatively unknown, and a lack of experience in dealing with mosquito
vectors of DENV can generate a high level of stress making the Mental Noise Model a useful
theory for risk communication. Of additional concern will be the high levels of concern and
mental stress surrounding the impacts these outbreaks will have on child health. Communication
strategies will have to address the high levels of mental noise present by calming fears
concerning the outbreak. Communication efforts should be short and succinct coming from the
local health authorities, as recommended under the Trust Determination Model, giving people a
list of behaviors to not to perform in order to reduce hazard. For example, explaining to not
16
leave containers of stagnant water sitting out would be utilizing the Mental Noise Theory to
enforce a behavior that eliminates breeding sites and reduces hazard while addressing the levels
of stress the community/population will be experiencing.
The Trust Determination Model will also be integral in communicating the continued
safety of the blood supply. Messages should emphasize continued efforts to ensure the safety of
blood products and collection services need to maintain transparency on the status of the blood
supply. Updates should be frequent and regular in order to maintain the trust of the public. The
Mental Noise Theory and Negative Dominance Theory will also be useful to handle the high
levels of mental stress and negative implications of blood shortages. Additionally,
communications need to find ways to ensure that viable donors are reached and donate blood
products to meet demand.
C. THE SEASONAL OUTBREAK SCENARIO
The seasonal outbreak scenario is characterized by the regular outbreak of DENV as a
result of local climate patterns. During the wet and warm season vector populations lying
dormant through diapause, or neighboring vector populations spurred by favorable conditions,
begin establishing themselves in higher numbers compared to the initial outbreak. Proportions of
the population that have already been exposed to DENV will maintain their immunity, unless a
new viral serotype is introduced. The introduction of a new serotype will increase the chances of
an individual developing more serious forms of DF such as DHF and DSS.
17
1. Environmental Management Focus
As outbreaks have shifted from being rare occurrences to annual incidents, environmental
management may focus on large scale projects to eliminate important sources of stagnant water
for breeding sites. This may include updating and revising infrastructure in the waste and storm
water collection systems, as well as the modification of nearby wetlands. There should also be a
continued effort to include local communities in the management effort through continued efforts
at limiting exposure on private property by limiting breeding sties. Additionally, areas that are
known to be likely mosquito breeding hotspots, such as cemeteries or construction sites should
be closely monitored for activity. Long term prevention strategies should be developed such as
spraying schedules for insecticidal efforts that coincide with the seasonality of the outbreaks to
limit vector populations from becoming unmanageable.
2. Blood Collection Focus
Stricter criteria for donation may be need to be established including performance of
medical examinations to determine donor status. Collection services may either consider
screening units of blood for DENV infection if transfusion associated infections are a concern.
Additionally, during seasonal outbreaks the potential stockpiling of products such as red blood
cells and plasma may be considered prior to the outbreak season to alleviate issues of donor
deferral during the event. Transfusion of short shelf life products such as platelets should be
carefully considered to maintain the stock to prevent shortages during emergent situations and
clinical practice should perform platelet counts to determine patient need of platelet pools prior
to transfusion.
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3. Communication Focus
Risk communication during the seasonal outbreak scenario should focus on the
increasing hazard levels as a result of the potential introduction of new viral serotypes to a
population. Additionally, the outrage level will have dropped from the initial outbreak since
DENV outbreaks are a seasonal annual event, no longer making them exotic and rare. Outrage is
still a concern because anxiety will be felt over the depletion of blood products, and concerns of
the safety of the blood system from pathogens increases. Fortunately there is the ability to
prepare the community in advance for the seasonal outbreak and messages prior to the outbreak
should focus on the Trust Determination Model, and the Risk Perception Model for
communication approaches. These efforts should address public concern over the outbreak and
what the perceived level of risk is by providing expert advice on how to limit exposure to vectors
and the virus. Additionally, during the outbreak, it is likely that there will be significant levels of
stress making the Mental Noise Model applicable to help limit exposures and hazard. Finally,
the increase in donor deferral for blood collection services will need to utilize the Negative
Dominance Model. In order to curb the potential shortages of blood products positive messages
that give deferred donors opportunities to still be involved and participate in the donation process
hopefully may be effective in decreasing the burden of shortages on the healthcare system.
D. THE ENDEMIC SCENARIO
The endemic scenario is characterized by a year round presence of DENV and
introduction of multiple serotypes. There will be seasonal variance in the degree of infection as
a result of improved conditions for vector survival. Cases of DHF and DSS will be more likely
as a result of infection by different viral serotypes.
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1. Environmental Management Focus
Environmental management should focus on creating integrated management plans that
focus on utilizing a wider array of methods to temper mosquito populations. The use of
biological control through the maintenance of natural predators may be a viable option.
Additionally, if vector populations are becoming increasingly unmanageable introduction of
predators may be required. Investment into bacterial control of vectors and genetic sterilization
techniques should be considered and large projects to update infrastructure to eliminate breeding
sites should be undertaken immediately. Community involvement in the elimination of private
property breeding sites should be a year round activity.
2. Blood Collection Focus
Blood collection systems should spend the time and money on a full screening process of
donated units of blood products. Products should be quarantined from available stock until
testing has confirmed it to be negative for DENV. Additionally, increased screening prior to
donation should be utilized to try and alleviate the cost of screening the entire supply. In the
case of an endemic scenario airing on the side of caution may be necessary even if it results in
the deferral of some donors who do meet qualifications for donation.
3. Communication Focus
Communication efforts will now be confronted with a scenario with high hazard, and a
decrease in outrage. Hazard has increased as the multiple serotypes and subsequent infections
become more common place. These will lead to an increase in cases of DHF and development
of DSS. Outrage will have decreased because DF is a year round threat and will have lost its
status as a rare or exotic disease. Additionally, dengue will be accepted as an element of the
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environment and something that is out of the control of the individual. Communications should
emphasize the Risk Perception Model since the perception of risk will govern an individual’s
actions. Additionally the Negative Dominance Theory will play an increasing role in blood
donation activities as deferrals continue to occur and increase in frequency.
III. FUTURE DIRECTIONS: WHAT CAN WE DO BETTER?
Dengue is a complex issue that has a number of areas that can be focused upon for
improvement in human health. There remains a lot left to be done in research and practice, and
as dengue becomes a larger threat focusing on control and development of methods and research
into DENV will become increasingly important.
A. BLOOD SAFETY AND DONOR RETENTION
One area that will always need a constant amount of focus and attention will be in
maintaining the safety and security of our blood supply. Without a stable blood supply surgical
and medical procedures simply cannot be done, and communities should not have to worry if a
unit of blood is harmful or helpful. Therefore research into more efficient screening assays, and
improving our pre-donation screening for deferrals will always be a challenge that has room for
expansion as blood collection systems try to achieve 100% efficiency from donors.
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B. COMMUNICATIONS
From a risk communications standpoint for dengue control and management it is
important that a constant upkeep of strategies be maintained. Particularly, in areas where dengue
is at an endemic level a need for constant communication between agencies, healthcare
professionals, and the community should be maintained. Communication methods also need to
improve the blood collection process. Deferrals send an extremely negative message to an
individual especially when it comes to donating a product that is always in demand and can save
a life. Pre-donation screening should always try to find new ways to communicate better in
order to better donor retention rates to eliminate blood shortages. Additionally, communication
messages need to be developed for the outreach of blood collection services to viable donors and
continued efforts should be made to ensure donor retention after DENV infection has been
cleared.
C. VECTOR AND PATHOGEN CONTROL
There will also be a further need to understand vector biology, in order to eliminate
contact between vectors and human populations. Proper analysis and review of methods should
always be factored into an integrated vector management strategy and these results should
always be reported to the community and general public so that feedback can be utilized to
develop more cohesive strategies. Additionally, research into vaccination development needs to
find ways to account for the potential of new viral serotypes developing in the sylvatic cycle of
non-human primates. An inflexible vaccine could potentially cause more harm then good if it
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does not adequately protect, and as a result primes a population for a hger number of DHF or
DSS cases.
IV. CONCLUSIONS
There is a real need for the United States to begin preparations for outbreaks of DENV.
Among these preparations drafting of communication messages for communities will be crucial
for reducing the impacts any outbreak may have. In particular, ensuring that communities are
educated on mosquito vector control could eliminate many vector habitats and halt the
transmission cycle. Further-more, the ability to plan in advance will allow for the establishment
of appropriate communication channels between blood collection services and oversight
agencies, creating a unified message for the public with minimal inconsistencies. There should
also be efforts placed into developing ways to evaluate planned communication messages. In the
case of an outbreak it will be extremely useful to understand what messages achieved the desired
goals and where improvements need to be made for future outbreaks.
The creation of efficient DENV assays for blood collection services must be undertaken.
Development before an outbreak allows for appropriate quality control measures to be
implemented ensuring the safety of the blood supply, which can eliminate of mental noise from
an outbreak scenario. This would allow for efforts to be spent addressing other major concerns
of communities during outbreaks.
Finally, monitoring and investigation into the development of new serotypes should be
undertaken. Likewise, as monitoring occurs vaccine development needs to continue. With
appropriate monitoring vaccine development will be able to address new serotypes and
incorporate them into research strategies to provide protection to all serotypes of DENV.
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