Dengue Fever

 

 by Melissa Wiatrek 

 

 

*     Disease: The universal name for the disease is Dengue Fever. Other names that are commonly associated with this disease include: Dengue Hemorrhagic Fever ((DHF) Disease caused by Dengue Fever), Breakbone Fever, Dandy Fever, O'nyong-nyong Fever, Dengue shock syndrome (DSS) and Dengue-like Disease (5).

 

*     Etiological Agent: Dengue Fever belongs to the family Flaviviridae and is caused by a single-stranded RNA Flavivirus and is compromised of four different types of etiological agents, which include: Dengue Virus 1 (DEN-1), Dengue Virus 2 (DEN-2), Dengue Virus 3 (DEN-3) and Dengue Virus 4 (DEN-4) (8).

 

*     Transmission: The disease is transmitted through two in particular mosquito species, Aedes aegypti and Aedes albopictus. The mode of transmission is as follows: One of the mosquito species bites and individual who is infected with one of the four strains of the virus. The mosquito becomes infected with the dengue virus and bites a healthy person without the virus. One mosquito can inflict the virus and it cannot be spread directly from person to person (1).

 

*     Reservoirs: Researchers have concluded that there are two mosquito species that were identified as the natural reservoirs/hosts, Aedes aegypti and Aedes albopictus. Humans and other primates are also considered reservoirs. These mosquito species are more predominant in the tropics and subtropics (2). They flourish during the rainy seasons, but can breed in water-filled flowerpots, plastic bags and cans year round (2). Usually breeding in stagnant water, they are active in dark or shaded places and are most active about two hours before sunset and sunrise (8).

 

*     General Characteristics: The Dengue Virus is a membrane-enveloped positive strand RNA virus that belongs to the Flavivirus genus, a member of the Flaviviridae family (9). Four closely related viral stereotypes of the virus include: Dengue Virus 1 (DEN-1), Dengue Virus 2 (DEN-2), Dengue Virus 3 (DEN-3) and Dengue Virus 4 (DEN-4) (8).    

 

"The genetic characteristics that distinguish the virus are: a spherical icosahedral capsid about 50-60 nm and a genome surrounded by a lipid bilayer that encodes a single large open reading frame that is translated to form a viral polyprotein. The dengue polyprotein is cleaved by viral and host proteases to produce 3 structural proteins and 7 non-structural (NS) proteins" (9).

 

*     Key Tests: There are several different laboratory tests used to diagnose the Dengue Virus. Blood tests such as complete blood counts, serology studies and antibody titers are some of the general laboratory tests that can be done to diagnose this condition.

 

"Other more specialized testing includes: virus isolation of cultured mosquito cells, detection of a fourfold or greater change in serum samples of IgG or IgM by ELISA or Hemagglutination Inhibition Assay (HAI), demonstration of dengue virus antigen in autopsy tissue by immunohistochemistry or immunofluorescence or in serum samples by EIA, detection of viral genomic sequences in autopsy tissue, serum, or CSF samples using PCR" (9).

 

*     Signs/Symptoms: The disease ranges from mild to severe. Mild dengue fever causes chills, high fever (that lasts about five to seven days), rash, severe headache, pain behind the eyes and muscle and joint pain (3, 4). The severe joint pain has given dengue the name "Breakbone Fever" (3). The rash develops on the feet or legs about three to four days early during the disease with a second rash, measle-like in appearance occuring later in the disease (6, 5). Generally, younger children have a milder illness (presence of no rash) than older children or adults which can lead to a misdiagnoses (1). Other symptoms such as nausea, vomiting, and adominal pain may be present. More severe forms of the disease can progress into "Dengue Hemorrhagic Fever," where the blood vessels start to leak and cause bleeding from the nose, mouth and gums as well as internal bleeding (3). Bleeding with easy bruising, blood spots in the skin and blood in the stool may also appear (2).The blood vessels can collapse with a sudden drop in blood pressure causing "Dengue Shock Syndrome" (3, 4).

 

*     Historical Information: The first description of Dengue Fever was provided in 1780 by Benjamin Rush, signer of the Declaration of Independence,

 

"This fever generally came on with rigor, but seldom with a regular chilly fit. The pains, which accompanied this fever, were exquisitely severe in the head, back, and limbs. The pains in the head were sometimes in the back parts of it and other times they occupied only the eyeballs. A few complained of their flesh being sore to the touch in every part of the body. Its general name among all classes of people was the Break-bone fever" (7).

 

To this day, the orgins of the word "dengue" are still debatable. Some believe that it is derived from the Swahili phrase "Ka-dinga pepo," meaning that the disease is caused by an evil spirit, which may have its orgins in the Spanish word "dengue," meaning fastidious or careful (7). During the twenwth century, Joseph Franklin Siler discovered the viral etiology and the tranmission of the disease as the disease began to spread globally due to population movements (7).

 

*     Virulence Factors: After the disease is transmitted to its host, the Dengue Virus is capable of replicating in many types of cells, but targets mainly cells of the monocyte/macrophage lineage (7).  Within this lineage, the (+ssRNA) genome of the virus directs the synthesis of viral proteins (9). Once these proteins are synthesized the viral RNA generates complementary (-ssRNA), which is transcribed into new molecules of the (+) strand (9). A virus-encoded RNA-dependent RNA polymerase (RdRp), in combination with other viral and cellular factors, catalyzes this process (7). As the macrophages are signaled by the antiboides attached on the viral cell, the virus replicates inside the macrophage instead of being destroyed by it. The virus is then transported through the body via macrophage transports (7).

 

*     Control/Prevention:  A strong emphasis of prevention has been placed on community efforts to increase awareness about the disease, how to recognize it and how to control the mosquito population that transmits it. Other important preventative measures include mosquito contol by eliminating breeding sites and personal protection. Traveling during periods of minimal mosquito activity can also be helpful (5). When traveling to tropical areas it is important to remember to use mosquito repellants containing DEET or NNDB on skin and clothing (3). One should wear long-sleeved shirts and long pants tucked into socks when mosquitos are biting outdoors and avoid heavily populated residential areas. It is also recommened that one should stay in screened areas with aircondition and bednets that readily available (3). Breeding sites can be eliminated by discarding items that collect rainwater and regualarly changing outside animal containers (3). Public sprayings have also proved to be helpful in areas that are infected by the disease.

 

*     Treatment: There is no specific treatment available as well as no vaccine for preventing the disease (6). Analgesics with acetaminophen should be used for pain and those containing aspirin should be avoided (1). The more severe forms of the disease can be treated by fluid replacement, oxygen therapy and blood transfusions (6). Other recommendations include drinking plenty of fluids, rest and isolation in a mosquito-free enviroment to prevent the spread of the disease (8). Recovery time is usually one to two weeks and longer for the more serious cases. Immunity is gained against the particular serotype after recovery from its infection (8).

 

*     Current Global Outbreaks: All four types of the Dengue Virus are re-emerging worldwide and causing more frequent epidemics (3). According to the Centers for Disease Control, there have been several cases of Dengue Fever and Dengue Hemorrhagic Fever documented this year alone. In Central America 3,431 cases of DF and 358 cases of DHF were reported during week 8 (late February/early March) of this year. Only one death occurred (1). During the year 2007, major outbreaks were reported in Paraguay ( with more than 100,000 cases) and ten deaths. India recorded over 90,000 cases with more than 1,500 deaths (1).

 

*     Current Local Outbreaks: According to the Centers for Disease Control, the United States has not seen any outbreaks of  Dengue Fever for the year 2008. In 1999, Texas expereinced the first Dengue outbreak in almost twenety years (1). The border town of Laredo confirmed 14 cases of the virus, while 100 cases south of the Border were confirmed (1). No known deaths were reported. In July 2005, a case of DHF was reported in a resident of Brownsville, Texas. In August 2005, health authorities in the neighboring state of Tamaulipas, Mexico, reported an ongoing dengue outbreak with 1,251 cases of dengue fever, including 223 cases (17.8%) of DHF (1).  

 

References:

 

 (1). ANON. Center for Disease Control and Prevention: Dengue and Dengue Hemorrhagic Fever: Question and Answers. Written October 19, 2007. Accessed March 1, 2008. http://www.cdc.gov/ncidod/dvbid/dengue/dengue-qa.htm

 

 (2). Magar, Shalu and Shardiwal, Rakesh. Dengue DT-DB: Drug Targets Database for Dengue. Written May 2007. Accessed March 1, 2008. http://www.bioinformatics.org/dengueDTDB/Pages/FAQ.htm

 

(3). ANON. Directors of Health Promotion and Education: Dengue. Written May 2005. Accessed March 1, 2008. http://www.dhpe.org/infect/dengue.html

 

 (4). ANON. Mayo Clinic: Dengue Fever. Written September 28, 2007. Accessed March 4, 2008. http://www.mayoclinic.com/health/dengue-fever/DS01028/rss=1

 

 (5). ANON. Medline Plus: Dengue Fever. Written June 20, 2007. Accessed March 4, 2008. http://www.nlm.nih.gov/medlineplus/ency/article/001374.htm

 

 (6.) ANON. New York State Department of Health: Dengue Fever. Written November 2006. Accessed March 4, 2008. 

http://www.health.state.ny.us/diseases/communicable/dengue_fever/docs/fact_sheet.pdf

 

(7.) Vaughn, David W. The New York Academy of Sciences: Dengue: a clinical   perspective. Written June  2008. Accessed March 9, 2008. http://www.nyas.org/ebriefreps/main.asp?intSubSectionID=2628

 

(8). ANON. Central Health Education Unit: Prevention of Mosquito-borne Diseases. Written June 2007. Accessed March 9, 2008.sc.info.gov.hk/gb/www.chp.gov.hk/files/her/dengue_eng.ppt <http://rds.yahoo.com/_ylt=A0oGkj0IBdRHmmEAPVNXNyoA;_ylu=X3oDMTE4Z2RkdW5zBHNlYwNzcgRwb3MDMgRjb2xvA3NrMQR2dGlkA0Y4NjFfNzcEbANXUzE-/SIG=12koprhj3/EXP=1205163656/**http%3a//sc.info.gov.hk/gb/www.chp.gov.hk/files/her/dengue_eng.ppt>

 

(9). Rose, Bob. MBI 456: Yellow Fever Virus and Dengue Viruses. Written February 28, 2007. Accessed March 9, 2008.

http://www.urmc.rochester.edu/smd/mbi/education/courses/MBI456files/070228.pdf