Anthony Karabanow, MD
Dengue fever is a mosquito borne viral illness. It typically results in a nonspecific febrile illness associated with severe myalgias (muscle pain). In 2001, Scott Halstead published the most important study on dengue fever in Haiti to date1. He studies dengue transmission rates amongst 210 school children in Port au Prince. Nearly 85% of the children had antibody evidence of exposure to 2 or more dengue virus serotypes. He subsequently calculated a 30% annual infection rate for dengue fever. However, not a single case of severe dengue fever (previously called dengue hemorrhagic fever) was identified. The author concluded that this latter finding provided “ further evidence of a dengue resistance gene in black populations.” A team of Israeli physicians found 6 cases of dengue fever amongst 255 patients presenting with undifferentiated fever to a primary care clinic in Leogane2.
There are in fact four different dengue viruses (DENV 1-4). All four serotypes have been identified in recent years in Haiti. Typically one or two serotypes circulate at any given time. Infection with one type of dengue virus confers lifelong immunity to that serotype only. It does not provide immunity to infections with other dengue viruses. Indeed, the risk of severe disease rises with sequential infection. This is because antibodies produced against one dengue serotype paradoxically enhance later infection with a different serotype. Haitians are protected against this phenomenon by their genetic ancestry.
Dengue infection has an incubation period of 3-14 days. Thus, dengue cannot be the source of fever developing in a traveler more than 2 weeks after returning home. The overwhelming majority of dengue infections produce no symptoms. This is particularly the case with childhood infections. Most symptomatic infections produce the syndrome of uncomplicated dengue fever. A minority of cases evolve into severe dengue fever.
Severe dengue will not be discussed further as Haitians are not susceptible to this manifestation as indicated earlier. However, non-Haitians working or visiting Haiti are most certainly capable of suffering from this severe and potentially life threatening illness.
Dengue fever is a non-specific febrile illness characterized by severe muscle and joint pain (hence its nickname “break-bone fever.”) Headache, retro-orbital pain (pain behind the eyes) and rash are also common. However, gastrointestinal and upper respiratory illness symptoms can also occur with dengue.
The diagnosis of dengue fever is made by serology (i.e. measuring antibodies against the dengue virus.) However, this test is not routinely available in Haiti. Non-specific laboratory abnormalities associated with dengue include leucopenia, (low white cell count,) thrombocytopenia (low platelet count) and transaminitis (elevated ALT/AST.) Bleeding is common in dengue due to the low platelet count. Usually this is limited to petechiae or mucosal bleeding. More severe bleeding can also occur but is uncommon. The “tourniquet test” has been used to help identify dengue fever via this bleeding diathesis In this test, a blood pressure cough is inflated to midway between systolic and diastolic pressure for 5 minutes. A positive test is > 20 petechiae per square inch on the skin distal to the cuff. However, this test is more difficult to apply in dark skinned patients.
There is no specific therapy for dengue. Thus, the key is not to miss the possibility of a treatable mimic such as malaria, typhoid fever, leptospirosis or influenza. The care of the dengue patient is supportive. Of note, only acetaminophen or opiates should be administered to treat pain. NSAIDs should be avoided due to the risk of bleeding and Reye’s syndrome (in children.) The symptoms of uncomplicated dengue fever typically last 5-7 days.
A dengue vaccine is currently on the horizon. However, at this time, the key preventative measures are mosquito control and avoidance. The dengue carrying mosquito (Aedes aegypti) is day biting (unlike that for malaria.) This mosquito typically lives in and around houses. Thus, removal of breeding site (stagnant water,) insecticide spraying and the use of mosquito repellants are all advised.
1. Halstead SB et al., “Haiti: Absence of dengue hemorrhagic fever despite hyperendemic dengue virus transmission,” Am. J. Trop. Med. Hyg, 2001, 65(3), 180–183.
2. Neuberger A et al. “Infectious diseases seen in a primary care clinic in Leogane, Haiti,” Am. J. Trop. Med. Hy, 2012, 86(1) 11-15.by