Dengue is back with a vengeance
By Henrylito D. Tacio
Dengue is rampaging around the world. In the first quarter of 2024, over 7.6 million dengue cases have been reported to the World Health Organization (WHO), including 3.4 million confirmed cases, over 16,000 severe cases, and over 3,000 deaths.
“Currently, 90 countries have known active dengue transmission in 2024, not all of which have been captured in formal reporting,” said the Geneva-based United Nations health agency.
In the Philippines, the Department of Health has reported a total of 208,000 dengue cases as of September this year, marking a 68% increase compared to the corresponding period last year, according to Health Secretary Teodoro Herbosa.
“Dengue is the world’s most important viral disease transmitted by mosquitoes,” said Dr. Duane Gubler, health administrator of the US Centers for Disease Control and Prevention. “The mosquitoes become infected when they feed on someone who has the virus.”
Signs and symptoms
Medical scientists identify four distinct viruses, which are transmitted through the bite of a mosquito. Most people infected with dengue viruses have dengue fever. Patients suddenly develop a high fever. They also may have a headache around their eyes or on their forehead.
A rash, which usually appears 24-48 hours after the fever starts, begins at the trunk and then develops on the arms and legs. Patients experience muscle aches and severe bone pain (this is the reason why it is sometimes called “breakbone fever”). Two-to-six days later, nausea and vomiting may take place.
According to the WHO, the fever usually lasts three to nine days and then goes away. One to two days after the fever goes away a second rash appears. This rash disappears in one to five days and is accompanied by a slight fever (also known as “saddleback fever”).
Dengue hemorrhagic fever
As stated earlier, there are four strains of dengue viruses – all of which can cause dengue. However, if there is an infection with a second strain in a patient who has had dengue fever caused by another previous strain, this person is likely to develop dengue hemorrhagic fever (DHF).
The exact reason for this is not clear, but medical science believes that antibodies produced after the first infection enhances the subsequent infection related complement activation.
On the other hand, if more than one strain causes the disease, DHF will occur too. Not all people who develop sequential infections get DHF. Again, the reason is not clear.
DHF develops in one in 20 people with symptomatic dengue and can lead to shock within hours, according to Dr. Joshua Wong of the US Centers for Disease Control and Prevention (CDC).
“Knowing the warning signs of severe dengue can save lives,” Dr. Wong says. The DHF warning signs include intense abdominal pain or tenderness, persistent vomiting, clinical fluid accumulation, mucosal bleeding, lethargy or restlessness, liver enlargement, and hemoconcentration.
“Patients with warning signs should be monitored closely because they can be more likely to progress to severe disease,” Dr. Wong urges. “Severe dengue can result in severe bleeding, shock caused by plasma leakage, or end-organ impairment.”
Dr. Wong suggests that those who watch dengue patients should recognize the critical phase of the disease. The critical phase begins when fever starts to decline and lasts for 24-48 hours. During this phase, some patients may deteriorate within hours without appropriate intravenous fluid management and require close monitoring.
Among the people at higher risk for severe disease include pregnant people, infants less than one year old, adults aged 65 years or older, and those with underlying conditions including diabetes, asthma, hypertension, chronic kidney disease, chronic liver disease, peptic ulcer disease and other gastritis and obesity, and conditions requiring anticoagulation medications.
Four strains of dengue
As stated earlier, there are four strains of dengue viruses – all of which can cause dengue fever. However, if there is an infection with a second strain in a patient who has had dengue fever caused by another strain previously, this person is likely to develop DHF. The exact reason for this is not clear, but medical science believes that antibodies produced after the first infection enhances the subsequent infection related complement activation.
On the other hand, if more than one strain causes the disease, DHF will occur too. Not all people who develop sequential infections get DHF. Again, the reason is not clear.
Dr. Scott Halstead, of the Health Sciences Division of New York-based Rockefeller Foundation suggests that if antibodies are of “neutralizing type,” they do not enhance the growth of subsequent dengue viral infection. However, if there are no neutralizing antibodies, the other antibodies enhance the viral replication.
Dying children
Most dengue patients are children. A research study conducted by the Department of Health (DOH) sometime in 1991 pointed out that the majority of the patients are between the ages 5 and 9 years old.
“It is a big problem among children because it is a major cause of illness and deaths,” says Dr. Lulu Bravo, a professor at the College of Medicine at the University of the Philippines.
But the risk of dying is higher among teenagers. “This is a common observation and maybe it’s related to the fact that DHF has a more severe illness with bleeding and shock after an initial infection,” explains Dr Bravo. “The appearance of a second infection triggers a more severe reaction and high response of antibodies. Thus, minor illnesses are expected during the first encounter, usually in the younger age group.”
According to Dr Bravo, dengue death is due to the body fluids leaving the blood vessels and accumulating in body cavities or spacing, thus causing shock. It may be also due to severe bleeding either internally into the intestines, in the brain, or in other organs of the body.
“The outcome could be fatal within hours of severe bleeding or in many cases children are pulled out of shock by adequate management of fluids and blood or blood products replacement,” the UP professor says.
Dengue virus carrier
Dengue viruses are transmitted to humans through the bite of infected Aedes aegypti mosquitoes. Also known as tiger mosquito, because of its peculiar white stripes, this species is quite small, measuring only five millimeters. It is attracted to the odor and sweat of human beings and bites only during daytime. However, its peak biting time is after sunrise and at dusk – especially one hour before sunset.
Like all other mosquitoes, only the female bites. The adult female Aedes mates and takes its first blood meal about 48 hours after coming off its pupa stage. It can bite several people, depending on how much blood it sucks.
To lay eggs, it has to be engorged with blood, which may take two to five days. Each Aedes female can lay up to four batches of eggs – at least 40 eggs per batch – during its life cycles. The eggs hatch into “wrigglers” in two days, and after four days become “tumblers.”
Scientists have discovered that the eggs of Aedes mosquitoes can survive for up to six months – even when their breeding grounds go dry under natural conditions. Some of the remaining eggs can still go on when the breeding sites become filled with water again.
Treatment
Until now, there has been no specific treatment for dengue infection. However, early detection and access to appropriate healthcare for case management can reduce mortality, as can rapid detection of severe dengue cases and timely referrals to tertiary healthcare facilities.
“People with these severe symptoms, admission is necessary,” said Dr. Lulu C. Bravo, a professor of infectious and tropical diseases. “The patient is subjected to regular blood test monitoring until stable. Fluids are carefully computed and monitored plus as soon as needed, blood or blood components are transfused.”
The best way to beat dengue fever is not to be bitten by dengue-carrying mosquitoes. When going out, people are advised to wear long-sleeved shirts and long pants. When indoors, it is advisable to stay in air-conditioned or screened areas. All windows and doors must have screens to prevent mosquitoes from getting in. Children must not play near still water.
