The number of dengue patients on the Big Island is increasing daily. After being bitten by an infected mosquito, some people get infected but never get sick. Those that do, develop symptoms in three to seven days, usually in three phases. First there is high fever (38.5 degrees C/ 101.3 degrees F or higher) accompanied by headache, nausea and vomiting, muscle and joint pain (giving it the name of “breakbone fever” because that’s how it feels, but it does actually nothing to your bones), and sometimes a rash. A small percentage of patients will have increased bleeding tendencies. Very rarely there are severe bleeding tendencies and possibly shock. The recovery phase, with a rapid improvement in all symptoms, takes 48 to 72 hours. There can be a milder second rash. Adults may experience extreme fatigue for several weeks after recovery.
Patients should seek medical attention if they believe they have dengue fever. As reported in the newspaper, there is not yet a dengue telephone hotline established here and individuals without insurance and with low incomes may not be well cared for. Blood tests are positive only after there is fever. Certain test results can be known after an hour. Other results take longer. No lab test can predict whether or not the infection will progress to the more severe form.
For moderate levels of the disease, medicines can be prescribed for fever, for nausea and vomiting, and for pain. For the rare severe conditions, patients are hospitalized to receive supportive treatment. There are currently trials of different drugs that target the virus itself or target the body’s immune response, but none have been confirmed as definitely beneficial.
The mosquitoes
Two mosquito species transmit the dengue virus on the Big Island: Aedes aegypti (also known as the yellow fever mosquito) and Aedes albopictus (sometimes called Asian tiger mosquito). The females do the biting. The virus is in the salivary glands of the mosquito. When she bites a human for food (blood), the mosquito injects saliva into the wound to keep the blood from clotting, thus injecting the dengue virus.
Aedes aegypti is a small dark mosquito of approximately four to seven millimeters with white lyre-shaped (the letter “S” back-to-back) markings and banded white-striped legs. The abdomen is generally dark brown to black, but may possess white scales. It is a day-biting mosquito, most active for approximately two hours after sunrise, and several hours before sunset. It prefers to bite indoors. Outside, it rests where it is cool and shaded. The mosquito attacks generally from below or behind, usually from underneath desks or chairs and mainly at the feet and ankles.
Aedes aegypti mosquitoes are highly resilient. Their eggs can survive without water for several months on the inner walls of containers. Even if we eliminated all larvae, pupae and adult mosquitoes at once from a site, its population could recover two weeks later as a result of egg hatching following rainfall, or the addition of water to containers harboring eggs.
The second dengue carrying mosquito here is Aedes albopictus, a small (less than 10 mm), dark mosquito with a white stripe on its back and banded legs. It is a very aggressive daytime biter, outdoors and indoors. It is strongly attracted to humans and will bite any exposed skin surface. Its peak feeding times are during the early morning and late afternoon. This mosquito has a rapid bite that allows it to escape most attempts by people to swat it.
Mosquito protection
The only prevention is to not get bitten by a mosquito carrying the virus. Quarantining dengue patients is not useful. People can carry the disease and not know it.
Mosquitoes are attracted to exhaled carbon dioxide, to sweat and certain skin oils secreted by humans. Wearing mosquito repellent, especially during the daytime, will help protect you, and will help prevent spreading the disease if you carry it. How long repellents work depends on their concentration, varying from five hours down to 20 minutes.
Products with DEET are effective but are not for use on infants younger than 2 months. Picaridin (KBR 3023) products are effective. Oil of lemon-eucalyptus products should not be used on children younger than 3 years of age. Citronella products applied to the skin typically last less then 20 minutes, but citronella candles repel mosquitoes in the vicinity while they burn. Mosquito coils help repel mosquitoes but can cause fires. Products containing permethrin put onto clothing and gear repel mosquitoes. Don’t apply permethrin to your skin.
Dryer sheets like Bounce tied to a hat or belt may be helpful, but have not been tested scientifically. Garlic on the skin will make you repellent to mosquitoes (and everyone else) for only about 20 to 40 minutes. Other aromatic oils have been used but not scientifically tested include cinnamon leaf oil, and clear vanilla oil mixed with olive oil. Despite some advocates, vitamin B1 taken orally has not been confirmed to be repellent but may help. Drinking beer may make you more attractive to mosquitoes, probably because you sweat more. Wearing long pants and long-sleeved shirts definitely reduces risk of getting bitten.
Mosquito control
Reducing the number of mosquitoes reduces the risk of spreading the disease. Standing water is their breeding ground. Surface tension enables mosquito larvae to cling to the surface of standing water until they mature and fly off. Oil or soap sprayed on standing water breaks down surface tension and drowns any larvae. Repeat the spray at least weekly.
Check your yard weekly and eliminate unused water-filled containers. Clean and scrub bird baths and pet-watering dishes weekly. Dump the water from dishes under flower pots. Spray bromeliads with solutions of soapy water or vegetable oil. Check that gutters are not holding water.
The idea of spraying the island with a poison such as DDT (not a good idea) comes from methods used to combat malaria mosquitoes. Those mosquitoes only fly 15 feet after they bite and drink your blood, and then they have to land and rest somewhere, like the wall of your bedroom. If you spray the walls of bedrooms in malaria-infested regions with chemicals that kill mosquitoes, the disease cycle can be interrupted. Dengue mosquitoes do not have this flight distance limitation. Fogging the entire island with poison vapor frequently does not penetrate into buildings where mosquitoes rest, although it is often used as a visible symbol of governmental action during emergencies. DDT is illegal because it is highly toxic if swallowed. It also damages bird eggs.
Flowing water will not be a breeding spot. Water that contains minnows is not usually a problem because the fish eat the mosquito larvae. Dragonflies are also helpful. Dragonfly larvae eat mosquito larvae in the water, and adults will snatch adult mosquitoes as they fly.
Permanent eradication programs for these mosquitoes have been ineffective. The mosquitoes come back so the goal of any program is to reduce the number of dengue-infected mosquitoes below epidemic level. There is experimentation to release of genetically modified male mosquitoes to sterilize the wild-type female population. There is a strategy to infect mosquitoes with a bacterium that makes the mosquito resistant to the dengue virus. There is as yet no vaccine for dengue.
Most material for this article is taken from the New England Journal of Medicine and the U.S. Center for Disease Control. Based on the latest available information, best behavior is to anoint and re-anoint yourself with bug spray. Wear long pants and long-sleeved shirts. You’re probably OK at night. Spray areas that hold water with diluted soap and water or vegetable oil at least every week. Seek medical help right away if you develop a high fever, nausea or vomiting, serious muscle or joint pains, and rash, and go to the hospital if you notice any of that and any abnormal bleeding tendencies. Meanwhile, train your coqui frogs to eat mosquitoes after they gobble up those pesky fire ants.
Barry Blum and Stephen S. Denzer are physicians based in Kailua-Kona.
My Turn articles are the opinion of the writer and not necessarily the opinion of West Hawaii Today.