“Mosquitoes are the greatest mass murderers on planet Earth.” — Katherine Applegate
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If you were in “Who wants to be a millionaire?” segment and the host asked you this question: “What is the deadliest animal?” what would be your answer? The choices are: (1) crocodiles, (2) snakes, (3) mosquitoes, (4) sharks, and (5) scorpions.
The answer is mosquitoes as it kills about one million people every year. These insects do not kill humans directly. Rather, they are a vector that transmits mosquito-borne diseases, which include malaria, dengue, West Nile virus, chikungunya, yellow fever, and Zika.
“When a mosquito feeds on blood, it also swallows any viruses or parasites living in the blood,” explains the World Mosquito Program. “These viruses and parasites can be transferred to the next person the mosquito bites through its saliva. Any disease that is spread in this way from mosquito to human is known as a ‘mosquito-borne disease.’”
Most Filipinos are familiar with dengue, although malaria continues to pose a significant health threat in the country. Recently, dengue has garnered attention once more, as the Department of Health (DOH) reported over 43,000 dengue cases nationwide as of February 15.
“The total number of dengue cases from January to February 15, 2025, well ahead of the usual wet or rainy season in June, is now at 43,732,” said the health department in a statement.
On a concerning note, the health department indicated a 56 percent rise compared to the 27,995 cases recorded during the same time frame last year.
Conversely, there is a positive development: a five percent decrease in the trend of cases has been observed over the past four weeks.
The regions most affected by the outbreak include Calabarzon (9,113 cases), National Capital Region (7,551) and Central Luzon (7,362). These areas account for more than half of the total number of reported cases.
It must be recalled that dengue cases in Davao Region went up in the first half of 2024. About 54 people died of dengue at the same period, with 17 of those deaths coming from Davao City.
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.
This type of mosquitoes 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.
As adults, the mosquitoes prefer warm weather, according to the World Health Organization (WHO). Mosquitoes, in general, are active in areas with temperatures ranging from 25 to 40 degrees Celsius and with moderate to high humidity. They cease to function at temperatures below 14 degrees Celsius.
Temperature, clearly, is important: for the mosquito as well as the virus it carries. In Aedes, slight changes in temperature can mean a lot in terms of transmission potentials. “At high temperatures, it takes the virus faster to develop in a mosquito,” explained a government health official. “This means there is a faster potential for dengue transmission.”
Like all other mosquitoes, only the female bites. The WHO says 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 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.
The breeding sites are never far from human habitation. They live in such “places” as tree holes, bamboo stumps, earthen jars for water storage, discarded bottles and tins, old rubber tires, rain barrels for collecting rainwater, clogged roof gutters, coconut shells and husks, and canoes and small fishing boats.
Inside the house or office buildings, the potential sites for the mosquito larvae are “any container that can accumulate water for up to seven days,” according to the DOH. These include uncovered water storage tanks, flower vases, saucers for ornamental plants, soft drink bottles, and metal and plastic pails for water storage.
Dr. Michael MacDonald, an American entomologist from Johns Hopkins University in Baltimore, said that only the tiger mosquitoes, which have bitten a person infected with dengue fever, are carriers of the dengue virus. And it is not directly transmitted from one person to person.
“Once infected, a mosquito remains infectious for life, transmitting the virus to susceptible individuals during probing and blood feeding,” Dr. MacDonald points out.
Health experts say that when a person is bitten and the dengue virus is deposited in the bloodstream, it usually takes an incubation period of four to six days before symptoms appear.
In some adults, dengue is not generally fatal. After contracting the virus from infected mosquitoes, some people develop a silent infection, exhibiting few – if any – symptoms. Their immune systems are able to fight off the disease. Others develop symptoms that are like the flu’s: fever and fatigue that disappear in two weeks.
