By EDUARDO GONZALES
Q: Aside from dengue, what other diseases can be transmitted by mosquitoes? How extensive is the mosquito menace in the Philippines? —[email protected]
A: Believe it or not, the puny mosquito is not only the Philippines’ but the world’s deadliest predator. While a few thousands die from snake bites and attacks of large land and sea animals, mosquito-borne diseases account for two million deaths worldwide every year. In the Philippines, mosquitoes are responsible for thousands of death annually. This year, for example, as of the end of August, about a thousand Filipinos, mostly children, have already succumbed to dengue alone.
Mosquitoes can transmit many infectious diseases but these diseases are mostly confined to certain geographical areas. In the Philippines, the deadliest mosquito-borne illness is dengue. But aside from dengue, mosquitoes also spread chinkungunya, Japanese encephalitis, malaria, and filariasis. Dengue, chinkungunya, and Japanese encephalitis are caused by viruses, while malaria and filariasis are caused by parasites.
A mosquito-borne disease is transmitted to us humans when we are bitten by a mosquito that is infected with a disease-causing microorganism. As a rule, only female mosquitoes bite. They do so because animal or human blood is needed for the proper development of their eggs.
Dengue and Chinkungunya
Dengue and chikungunya are both caused by RNA viruses, albeit from different families. Also, they are transmitted by the same mosquitoes, Aedesaegypti and Aedesalbopictus. Furthermore, their signs and symptoms, which appear three to seven days after being bitten by an infected mosquito, are similar—high grade fever, joint pain, joint swelling, rash, headache, muscle pain, nausea, vomiting, and fatigue.
However, chinkungunyas are generally more benign than dengue (serious complications and fatalities occur rarely) although the joint pains that it produces are often more severe and incapacitating.
Japanese encephalitis is caused by the Japanese encephalitis virus (JEV) whose most important vectors are the mosquitoes Culextritaeniorhynchus and Culexvishnui.
The vast majority of JEV infections are asymptomatic. Symptoms, if they occur, appear five to 15 days after the bite of an infected mosquito. They are flu-like and include headaches, fever, and fatigue, and in children, nausea, vomiting, and abdominal pain. Although generally benign, one in 250 patients infected by JEV develop encephalitis or inflammation of the brain, which can be fatal especially in children. Lifelong neurological defects such as deafness, emotional liability, and hemiparesis may likewise plague those who survive the encephalitis.
Malaria is a serious disease that is still a major public health problem inthe Philippines although the number of reported cases has been decreasing since 1990 because of the anti-malarial program of the government.
Malaria is caused by a parasite, a protozoon (i.e., a single-celled organism) that belongs to the genus plasmodium. There are four known species of this genus that cause disease in man—Plasmodium falciparum,
P.vivax, P.ovale, and P. malariae—all are present in the Philippines. The parasites are transmitted to people by Anopheles mosquitoes.
Malaria is endemic in practically all provinces of our country, but most cases occur in rural areas, especially in forested, swampy, hilly, and mountainous regions, the preferred habitat of the Anopheles mosquito.
The typical presentation of malaria is high grade fever that periodically recurs every two to three days. The fever is preceded by several hours of shaking chills, and as the fever subsides, the patient experiences marked sweating.
Malaria patients sooner or later develop anemia, but the more dreadful and sometimes fatal complications of the disease are kidney and liver failure, and cerebral malaria.
The causative agent of filariasis in the Philippines are two microscopic, thread-like roundworms: Wuchereriabancrofti and Brugiamalayi. The formeris transmitted by several species of Aedes, Culex, and Anopheles mosquitoes
while the latter by at least two species of the Mansonia mosquito.
Filariasis is endemic in 44 provinces in the Philippines according to the DOH, but most cases occur in the rural areas of Bicol, Quezon, Mindoro, mMasbate, Mindanao, Palawan, Agusan, and the Mountain Province.
Repeated mosquito bites over several months to years are needed to get filariasis. Most people with filaria worms stay asymptomatic, but a small percentage will develop a condition called elepanthiasis in which the limbs, genital organs, and the breasts swell to monstrous proportions.
(Note: Email inquiries on health matters to: [email protected])