The buzz of mosquito (Spanish for little fly) has become louder again since some sporting people got malaria during Rio 2016 Olympics in Brazil, and Zika virus has reached Florida in the US. In the battle for survival there is a recent discovery of how mosquitoes find their “attractive” victims.
It seemed malaria was headed for history books but it is now staging a comeback with the resurrection of mosquitoes from the dead. Mosquitoes have a nasty habit. I haven’t heard anybody say a good word about them. Some insects like honeybees provide us with food by their pollination while mosquitoes have been killers like Mafia. Have a heart! Mosquitoes are like the Hindu Trinity: creator, destroyer and preserver of humanity. They could have been our ancestors as the evolution of insects to animal groups remain unclear. While they are destroyers, they are also an important part of food chain for fish such as catfish that eat mosquito larvae, and birds like ducks, geese and migratory birds.
Mosquitoes are still killing 2 millions in Africa, mostly children. Genghis Khan, who is said to have killed 1,748,000 people in one hour will pale into shame. Mosquitoes as carriers of malarial parasites were only discovered in 1897 when Dr Ronal Ross, who was born at Almora near Nainital, discovered malarial parasites in the stomachs of four female Anopheles mosquitoes in the Secunderabad cantonment in South India.
Most species of mosquitoes are vegetarians and do not drink blood at all. They feed on plants and nectar. Out of 3,500 species only the Anopheles, Culex and Aedes are blood sucking baddies. It’s not known how some species of mosquitoes have evolved as blood sucking insects. The species Aedes aegypti, for example, that spread dengue fever, chikungunya and yellow fever, is currently responsible for spreading the Zika virus to Americas.
Some mosquitoes do not like the blood of mammals but prefer blood of amphibians such as snakes, or birds (avian malaria). There have been debates among the scientists whether we should eradicate mosquitoes or at least the 100 species or so that serve as disease transmitters for humans. Some feel their elimination will not probably harm the eco system.
Malaria is an ancient disease noted for more than 3000 years. The origin of malarial parasite stretches to prehistory in Africa, where they evolved with their human and nonhuman hosts. They contributed to the fall of Rome. They helped to turn the tide of major battles as that of Japanese against British in Burma. The Japanese, ignorant of quinine, died in their thousands from malaria during WWII, while it killed 60,000 American soldiers in the South Pacific because of shortage of quinine.
I have childhood memories of having malaria during WWII in Senjam-Chirang village, where half of the refugees from Imphal (hundreds) including our next door family were wiped out in 3 months. Luckily, my father knew about quinine. Only In the early 1950s, death from malaria dropped because of quinine and the WHO malaria control programme with DDT. Imphal Civil Hospital had an anti-malaria unit led by Dr Chandrahas.
In 1964, while I was looking after the medical ward in Imphal civil hospital, a Bengali man who had been to Morey was admitted with fever. Before I knew what was happening to him, and while I was off for the afternoon, apparently, a Bengali doctor who knew him, came to the ward and having diagnosed cerebral Malaria, gave him an intravenous quinine injection. He walked out the next morning before I went for the round.
Early this year (2016) mosquito brought quite a scare among Europeans who visited Uganda because of the outbreak of Zika virus. The virus was spread by mosquitoes from monkeys in the Zika Forest. Humans in Uganda never suffered Zika virus infection or Zika fever. The infections were last identified in Brazil in 2015 with a surge of babies with brain and skull defects, born of infected mothers. The virus looks like a crank of a bicycle.
The virus has now indeed arrived in Florida. The first case was officially reported on August 23 2016. Since early August 2016 it has been the focus of research by the US Drug Administration to launch a project in which genetically modified Zika-fighting mosquitoes to be released into the Florida Keys areas. Very recently two cases have been found in New York, believed to be sexually transmitted.
Here in the UK, in mid August 2016, it became news when the television sports presenter Charlie Webster was in coma due to cerebral malaria during a charity bicycle ride in Brazil. About 30 years ago when malaria was still present worldwide, British citizens who wanted to travel to a malaria risk country like India – were given free preventive anti-malarial tablets.
Mosquitoes have been buzzing on Earth for 400 million years ago – long before the evolution of human beings that was merely 200,000 years ago. The oldest mosquito fossil with blood in its abdomen – 90 million years old – was found in Burmese amber (amber is fossilised yellowish tree resin, used as jewellery and as ingredient of perfumes) in Myanmar. Another fossil of mosquito with an anatomy similar to modern species was found in 79 million old Canadian amber.
These two mosquito fossils show very little morphological change from modern mosquitoes and against their counterpart from 46 million years ago. Recent studies suggest that the earliest divergence of mosquitoes leading to Anopheles and Culex lineages occurred 226 million years ago.
I didn’t know why some people attract mosquitoes more than the others. Every time my wife, my son and I come to India, she always has many bites and not us. I now know why. Dr James Logan, associate professor in the London School of Hygiene and Tropical Medicine, who published a study in 2005, explains. It’s about how we smell.
His team took people who say they often got bitten, referred to as “attractive” and those who said they rarely did, “unattractive” and connected microelectrodes to mosquitoes to see what they were smelling before they took a bite. The attractive people’s bodies contained more of a type of chemicals called kairomones, while the unattractive emitted more chemicals called allomones, which repelled mosquitoes.”Products based on these chemicals are now being tested with the aim to develop a drug or pill to be used as repellents before you go on a holiday.
Mosquitoes have a nervous system with a rudimentary brain (ganglion). Despite it they are outsmarting brainy humans in the survival of the fittest. Their ability to obtain their dinner as blood suckers while avoiding host defences like nets, various chemical and ultrasound repellents, and many predators, such as spiders, dragonflies and bats, will outfox many army generals.
Mosquitoes live worldwide except in Iceland – perhaps due to a quirk of climate. Males live typically 5-7 days while females like human females, live longer up to one month. Their size varies from 2mm to 6mm and typically weigh about 5mg. Average female mosquito can have a blood meal three times its weight. They can sense human target from the carbon dioxide in human breath from a distance up to 50km (30)miles) away.
Mosquitoes are deadliest animals, built like the American F-100 fighter-bombers, used in the Vietnam war. Once they have tracked and locked on to their targets with their antennae as radar, they zero in with visual guides with great precision, avoiding various anti-mosquito defences, zooming in through a small opening in the mosquito net where they often sidetrack missiles like a palm of human hand.
They are equipped with a pair of antennae with gadgets that have hearing receptors; detect host odours; find breeding sites for females; and can send signals by vibration to each other for mating. They have visual sensors with compound eyes (like small bits of diamond on a ring) and mouth for eating. They have thermal sensors that can detect warm-blooded animals.
Both male and female eat fruit and plant nectar but the female sucks blood for protein and iron to help her eggs develop – through a flexible tube – proboscis – like a drinking straw with pin-sharp end for piercing the skin. She releases her saliva into the wound. That causes slight irritation. Once her proboscis hits a blood vessel underneath the skin she injects a cocktail of chemicals into your skin, which act as a local anaesthetic, and anticoagulant that keeps the blood in fluid form. Her saliva also contains digestive enzymes and anti-bacterial agents to control infection in their sugar meals.
Mosquitoes are active only during dusk to dawn except a variety, which are active during day hours, known as Asian Tiger Mosquitoes (black and white).During daytime they rest and sleep in a dark sheltered place. Otherwise, they will die of dehydration.
Mosquito bite per se, does not make you itch. It’s your body’s defence mechanism ie immune system that organises to destroy the chemicals by releasing histamine, which causes the blood vessels around the bite to swell up and become red to contain the chemicals in that area only. When you have a bad reaction, the best thing to do is wash the spot with soap and water and apply an anti-histaminic cream like Benadryl or steroid cream.