Why mosquitoes are more attracted to some of us than others

According to the WHO, over 500 million people are affected by mosquito-borne illnesses and it leads to around a million deaths every year

Illustration: Ajit Bajaj

Researches in the past have found that insects like mosquitoes are choosy predators. From genetic factors like blood group to characteristics like colour of clothes and body temperature, a lot of study has gone into what attracts mosquitoes to their prey. But a recent research has tried to understand the extent to which human genes influence attractiveness of mosquitoes.

Body odour is believed to be the single most important factor which attracts mosquitoes to humans. But body odour is at least partly controlled by our genetic makeup.

In a recent study titled ‘Heritability of Attractiveness to Mosquitoes’, with G Mandela Fernandez-Grandon of the London School of Hygiene and Tropical Medicine as the lead author, the researchers have found a sharp correlation between genetic variations and differential attractiveness to mosquitoes The paper was published in the open access journal PLOS One on April 22, 2015.

How the link was strengthened

The trials for this study were conducted on identical and non-identical twins through the Y-tube olfactometer test. To do this, a set up was created where a Y-tube made of flexiglass had mosquitoes entering from the vertical end of the tube and the participants placing their hands at the ends of both arms of the Y tube. This meant that the mosquitoes were free to choose a path towards or away from the odours emanating from hands of the participants.

The behavioural response of mosquitoes was observed using different combinations of stimuli and it was found that the identical twins had a more similar level of attractiveness as compared to non identical twins. The heritability values, or the extent of variation that can be attributed to genetic factors, for attractiveness to mosquitoes was observed to be 0.83 on a scale of 0 to 1 (0 means genes have no effect). The results suggest that the level to which genes are responsible for attractiveness of mosquitoes is at par with levels observed for influence of genes on traits like height (0.8) and IQ (0.5 to 0.8). The paper, however, reminds us that the small sample size and the nature of the variable which was analysed places limits on the precision of the conclusions.

The researchers say that a deeper investigation on the role of genetic variations in attracting mosquitoes could lead to the development of novel insect repellents and individualised strategies for avoiding insect bites.

What older studies say

In the past, several studies have explored why some people are found to be mosquito magnets while others remain relatively unattractive. Carbon dioxide and octenol in exhaled air, amount of lactic acid emitted, body heat, secretor status, moisture, physical movements and the colour of clothing are some factors that lead to differences in attractiveness to mosquitoes.

Mosquitoes are attracted to carbon dioxide that humans exhale and it has been observed that adults are more susceptible to mosquito bites than children due to the larger amounts of carbon dioxide exhaled. Octenol, a chemical found in the human breath, also attracts mosquitoes and forms a potent combination with carbon dioxide in alluring mosquitoes. Additionally, the presence of larger amounts of lactic acid that is emitted through the skin of humans and the production of which is linked with physical activity as well as consumption of certain foods, are other factors associated with an increased attractiveness for mosquitoes. This is why people who sweat profusely tend to be ambushed by mosquitoes. A study of these three factors was conducted in 2007 and was led by D F Hoel. It was published in the journal of the American Mosquito Control Association.

The blood type of a person also plays a role in secretion of different scents. It has been found that mosquitoes are most attracted to Type O and least attracted to Type A.  This was demonstrated in a study that was published in Nature in 1972 (titled Wood and Dore) and has been re-confirmed in later studies.  “Secretor” status is another factor which determines attraction. A “secretor” is a person who secretes the antigens of their blood type into body fluids and secretions like sweat and saliva. Mosquitoes have more affinity for “secretors” than “non secretors”.

Mosquitoes have highly developed thermo sensors that can detect body heat. Warmer bodies are more attractive for mosquitos. Pregnant women have been found to be more attractive to mosquitoes due to a combination of increased body temperatures and carbon dioxide output.

Mosquitoes can observe changes in movements by detecting fluctuations in radiation and use it to approach the human prey. The moisture in one’s breath or on the skin also attracts mosquitoes. Lastly, darker clothing and alcohol consumption are also known to attract mosquitoes. Some of these would be worth remembering as the mosquito menace intensifies in the summer.

According to the WHO, over 500 million people are affected by mosquito-borne illnesses and it leads to around a million deaths every year

Global vaccination target ‘off-track’, says WHO

The health agency has called for renewed efforts to get immunisation back on track in view of the World Immunization Week, beginning April 24

Routine life-saving immunisation can avert 1.5 million deaths every year from preventable diseases, says WHO (Photo: World Health Organization (WHO))

The progress made to achieve the 2015 global vaccination target is still off-track with one in five children still missing out on routine life-saving immunisations that could avert 1.5 million deaths every year from preventable diseases, a World Health Organization (WHO) report says.

In a bid to set things right, WHO has called for renewed efforts to get immunisation back on track in view of the World Immunization Week 2015 (24–30 April).

“World Immunization Week creates a focused global platform to reinvigorate our collective efforts to ensure vaccination for every child, whoever they are and wherever they live,” Flavia Bustreo, WHO assistant director-general, family, women’s and children’s Health, said.

In 2013, nearly 22 million infants missed out on the required three doses of diphtheria-tetanus-pertussis (DTP3) immunisation coverage. Many of these infants were from poor countries. According to Hayatee Hasan, technical officer (immunisation), vaccines and biological at WHO, close to 70 per cent of these children live in 10 countries. The countries are— Democratic Republic of the Congo, Ethiopia, India, Indonesia, Kenya, Mexico, Nigeria, Pakistan, Vietnam and South Africa.

The reasons for low immunisation coverage rates are lack of access to health services, insufficient number of health care workers to deliver vaccinations, inadequate supply of vaccines, insecurity caused by civil strife and conflict and insufficient financial resources for programme to manage the increasing complexity of immunisation programmes, Hasan told Down To Earth.

The health organisation is calling for an end to unnecessary disability and deaths caused by vaccination failures.

“It is critical that the global community now makes a collective and cohesive effort to put progress towards our targets back on track,” Bustreo added.

Immunisation commitment

In 2012, all 194 WHO member states endorsed the Global Vaccine Action Plan (GVAP) at the World Health Assembly. This was a commitment to ensure that no infant misses out on the vital immunisation dose.

However, a recent independent assessment report on the GVAP progress has sent the alarm bells ringing. It warns that vaccines are not being delivered equitably or reliably and that only one out of the six key vaccination targets set for 2015 is currently on track–the introduction of under-utilised vaccines.

According to Hasan, under-utilised vaccines refer to those such as Haemophilus Influenzaetype b (Hib), pneumococcal, rotavirus, human papillomavirus (HPV), rubella and Inactivated Polio Vaccine (IPV).

Many countries have experienced large measles outbreaks in the past year, thus threatening efforts to achieve the GVAP target of eliminating measles in three WHO regions by the end of 2015.

These three regions are the eastern Mediterranean, Europe and the western Pacific. Of these, the eastern Mediterranean and European regions are markedly off-track, Hasan added.

According to an assessment report, GVAP has two aims. The first is to deliver vaccination to all. The second plan is to unleash vaccines’ vast future potential. With these two great ambitions, GVAP aims to make 2011-2020 the ‘Decade of Vaccines’.

Though targets relate to different types of vaccines and diseases, a common thread runs throughout. This is the failure to extend vaccination services to those who cannot currently access them and the inability to strengthen the healthcare system so that all doses of vaccine are reliably provided.

A global collaborative drive for immunisation started in the mid-1970s with the establishment of the Expanded Programme on Immunization. It achieved dramatic results in many countries, raising vaccination levels from as low as 5 per cent to more than 80 per cent by 2013.

Importance of immunisation

According to WHO estimates, immunisation prevents between two and three million deaths annually and protects many more people from illness and disability. In 2014, WHO declared two Public Health Emergencies of International Concern–the Ebola crisis in West Africa and the international spread of polio virus. Both are communicable diseases. Polio is vaccine-preventable and Ebola may soon become so.

Although the progress has somewhat stalled in recent years, early success stories demonstrate the potential of vaccines, which are now being increasingly extended to adolescents and adults as well to provide protection against influenza, meningitis and cervical and liver cancers.

WHO committed to vaccination

Jean-Marie Okwo-Belé, director of immunisation, vaccines and biologicals at WHO, said the organisation would work to increase its support to all countries that were still lagging behind in meeting their targets.

In May this year, WHO will bring together high-level representatives of 34 countries with routine vaccination (three doses of DTP3) coverage of less than 80 per cent to discuss the challenges faced by countries and to explore solutions on how to overcome them.

Although many countries are vaccinating four out of five children with DTP3, a full one-third of the countries are still struggling to reach the ‘fifth child’, meaning that millions of children are at risk of illness, disability or death.

“There is no one centralised approach that can ensure vaccines are delivered and administered to each child. Vaccination plans on the ground need to be adapted not just to countries, but to districts and communities,” Okwo-Belé added.

A truly concerted effort and much stronger accountability is required so that each one of the key players involved fulfills its mandate and helps close the immunisation gap, Okwo-Belé said.

Earlier this year, donor countries and institutions pledged to meet the funding needs of Gavi, the Vaccine Alliance that brings together public and private sectors to create access to new and underused vaccines for children in poor countries.

Gujarat's burgeoning crocodilopolis

Vadodara plans a park for crocodiles to keep their numbers and attacks on humans in check

During monsoons, residents of the industrial city of Vadodara face a strange problem. As the rains swell the Vishwamitri river, which passes through the heart of the city, crocodiles pop up at the most unlikely places—roads, rail tracks and parks. Travelling through the sewer line, baby crocodiles have sometimes even appeared in bathrooms.

Vadodara is an island of crocodiles, says B C Choudhury, conservationist and former scientist at the Wildlife Institute of India, Dehradun. The statement is not without basis. The Gujarat district, with a population of over 3.6 million, is home to hundreds of mugger crocodiles (Crocodyluspalustris), a species found throughout the subcontinent. And their numbers are rising. With the spike in crocodile numbers, cases of attacks on humans have also increased in the past two decades.

“I have been collecting data on crocodile attacks in Gujarat since 1960. Till 2013, some 60 attacks were reported in the state—an average of one attack a year. But in 2014, the number of attack was 24. Of these, 12 were in the Vishwamitri basin,” says Raju Vyas, crocodile expert and an official with the city administration. The reptiles inhabit the Vishwamitr iriver, its tributaries—the Dhadhar, Surya and Dev—and numerous ponds in the district. They are also found in the Narmada, which forms the district’s southern border. People who live in close proximity of the water bodies and use them for fishing and washing, or defecate near them, are particularly vulnerable to crocodile attacks.

“The attacks take place because of mistaken identity. A human being washing clothes on the river bank may appear something similar to a four-legged prey animal to a crocodile,” says Choudhury.

Rising threat

“In the last census in 2010, there were 206 crocodiles in Vadodara city, but in a district-wide survey done on January 20-21 this year, we counted 450 crocodiles. The city alone accounted for 250,” says V K Saxena, deputy conservator of forests (in-charge), Vadodara Range. “The census is usually conducted in winters because cold blooded crocodiles bask on the banks of water-bodies during the day, making it easy to count them. Counting is also done in the night because their eyes glow in the dark, making it easy to identify them,” says Saxena.

Officials set up a signboard warning about the presence of crocodiles in a pond near Laxmi Vilas Palace in Vadodara (Photo: Rakesh D Vadhwana)

So, what is the reason behind the increase in numbers? “Being listed under Schedule–I of the Wildlife Protection Act, 1972, crocodiles have legal protection. Moreover, unlike in other parts of the country, they are not killed in Gujarat because the mugger crocodile is the mount of Khodiyar Maa, a form of the Mother Goddess worshipped widely in state. “But the single biggest reason is the animal itself. It is a very tough species, found from southern Iran to Bangladesh. It has evolved to survive in a drought-prone region and is very adaptable,” Vyas adds.

There is another reason, he says. “The Vishwamitri and its tributaries are flush with fish stocks and help the crocodile population thrive.”

Protected area for crocodiles

City planners have mooted a proposal to declare a certain stretch of the Vishwamitri passing through the city a protected zone for crocodiles and beautify it. This, they say, will prevent the attacks. “It will not be a protected zone as defined under the Wildlife Protection Act. But we will ensure that the animals are not disturbed,” says Vyas.

The initiative has been proposed under the Vishwamitri River front Development Project. The project has been conceptualised on the lines of the Sabarmati Riverfront project in Ahmedabad that came about when Prime Minister NarendraModi was the chief minister of Gujarat. A feasibility study has been done and the report has been sent to the state government for approval.

“We are still scouting for a stretch alongside the Vishwamitri between Vadodara and Jambughoda (in neighbouring Panchmahal district) to set up the protected zone. It is going to be a long process. First, the approval of the state government and then of the Centre will have to be sought. But in the next two-three years, we hope to have such a zone for the Vishwamitri crocodiles,” says Saxena.

“This is a very enlightened move,” says Romulus Whitaker, founder and trustee of the Madras Crocodile Bank, the biggest crocodile sanctuary in India. Though encouraging big reptilian predators near an area may seem a bit strange, there are plenty of examples, both in India as well as other parts of the world where crocodiles or other mammalian predators live side by side with humans with little or no conflict, he adds.

However, Whitaker has a word of caution. “What is important is how the forest department and municipal officials implement the idea, keeping in mind the need to teach people to live safely with predators. And of course, determining the crocodile carrying capacity of the ‘protected zone’ is crucial,” he says.

Choudhury echoes Whitaker’s views. “Maintaining the crocodile population is not difficult. The administration should look at it as an opportunity rather than as a constraint. They should work out the carrying capacity of the proposed crocodile park. They can always remove crocodile eggs before they hatch to control the population. Most importantly, they should provide suitable conditions: water all year round so as to maintain a metre-and-a-half depth (optimum level for crocodiles) in a kilometre-long stretch of the river,” he says.

Will the project succeed? “Knowing the Gujarati crowd, they would never kill an animal, however dangerous it might be. I am sure there is an opportunity here,” says Choudhury.

CURRENT AFFAIRS APRIL/24/2015

CURRENT AFFAIRS APRIL/24/2015

1. WORLD BOOK AND COPYRIGHT DAY OBSERVED ACROSS WORLD:

.    UN has observed World Book and Copyright Day across the world on 23^rd April 2015.

.    UNESCO has designated Inchon, South Korea as the World Book Capital for the year 2015

.    World Book Day was celebrated first time on 23^rd April 1995 by UNESCO.

.    UNESCO – United Nations Educational, Scientific and Cultural Organisation

2.   VIVEK MURTHY TOOK OATH AS THE NEW US SURGEON GENERAL:

.         Indian-American Vivek Murthy took oath as 19^th US Surgeon General.

.    Vivek Murthy’s oath was administered by the Vice-President of US, Joe Biden.

.    Vivek Murthy succeeded Boris D. Lushniak to be the youngest ever in charge of US Public Health

3. KPMG ELECTED NEW CEO AND CHAIRMAN:

.    Renowned US Accounting firm KPMG elected Lynne Doughite to be the new CEO and Chairman.

.    Lynne Doughite succeeded John Veihmeyer to be the first women CEO and Chairman of KPMG International

.    KPMG is among the World’s leading professional services and one of the four biggest accounting firms is US.

.    CEO –Chief Executive Officer

4. SHAHRUKH KHAN HONOURED WITH DADASAHEB PHALKE AWARD:

.    Bollywood king Shahrukh Khan is honoured with Dada Saheb Phalke film foundation Award 2015.

.    Shahrukh Khan was conferred with the award for his performance in the movie ‘ Happy New Year’

5. RAILWAYS LAUNCHED NEW MOBILE APP‘UTSONMOBILE’:

.    Railway ministry has launched a new mobile app, ‘Utsonmobile’ for paperless unreserved tickets.

.    The application will cover 15 stations between Egmore and Tambram Suburban sections in Chennai of the southern Railway.

.    The application is developed by centre for Railway Information Systems (CRIS).

Note: Suresh Prabhu is Union Railway Minister.

6. PARALYMPIC COMMITTEE OF INDIA SUSPENDED BY SPORTS MINISTRY:

.    Union Sports ministry has suspended the recognisation of Paralympics Committee of India (PCI)

.    PCI was suspended for poor management and conduct of 15^thNational Para Athletics Championships held in Ghaziabad.

.    Earlier PCI was indefinitely suspended by the International Paralympics Committee (IPC).

Note: Sarvanan Sonwal is the Union Sports Minister.