Combatting malaria and dengue fever

WHILST our world is presently bedevilled with wars, famine, climate change, refuge problems, and the knock-on effects of the Covid-19 pandemic, there is good news with the recent discoveries of vaccines to combat the dreaded diseases of malaria and dengue fever. The World Health Organisation (WHO) has recommended the use of two vaccines for malaria and two for dengue.

The first malaria vaccine RTS, S/ASO1, developed by a British Drug Company, was distributed to 12 African countries in July 2023 having been successfully tested on 1.7 million children in Ghana, Kenya, and Malawi since 2019. This vaccine was shown to be safe and effective. The simple facts are that in nearly every minute of our day, a child dies from malaria, and this accounts for nearly 95 per cent of the world’s malaria cases and 96 per cent of deaths since 2021.

New vaccine

A cheaper and equally effective vaccine, R21/Matrix-M, and approved by WHO in October 2023, has been developed by Oxford University’s Jenner Institute, costing only US$4 per dose.

The Serum Institute in India, which is the world’s largest manufacturer of vaccines by volume, can produce 100 million doses of this jab per annum. Each vaccinated child needs three doses to prevent Plasmodium falciparum – one of the deadliest of the five parasites in Africa.

Malaria and its vectors

The term malaria comes from an Old Italian word ‘mala aria’ meaning bad air and was formerly known as ‘marsh fever’ or ‘ague’. It was once prevalent in Medieval times in my county of Somerset, and in the Fenlands of East Anglia in England. Both areas of lowland peat held vast quantities of standing water before Dutch engineers drained these wetlands in the early 17th century. Malaria has been recorded in France and Italy and is now in the UK. The frequency of international travellers and boatloads of refugees crossing the English Channel seem to be the sources.

In 1880, a French army doctor, Charles Leveran, whilst working in Algeria, found parasites inside the red blood cells of his patients. In 1907 he was awarded the Nobel Prize for Medicine.

Sabahans and Sarawakians are all aware that female mosquitoes have a penchant for human and other invertebrates’ blood particularly at night and in the rainy season. Bites from these insects leave parasites from their saliva in our blood stream thus causing itching of the skin.

When bitten by these critters, I immediately apply an old Chinese medicine known as Double Prawn Brand herbal oil. It works and to date for now nearly 30 years of visits to Malaysia, I’ve been malaria free!

Anopheles mosquito

This species of mosquito was named ‘Anopheles’ by a prominent German entomologist, Johann Wilhelm Meiger in 1818. There are now more than 220 species of this insect. As with all mosquito types, they undergo four stages of life from egg, lava, pupa, and imago. The adult female lays between 50 and 200 eggs each time in her short lifespan of about two weeks, preferring clean water in which to lay the eggs. Such habitats vary from mangrove swamps, rice fields, grassy ditches, small streams, freshwater marshes, and in small rain pools, all with nearby vegetation.

Male mosquitoes live for no more than seven days feeding on nectar and other sugar sources. They never feed on blood for it produces sudden death and swarms in vast numbers at dusk with females flying into the swarms to mate. The parasite that they contain seems to improve the female’s sense of smell and thus they are attracted to carbon dioxide emissions of human’s, animal’s and bird’s breath, bodily odours, and particularly those of the feet! They need an ingestion of blood to develop their eggs.

Anopheles controls

Various studies have been and are in process in the understanding of how malaria is transmitted and the mosquito’s innate susceptibility to the Plasmodium parasite. Sprayed insecticide bed nets are used in families without air conditioning in their homes together with window and door mesh screens. Outdoors, fogging is the best answer to eliminate breeding grounds and the resting places of these mosquitoes in vegetation.

However, nearly 130 species of this insect have developed resistance to insecticides probably through the increasing use of insecticides in agriculture.

The most effective and cheapest form of eradication is by introducing a modified gene into male mosquitoes rendering them sterile and then releasing them into the wild. As female mosquitoes only mate once in their short lifetime with sterile males, this insect population would rapidly decrease. This sterile insect technique has been seen to be effective in reducing malaria in some countries.

Within our houses, we sometimes see the jumping spider (Evarcha culicivora) which destroys household mosquitoes as they rest with their abdomens pointing upwards. By stealth this spider comes from below and attacks the abdomen of the unsuspecting mosquito.

Dreaded dengue fever

This disease is spread by the Aedes aegypti mosquito found between latitudes 35 degrees North and South of the Equator but with global warming, the conditions for the species will become a major threat in the southern USA, southern Europe, and North Africa in the next seven years.

This mosquito species moves easily from person to person and with a single bite at any time of the day and night can spread the virus through its saliva glands to infect humans.

Out of Africa

It was partly due to the slave trade that this Egyptian mosquito spread from Africa in the 15th to 19th centuries. Between 1779 and 1780 very serious epidemics broke out in Southeast Asia, Africa, and North America.

Bangladesh is currently experiencing its worst ever outbreak, with more than 1,000 deaths. Climate change, increasing movement of people, and urbanisation have caused eight-fold increase in the rates of this disease worldwide since 2000. Near record levels of transmission are expected in 2023 as warmer temperatures create the right conditions for these mosquitoes carrying the infection to spread.

The name ‘dengue’ originated from the Kiswahili word ‘kidingapopo’ meaning ‘a disease caused by an evil spirit’ and came into the English language in the 19th century via West Indian Spanish. The spread of this disease is nearly universal, and it is thought that more than six billion people will be at risk in just 50 years from now putting considerable pressure on hospitals in many countries.

Reducing risk of infection

The most effective way of controlling this mosquito type is by ridding sources of open water where it may lay eggs. Fogging can only work in areas where a suitable chemical is used which does not contaminate water thereby creating other health hazards. The removal of open drains, particularly alongside roads and establishing an efficient underground water drainage system is a possible solution.

Urban planning has a part to play by avoiding housing developments near sources of standing water, reservoirs, and lakes. We, too, can play our parts in wearing long sleeved garments which cover our skin, installing air conditioning, as well as frequently using DEET-based repellents, ridding our gardens of open water butts, and old car tyres, which easily collect rainfall. A half full bucket of water is an open invitation to these insects.

Vaccines

In 2016, the Dengvaxia became available in Indonesia and the Philippines, but it has proven to have its limitations. Another vaccine, TAK-003, developed by Takeda, may be delivered in two doses to children between the ages of six and 16 years of age, with a three-month interval between each dose.

Mosquitoes are found wherever humans, animals, and birds live and with ever-increasing urban populations and denser housing their numbers are likely to increase unless positive steps are taken in prevention, control, and the use of vaccines.

Climate change is beginning to spread these insects as I have noticed in my rural home in the UK, discovering mosquitoes in my garden in late October!