Port Essington on the rugged coastline of the Northern Territory was a horror for early European settlers.

The colonists in the 1800s had to contend with sharks, crocodiles, a cyclone, and hot weather unlike anything they knew from their homeland.

In the short-lived colony, one of the key causes of death was malaria, the mosquito-borne illness that caused terrible fevers and plagued the early settlers.

Fast forward almost 200 years, and while the crocodiles and sharks are still there, the malaria has gone, in the same way it has been banished from across northern Australia.

The question

Australia's victory over malaria is what prompted this month's Curious Darwin question from Paul Irving, who works at Charles Darwin University.

Malaria facts: Nearly half of the world's population is at risk of malaria

Nearly half of the world's population is at risk of malaria There were about 212 million cases in 2015

There were about 212 million cases in 2015 There were an estimated 429,000 deaths from malaria in the same year

There were an estimated 429,000 deaths from malaria in the same year About 90 per cent of malaria cases occur in Sub-Saharan Africa

About 90 per cent of malaria cases occur in Sub-Saharan Africa Australia was certified as malaria free in 1982

"Malaria is endemic throughout the region, and the tropics right around the world, except here in the Northern Territory," he said.

"I know it used to be here and every third headstone you see in the Pioneer's Cemetery says that they died of malaria, but we don't now have it anymore.

"I would like to know why."

He is right that Darwin once had malaria; if you look at a map of malaria distribution around the world, northern Australia does stand out as one of the few places in the tropics that is malaria free.

Northern Australia is one of the few places in the tropics where malaria is not found. ( Wikimedia Commons )

This is despite the mosquitoes that carry the illness — the anopheles species — living in parts of the NT.

In fact, the Northern Territory was not certified as malaria-free until 1981, 19 years after the last known case was contracted in Roper River.

The short answer

Professor Ric Price is an expert in malaria who works at the Menzies School of Health Research in Darwin.

He said the victory over malaria was a result of prompt and effective diagnosis, actions to control mosquito numbers, and close follow-up of people who returned home from overseas who were sick with malaria.

"Malaria is a disease that affected the whole world 200 years ago — nearly 198 countries — and not just tropical countries, but England, Italy, Russia, Korea, China and America," Professor Price said.

"Malaria now is mainly a disease of poor countries."

The long answer

To understand how malaria has disappeared from northern Australia, you need to understand how it is transmitted.

Anopheles mosquitoes: There are about 400 types of anopheles mosquitoes

There are about 400 types of anopheles mosquitoes Only one-quarter of the anopheles species can carry malaria parasites

Only one-quarter of the anopheles species can carry malaria parasites Ten species of anopheles mosquito live on mainland Australia

Ten species of anopheles mosquito live on mainland Australia They can often be identified by black and white scales on their bodies

They can often be identified by black and white scales on their bodies Of those that carry malaria, only the female mosquitoes can spread it

The only mosquitoes that can carry a parasite called plasmodium, which causes malaria, are female anopheles mosquitoes.

Although you can catch malaria through blood transfusions, organ transplants, or by sharing a syringe with someone who has it, it's primarily transmitted by mosquito bites and is not considered a contagious disease since it cannot spread readily from one person to another like a cold or flu.

So if you can stop infected people passing on the parasite to mosquitoes, or stop infected mosquitoes passing on the parasite to humans, malaria cannot spread (although in parts of South-East Asia monkeys can also harbour a variety that infects people).

Australian health authorities tackle both ends of the problem, with regular large, organised programs to kill mosquitoes, and strategies to isolate and treat people who have the disease before they can spread it to others.

But arriving at this point after initially ridding the area of malaria has been a long and interesting journey.

World War II troops used as guinea pigs

Questioner Paul Irving also wondered if World War II and the amount of effort put into protecting troops stationed in Northern Australia may have prompted the eradication of malaria.

"There were a lot of people then, and they weren't short of money to protect people so perhaps they fogged everything," he speculated.

He was right that during World War II the Australian Army was very interested in malaria, and put a lot of effort into understanding the disease, especially because 90 per cent of the world's supply of quinine — used to treat malaria — was produced in Indonesia, in a direct line of the advancing Japanese Army.

During World War II Australian soldiers were shown how to control mosquito larvae. ( Supplied: Australian War Memorial )

In a 13-week period in Papua New Guinea there were said to have been a little over 4,000 Australian battle casualties, but nearly three times as many troops affected by malaria.

An anti-malaria control unit was created, and Dr Neil Hamilton Fairley — later to be knighted and given the rank of Brigadier — led the Allied forces' fight against the disease.

In what would perhaps be frowned upon now, Sir Neil deliberately infected several hundred volunteers in the Army with malaria and treated them in Australia with various drugs.

The breakthroughs he made — including demonstrating the importance of preventative drugs — had long-lasting impacts on the battle against malaria, by breaking the cycle of transmission, ultimately helping eradication efforts in a host of countries.

The war also hastened efforts to control the numbers of the troublesome insects in Darwin, according to local historian Mike Owen.

"Certainly during the war there were serious chemicals [including] arsenic and strychnine — sprayed with great abandon on all airstrips and where people were living, so there was a very considerable amount of effort that went into reducing the number of mosquitoes," Mr Owen said.

"Really, bugger-all was done before that in almost every regard."

DDT: 'Kryptonite to mosquitoes'

Authorities in the 1950s and 1960s were also assisted with the use of the chemical commonly known as DDT, which later became infamous for its harmful impact on the environment, but was extremely effective in combating mosquitoes.

DDT — variously described in the past as "kryptonite to mosquitoes" or a "miracle weapon" against malaria — was eventually banned in Australia in 1987 after evidence appeared that it was thinning the eggshells of birds and remained toxic in the environment for a long time.

It is now banned in many other countries, or has had its use heavily restricted.

Aerial spraying of DDT in the United States, with a can of DDT (inset). ( Supllied: USDA Forest Service and for inset Wikimedia Commons (Xanthis) )

But prior to it being banned, DDT was used extensively in Australia as part of a World Health Organisation program to eradicate malaria from countries with low-to-moderate transmission rates.

While DDT was very useful in eradicating malaria from many countries, even before bans were introduced it was becoming less effective in tropical regions and mosquitoes began to show resistance to the chemical.

Its use to control mosquito numbers is now considered hugely controversial but continues in some places.

Fogging, draining

The other thing that authorities in the Northern Territory have done is to effectively drain areas where lots of people live, and fog swamps where mosquitoes live near urban areas; in doing so have eradicated the anopheles mosquito species from around Darwin.

Professor Price said a good understanding of the breeding habits of mosquitoes had allowed the anopheles variety to be eradicated around Darwin, but there were simply too many mosquitoes to wipe them all out, and the ones that could carry malaria still existed in Darwin's rural area and elsewhere in the NT.

A fogging machine used at the Darwin RAAF base in 1962 to kill insects. ( Flickr: Ken Hodge )

"When there are bursts of mosquitoes, the entomology department go in and they have interventions such as fogging or other interventions that can reduce the mosquito numbers," he said.

Stormwater and drainage rules are also designed to prevent water stagnating, which allows mosquitoes to breed.

Could malaria come back?

Given the anopheles mosquitoes do live on Darwin's outskirts and elsewhere in Australia, in theory malaria could return.

There has been speculation that climate change could also increase the numbers of mosquitoes, and make malaria harder to control.

Professor Price said steps were being taken to ensure malaria did not re-establish itself in Australia, and if people did enter the country with malaria that it was diagnosed quickly.

"We keep them in hospital usually for about one or two days if they are not too sick," he said.

"We treat them with very effective drugs and we prevent them from being able to transmit to mosquitoes.

"We also have a very strong Centre for Disease Control and they contact the person and also go and see where they live, and the entomology department goes out to that house and makes sure that there are no anopheles in that area.

"So that we don't let them go back out with disease where they might reintroduce malaria."