Measles explained: Signs, symptoms and the outbreak threat.

By Loretta Florance.

The measles is an infectious disease caused by the morbillivirus.

It once infected hundreds of thousands of Australian kids, but was declared eradicated in Australia in 2014.

But every once in a while, a new case of the measles is brought in from overseas, prompting state health departments to issue a warning for people to look out for signs and symptoms.

What are the symptoms?

Symptoms can take 10 to 14 days to develop after infection.

The most distinctive is the measles rash.

“The classic rash is quite an obvious lumpy red rash, that starts on the head but progresses all over the body,” said Robert Booy, from the National Centre for Immunisations and Research Surveillance.

Otherwise, expect the same sorts of symptoms you’d have when you catch a really bad cold.

That doesn’t sound so bad…

If it’s a mild to moderate case, you’re in good health, you keep up your fluids and treat the fever, it’s usually not so bad — but there are a couple of catches.

Firstly, it knocks your immune system around and can leave you susceptible to other infectious diseases for about three years.

Secondly, many years later, if you’re very unlucky, you might develop subacute sclerosing panencephalitis (SSPE), a progressive and disabling brain disorder, which will eventually kill you.

“Unfortunately SSPE may well manifest itself many years, sometimes decades, after the actual initial measles infection,” said Angela Newbound, the co-convenor for the immunisation special interest group for the Public Health Association of Australia.

“SSPE is a life-threatening condition, it is very rare, but it is a possibility for anybody that’s had measles disease.”

If you have a bad case of the measles, complications can include ear, eye, brain and lung infections, which can be life-threatening.

“Measles encephalitis would probably be one of the most serious complications, so you get inflammation and swelling of the brain, so that can lead to very long-term disabilities,” Ms Newbound said.

Measles encephalitis itself can also kill you.

So, back in the day, when major outbreaks of measles happened every few years, it was very grim.

“Before we had immunisation, we would have major outbreaks of measles every two to three years, in which many thousands of children would be affected,” Professor Booy said.

“[Around] one in 1000 die, so if you had 100,000 cases you could have up to 100 deaths.

“So there were certainly scores of deaths in the pre-immunisation era every time we had a major outbreak, and many hospitalisations as well.”

But that’s all in the past, right?

In many places around the world it’s not, but Australia has had a routine publicly-funded measles, mumps and rubella vaccination program for almost 50 years. It has been extremely effective.

“The program usually only entailed one dose of vaccine, but in recent years we actually offer two doses of measles vaccination because it maximises the chance of getting a very high proportion of children immune,” Professor Booy said.

The first dose is administered to babies around their first birthday and a second at around 18 months.

“One dose might get 90 per cent of people immune, but the second dose ensures that you get 95 per cent or more of children immune,” Professor Booy said.

In 2014, the World Health Organisation announced that the disease was officially eradicated in Australia.

So why the outbreak warnings?

While there is no longer a local strain of measles, Australia still sees the occasional case brought in from overseas, which usually leads to state health departments issuing a warning of a potential outbreak.

The virus that causes measles lives in mucus or saliva droplets and is most commonly spread when someone inhales an infected person’s cough or sneeze droplets, or comes into contact with contaminated surfaces.

If you have it, you’ll be contagious for about eight days.

According to the Victorian health department, it’s estimated that you’ll infect nine out of 10 unimmunised or previously uninfected people you come into contact with.

Even if almost everyone has been vaccinated, there is a very small proportion of the immunised population for whom the shots will not be effective.

Then there are those unable to be vaccinated, including people:

• with HIV or AIDs, and other immune deficiency conditions
• receiving immunosuppressive treatments such as chemotherapy or radiotherapy
• taking certain medications, such as corticosteroids
• with chronic lung diseases

Babies under one year old are also not vaccinated. If the baby’s mother has immunity, the baby will have some maternal antibodies until they’re about 10 months old, but the antibodies might not be strong enough to ward off the infection.

Medical practitioners have to wait until the maternal antibodies have waned before they can vaccinate infants, to ensure the infant’s antibodies don’t compete with the maternal ones. So until they have their shots, they’re vulnerable.

Even with very high vaccination rates, there are enough vulnerable people for the infection to spread locally.

“Even if you have 95 per cent of the population vaccinated with two doses, that means that 90 per cent are immune, because 95 per cent of 95 per cent is 90,” Professor Booy said.

“So there’s always 10 per cent who are susceptible, and if they are congregated in a particular suburb, or church or mosque, then they can not only catch the infection but spread it to each other.”

What would it take for measles to come back?

Immunisation rates have to be at 95 per cent or more to keep the disease under control in the population, experts believe.

Right now, we’re almost achieving that rate, at around 92 to 94 per cent.

“We’re doing very, very well, however we do not want to underestimate the return of this disease in Australia if our vaccination rates fall,” Ms Newbound said.

Professor Booy said if the proportion of vaccinated Australians dropped to 90 per cent, we would start to get small outbreaks.

“If it went under 70 to 80 per cent, you’d get bigger outbreaks and it would be more widely spread across the country,” he said.

Ms Newbound said if enough parents chose not to vaccinate their children because they had faith in their immune system, the disease could make a comeback.

“Unfortunately in our community not every child is healthy, so their child may not end up with a serious complication, and may not end up in hospital,” she said.

“But the issue that we actually have is that these children are infectious before the parent even realises that they’re sick, let alone sick with measles, so they have the ability to then transmit this disease to other members of the community.

“Some of those members of the community may not be in good health, and they may be too young to be vaccinated, and those maternity antibodies haven’t been strong enough to protect the baby from measles disease.”

This post originally appeared on ABC News.