Online only
In the first of a three-part online only feature, Dionne Christian looks at the infectious illnesses we’ll continue to read more about as the year progresses. Tomorrow: Climate Change and mental health; Thursday: Risk factors for chronic illness.
Since the start of the Covid pandemic in 2019-20, we’re all more aware of “communicable diseases” – the infectious illnesses that spread from person to person.
Epidemiologist professor Michael Baker says they will always make the news, partly because of the Covid effect – we now realise what far-reaching and life-changing impacts these invisible (at least to the naked eye) agents can have – but also because they are everchanging.
“Non-communicable diseases [things like heart disease, stroke, cancer and diabetes] are the major threats to health in terms of years of life lost, but they are often measured by one data point per year. With infectious diseases, you have to look sometimes day by day and certainly month by month.”
For example, a whooping cough (pertussis) epidemic was declared in New Zealand in November 2024 after 263 cases were reported in four weeks from October 19-November 15, the highest number over a four-week period for the 2024 year to date. Since then, that number has risen to around 2213 cases and, sadly, a baby died during the Christmas break. A highly contagious respiratory infection that can cause serious harm to babies, whooping cough killed three infants in 2023.
Baker says immunisation rates are down, which goes part way to explaining this latest epidemic. Falling immunisation is also making a measles epidemic more likely in New Zealand. About 77% of the population is vaccinated against measles, but to provide effective herd immunity, close to 95% of the population needs to be fully immunised, says Baker.
“It’s 77% coverage overall, but for Māori it’s only 63%, for Pasifika it’s 72%. All those levels are far too low to stop a national measles epidemic. Measles is highly infectious; an infected person might infect 12-15 other people in an unvaccinated population.”
The World Health Organisation has warned that “measles in back”, with the British Medical Journal noting that cases are at a 25 year high in Europe, while North America has joined Afghanistan in dealing with major outbreaks. According to the BMJ, measles kills a child everyday in Afghanistan while in the United States, two people have died including a child with no underlying medical conditions.
Baker is less concerned about Human metapneumovirus (HMPV), which made headlines earlier this year as cases appeared to surge in China. He says HMPV, which causes respiratory infections, has been known for several decades and better testing means more cases are being detected.
“Any news containing the words ‘virus’ and ‘China’ tends to set off alarm bells now,” says Baker. “That vigilance is, in some ways, a good thing but equally we have to point out when something is not a major concern.
“In New Zealand, we’ve been testing for HMPV for about a decade and we get around 500 confirmed cases a year. That’s just a small sample of those with respiratory symptoms. There’s probably a lot more going undetected.
“But for immune-compromised people and very young children and elderly people, any of these viruses can be lethal.”
Covid remains our biggest infectious disease killer, current claiming around 700 lives and resulting in about 10,000 hospitalisations each year. More details can be found here.
“People will die from diseases that are recorded as heart attacks and strokes, but Covid may be the underlying cause because of the damage it does to blood vessels and multiple organs,” says Baker. “Those deaths aren’t being counted as Covid deaths because affected people often die suddenly in the community from a heart attack or another circulatory disease without being tested for Covid. But if we didn’t have Covid-19, we’d have a lot fewer deaths.”
Baker says Covid is yet to settle into any sort of seasonal pattern, nor do troughs and peaks occur with any sort of pattern.
“But it’s still very much with us.”
In terms of research and expanding our knowledge about communicable diseases, scientists are increasingly finding that the boundaries between these and non-communicable disease aren’t as clear as previously thought, says the University of Auckland’s professor Chris Bullen, a GP and primary health practitioner.
We know about things like liver cancers being caused by hepatitis B and C viruses and there is science that looks at the relationship between, say, cardiovascular disease and early infectious disease, so those hard silos between communicable and non-communicable aren’t as watertight as we thought. This will make preventive treatment and strategies more important than ever.
But there are successes to recognise and celebrate. Human papillomavirus (HPV) is the cause of nearly all cervical cancers, but rates have dropped significantly since the introduction of an HPV vaccine in New Zealand in 2008.
Bird flu
Two strains of bird flu – avian flu – have made recent news. The first is H5N1 (HPAI), widespread in and responsible for the mass deaths of wild birds around the world. In her article Spreading death: The devastating impact of avian flu on a remote island” science journalist Kerrie Waterworth wrote of the impact H5N1 has had on birds and mammals on the geographically isolated South Georgia Island.
Globally, H5N1 has caused outbreaks on poultry and dairy farms, and a small number of those who work directly with hens and cows have been infected. The US recorded its first death in January, a person from the southern state of Louisiana who was aged over 65, had underlying health conditions and worked closely with poultry. So far, H5N1 has not spread person-to-person and while most cases have been treatable, it has a high mortality rate.
“It’s very widespread across the United States,” says Baker, “and it is starting to have an impact on things like the supply of eggs and unpasteurised milk there.”
New Zealand has so far avoided H5N1; the strain of avian flu detected on a commercial poultry farm at Hillgrove late last year was H7N6. It led to a strict biosecurity lockdown and the culling of some 200,000 birds.
Biosecurity New Zealand deputy director-general Stuart Anderson said it was not a “wildlife-adapted strain like H5N1, so we believe it is unlikely to be transmitted to mammals.”
Nevertheless, it was the country’s first case of HPAI - High Pathogenicity Avian Influenza – and officials will be staying vigilant about it.
This year we’ll also read more about why, in some cases, it’s getting trickier to treat communicable diseases. Partly this is because of antimicrobial resistance, which is now a major growing global health threat after years of warnings about drugs, like antibiotics, becoming less effective.
In the US alone, four people now die hourly from a bacterial infection that no longer responds to any antibiotic drug. Worldwide, 1.27 million deaths were attributed to resistant microbial pathogens in 2019.
As infectious diseases become more common and get harder to treat, there will be increased illness, death and higher healthcare costs.
