Not quite Monday Micro – which nasty microbes would you rank in the top 10?

By Siouxsie Wiles 01/08/2014 1


On Monday I was asked to go on the radio and comment on an article that appeared in the NZ Herald (syndicated from The Independent) entitled “What’s the world’s biggest health risk?”.

The article lists an infectious diseases ‘Top Ten’ which looks like this:

1. Ebola – as of 23 July 2014, there have been 1,201 cases, including 672 deaths in the most recent outbreak.

2. Plague – in the past week there were four cases of plague in Colorado, and in China, a city was placed in lock down after a man died of in Yumen.

3. MERS – Globally, 837 laboratory-confirmed cases of MERS infection, including at least 291 related deaths, have been reported since the virus appeared in 2012.

4. H7N9/avian flu – since it emerged in China in 2013 there have been over 450 cases, including 165 deaths.

5. HIV/AIDS – over 35 million people infected worldwide, with approximately 1.5 million deaths per year.

6. Polio – virus endemic in Afghanistan, Nigeria and Pakistan.

7. Viral hepatitis – Monday 28 July was World Hepatitis Day. Viral hepatitis is caused by a number of different viruses and results in liver disease which kills close to 1.4 million people every year

8. Measles – will forever be associated with the MMR hoax and disgraced former doctor Andrew Wakefield. Preventable by vaccine, there are estimated to be 120,000 deaths from measles every year. Between December 2013 and 22 July 2014, there were cases of 263 measles reported in New Zealand.

9. Meningitis – meningitis caused by the bacterium Neisseria meningitidis is a big problem in sub-Saharan Africa with over 88,000 suspected cases, including 5352 deaths reported during the 2009 epidemic season.

10. Cholera – a diarrhoeal infection caused by the bacterium Vibrio cholerae. Every year, there are an estimated 3–5 million cholera cases resulting in over 100,000 deaths.

I found the list absolutely fascinating. I doubt very much that Ebola would have featured anywhere in the top ten had this list been drawn up even just a couple of months ago. What a difference a single outbreak can make! And where are malaria and tuberculosis?!

What’s more interesting about the list though is that the diseases listed can be divided into several different categories which highlight the difficulties we face fighting infection.

1. Diseases preventable (or partially preventable) by vaccination – e.g. measles, polio, cholera and (some causes of) meningitis
Some of these diseases, such as polio and measles, are making a comeback because of issues getting people vaccinated. This can be because of spreading misinformation about the safety of vaccination, or due to breakdowns in vaccination programmes because of conflict.

2. Diseases that are treatable but treatment not easily available or is rejected – e.g. HIV
In the space of 30 years, HIV has changed from a death sentence to a chronic disease, provided those infected have access to antiretroviral drugs. The issue of course, is that those countries in which HIV is endemic, do not have ready access to all the drugs they need. This is not helped by ridiculous myths, such as HIV can be cured by having sex with a virgin. Not the best belief to stop the spread of a sexually transmitted disease!

3. Preventable/treatable diseases which reappear due to unsanitary conditions – e.g. cholera
Conflict and natural disasters that lead to masses of people living in unsanitary conditions are a recipe for disease.

4. Diseases in which human infection is incidental – e.g. plague, Ebola
The microbes responsible for Ebola and plague have other hosts in their natural habitat and infection of humans is almost accidental, or a case of wrong place, wrong time. In the case of Ebola, outbreaks are thought to start when someone eats a wild animal (so-called bushmeat) that has died from Ebola. This is pretty disastrous for humans, with no vaccine or treatment available. In the case of plague, the bacterium responsible (Yersinia pestis) still lives in many countries, spread among rodents and other animals by fleas. Humans become accidentally infected when bitten by a flea after coming in to contact with an infected animal. Y. pestis is treatable with antibiotics.

5. New infections caused by an increasing human population and habitat encroachment/destruction – e.g. possibly MERS, avian flu
As our population increases and we encroach on the habitats of other animals, we bring people and their livestock into close contact with species it would be best not to. One outcome of this seems to be increasing our exposure to microbes we have never encountered before or the emergence of new microbes which have modified themselves after passing through several different hosts. Bats seem to be one of the biggest sources of novel viruses.

Interestingly, the list doesn’t include two other big drivers of infectious disease in humans:

6. The increasing resistance of bacteria to antibiotics, which has given rise to untreatable strains of the bacteria responsible for diseases like tuberculosis.

7. Climate change increasing the habitat range of insects which carry the microbes responsible for diseases like malaria and dengue fever.

It’s pretty bleak isn’t it?!

You can listen to my chat with Mike Hosking here.


One Response to “Not quite Monday Micro – which nasty microbes would you rank in the top 10?”

  • Great article Siouxsie. As you say, if this list were made a couple of months ago it seems unlikely Ebola would feature on it, making it sound more like a list of the current “top 10 scariest sounding infectious diseases” than anything else.

    Looking at the WHO’s FAQ page on infectious diseases (http://www.who.int/topics/infectious_diseases/qa/en/), just because it’s the first other place I thought to look, it seems when that list was compiled the scariest sounding diseases would have included:
    – Malaria
    – Measles
    – TB
    – Hepatitis B
    – Polio
    – Dengue
    – Avian influenza
    – Yellow fever

    When it comes to making a more rigorous and useful list, I’d expect it would be based on qualitative data. But which measurement(s)? Ebola has a high fatality rate, which makes it scary, but it also a relatively low prevalence. If a given person is going to die of an infectious disease, it’s unlikely that disease will be ebola.

    Perhaps the most useful list, although still a bit subjective, would be the infectious diseases for which we could prevent the most deaths. Ordering by this, I’d expect diseases in your first 3 categories would be at the top, as these seem to be the ones about which we could make the biggest difference without needing to develop new technologies.

    That said, increasing resistance to bacterial antibiotics means we will *have* to develop new technologies. I’m glad we (speaking of humanity as a whole) don’t just have to choose just one of these categories to focus on!

    Given that the technology largely exists to make a difference with diseases in your 1st 3 categories it feels to me like more of an engineering/logistics issue, whereas the category for which new scientific research might be able to make the biggest difference would be category 6?