Monkeypox – a zoonotic disease

‘If we have allowed monkeypox to become an endemic virus in the U.S. … it will be among the most unfortunate public health failures in recent times.’

Declan Garvey and Esther Eaton, The Dispatch
BROOKLYN, NYC, US, October 1 2013: Street art in Brooklyn. Old paper billboard saying welcome to New York, with scary drawings of mouse, roaches and pigeon. New York, US.

As monkeypox continues to spread both within and between countries, it is worth reminding that it is a zoonotic disease.

In parts of Africa, where monkeypox outbreaks are much more frequent, the virus appears to persist in other mammal populations. Although it was first discovered in a monkey (hence the name), rodents are thought to be a more likely reservoir.

Monkeypox is not as infectious as COVID-19 and not as dangerous as smallpox. It currently spreads largely in an MSM community (men having Sex with Men), but it is properly not a Sexually Transmitted Disease (STD).

Rather, it spreads through close personal contact, mainly through skin contact. Hence, there have been cases among women and children.

It is disappointing that we did not manage to stop it early. Unlike COVID-19 virus (SARS-CoV-2), monkeypox is not a new disease, it does not spread very fast and easily, we do have relatively safe and sterilising vaccines, and we know how to use them.

Monkeypox has been spreading in a relatively limited network with only sporadic breakthroughs to the general population. Although the long incubation period makes contact tracing somewhat problematic, it would not have been difficult to implement “ring” vaccination.

Once monkeypox becomes established in the ubiquitous rodent population, it will be almost impossible to eradicate. The risk to humans might not be very high,

Is there still a chance to stop it? Yes, but (as with COVID-19) it needs a swift action built on trust with the affected community. We must make sure that we work with the MSM community and not against them.

We must not end up stigmatising the infection but rather encouraging those most at risk to take appropriate actions.

COVID-19: The new summer wave

Tourist crisis in the summers of 2020-22

Back in April 2022, I was talking to Mark McLaughlin @mark_mclaughlin about the future developments for the #COVID-19 epidemic in the UK. I made a prediction:

Coronavirus hospital admissions have dropped sharply but waning immunity means that Scotland faces a resurgence this summer, an epidemiologist has warned.

Covid in Scotland: Hospital admissions fall ‘but cases could surge again in summer’ | Scotland | The Times

I really hate to be a bearer of bad news but I am afraid my prophecy has turned true. The UK in general, and Scotland in particular have followed many other countries into a new coronavirus wave.

What I perhaps did not fully appreciate at that time was the rise of new variants, but I think they simply added to the general picture. I suspect the summer wave would have come anyway, fueled by immunity waning. And, remember that we have practically no restrictions.

What does it tell us for the future? The virus itself is now basically “endemic” in the sense that it does not disappear – or even go significantly down – between peaks. We actually entered this “endemic” state in May-June 2021, as the graph above (from the ZOE reporting) shows.

While the vaccines (and immunity from past infections) help in reducing hospitalisation and deaths, the virus is simply refusing to go away.

COVID-19 reported death rates per million, for 5 waves, centred at the peak. Note logarithmic vertical scale.

However, not only has the #COVID-19 been “normalised”, but I think the risk of getting (repeatedly) ill with possible complications has now become “priced in” by the general population.

In many “usual” everyday activities we take risks. Some people, who for example do extreme sports, take very serious risks but even crossing the road, or jogging in the park, might be (and often is) dangerous.

But we accept these risks – consciously, or subconsciously, or because others do it.

Of course, with infectious diseases, there is a problem that my actions – of not masking, not getting vaccinated, or not staying at home despite clear #COVID-19 symptoms – often have a severe impact on others. But, this is a topic for another post…

Monkeypox update: Why does it continue to spread?

The #Monkeypox epidemic continues to expand both in the UK and globally. It has now been detected in 82 countries/regions, with nearly 6,200 (confirmed) cases reported.

OWD hMPXV confirmed cases

On my blog, I have introduced a very simple model which I used to explore the future scenarios of the epidemic. I have been playing a bit more with the model, to see whether it is still compatible with the data as they are released by UKHSA and OWD.

Now, I am very aware that there are many better-suited experts to analyse the current outbreak and much better models to predict its course. But, what follows is a brief summary of how I see the current epidemic.

OWD hMPXV confirmed cases, logarithmic scale

A quick look at a log scale plot shows that the epidemic clearly has had two phases: rapid initial growth followed by a slow increase. The initial increase is most likely influenced by catching up on reported cases.

But, a very detailed study of the cohort of cases done by UKHSA also shows similar behaviour in the data of cases by symptoms.

Note the log vertical scale; black line is my Scenario 3.

More importantly, the outbreak in April and May could conceivably be approximated by an exponential function – a straight line on the logarithmic plot – a tell-tale sign of a SIR model.

However, the overall picture is more of a curve than a straight line or a piece-wise linear behaviour – which would correspond to two phases.

I explain the difference between black, red and blue data points elsewhere on my blog.

What modification of a standard SIR model can describe such a behaviour? Under Scenario 3, I suggested a model in which the disease spreads initially in a small network, mostly consisting of Men who have Sex with Men (MSM).

Although my model is too simple to draw firm conclusions, I suggest that this initial size for the UK to be of an order of 1,300.

But the total number of reported, confirmed, cases has now exceeded 1,000 and the epidemic is still going strong. I believe that what we now see is the virus “leaking” outside the original network, perhaps into a wider MSM network, perhaps into the general population.

In my model, this is captured by a SIR model, with an initial population of 1,300, but also with a process that brings in new susceptible individuals. Formally, this is a SIRS model in which immune individuals (as well as infected ones) are replaced with susceptible ones.

I am not suggesting loss of immunity, or a birth/death process. Rather, I am thinking that those who already had the disease are becoming more cautious and essentially “drop out” of the contact network.

But then those who are still within the network initiate close contacts with others, thus effectively increasing the susceptible numbers by drawing people from the “reserve” pool. How does this impact the long-term dynamics?

If this process continues for some time, the epidemic will slow down a bit in the next couple of weeks, but would then continue to spread at a slower rate. In a sense, #Monkeypox will become endemic in the UK.

Of course, at some point, the epidemic will reach the end of the “reserve” pool, or will be stopped by a combination of NPIs and targeted vaccination. So, in the really long term, I am optimistic about the outcome.

But in the short term, we are in for a long haul.