Monkeypox

In view of the concerns about the spread of this virus, I'm reproducing the text of a recent blog on the subject. Hopefully this will help put the current UK outbreak of this well-established virus in context. As always, comments are welcome via the contacts page. I will endeavour to keep this page updated as the epidemic progresses....

Monkeypox – How dangerous is it, and what should we do about it ?

There has been much speculation in the media recently about the current Monkeypox outbreak – not surprisingly perhaps, in view of our recent experience with Covid…

Some pundits are even predicting that this could be the fore-runner of the next pandemic  - how realistic a view is this, and should we be worried ?

Looking at the evidence objectively, at present the answer to both questions is: Not very….

First, let’s look at the nature of the virus that causes the illness, and its origins and recent epidemiology.

The causative agent is a close relative of the much more notorious smallpox virus, which caused widespread suffering and countless deaths throughout the world before its eradication in 1980 (1). It is an enveloped double-stranded DNA virus that belongs to the Orthopoxvirus genus of the Poxviridae family. Like the Covid virus, and probably most other existing human viruses, it origin is zoonotic  i.e. it was originally transmitted from animals to humans. 

Animal species so far identified as Monkeypox hosts are varied and include rope squirrels, tree squirrels, Gambian pouched rats, dormice, non-human primates and other species; there have been many outbreaks in the human population since the original one in 1970, but the exact origin of each specific outbreak is often difficult to determine. The disease was first identified in humans in the Democratic Republic of the Congo in a region where smallpox had been eliminated in 1968, and it is not thought to have originated from smallpox directly.

Monkeypox is a disease of global public health importance as it not only affects countries in west and central Africa, but the rest of the world. In 2003, the first Monkeypox outbreak outside of Africa was in the United States of America and was linked to contact with infected pet prairie dogs. These pets had been housed with infected Gambian pouched rats and dormice that had been imported into the country from Ghana.

More recently, outbreaks of Monkeypox have been reported in travellers from Nigeria to Israel in September 2018, to the United Kingdom in September 2018, December 2019, May 2021 and May 2022, to Singapore in May 2019, and to the United States of America in July and November 2021. In May 2022, multiple cases of Monkeypox were identified in several  countries where the virus was non-endemic. This was atypical for the virus, whose spread is normally associated with travel between continents. Studies are currently underway to further understand the epidemiology, sources of infection, and transmission patterns. Although case numbers are relatively small to date, it is now evident that the disease is spreading independently of foreign travel.

Human-to-human transmission can result from close contact with respiratory secretions, skin lesions of an infected person or recently contaminated objects. Transmission via droplet respiratory particles usually requires prolonged face-to-face contact, which puts health workers, household members and other close contacts of active cases at greater risk. The incidence of human transmission has risen in recent years - this may reflect declining immunity in all communities due to cessation of smallpox vaccination. Close physical contact is a well-known risk factor for transmission. Although the disease isn’t exclusively a sexually-transmitted disease (STD), so far the incidence in homosexual males has been higher than in the general population, and heterosexual transmission may also turn out to be a key route of spread as the epidemic progresses.

How does the disease progress and how serious is it ?

The incubation period (interval from infection to onset of symptoms) of Monkeypox is usually from 6 to 13 days but can range from 5 to 21 days. The virus causes generally relatively mild disease in otherwise healthy individuals, with initial symptoms of fever and lymph node swelling giving way to rashes and skin eruptions, primarily on the face and extremities. The disease usually self-limiting without anti-viral treatment, with the symptoms lasting from 2 to 4 weeks.

Severe cases occur more commonly among children and are related to the extent of virus exposure, patient health status and nature of complications. Underlying immune deficiencies may lead to worse outcomes. Although vaccination against smallpox was protective in the past, those younger than 40 to 50 years of age now (depending on the country) may be more susceptible to Monkeypox due to cessation of smallpox vaccination campaigns globally after eradication of the disease.  Complications of Monkeypox can include secondary infections, bronchopneumonia, sepsis, encephalitis, and infection of the cornea with ensuing loss of vision. The extent to which asymptomatic infection may occur is so far unknown.

The case fatality ratio of Monkeypox has ranged historically from 0 to 11 % in the general population and has been higher among young children. In recent times, the case fatality ratio has been around 3–6%. It should be noted that this is significantly higher than Covid (ca 1-2% in the general population, much lower in the fully-vaccinated).

How likely is Monkeypox to progress to a full-blown pandemic ? Although, as already discussed, the fatality ratio is worryingly high as compared with Covid, salvation may lie in the nature of the virus and its relatively low infectivity compared with seasonal respiratory viruses like SARS-CoV-2 and influenza. Thanks to the Smallpox eradication programme, we also have approved smallpox vaccines ‘on the shelf’ which we know are effective (against the current Monkeypox ‘variants’ at least). Spread should also be restricted by pre-induced immunity in the over-40s, many of whom will have been vaccinated against smallpox as children. We also know a lot more about the nature of the virus and ways to manage it than we did about Covid at the start of the pandemic in early 2020.

The main concern is whether zoonotic transmission and the attendant risk of viral mutation will again raise its ugly head and create another smallpox-like ‘monster’. Most Monkeypox outbreaks in recent years have originated from animal to human transmission. Fortunately double-stranded DNA viruses are far less subject to rapid variant evolution of the sort we saw with SARS-CoV-2. This is because the DNA replication mechanism is much more efficient at correcting errors than for the RNA viruses, so the spontaneous mutation rates which normally drive viral evolution are much lower. 

Set against that, however, is the heightened risk of transmission of the virus to and from pet animal species – the UK, in common with many countries in the developed world, harbours literally millions of pet cats and dogs, and these could become a significant problem if cat/dog to human transmission becomes prevalent. This is due to the close contact we naturally have with these animals as pets, and hence the sheer volume of potential cross-species transmission events.

So far, mercifully, this issue does not seem to have arisen in UK, but we should not become complacent about the risk, given the implication of pet species in the 2003 USA outbreak. We should remember that viruses are highly adaptable and have a habit of taking advantage of the propensities and behavioural 'weaknesses' of their chosen hosts – in particular their habitual close contacts with animal species, and the current obsession with personal air travel. Their potential to do us harm should never be under-estimated.

What precautions should we take at this stage ?

Much epidemiological research is ongoing regarding the origins of the virus and methods of control. We need urgently to identify what factors are responsible for the switch to more frequent human to human transmission and counter them before the virus gets a chance to spread out of control. Existing smallpox vaccines are being investigated for their efficacy against Monkeypox, and new vaccines specific to it are being developed. 

Individuals showing symptoms themselves or who have had recent contacts with confirmed cases, are already recommended by the health authorities to self-isolate for at least 21 days. Pet owners should keep a close eye on their pets’ health and report any symptoms which might indicate pox infection. If the epidemic progresses, it may become necessary to classify the disease as legally notifiable, and this should apply both to humans and to pet species to minimise further zoonotic transmission.

Only time will tell how well we are able to control this outbreak.

Hopefully it will turn out to be an epidemiological ‘damp squib’ and fizzle out in due course….

Viv

References

       1) WHO Newsroom Article (19th May 2022): https://www.who.int/news-room/fact-sheets/detail/monkeypox

Update 8.6.22: It has just been announced that the UK authorities have classified Monkeypox as a notifiable disease, as I suggested in yesterday's blog. This demonstrates significant concern that the epidemic could spread out of control. There has been no mention as yet of a requirement for additional surveillance of pet species. 

Update 2.10.22: Looks like we may be winning the fight against this particular epidemic. Case numbers have fallen steadily since the summer peak, due in part by all accounts to changes in behaviour, particularly in the gay and bisexual male community which are the group most prone to transmission. We must however remain vigilant to ensure things don't flare up again, and health authorities need to ensure adequate supplies of vaccine remain available. 

Update 13.8.23: The picture over the last 10 months appears to confirm that case numbers, although still increasing, have slowed to a trickle, particularly during the summer months. A summary of the epidemiological evidence to 31.7.23 is provided here. The epidemic is clearly well-controlled at present, presumably due to precautions introduced in 2022, but we should remain vigilant, particularly as the season advances.

See this link for more details.

Version Date: 13.8.23