so what is this new plague going around?
Why am I hearing about monkeypox?
Because the WHO is reporting 92 new cases across 12 countries between May 13th and May 21.
What is monkeypox?
It’s a disease caused by the monkeypox virus, a double-stranded DNA virus in the same family as cowpox, chicken pox, and smallpox. Monkeypox is carried by monkeys and other animals, and is endemic in Western and Central Africa.
What are the symptoms of monkeypox?
Fever, chills, headache muscle pains, swollen lymph nodes, and a bumpy rash are the typical symptoms of monkeypox.
During a 2003 outbreak of monkeypox in the US spread by pet prairie dogs, 9 out of 34 (26%) were ill enough to be admitted to the ICU, mostly children.
Some reported complications include vomiting and diarrhea, conjunctivitis and corneal scarring, sepsis, encephalitis, and bronchopneumonia.
How does monkeypox spread?
Consumption of bush meat.
A patient in 2018 who was diagnosed with monkeypox after returning to the UK from a family event in Nigeria reported “contact with an individual with a monkeypox-like rash” and “consumption of bush meat.”
“With few exceptions, outbreaks of monkeypox have consistently occurred in populations living in rural areas, in small villages (less than 1000 people) adjacent to or within humid evergreen tropical forests – at the so-called human-animal interface.” (Source)
A patient diagnosed with monkeypox in Singapore in 2019 reported consuming bushmeat during his recent trip to Nigeria.
Contact with rodents.
A patient diagnosed in Israel in 2018 had “disposed of two rodent carcasses” on his last trip to Nigeria.
During the 2003 US outbreak of monkeypox spread by prairie dogs, touching or handling the bedding of sick animals was associated with infection, but coming within 6 feet of the animals without touching them was not.
Living with infected people.
In the 2017-18 Nigerian outbreak, 30% of cases had a close contact with another case; they shared a household with an infected person, were inmates in the same prison as an infected person, or were a healthcare worker caring for an infected person.
“Among household contacts, those who had direct physical contact with the infected person, by playing with the patient or sharing the same bed, and those who provided nursing care had an increased risk of subsequent attack” in the 1981-1986 outbreak in Zaire.
Social contact with infected people.
A man who traveled from Nigeria to Dallas, Texas in July 2021 was diagnosed with monkeypox and reported attending a “large social gathering” in Nigeria.
A man who traveled from Nigeria to Maryland in 2021 and was diagnosed with monkeypox reported “visiting relatives” but stayed in hotels and did not have contact with animals or animal carcasses.
Sexual contact with infected people.
The 2022 cases of monkeypox outside Africa are “occurring within sexual networks”, according to the CDC’s Inger Damon. BMJ reports, “the latest cases have mainly been among men who have sex with men.”
Out of 246 confirmed or suspected cases in the current outbreak (h/t Michael Story) the vast majority are male, and 33 were either MSM or had “suspected sexual transmission” or were diagnosed at an STD clinic.
Out of the 246 confirmed or suspected cases in the current outbreak, 15 could trace the source of infection to a sauna in Spain.
Infected clothing and bedding.
In 2018, a UK healthcare worker caught monkeypox from a monkeypox patient who had recently returned from Nigeria. The healthcare worker had touched the patient’s bedding and clothing, after the patient had several lesions but before the patient was diagnosed with monkeypox.
How contagious is monkeypox?
The only study to calculate an R_0 looked at outbreak data from 1980-1984, and calculates an R_0 of 1.0.
This is fairly low compared to other viruses; for instance, seasonal influenza variants have an R_0 of 1.3, and COVID-19 has an R_0 of 2.9-10, depending on strain.
Preliminary sequencing data suggests that the current outbreak is genetically similar to the cases observed in 2018, and belongs to the West African clade. We’re not seeing evidence so far that this outbreak has mutated to become more contagious than past outbreaks, though it could still be possible.
We don’t have a measured R_0 yet for the current outbreak.
Some data suggests that most infections come from direct contact with infected people or animals, or their belongings.
However, aerosol transmission is definitely physically possible. If you aerosolize the virus, macaque monkeys can get infected.
Monkeypox is not exclusively sexually transmitted or confined to men who have sex with men. The larger African outbreaks have similar numbers of male and female cases, significant transmission within households, and higher risk among children than adults.
How deadly is monkeypox?
The milder West African strain, which is the only strain found in the current outbreak, has 6/285 = 2.1% reported deaths to date, all from a 2017-18 outbreak in Nigeria. 4 out of the 6 deaths were in people already immunocompromised due to AIDS.
Vaccination against monkeypox?
Data from the 1980-1984 outbreak in Zaire indicated that the smallpox vaccine was 85% effective against monkeypox.
What does that really mean?
If you shared a household with a monkeypox patient, and you were unvaccinated against smallpox, you had an 11% chance of catching monkeypox; if you were vaccinated against smallpox, you had a 1.7% chance of catching monkeypox.
Note that this is the Central African strain; it may not translate to the West African strain in the current outbreak.
Vaccination against smallpox in the US ended in 1972 because the disease had become so rare. The US has a Strategic National Stockpile of smallpox vaccine, according to the CDC, and has purchased millions of new doses of the Jynneos vaccine, but there are no immediate plans to deploy it.
Governments around the world should:
Record suspected cases of monkeypox, test them with PCR and record their contacts.
Order enough smallpox/monkeypox vaccines for the whole population if necessary.
Approve and purchase PCR tests for monkeypox. (Currently I don’t see any commercial manufacturers, but some research institutes like the Institute for Tropical Medicine in Antwerp conduct PCR testing.)