Qué es la viruela del mono y otras preguntas frecuentes sobre este virus zoonótico

What is Monkeypox and Other Frequently Asked Questions about this Zoonotic Virus

18.5.2022
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Photo: CDC's Public Health Image Library

On May 7, the UK authorities confirmed a case of monkeypox in a person who had travelled to Nigeria. As of the moment of writing these lines, there are nine confirmed cases in the UK, five confirmed cases and at least 20 suspected cases in Portugal, 21 confirmed cases and near 20 suspected cases in Spain, as well as a number of confirmed and suspected cases in other countries such as Canada, United States, Sweden, Belgium, Italy or Australia, among others. In this article we provide basic information on this zoonotic viral disease.

What is monkeypox?

Monkeypox is an emerging zoonotic disease, meaning that it can spread from animals to humans. It is caused by a virus of the same name that belongs to the genus Orthopoxvirus, the same as smallpox, vaccinia (the virus used as a smallpox vaccine) or cowpox.

It is known as monkeypox because it was discovered in 1958 in colonies of monkeys used for research purposes. The animal reservoir of the virus is unknown, although it is known that rodents and primates in Africa can harbour and transmit the virus.

Since the first human case was identified in 1970 in the Democratic Republic of Congo , cases have been reported sporadically in several countries in Central and West Africa, and occasional imported cases have been recorded in countries such as the United States, Israel and the United Kingdom.

What are the symptoms of monkeypox?

The initial symptoms of monkeypox usually include fever, chills, muscle pain, back pain, headache, fatigue or swollen lymph nodes. After a period of one to five days, it is usual to develop a rash or lesions on the mucous membranes of the mouth, followed by rashes that may appear on the face and spread to other areas of the body, affecting the palms and soles. The rashes go through different stages until they develop into pus-containing pustules and eventually crust over and fall off after 14 days.

What is the fatality rate of monkeypox?

Generally, monkeypox is a self-limiting disease and most people who catch the disease make a full recovery. Children and immunocompromised people are more vulnerable than adults with healthy immune systems.

There are two known clades of the virus: the West African clade and the Congo Basin clade. The WHO puts the fatality rate for the West African clade at around 1% and warns that the Congo Basin clade may have a fatality rate of 10%.

The current outbreak seems to be associated to the West Africant clade.

How is monkeypox treated?

There are no specific treatments for monkeypox, however there are three antiviral treatments that have been shown to be effective against smallpox in in vitro trials and could be potentially used against monkeypox.

Is there a vaccine against monkeypox?

According to the CDC, data from research in Africa demonstrates that the smallpox vaccine offers at least 85% protection from monkeypox virus and reduces both transmission and severity. Historical data, as well as evidence from previous outbreaks points towards long lasting (decades) cross-protection from monkeypox after vaccination with the smallpox vaccine.

However, since smallpox was declared to be eradicated in 1980, vaccination against the disease has been progressively halted. In the UK, for example, it was withdrawn in 1971, in the US in 1972 and in Spain in 1980. It is therefore possible that the percentage of the adult population that has already received the smallpox vaccine before that time may also enjoy some level of protection against monkeypox.

In addition, in 2021, the US FDA approved the JYNNEOS vaccine against smallpox and monkeypox. This vaccine has not yet been approved in Europe.

How is monkeypox transmitted?

The monkeypox virus is transmitted mainly through close contact with infected people, animals (also with their samples), or through respiratory droplets caused by cough and sneezing. Entry occurs through breaks in the skin, mucous membranes or respiratory tract. Transmission through fomites (contact with contaminated material, e.g. bedding or towels of an infected person) is also possible. Although sexual transmission per se has not been proven, the intimate contact occurring during sex may lead to transmission.

How is monkeypox diagnosed?

It is first diagnosed by clinical suspicion based on epidemiological history, usually travel, contact with infected persons or occupational exposure. This is followed by identification of compatible signs and symptoms, and finally by detection of the virus by PCR tests, based on a sample of lesions, usually skin lesions. Serological testing can also be performed to demonstrate a specific immune response to the virus.

What is the incubation period for monkeypox?

The incubation period for monkeypox is usually between 7 and 14 days, although it can be as short as 5 days or as long as 21 days.

What do the confirmed cases have in common?

The information provided by the UK authorities refers to at least two apparently unrelated groups of infected people.

Most of the confirmed cases, both in Spain and in the UK, are men who identify themselves as gay, bisexual or men who have sex with men. For this reason the UK authorities have urged these population groups to remain vigilant for possible symptoms consistent with the virus, such as rashes or skin lesions.

It is also known that many of the infected men are young, which may be related to the fact that younger populations did not receive the smallpox vaccine.

Should we be concerned about this health alert?

Cases of monkeypox, a virus that has so far not been noted as highly transmissible, are very rare outside certain countries in West and Central Africa. The first outbreak outside the African continent occurred in the United States in 2003 and consisted of 47 cases. However - or precisely because of this - there are some worrying signs surrounding the current health alert in Europe.

The fact that imported cases are appearing virtually simultaneously in different countries is certainly not an encouraging sign. Beyond the first case detected in the UK, which was imported in nature, there is evidence suggestive of EU-wide transmission. Indeed, based on the information available to date, the lack of connection between some of the confirmed cases suggests that there is more than one chain of transmission, which in turn raises the possibility that there are additional cases still undetected.

It is therefore too early to predict the severity of the situation or the direction it will take. However, there are a number of lessons learned from the COVID-19 pandemic that we can take into account:

  • We should not underestimate emerging diseases, to conclude prematurely that we will only have a small number of cases is irresponsible until we have real data on the magnitude of the problem, this includes number of active cases, transmissibility, risk groups, etc.
  • Sustained transmission in neighboring countries generally correlates well with transmission in our country.
  • Alarm generates fear and misinformation; this can be managed with transparency and comprehensive, quality information.
  • We can expect denialism, conspiracies and xenophobia, but we need to be prepared to counter this with detailed and transparent information.

What are the precautions to be taken?

The fact that most of the recently detected cases in Europe include men who have sex with other men, does not mean that it is a sexually transmitted disease. Transmission of the virus occurs via close contact, whether sexual or not. Neither does it imply that these population groups are especially at risk because of their sexual preferences.

Anyone with symptoms – especially skin lesions – should consider the possibility of having contracted the virus and should seek diagnosis immediately. This precaution is directed at everyone, regardless of gender or sexual status, who may have had close contact with any networks in which the virus has been detected.

What are some of the open questions?

Another situation we have experienced with the COVID-19 pandemic is that the most pressing questions change over time. As far as monkeypox cases are concerned, as of today, these are some of the questions that would need to be answered most urgently:

  • How many cases are there really?
  • Since when has the virus been circulating in Europe?
  • Were there already chains of transmission in the United Kingdom when the first case was detected in a man who had recently traveled to Nigeria?
  • Is it possible that the virus travelled back and forth from Europe to Nigeria?
  • What answers will contact tracing and sequencing of samples provide?