MONKEYPOX: WHAT IS KNOWN SO FAR

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Introduction

Monkeypox is a disease caused by infection with the monkeypox virus. In recent weeks monkeypox infections have been noted in a number of countries. It is the largest outbreak of monkeypox infection outside Sub-Saharan Africa. This article would outline some clinical information on monkeypox infections, their detection and management.  

What is the monkeypox virus

Monkeypox is a double stranded DNA virus. It was first discovered in 1958 and is a member of human orthopoxoviruses. Other members in this genus includes, cowpox, smallpox (variola) and vaccinia viruses. It is called monkeypox as it was first identified within a colony of laboratory macaques in Denmark. It mutates at a slower rate than RNA viruses (such as Influenza, HIV or SARS-CoV-2).

Epidemiology of monkeypox viral infections

Monkeypox infections occur mainly in Central and Western Africa. The first human case was reported in 1970, from the Democratic Republic of Congo. Transmission occurs when a person comes into contact with the virus from another human, animal or materials contaminated with the virus. The virus may enter the body through broken skin, the respiratory tract, or mucous membranes (eyes, mouth, or nose). Human-to-human transmission primarily occurs through large respiratory droplets. As these cannot travel more than a few feet, prolonged face-to-face contact is required. Direct contact with body fluids or lesion material and indirect contact with lesion material (such as contaminated clothing) may also transmit the virus. Animal-to-human transmission may occur by a bite or scratch, direct contact with body fluids or indirect contact with lesion material. Currently, the exact reservoir hosts are uncertain. Monkeys are not the natural hosts, and the virus is more common in rats and mice. 

As of 23 May 2022, around 110 confirmed cases of monkeypox infections have been reported from nearly 20 countries. Most cases have been in Europe and the United States (US). All have been due to the West-African strain of monkeypox. So far, there have been 57 cases in the UK. The first patient was a returnee from Nigeria. Subsequently, there has been evidence of local transmission. A proportion of the recent cases in Europe have been in gay or bisexual men and this may be linked to close social contact.

Clinical findings and presentations

The time from infection to symptoms (incubation period) can range from 5 – 21 days. The illness begins with fever, chills, headache, backache, muscle aches, and exhaustion (Figure). Lymph node swelling (lymphadenopathy) is commonly observed. A rash is noted around 1 to 3 days after the onset of fever. This often begins in the face and then spreads to other parts of the body (most commonly palms of hands and soles of feet). The rash progresses through different stages: macules, papules, vesicles, pustules and scabs. The illness usually lasts for around 14 to 28 days. 

Complications and reported case fatality rates

Most infections are mild and self-limiting. People infected with monkeypox in Central Africa have a case fatality rate (CFR) of around 10%. The CFR in the West African strain is lower at 3.6%. More severe disease occurs in children, pregnant women and immunocompromised individuals.

Methods available for diagnosis

Real-time Polymerase Chain Reaction (RT-PCR) is done on swabs from lesion material to diagnose a potential infection with the monkeypox virus. More than one lesion should be sampled. This should preferably be from different locations on the body and/or from lesions with differing appearances. There should be effective communication between the specimen collection teams and laboratory staff and appropriate preventive measures should be in place during collection, transport and testing of potential monkeypox specimens. A labelling system should clearly distinguish all specimens from potential monkeypox patients that require special handling.

Treatment of monkeypox infections

Currently, there is no proven and safe treatment for monkeypox infections. Some centres use, antivirals, the smallpox vaccine or vaccinia immune globulin (VIG). The antivirals, Cidofovir and Brincidofovir have proven activity against poxviruses both in vitro and in animal studies. Robust data are currently not available on their effectiveness in treating human monkeypox infections. Their use may be considered in selected circumstances. Brincidofovir may have an improved safety profile over Cidofovir. Tecovirimat (ST-246) blocks cellular transmission of the virus. It has been found to be effective in treating orthopoxvirus-induced disease in animals. Human clinical trials found this drug to be safe and tolerable, but effectiveness data is not available. VIG may be considered for prophylactic use in persons with T cell immunodeficiency exposed to monkeypox, as smallpox vaccination (using a live attenuated vaccine) is contraindicated in such patients.

Prevention of monkeypox infections

Some of the methods for preventing monkeypox infections include: isolation of infected patients from others who may be at risk for infection, practicing good hand hygiene after contact with infected animals or humans and the use of appropriate personal protective equipment (PPE) when caring for patients. In addition, avoiding contact with animals that may harbour the virus or any materials (for example bedding) that has been in contact with sick animals are also recommended. Those who are in close contact with someone who has monkeypox are asked to self-isolate for 21 days.

Imvanex (JYNNEOS) is a live attenuated non-replicating viral vaccine. It contains a live modified form of the vaccinia virus called vaccinia Ankara and is made by Bavarian Nordic. It has been approved by the US Food and Drug Administration (US FDA) in 2019, for the prevention of monkeypox infections in those 18 years and older. Two subcutaneous injections are given four weeks apart. A person is considered vaccinated only when they receive both doses of the vaccine. As the monkeypox virus is closely related to the smallpox virus, the smallpox vaccine may protect people from getting monkeypox. In Africa, the smallpox vaccine is at least 85% effective in preventing monkeypox.

The smallpox and monkeypox vaccines are effective in protecting persons against monkeypox when given before exposure to monkeypox. It is also believed that vaccination after a monkeypox exposure may help prevent the disease or make it less severe. The European and UK health authorities are using ring vaccination, where close contacts of those who present with symptoms are immunised. It is recommended the vaccine be given within four days from the date of exposure. Between four–14 days after the date of exposure, vaccination may reduce the symptoms of disease, but may not prevent the disease. Persons exposed to the monkeypox virus and who have not received the smallpox vaccine within the past 3 years, should consider getting vaccinated.

Conclusions

With the recent identification of monkeypox infections in several countries, clinicians and the general public need to be aware of some basic information on this virus, the clinical effects it causes and how this infection is prevented and managed.

Prof. Suranjith L Seneviratne, Dr Visula Abeysuriya