Mpox virus
Mpox, formerly known as monkeypox, is a zoonotic viral disease caused by the mpox virus, which is part of the Orthopoxvirus genus. This virus is closely related to the viruses that cause smallpox and cowpox, but mpox is generally less severe than smallpox. Originally identified in laboratory monkeys in 1958, mpox was first observed in humans in 1970 in the Democratic Republic of Congo. Since then, it has become endemic in Central and West African countries, with sporadic outbreaks occurring in other parts of the world.
Mpox virus (formerly known as monkeypox virus) has two primary strains, also referred to as clades or lineages. These strains exhibit differences in their genetic makeup, geographical distribution, and the severity of the disease they cause. The two main strains are:
Mpox strain
1. West African Clade
- Geographical Distribution: The West African clade is primarily found in West African countries such as Nigeria, Sierra Leone, and Liberia. It has also been associated with some outbreaks outside Africa, including the significant global outbreak that began in 2022.
- Severity: The West African strain is generally less severe compared to the Central African strain. It is associated with a lower case fatality rate, historically around 1% to 3%.
- Transmission: While human-to-human transmission can occur, it is less efficient in the West African clade. Most cases in West Africa are due to zoonotic transmission, though outbreaks can occur in human populations.
- Symptoms: The disease presentation is similar in both clades, but the West African clade typically results in a milder illness. Symptoms include fever, rash, and swollen lymph nodes, progressing through the usual stages of rash development.
2. Central African (Congo Basin) Clade
- Geographical Distribution: The Central African clade is found in Central African countries, particularly in the Congo Basin region, which includes the Democratic Republic of Congo (DRC) and surrounding areas.
- Severity: The Central African strain is more virulent, with a higher case fatality rate, historically ranging from 3% to 10%. It is associated with more severe disease and a higher likelihood of complications, such as secondary bacterial infections, encephalitis, and respiratory distress.
- Transmission: This strain is more transmissible between humans compared to the West African clade. Sustained human-to-human transmission has been documented in this clade, making outbreaks in the region more challenging to control.
- Symptoms: While the general symptoms are similar, patients infected with the Central African strain often experience a more severe clinical course, with a higher incidence of complications and a longer duration of illness.
Genetic Differences
The two clades differ genetically, with the Central African clade showing greater genetic diversity. These genetic differences may contribute to the observed variations in disease severity, transmissibility, and geographic distribution. The Central African strain has more genetic variations that might contribute to its higher virulence and transmissibility.
Implications for Public Health
Understanding the differences between these two clades is crucial for public health efforts. The higher severity and transmissibility of the Central African clade necessitate more stringent control measures, including surveillance, vaccination, and patient isolation, especially in regions where this clade is endemic. The West African clade, while less severe, still requires careful monitoring, particularly in non-endemic regions where imported cases could lead to outbreaks.
In 2022, the global outbreak primarily involved the West African clade, which spread to multiple countries outside Africa. This highlighted the importance of international collaboration in surveillance and response efforts, especially as the world faces the challenge of emerging infectious diseases.
Transmission
Mpox is primarily transmitted from animals to humans, with the virus residing naturally in certain wild animals, particularly rodents like squirrels and rats. Human infection can occur through direct contact with the blood, bodily fluids, or cutaneous or mucosal lesions of infected animals. Consumption of inadequately cooked meat from infected animals can also lead to transmission.
Human-to-human transmission is less common but can occur through close contact with respiratory secretions, skin lesions of an infected person, or recently contaminated objects like bedding or clothing. The virus enters the body through broken skin, respiratory tract, or mucous membranes such as the eyes, nose, or mouth. Notably, the spread between humans is relatively limited compared to diseases like COVID-19, but close physical contact does increase the risk.
Symptoms
The incubation period for mpox typically ranges from 6 to 13 days but can vary from 5 to 21 days. The disease begins with an initial set of symptoms that are often flu-like, including fever, headache, muscle aches, back pain, swollen lymph nodes, chills, and exhaustion. The presence of swollen lymph nodes is a key feature that distinguishes mpox from other similar illnesses such as chickenpox or smallpox.
Within a few days of the onset of fever, a rash usually develops, initially on the face and then spreading to other parts of the body, including the palms and soles. The rash progresses through several stages: macules (flat, discolored spots), papules (raised bumps), vesicles (small, fluid-filled blisters), pustules (filled with pus), and finally, scabs that eventually fall off. The lesions can number from a few to several thousand and can cause significant discomfort.
Severity and Complications
Mpox is generally a self-limiting disease, meaning it usually resolves on its own without the need for specific medical treatment. Symptoms typically last between 2 to 4 weeks. However, the disease can be more severe in certain populations, such as young children, pregnant women, and individuals with compromised immune systems. Complications can include secondary bacterial infections, bronchopneumonia, sepsis, encephalitis, and infection of the cornea, leading to vision loss.
The case fatality rate for mpox has historically varied between 1% and 10%, depending on the strain of the virus and the availability of medical care. The West African clade of the virus, which has a lower mortality rate, is less severe compared to the Central African (Congo Basin) clade.
Diagnosis and Treatment
Diagnosis of mpox is primarily clinical, based on the characteristic rash and other symptoms, but confirmation is typically done through laboratory testing, including PCR (polymerase chain reaction) to detect viral DNA. Other methods include virus isolation and electron microscopy.
There is no specific antiviral treatment for mpox, but supportive care is essential to manage symptoms. Smallpox vaccines have been shown to be about 85% effective in preventing mpox, and they are used in outbreak settings to control the spread. In some cases, antiviral drugs such as tecovirimat, originally developed for smallpox, may be used.
Prevention
Preventive measures include avoiding contact with animals that could harbor the virus, particularly in endemic regions. Individuals should avoid consuming undercooked or raw meat from wild animals and practice good hygiene, such as handwashing with soap and water. In healthcare settings, standard precautions including the use of personal protective equipment (PPE) are vital for preventing the spread of the virus.
In summary, mpox is a serious viral disease that poses a public health threat, particularly in regions where it is endemic. While it is generally less severe than smallpox, its potential for causing outbreaks, especially in vulnerable populations, necessitates ongoing surveillance, research, and preparedness efforts to prevent and control its spread.
