Dr. Francis SANWO

Monkeypox is a viral zoonosis (a virus transmitted to humans from animals) with symptoms similar to those seen in the past in smallpox patients, although it is clinically less severe. It is usually a self-limited disease with the symptoms lasting from 2 to 4 weeks. Severe cases can occur.  With the eradication of smallpox in 1980 and subsequent cessation of smallpox vaccination, monkeypox has emerged as the most important orthopoxvirus for public health. Monkeypox primarily occurs in central and west Africa, often in proximity to tropical rainforests, and has been increasingly appearing in urban areas. Animal hosts include a range of rodents.

It is a relatively rare disease that was first detected in monkeys in Africa in 1958 and resembles smallpox in terms of the skin lesions (pox) seen in humans as part of the physical findings and also because the cause is a virus that is closely related to the smallpox (variola) virus. Monkeypox, smallpox, cowpox, and vaccinia viruses all belong to the same family of viruses, the Poxviridae. Monkeypox belongs to same genus (Orthopoxvirus) as smallpox. The disease is different from smallpox.

Transmission. Animal-to-human (zoonotic) transmission can occur from direct contact with the blood, bodily fluids, or cutaneous or mucosal lesions of infected animals. In Africa, evidence of monkeypox virus infection has been found in many animals including rope squirrels, tree squirrels, Gambian poached rats, dormice, different species of monkeys and others. The natural reservoir of monkeypox has not yet been identified, though rodents are the most likely. People living in or near forested areas may have indirect or low-level exposure to infected animals.
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. Transmission can also occur via the placenta from mother to fetus (which can lead to congenital monkeypox) or during close contact during and after birth.

Monkeypox has far less mortality (death rate) than smallpox had. The case-fatality rate (death rate) for monkeypox virus infection in Africa varies from about 1%-15% and about 15%-20% in children. Monkeypox virus is endemic in rodent populations in Africa. 

Monkeypox has a relatively recent history. People first discovered it in monkeys in 1958, although a "vesicular disease in monkeys" was described in the 1860s. The disease, and eventually the causative virus, was named monkeypox because the lesions (pox) seen in monkeys developed like other known pox-forming diseases (pustules that eventually break open, ulcerate, crust over, and some pox form scars in the skin). It was not until 1970 in Africa (Democratic Republic of Congo ), when a 9-year-old boy (who developed smallpox-like lesions) was the first person to eventually be diagnosed with monkeypox. Since then, human cases of monkeypox have been reported in 11 African countries: Benin, Cameroon, the Central African Republic, the Democratic Republic of the Congo, Gabon, Cote d’Ivoire, Liberia, Nigeria, the Republic of the Congo, Sierra Leone and South Sudan.

In 2017, an outbreak of monkeypox began in Nigeria. This large outbreak is thought to be triggered by river flooding that has caused infected wild animals (especially rodents and monkeys) to more closely associate with humans, thus spreading this zoonotic (transmitted to humans from animals) disease. From 2017 to the present, Nigeria has recorded 446 cases. Another case was diagnosed in Maryland in 2021.

The current outbreak (May 2022) has spread to non-endemic countries according to the World Health Organization (WHO.

Risk factors for monkeypox. Risk factors include animal bites and scratches from infected animals (mainly African rodents or monkeys) or from other rodents (like prairie dogs) that have had contact with African animals infected with the virus. People should avoid eating any meat from such animals. Recent studies have shown that monkeypox can infect several species of mammals, even though the species had never been associated with the virus in their normal environment.

However, monkeypox is not considered a sexually transmitted disease; it may occur more frequently in sexually active groups because of skin to skin contact during sex. Transmission of monkeypox is usually by direct contact with infected animals or possibly by eating poorly cooked meat from an infected rodent or monkey. Cutaneous or mucosal lesions on the infected animals are a likely source of transmission to humans, especially when the human skin is broken due to bites, scratches, or other trauma -- are a likely source for virus infection. Human-to-human transfer, probably by infected respiratory droplets, is possible but is not often documented. Direct skin contacts with lesions, body fluids, and contaminated bedclothes or clothing are the most likely transmission methods.

 Symptoms and signs.

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 infected person is not contagious during the incubation period. However, human cases can be contagious as soon as symptoms develop. The person is contagious until all scabs from the pox lesions fall off. Consequently, the person is usually contagious for about four to five weeks.

The infection can be divided into two periods: The invasion period (lasts between 0–5 days) characterized by fever, intense headache, back pain, myalgia (muscle aches), intense asthenia (lack of energy),  sweating,  cough, nausea, and shortness of breath. These are nonspecific. Lymphadenopathy (swelling of the lymph nodes) is a distinctive feature of monkeypox compared to other diseases that may initially appear similar (chickenpox, measles, smallpox).

The skin eruption usually begins within 1–3 days of appearance of fever. The rash tends to be more concentrated on the face and extremities rather than on the trunk. It affects the face (in 95% of cases), and palms of the hands and soles of the feet (in 75% of cases). Also affected are oral mucous membranes (in 70% of cases), genitalia (30%), and conjunctivae (20%), as well as the cornea. The rash evolves sequentially from macules (lesions with a flat base) to papules (slightly raised firm lesions), vesicles (lesions filled with clear fluid), pustules (lesions filled with yellowish fluid), and crusts which dry up and fall off. The number of lesions varies from a few to several thousand. In severe cases, lesions can coalesce until large sections of skin slough off.

These skin and mucus membrane pox lesions can ulcerate, crust over, and then begin to heal in about 14-21 days. Some pox lesions may become necrotic and destroy sebaceous glands, leaving a depression or pox scar that, with monkeypox, may gradually become less pronounced over a few years. The toxemia that was seen with smallpox is not seen with monkeypox.

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 unknown.

Diagnosis. The history (especially association with rodents or other animals) and physical exam (present of pox lesions) is presumptive evidence for a diagnosis of monkeypox. Caution is advised. The clinical differential diagnosis that must be considered includes other rash illnesses, such as chickenpox, measles, bacterial skin infections, scabies, syphilis, and medication-associated allergies. Lymphadenopathy during the prodromal stage of illness can be a clinical feature to distinguish monkeypox from chickenpox or smallpox.
If monkeypox is suspected, health workers should collect an appropriate sample and have it transported safely to a laboratory with appropriate capability.  

 Prevention. Monkeypox can be prevented by avoiding eating or touching animals known to acquire the virus in the wild (mainly African rodents and monkeys). Patients who have the disease should physically isolate themselves until all of the pox lesions have healed. Caregivers should obtain a smallpox vaccination. Reduce or prevent person-to-person transfer, although infrequent, by avoiding direct physical contact with the patient and having the patient's caregivers wear gloves and face masks. Avoid skin contact and clothing with potentially infected people.

Because smallpox and monkeypox are so closely related, studies have suggested that people vaccinated against smallpox have about an 85% chance of being protected from monkeypox. Although vaccination against smallpox was protective in the past, today persons younger than 40 to 50 years of age (depending on the country) may be more susceptible to monkeypox due to cessation of smallpox vaccination campaigns globally after eradication of the disease.

Patients with depressed immune systems and those who are allergic to latex or smallpox vaccine should not get the smallpox vaccine.

Anyone else who has been exposed to monkeypox in the past 14 days should get the smallpox vaccine, including children under 1 year of age, pregnant women, and people with skin conditions.

.Therapeutics. Clinical care for monkeypox should be fully optimized to alleviate symptoms, manage complications and prevent long-term sequelae. Patients should be offered fluids and food to maintain adequate nutritional status. Secondary bacterial infections should be treated as indicated.  An antiviral agent known as tecovirimat that was developed for smallpox was licensed by the European Medicines Agency (EMA) for monkeypox in 2022 based on data in animal and human studies. It is not yet widely available.

Reducing the risk of human-to-human transmission. Surveillance and rapid identification of new cases is critical for outbreak containment.  Health workers caring for patients with suspected or confirmed monkeypox virus infection, or handling specimens from them, should implement standard infection control precautions. If possible, persons previously vaccinated against smallpox should be selected to care for the patient.

 Picture of the pustules/papules of characteristic monkeypox rash; SOURCE: World Health Organization (WHO)/