Monkeypox virus

  1. Maintains a reservoir in wild animals and sporadically causes human disease.

Occurs primarily in remote villages in rainforests of central and west Africa.

The current monkey pox outbreak appears to be caused by the west Africa Clade.

A zoonotic virus, typically transmitted through close contact between animal and human, often through a bite, scratch, large respiratory droplets, or contact with the rash and with fomite material like bedding  or clothes contaminated with material from monkeypox lesions.

It may even be transferred via fomites such as towels, bedding, and sex toys.

Case fatality 1-10%, and infection is generally self-limited.

No effective vaccine but smallpox vaccine is 85% effective in preventing MPV.

Monkeypox virus causes disease in both humans and animals. 

Monkeypox virus is an Orthopoxvirus.

It is a zoonotic disease, but its animal reservoir remains unknown.

Various rodent species from central west African tropical rain forests including including tree squirrels and Gambian pouched rats are currently considered the strongest candidates.

African apes and monkeys can be infected and are thought to be intermediate hosts.

Many animals such as rabbits, prairie dogs, other rodents, and monkeys are susceptible to infection in captivity, including laboratory animals.

Monkeypox virus is a genus of the family Poxviridae that contains other viral species that target mammals.

This genus encompasses other pox viruses including: smallpox, vaccinia, cowpox, and camelpox viruses.

It is a double stranded DNA virus.

The virus is found mainly in tropical rainforest regions of Central and West Africa.

The virus was first discovered in monkeys in 1958, and in humans in 1970. 

Small viral outbreaks with a death rate in the range of 10% and a secondary human-to-human infection rate of about the same amount occur routinely in equatorial Central and West Africa.

The primary route of infection is thought to be contact with the infected animals or their bodily fluids.

Human to human transmission is less common and is believed to be due to direct contact with lesions material or respiratory droplets.

Humans can be infected by an animal via a bite, or by direct contact with an infected animal’s bodily fluids. 

The virus can also spread from human to human, by airborne contact or by contact with an infected person’s bodily fluids. 

Risk factors for transmission include:  sharing a bed or room, or using the same utensils as an infected person, introduction of virus to the oral mucosa.

The incubation period is 10–14 days. 

Prodromal symptoms include swelling of lymph nodes, muscle pain, headache, and fever prior to the emergence of the rash.


It affects both children and adults and typically has three phases: incubation, prodrome, and the eruptive stage.

The  prodromal phase lasts for 1 to 4 days and is characterized by high fever, headache, fatigue, and often lymphadenopathy in the cervical and maxillary regions.

Lymphadenopathy distinguish is monkeypox from chickenpox.

The eruptive phase lasts for 14 to 28 days, and skin lesions appear in a centrifugal distribution and progress through several stages: macules, papules, vesicles, and finally pustules.

Skin lesions are firm, well defined and display umbilivation.

Skin lesions often develop crusts that desquamate and leave areas of hypo pigmentation, followed by hyper pigmentation.

Lesions may number a few to several thousands and are located primarily on the face, trunk, arms, and legs.

Palm and soul involvement distinguishes monkeypox from chickenpox, with fewer lesions.

People with monkeypox typically experienced prodromal symptoms of fever, headaches, muscle aches, chills, and drenching sweats. 

Roughly one-third of infected people had nonproductive coughs. 

This prodromal phase is followed 1–10 days later by the development of a papular rash that typically progressed through stages of vesiculation, pustulation, umbilication, and crusting. 

The incubation period is wide, ranging from five days to three weeks.

Rash distribution and lesions occurred on head, trunk, and extremities; many of the people had initial and satellite lesions on palms, soles, and extremities.

Current cases have started in the genital or perianal region before spreading to the person’s extremities.

In a study of 528 infections, at 43 sites and 16 countries 98% of the persons infected are gay or bisexual men, 75% were White, and 41% had  HIV infection, with the median age of 38 years (Thornhill JP).

Rashes are generalized in some people.

The rash is usually only present on the trunk, but may spread to the palms and soles of the feet in a centrifugal distribution. 

The initial macular rash lesions exhibit a papular, then vesicular and pustular appearance.

Skin lesions evolve from macules, papules to vesicles and pustules that ulcerate and crust before healing over several weeks.

The skin lesions usually occur in crops.

The initial lesions are usually the side of inoculation.

Most often monkeypox infection is self-limited and lasts 2 to 4 weeks.

Can cause serious illness, including ocular involvement, soft tissue super infections, and excruciating anogenital lesions.

Complications: pneumonia, encephalitis, keratitis, secondary bacterial infections which occur mostly in children younger than eight years, pregnant people, or individuals who have immunosuppression.

The pathology is characterized by intracytoplasmic eosinophilic inclusions in epithelial changes, ballooning degeneration, keratinocyte necrosis and hyperplasia of the epidermis.

The pathology is characterized by intracytoplasmic eosinophilic inclusions in epithelial changes, ballooning degeneration, keratinocyte necrosis and hyperplasia of the epidermis.

The dermis presents with lymphocytic inflammation, subsequent ulceration, infiltration by neutrophils, eosinophils, and multinucleated giant cells.

In addition to monkeys, reservoirs for the virus are found in Gambian pouched rats, dormice and African squirrels.

The use of these animals as food may be an important source of transmission to humans.

Differential diagnosis:

chickenpox, measles, bacterial skin infections, scabies, syphilis and medication-associated allergies. 

Lymphadenopathy during the prodromal stage of illness can distinguish monkeypox from chickenpox or smallpox. 

Polymerase chain reaction (PCR) testing of samples from skin lesions is the preferred laboratory test.

PCR blood tests are usually inconclusive because the virus does not remain very long in the blood.

Vaccination against smallpox is assumed to provide protection against human monkeypox infection, because they are closely related viruses and the vaccine protects animals from experimental lethal monkeypox challenges: not been conclusively demonstrated in humans, because routine smallpox vaccination was discontinued following the eradication of smallpox.

Smallpox vaccine has been reported to reduce the risk of monkeypox.

Smallpox vaccination is thought to provide up to 85% across protection against monkeypox, although the duration is unknown.

Vaccination is recommended for individuals with exposure and close contact with an infected individual.

CDC recommends that persons investigating monkeypox outbreaks and involved in caring for infected individuals or animals should receive a smallpox vaccination to protect against monkeypox. 

Persons who have had close or intimate contact with individuals or animals confirmed to have monkeypox should also be vaccinated.

It is traditionally restricted to the ecology of tropical rainforests.

The number of reported monkeypox cases had increased and the geographical occurrence broadened.

It is suspected the upward trend in monkeypox cases is due in the decline in smallpox vaccinations.

40 years ago 80% of the population was vaccinated against smallpox and now that number is closer to 30%.

Many of recently confirmed cases have been identified as men who have sex with men.

Prevention is to avoid direct contact with skin lesions or with materials used by patients with monkeypox.

Patients with suspected or confirmed monkeypox should have their lesions covered, should be masked, and the in isolation.

Treatment is mostly symptomatic without currently available specific antiviral treatment.

Tecovirimat is used for the treatment of several poxviruses, including monkeypox.

Tecovirimat is an antiviral drug approved for the treatment of smallpox disease.

The drug was approved for smallpox on the basis of studies in animal models.

Brincidor has also been approved for treatment of smallpox.

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