Monkeypox: Zoonotic Aspects

The current rise in number of cases across various continents is concerning both for the public health regulatory authorities and the scientific community
"The current rise in number of cases across various continents is concerning both for the public health, regulatory authorities and the scientific community." [Representational Image]
"The current rise in number of cases across various continents is concerning both for the public health, regulatory authorities and the scientific community." [Representational Image] Pixabay [Creative Commons]

Monkeypox is viral zoonotic disease that is currently spreading from endemic Western and Central African countries to non-endemic countries in the world including America, Europe, Australia, Canada and is risking lives across the globe thus emerging as global public health threat with moderate risk. It affects both animals and humans.

At present more than 23 nonendemic countries have been affected with more than 400 confirmed cases in United Kingdom, Spain, Portugal, Netherlands, Germany, France, Canada, Italy, United States of America, Belgium, Czech Republic, United Arab Emirates, Ireland, Sweden, Argentina, Switzerland, Israel, Thailand, Finland, Malta, and Slovenia when the endemic countries in Western and Central Africa have more than 1500 cases; possessing risk around the world.

Though discovered in 1958 from experimental monkeys, the first human case was reported in 1970 in Democratic Republic of the Congo (DRC) during a period of intensified effort to eliminate smallpox. The current rise in number of cases across various continents is concerning both for the public health, regulatory authorities and the scientific community.

Hence awareness among public about the disease, guidelines for management, necessary prevention and control strategies is the need of hour.

Monkeypox is caused by monkeypox virus (MPXV) belonging to the Orthopoxvirus genus in the family Poxviridae. This virus is close relative of variola virus (which causes smallpox), vaccinia virus (used in the smallpox vaccine), and cowpox virus.

Being zoonotic in nature, monkeypox is transmitted from an animal source to humans followed by intraspecies transmission. Actual natural host or reservoir of monkeypox virus is yet to be established however African nonhuman primates (monkeys) or rodents may harbor virus that infect humans.

Old and New World monkeys and apes (rhesus macaques, cynomolgus monkeys, languors, baboons, chimpanzees, orangutans, marmosets, gorillas, gibbons, owl-faced monkeys (Cercopithecus hamlyn), and squirrel monkeys), a variety of rodents (including Gambian giant rats, brushtail porcupines (Atherurus sp.), dormice (Graphiurus sp.), striped mice (Hybomys sp.), rope squirrels (Funiscuirus sp.), tree squirrels (Heliosciurus sp.), and prairie dogs) and rabbits are susceptible. No cases have been reported in dogs, cats or other domestic species to date; however, the full host range is still unknown.

The natural reservoir(s) of the monkeypox virus remains unclear but is thought to be mainly rodents. Two species of African squirrels, Funisciurus anerythrus and Heliosciurus rufobrachium, have been suggested as possible reservoirs or vectors.

It is not known whether primates also maintain the infection in the wild, or are only incidental hosts. In endemic areas, monkeypox virus probably circulates among a number of mammals. Occasional spill-over events to humans generate outbreaks.

Monkeypox virus is transmitted to humans through close contact with an infected person or animal, or with material contaminated with the virus.

Close physical contact with affected individual, direct contact with body fluids or sores on an infected person or with materials that have touched body fluids or sores, such as clothing or linens can spread this virus.

Infected animal’s blood, meat, bodily fluids, cutaneous/mucosal lesions, bite or scratches can also transmit this virus. Handling wild game or use of products made from infected animals can pose risk.

Thus far, there is no documented evidence of human to animal transmission of monkeypox but as per World Organization for Animal Health there can be potential risk of spillback to susceptible animals.

Monkeypox cases occurring in people outside of Africa are linked to international travel or imported animals, including cases in the United States, as well as Israel, Singapore, and the United Kingdom.

Considering the disease in animals, monkeypox in non-human primates usually occurs as a self-limiting rash. Symptoms usually develop in 6-7 days following exposure. Typical pock lesions can be seen on entire body or mostly on face and extremities like limbs, palms, soles, and tail.

The skin lesions can persist for 4-6 weeks. Some animals have only skin lesions. In more severe cases, fever, coughing, nasal discharge, dyspnea, conjunctivitis, anorexia, facial edema, oral ulcers, or lymphadenopathy may also be seen.

Disseminated disease, with visceral lesions, is uncommon in natural infections. Pneumonia is common only in monkeys infected experimentally by aerosol. Most naturally infected animals recover; however, fatalities are sometimes seen, particularly in infant monkeys. Asymptomatic infections also occur.

In humans monkeypox disease is usually mild in most of the cases but can be severe in cases where immune system is either under developed or compromised like neonates, pregnant ladies, co-morbid patients or those under immunosuppressant conditions or therapy. Incubation period is around 7-14 days. Affected person is infectious during this period. In recent times, the case fatality ratio has been around 3–6%.

Clinical signs and symptoms are similar to that of small pox but in milder form with slight difference in lymph node swelling. In the initial phase affected humans show fever, malaise, headache, muscle aches, backache, rashes, swollen lymph nodes, chills, or exhaustion/ weakness. Lymphadenopathy in monkeypox is contrary to small pox with systemic or localized lymph node involvement.

Prodromal phase is followed by development of rashes, resulting in lesions in any part of body. The evolution of lesions progresses through four stages—macular, papular, vesicular, to pustular—before scabbing over and resolving.

For identification of monkeypox, lesions are well circumscribed, deep seated, and often develop umbilication (resembles a dot on the top of the lesion). They have relatively the same size and same stage of development on a single site of the body like palms, soles.

There is usually fever before rash. Disseminated rash is centrifugal (more lesions on extremities, face). Lesions are often described as painful until the healing phase when they become itchy (crusts). Lymphadenopathy is common.

Monkeypox disease cases necessitate healthcare management in both medical and veterinary health care. Regarding veterinarians who decide to treat animals with suspected monkeypox should use infection control precautions to protect themselves, staff, clients, as well as other animal patients in the clinic.

Centers for Disease Control and Prevention (CDC, USA) recommends one month quarantine for animals exposed to monkeypox. Animals suspected of being infected should not be allowed to enter through the waiting area of a veterinarian clinic nor should they be taken to a common treatment room.

All treatment and diagnostics should be performed in an examination room. The number of staff allowed in the exam room and that come in contact with the animal should be limited to as few persons as possible.

The most common route for transmission of monkeypox from animals to humans appears to be direct contact with infected animals; however, the possibility of airborne transmission cannot be excluded.

When examining animals with suspected monkeypox, veterinarians and staff should use necessary precautions including adequate hand hygiene, use of personal protective equipment, proper waste disposal, environmental cleaning and appropriate use of laundry.

Treatment of monkeypox is mainly supportive. Regarding management of affected cases, 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 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 however needs monitoring.

The antiretroviral drug cidofovir has been effective in vitro and in animal studies, but its efficacy against monkeypox in humans in unknown. The toxic effects of this drug must also be considered. The efficacy of vaccinia immune globulin (VIG) in cases of monkeypox is unknown.

For the prevention and control, vaccines developed against small pox are also providing protection against monkeypox. Newer vaccines have been developed of which only JYNNEOS, a small pox vaccine (also known as Imvamune or Imvanex) has been approved for prevention of monkeypox. It is licensed specifically to prevent monkeypox.

Smallpox and monkeypox vaccines are effective at protecting people against monkeypox when given before exposure to monkeypox. Experts also believe that vaccination after a monkeypox exposure may help prevent the disease or make it less severe.

There is no specific vaccine against monkeypox in animals, so isolating affected animals and treating appropriately can help in managing cases and preventing further spread, minising risk to humans.

Dr. Mohammad Iqbal Yatoo, Assistant Professor (Veterinary Medicine) FVSc and AH Shuhama (SKUAST-K)

Disclaimer: The views and opinions expressed in this article are the personal opinions of the author.

The facts, analysis, assumptions and perspective appearing in the article do not reflect the views of GK.

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