Mpox (monkeypox)

The name mpox stems from the fact that the virus was first discovered in colonies of research monkeys in 1958. In addition to nonhuman primates (monkeys and apes), more recent data indicate that African rodents (such as rope squirrels, tree squirrels, African giant pouched rats, and dormice) also can harbor the virus. While African rodents also are suspected to be the reservoir host species—the main disease carrier—for the mpox virus, this has yet to be confirmed.

The mpox virus is typically found in countries in western and central Africa, particularly within or near tropical forests. The first human case of mpox was reported in 1970 in the Democratic Republic of the Congo. International travel and animal importation have occasionally led to cases of animal and human mpox in countries outside Africa.

The first human cases reported outside Africa occurred in the United States in 2003. Those cases were traced to contact with pet prairie dogs that previously had been housed near small mammals, including rodents, imported from Ghana.

Since then, human mpox has surfaced sporadically in other non-African regions across the globe.

Most recently, in May 2022, multiple cases of human mpox began to surface, fueling outbreaks in several non-African regions, including the United States. Case counts escalated in just a few weeks to involve at least 75 countries, prompting the World Health Organization to declare mpox a global emergency on July 23, 2022. The White House followed suit on August 4, 2022, declaring a national public health emergency. Although this emergency status has since ended, mpox illness—including severe infections—continues to occur in people across the country. So far, disease transmission has mostly involved close, intimate contact with an infected person.

The mpox virus enters the body through the respiratory tract, eyes, mouth, or broken skin, or via sexual contact. Certain conditions can put animals and humans at risk of infection:

• Direct contact with contagious individuals, particularly with secretions from lesions
• Exposure to respiratory droplets (as with prolonged face-to-face contact)
• Contact with virus-contaminated surfaces (e.g., bedding or cages)
• Bites or scratches that break the skin
• Ingestion of infected animals or tissue (e.g., wild game or "bush meat")

The incubation period for mpox averages between 7 and 14 days. During this period, infected animals or people typically have no signs of illness and are not contagious.

Afterward, initial signs of infection in animals differ slightly from those in people, and likely even differ by animal species. What all infected individuals seem to have in common is fever and swollen lymph nodes. This helps to distinguish mpox from smallpox and chickenpox, which do not cause lymph nodes to swell. Nonhuman primates and prairie dogs also have been reported to have the following:

• Cough
• Conjunctivitis (reddened eyes)
• Runny nose
• Lack of appetite

In people, common symptoms during the initial disease stage include the following:

• Headache
• Muscle and back aches
• Exhaustion

As the disease progresses, people and most animals develop a characteristic skin rash that, in people, typically starts on the face and then spreads to other body areas. This rash develops in stages:

1. Macules (skin patches altered in color)
2. Papules (small bumps)
3. Vesicles (fluid-filled blisters)
4. Pustules (pus-filled bumps)
5. Scabs

Clinical signs and outcomes for animals with mpox have not been fully described. The disease in people is generally mild and self-limiting, and recovery is typically within two to four weeks. However, more severe disease and death have been reported, particularly in Africa and in children, young adults, and immunocompromised individuals. The World Health Organization estimates that 3% to 6% of infected people die from mpox.

The available information suggests mpox is a disease of mammals (including humans), but exactly which mammals is still being discovered. We know that nonhuman primates and African rodents are susceptible. However, according to the U.S. Centers for Disease Control and Prevention (CDC), the mpox virus has been recovered only twice from animals in the wild: first from a rope squirrel and later from a mangabey. Both animals were found in central or west Africa. In the United States and other non-endemic regions, a significant concern is the potential for spillover of mpox to wildlife from infected people or domestic mammals, emphasizing the importance of infection control measures to contain the disease.

We're still learning about whether dogs, cats, and other pet species can become infected with and ill from the mpox virus. Although one dog that had close contact with infected people tested positive for the virus, follow-up investigations found that the animal did not develop the disease. Given that many pet species can become infected with other orthopoxviruses, it is best to assume that any mammalian pet could catch the mpox virus and take appropriate measures to prevent infection or disease spread.

Besides susceptibility to infection, it is also important to consider the overall likelihood of clinical disease in pets naturally exposed to the mpox virus. Although the evidence is limited in this regard, results of mpox surveillance activities in the U.K. suggest this likelihood is low when it comes to exposure to infected people. In that study, which concluded mid-September 2022, none of the pets in homes of people with confirmed mpox—including a total of 42 dogs, 26 cats, and 2 rabbits or guinea pigs—were reported to have had signs of mpox. Because these animals weren’t tested for mpox, it remains unknown whether some may have had a subclinical infection.

Laboratory testing of people and animals with suspected mpox is critical to confirm the infection and prevent or contain outbreaks. Veterinarians can play an important role by collecting and submitting appropriate patient specimens to a reference laboratory in the Laboratory Response Network. Optimal specimens include swab samples from the skin lesions themselves, such as the roof or fluid of vesicles and pustules and dry scabs. To maximize the chance of virus detection, several samples are recommended, each from different body locations or lesion stages. To assist the lab in interpreting the results, the test requisition form needs to include the times when fever and rash were first noted (if known) and the stage of the patient's rash at the time of sample collection.

Mpox virus infection is currently confirmed by a real-time or conventional polymerase chain reaction (PCR) assay that detects viral DNA in specimens. Other confirmatory methods include next-generation sequencing of DNA and cell-based viral culture assays.

No specific treatment has been approved for people or animals with mpox. The CDC has made available the antiviral tecovirimat (TPOXX) for human use under a Food and Drug Administration authority called expanded access or "compassionate use." Supportive care (e.g., fluids or analgesics) can be provided to alleviate clinical signs, such as dehydration or discomfort. For animals, some evidence from prairie dogs indicates that buprenorphine—and not nonsteroidal anti-inflammatory drugs—may be useful for relieving discomfort in animals. Antimicrobials are rarely necessary but may be indicated for patients with secondary bacterial infections.

Separating animals and people who are infected or have been exposed to mpox can help stop mpox from spreading further.

To control human outbreaks in the United States, the FDA has approved the use of smallpox vaccines. The CDC recommends vaccination against mpox for persons with known or suspected exposure to mpox and persons with certain factors that put them at risk for exposure.

As yet, no orthopoxvirus vaccine has been deemed necessary or approved for use in animals in the United States.

To help prevent animal-to-human transmission of mpox in the United States, the CDC banned the importation of African rodents (rope squirrels, tree squirrels, African giant pouched rats, brush-tailed porcupines, dormice, and striped mice) following the 2003 outbreak linked to prairie dogs.

Although the likelihood is low, veterinarians may encounter an animal with suspected mpox. If this happens, infection control practices can help to protect the veterinary team, clients, and other patients from infection. Keep in mind that although direct contact appears to be the most common route for transmission of mpox from infected animals to humans, airborne transmission cannot be excluded.

• Have the animal enter and leave the clinic by a route that minimizes exposure to other animals and people.
• Take the animal to an examination or isolation room.
• Perform all treatments and diagnostics in the room.
• Limit staff access to the animal.
• Use personal protective equipment (PPE: gown, gloves, and N95 respirator or, if unavailable, surgical mask).
• Practice hand hygiene immediately after removing PPE.
• Consult with state or local health officials on how to dispose of contaminated waste. Do not dispose of waste, or any other contaminated materials, in landfills or dumps.
• Disinfect items that cannot be disposed of with standard hospital disinfectants (not quaternary ammonium products), using recommended dilutions and contact times.
• Clean and disinfect contaminated surfaces.
• Wash all launderable items (e.g., bedding or clothing) with hot water and detergent, taking care not to shake them (to avoid dispersing virus particles). Dry items in a hot-air dryer.
• Recommend to the owner that the animal, and any others that might have come into contact with it, be quarantined when returned home for at least 21 days after clinical signs were first noted.

As of August 1, 2022, mpox has been deemed a nationally notifiable condition. States are required to report confirmed or probable mpox cases to the CDC within 24 hours. Veterinarians who suspect an animal has mpox are advised to have the animal tested and to contact their state veterinarian or public health officials so they can investigate the source and circumstances of the infection and take measures to contain it.