Primate Monkeypox Study Guide

Overview and Clinical Importance

Monkeypox (mpox) is an emerging zoonotic viral disease caused by monkeypox virus (MPXV), a double-stranded DNA virus in the genus Orthopoxvirus, family Poxviridae. Although first discovered in captive cynomolgus monkeys in 1958, the virus primarily circulates in African rodents, with primates serving as accidental spillover hosts. Following smallpox eradication in 1980, mpox has become the most significant orthopoxvirus infection affecting humans and nonhuman primates.

Etiology and Viral Characteristics

Virus Classification

Monkeypox virus belongs to the Orthopoxvirus genus, which also includes variola virus (smallpox), vaccinia virus, and cowpox virus. MPXV is a complex, enveloped, double-stranded DNA virus approximately 200-250 nanometers in diameter with a characteristic brick or box-shaped morphology under electron microscopy.

Viral Clades

Two distinct genetic clades exist with different virulence and geographic distribution:

Transmission and Epidemiology

Natural Reservoirs

Despite the misleading name, African rodents are the primary natural reservoir hosts, not primates. Suspected reservoir species include rope squirrels (Funisciurus spp.), sun squirrels, Gambian pouched rats (Cricetomys gambianus), and African dormice. Nonhuman primates are accidental spillover hosts and can develop clinical disease similar to humans.

Routes of Transmission

Animal-to-Animal and Animal-to-Human:

Direct contact with infectious rash, scabs, crusts, or bodily fluids including respiratory secretions, saliva, blood, and potentially urine and feces. Transmission occurs through broken skin, respiratory tract, or mucous membranes (eyes, nose, mouth). Bites and scratches from infected animals can transmit the virus. Handling infected animals, bushmeat consumption, and proximity to wildlife in endemic areas are risk factors.

Human-to-Animal Transmission:

Infected humans can transmit MPXV to primates and other susceptible animals through close contact, shared bedding, or contaminated environments. The 2003 U.S. outbreak demonstrated spillover from imported African rodents to prairie dogs and subsequently to humans.

Susceptible Primate Species

Documented natural or experimental infections in nonhuman primates include:

Cynomolgus macaques (Macaca fascicularis) - First species in which virus was identified. Rhesus macaques (Macaca mulatta) - Commonly used in research models. Chimpanzees (Pan troglodytes). Orangutans (Pongo pygmaeus). Various Cercopithecus species including sooty mangabeys.

Clinical Signs and Disease Progression

Incubation Period

The incubation period ranges from 6-13 days (range 5-21 days). Infected animals are not contagious during this period and may appear healthy.

Disease Phases

Phase 1: Invasion Period (Days 0-5)

Prodromal Phase: Fever (often high, greater than 38.5°C or 101.3°F). Intense headache and malaise. Lymphadenopathy - this is the KEY distinguishing feature from smallpox. Myalgia and back pain. Intense asthenia (profound weakness). Respiratory signs including cough, sore throat, nasal discharge may occur. Conjunctivitis and ocular discharge. Decreased appetite and lethargy.

Phase 2: Skin Eruption Period (Begins 1-3 days after fever onset)

The characteristic rash develops in distinct stages:

Distribution of Rash

Lesions typically begin on the face (95 percent of cases) and spread centrifugally to the trunk and extremities. Palms and soles are commonly affected (75 percent). Oral mucosa, conjunctiva, and genital/perianal areas may have lesions. Lesions typically develop synchronously and are generally in the same stage of development on any body region. Number of lesions ranges from a few to several hundred, with average around 100 lesions.

Severity and Complications

Most cases are self-limiting with recovery in 2-4 weeks. Severe disease is more common in:

Young animals and juveniles. Immunocompromised individuals. Pregnant females (risk of fetal transmission, abortion, stillbirth). Animals with underlying health conditions.

Potential complications:

Secondary bacterial infections of skin lesions. Pneumonia (can be severe and life-threatening). Encephalitis. Sepsis. Ocular involvement with corneal scarring. Dehydration and electrolyte imbalances. Death (higher with Clade I, younger animals).

Diagnosis

Clinical Diagnosis

Suspect monkeypox in nonhuman primates presenting with fever, lymphadenopathy, and characteristic progressive rash, especially with known exposure to infected animals or endemic areas.

Laboratory Confirmation

Specimen Collection:

Optimal specimens include swabs from skin lesions (roof or fluid of vesicles and pustules, dry scabs). Multiple samples from different lesion stages and body locations maximize detection. Submit specimens with detailed information including timing of fever onset, rash appearance, and current lesion stage.

PCR Testing (Gold Standard):

Real-time or conventional polymerase chain reaction (PCR) detects viral DNA in specimens. High sensitivity and specificity. Can differentiate orthopoxviruses and identify specific MPXV clades. Results typically available within 24-48 hours.

Electron Microscopy:

Can identify orthopoxvirus based on characteristic brick-shaped virion morphology. Cannot distinguish between orthopoxvirus species. Requires specialized equipment and expertise. Less sensitive than PCR.

Differential Diagnosis

Treatment and Management

Supportive Care

Most cases require only supportive treatment as the disease is typically self-limiting:

Isolation of infected animals. Fluid therapy for dehydration. Nutritional support. Pain management. Antipyretics for fever. Wound care for skin lesions. Treatment of secondary bacterial infections with appropriate antibiotics. Monitoring for complications.

Antiviral Therapy

Note: Antiviral therapy is primarily reserved for severe cases, immunocompromised animals, or those at high risk of complications. Efficacy data in nonhuman primates is derived from experimental studies.

Prevention and Control

Vaccination

JYNNEOS (Modified Vaccinia Ankara-Bavarian Nordic) is a non-replicating smallpox and monkeypox vaccine approved for humans. Provides cross-protection against orthopoxviruses. Pre-exposure prophylaxis for high-risk individuals. Post-exposure prophylaxis within 4-14 days may prevent or reduce disease severity.

Traditional smallpox vaccine (vaccinia virus, e.g., ACAM2000) provides approximately 85 percent protection against monkeypox but has more adverse effects.

Infection Control in Veterinary Settings

Personal Protective Equipment (PPE):

Gown, gloves, N95 respirator or equivalent, eye protection for all contact with suspected or confirmed cases. Remove and properly dispose of PPE after animal contact.

Patient Handling:

Do not allow suspected animals in waiting areas. Use dedicated isolation rooms. Limit staff contact with infected animals. Minimize handling and procedures.

Environmental Decontamination:

Clean and disinfect all surfaces, equipment, and enclosures. Use EPA-registered disinfectants effective against enveloped viruses. Properly dispose of contaminated materials. Handle bedding and waste with appropriate precautions.

Public Health and Zoonotic Significance

Monkeypox is a reportable zoonotic disease with significant public health implications. Veterinarians must notify state public health veterinarians and state animal health officials of suspected or confirmed cases.

Key Public Health Concerns:

Zoonotic transmission from infected primates to humans (veterinary staff, animal caretakers, researchers). Potential for establishing new animal reservoirs in non-endemic regions. Wildlife spillover risk. Biosecurity in research facilities, zoos, and sanctuaries housing nonhuman primates.

Occupational Risk:

Veterinary personnel, animal caretakers, and researchers working with nonhuman primates are at increased risk. Close contact, handling bodily fluids, and aerosol exposure during procedures increase transmission risk. Strict biosafety protocols and PPE are essential.

Memory Aids for NAVLE

MPOX = M.P.O.X.

M - Macules to pustules (synchronous progression)

P - Primates are SPILLOVER hosts (rodents are reservoirs)

O - Orthopoxvirus (DNA virus, brick-shaped)

X - X-tra lymph nodes (lymphadenopathy distinguishes from smallpox)

Clade Memory:

Clade I = Intense (Congo Basin, more Intense/severe, higher mortality)

Clade II = IIlder (West African, milder disease, 2022 outbreak)

Diagnostic Triad: F.L.R.

F - Fever with prodrome

L - Lymphadenopathy (KEY FEATURE!)

R - Rash (synchronous, centrifugal)

Rash Progression: My Pants Very Promptly Came

Macules - Papules - Vesicles - Pustules - Crusts