Monkeypox Disease (MPX): Origin, Transmission, Epidemiology, Symptoms, and Prevention

Table of Content:

• Introduction
• Origin
• Transmission
• Epidemiology
• MPXV, Gender, and Hormones
• Genome organization and Viral Entry Mechanism of MPXV
• Evolution of the MPXV genome
• Clinical Symptoms of MPXV
• Therapeutic Options and Prevention for MPXV
• Susceptibility to MPX Disease
• Diagnostic Assays for MPXV
• References

 Introduction

• MPX is a DNA virus from the Poxviridae family, genus Orthopoxvirus.
• Causes smallpox-like disease and is zoonotic, affecting both animals and humans.
• The primary host of MPX is still unidentified.
• The virus was first discovered in 1958 in monkeys during vaccine research.
• MPX has been reported in various reservoirs, particularly rodents and other small mammals.
• The first human case was reported in 1970 in Congo, leading to the naming of the disease as monkeypox.
• Initial cases were endemic to African countries.
• Human-to-human transmission became severe during the 1996–1997 outbreak.
• Transmission occurs through long-term close contact, respiratory droplets, contaminated personal items, and direct contact with rash regions.
• The first case outside Africa was reported in the U.S., linked to zoonotic transmission.
• The spread of MPX was facilitated by travel from African countries and animal importation.
• In 2022, the outbreak became international, resulting in a global health emergency declaration.
• WHO recommended renaming "monkeypox" to "mpox" on November 28, 2022, with both terms being used for one year.
• As of January 16, 2023, 110 countries reported MPX cases, with 103 reporting it for the first time.
• The total number of confirmed cases reached 84,716, with the U.S. reporting the highest number (29,980).
• A total of 80 deaths were reported globally, with the highest numbers in the U.S. (21), Brazil (14), Peru (12), Nigeria (7), Mexico (4), Ghana (4), Spain (3), and Cameroon (3).
• WHO assessed the worldwide risk as moderate, with high risk in the Americas, moderate in Africa, Eastern Mediterranean, Europe, and South-East Asia, and low risk in the Western Pacific region.
• Global cases peaked in August 2022, followed by a gradual decrease and stabilization.
• Future outbreaks are possible due to the virus’s potential for mutation and relaxation of safety measures.
• MPX was previously seen as less fatal than smallpox, but has become more pathogenic over time, raising global concern.
• Initially considered an issue in African countries, MPX has now attracted global attention from authorities, organizations, and researchers.

Origin

The family Poxviridae consists of 22 genera and 83 species, divided into two subfamilies:

• Chordopoxvirinae: 18 genera and 52 species.
• Entomopoxvarinae: 4 genera and 31 species.

Genus Orthopoxvirus affects both humans and animals, with 12 identified members, including:

• Variola virus (causes smallpox)
• MPXV (Monkeypox virus)
• Vaccinia virus (smallpox vaccine virus)
• Abatino macacapox virus
• Akhmeta virus
• Camelpox virus
• Cowpox virus
• Ectromelia virus
• Raccoonpox virus
• Skunkpox virus
• Taterapox virus
• Volepox virus

Two viral clades of MPXV have been identified:

• West African clade
• Central African (Congo Basin) clade

The Central African clade is more virulent than the West African clade:

• Associated with higher morbidity, death, human-to-human transmission, and viremia during the 2003 U.S. outbreak.
• Has a higher fatality rate (10%) compared to the West African clade (4%).

Differences in virulence between the clades are due to:

• Variabilities in genome organization.
• Deleted gene regions.
• Gene fragmentation in open reading frames.

Sample collection from different areas, individuals, and clades is crucial:

• Helps determine the genetic properties of MPXV.
• Essential for confirming cases and aiding in research.

Transmission of MPXV

Geographic Occurrence:

MPX has primarily been observed in West and Central Africa.

Modes of Transmission:

• Animal-to-Animal: Transmission can occur between animals.
• Animal-to-Human: Most common mode involves direct contact with an infected animal or its bodily fluids.
• Human-to-Human: Possible through various means, including:
• Direct contact with skin lesions of an infected person.
• Contaminated objects or surfaces (e.g., living in the same home or using the same dishes as an infected person).
• Close contact, fomites, or exposure to large respiratory droplets.
• New Findings: The CDC has also identified that human-to-human transmission can occur through hugging, kissing, and sexual intercourse (oral, anal, vaginal). There are concerns about potential genetic changes in MPXV that may facilitate easier transmission among humans.

Challenges in Identifying Exposure:

• In regions with frequent animal contact (e.g., rodent infestations, hunting, or preparing bushmeat), it is challenging to pinpoint the exact exposure source for human cases.

Notable Outbreaks:

• 2003 U.S. Outbreak: Linked to contact with diseased prairie dogs but with some risk of person-to-person transmission.
• 2018 U.K. Case: MPXV was transmitted from a patient to a health worker via contaminated bedding.
• 2022 U.K. Outbreak: Initially reported as imported or related to contacts of imported cases; all previous cases were linked to travel or household/healthcare contacts.

Global Cases:

• MPX cases detected in Israel and Singapore were related to travel from Nigeria.
• Presence in multiple regions suggests possible long-term undiscovered transmission.

Recent Findings:

• The CDC revised possible transmission routes to include:
• Hugging, kissing, and sexual intercourse (oral, anal, vaginal).
• Potential genetic changes in MPXV that may facilitate easier human-to-human transmission.
• 2022 European Outbreak:
• Most cases originated from the West African clade.
• Indicates a limitation in inter-human transmission compared to other clades.

Recent Developments

Pakistan: A case of mpox was confirmed in a man who had recently returned from Saudi Arabia. Sequencing to determine the strain is underway. The case led to heightened airport surveillance and contact tracing efforts. The patient's location became uncertain after initial testing in Peshawar, and health authorities are actively searching for him.

Global Alerts:

• The WHO declared the recent outbreak as a public health emergency of international concern due to the new variant.
• There have been significant outbreaks in the Democratic Republic of Congo, with over 27,000 cases and more than 1,100 deaths since January 2023.

Epidemiology

Initial Human Identification:

• Between 1980 and 1985, 282 cases were reported in Zaire.
• Affected individuals ranged from 1 month to 69 years old, with 90% being under 15.
• No mortality was reported in vaccinated patients.
• Average fatality rate in unvaccinated cases was 11%, with higher rates in children (15%).

Impact of Vaccination:

• Immunity against MPXV was previously conferred by the smallpox vaccine (vaccinia).
• The eradication of smallpox and the subsequent decrease in vaccination efforts reduced immunity against MPXV.
• This decline in vaccination contributed to the undervaluation of MPXV's threat.

Re-emergence and Global Spread:

• MPXV re-emerged in Nigeria and Bayelsa state in 2017 after a 39-year period of non-reporting.
• The virus was estimated to have been exported by travelers to Israel and other countries.
• Subsequent outbreaks were reported in 2018 and 2019.

Factors Contributing to Global Outbreaks:

• Factors include importation, shipping, travel, contact with infected animals, and populations at risk of MPXV.
• The cessation of smallpox vaccination likely revealed cross-immunity against MPXV and contributed to human-to-human transmission.

Current Situation and Global Spread:

• MPXV has reached developed countries, with cases reported outside Africa.
• In July 2021, two cases were reported in the U.S. in individuals returning from Nigeria.
• A British man tested positive on May 6, 2022, after visiting Nigeria.
• As of June 2022, about 1500 cases were reported in more than 43 countries, including North America and Europe.

Epidemiological Concerns:

• MPXV is common in central and western Africa but has spread to developed countries.
• In the U.S., there were 29,980 cases and 80 fatalities.
• The spread of MPXV globally underscores the need for improved surveillance and diagnostic programs.
• There is a concern that MPXV could become a pandemic, highlighting the importance of strategic planning to prevent further spread.

MPXV, gender, and hormones

Sex Differences in Infectious Diseases:

• Endocrine-immune relationships differ between males and females.
• Males are generally more susceptible to infections due to the effects of gonadal steroid hormones.
• Male androgens and female estrogens influence the immune system, affecting susceptibility and resistance to infections.

Impact of Sex Hormones:

• Androgens: Can suppress immune responses, increasing infection susceptibility in males.
• Estrogens: Influence infection-resistance genes and immune responses in females.

Infection Rates by Gender:

• In African MPX outbreaks, males generally constitute ≥ 50% of cases.
• Outside Africa, MPXV cases occur more frequently in males, particularly in adults.
• In the 2022 outbreak, males accounted for 98% of the cases.

Importance of Surveillance:

• Effective surveillance is crucial for understanding the epidemiological fluctuations of MPXV.

Viral Protein COP-A44L:

• MPXV encodes an ortholog to COP-A44L, a 3-β-hydroxysteroid dehydrogenase enzyme.
• COP-A44L is involved in forming steroid hormones (sex hormones and glucocorticoids) by converting pregnenolone to progesterone and dehydroepiandrosterone to androstenedione.
• Glucocorticoids have immuno-inhibitory and anti-inflammatory effects, impacting the immune response against the virus.

Role of A44L in Virulence:

• While COP-A44L is not essential for viral replication, it affects virulence by promoting steroid release.
• This action suppresses the immune system’s response, potentially increasing the severity of the infection.

Genome organization and viral entry mechanism of MPXV

Genome Organization:

• MPXV has a double-stranded DNA (dsDNA) genome of approximately 197.2 kb.
• The genome encodes 181 proteins and features covalently closed hairpin ends with no free 3′ or 5′ ends.
• It includes 10 kb inverted terminal repeats (ITR) at both ends.
• Genes are densely packed with intergenic regions typically shorter than 100 bp.
• Central Area: Contains "housekeeping" genes responsible for transcription, replication, and virion assembly.
• Terminal Domains: Genes in these regions vary among poxviruses and are involved in disease and host range.
• The complete genome sequence for the current outbreak (MPXV_U.S._2022_MA001) is available in the GenBank database (Accession ID: ON563414).
• The genome size is confirmed as 197,205 bp by Oxford nanopore technology.

Viral Structure:

• MPXV particles range from 200 to 250 nm in size.
• The virus has a core area with lateral bodies, dsDNA, and a lipoprotein envelope.

Viral Entry Mechanism:

Entry Pathways:

• Micropinocytosis
• Viral endocytosis
• Cell membrane fusion

Entry Sites:

• Nasopharyngeal
• Oropharyngeal
• Subcutaneous
• Intradermal
• Intramuscular

Replication and Spread:

• MPXV replicates in the cytoplasm of the host cell.
• Initial infection triggers inflammatory immune-mediated phagocytosis.
• MPXV spreads to blood, lymph nodes, tonsils, bone marrow, spleen, and other organs.

Viral Assembly and Release:

• MPXV mRNA is transcribed and translated to produce intracellular mature virions (IMV).
• IMVs contain viral DNA and are wrapped in Golgi apparatus-derived membranes to form intracellular enveloped virions (IEV).
• IEVs fuse with the host inner cell membrane to create cell-associated virions (CEV).
• CEVs are released into extracellular spaces, forming extracellular enveloped virions (EEV).

Evolution of the MPXV genome

Mutation Rate:

• Poxviruses mutate at a rate of approximately 10^−5 to 10^−6 mutations per replication site.

2022 Outbreak Findings:

• Sequence analyses of MPXV from the 2022 U.S. outbreak revealed many mutations compared to earlier MPXV sequences.
• Mutations mainly observed as 5′ GA-to-AA within the Apolipoprotein B mRNA Editing Catalytic Polypeptide-like 3 (APOBEC3) motif, indicating APOBEC3 cytosine deaminase activity.
• G-to-A mutations were more frequent in recent West African MPXV sequences (2017-2022) compared to pre-2017 West African or Congo Basin MPXV clades.

APOBEC3 Proteins:

• APOBEC3 proteins primarily act on single-stranded DNA and are known for their role in blocking RNA virus replication, including HIV.
• Their role in DNA viruses like MPXV is less studied but important for understanding mutation effects.

Genome Rearrangements:

• Analysis of MPXV sequences from Berlin (May-July 2022) showed non-synonymous amino acid changes and a gene duplication.
• Four genes near the 3′ end were disrupted or deleted due to an 856-nucleotide translocation between genome termini.
• Such rearrangements may provide fitness advantages and contribute to the virus's adaptation and increased human-to-human transmission.

Genome Plasticity:

• MPXV genome shows plasticity, particularly in the inverted terminal repeats (ITR) regions at the genome ends.
• These regions contain immunomodulatory host range factors affecting virulence.
• Modifications in ITR regions are a key mechanism for orthopoxviruses' adaptability after host changes.

Differences in Clades:

• Significant differences in deletions and insertions in the ITR regions between Western and Central African MPXV clades.
• Similar differences were observed in sequences from the 2003 U.S. outbreak.

Implications:

• Mutation rate, adaptability, and genetic evolution contribute to MPXV's increased transmissibility, virulence, and immune evasion.
• These factors could lead to a rise in MPX cases globally in the near or long term.

Clinical Symptoms of MPXV

Overview of Symptoms and Demographics:

• Historical Data (1970-2019): Cases predominantly reported in males. Post-2022 outbreak, 98% of cases are men, primarily those who have sexual intercourse with other men (gay or bisexual) and are in their thirties.

Common Symptoms:

• 96% of cases exhibit rashes.
• 69% show flu-like symptoms.

Typical Symptoms and Complications:

• Common Symptoms: Fever, headache, myalgia, backache, lymphadenopathy, chills, exhaustion, and rashes.
• Complications: Respiratory distress/bronchopneumonia, sepsis, gastrointestinal/mouth and throat ulcers, fever, superinfection of skin, inflammation/lymphadenopathy, corneal infection, skin scarring/cellulitis, and skin lesions.
• Duration: Clinical signs generally last 2-4 weeks and may present suddenly or mildly.
• Severity: Varies between individuals.

Incubation and Progression:

• Incubation Period: Approximately 7-21 days post-infection.
• Initial Symptoms: Fever, headache, myalgia, backache, lymphadenopathy, chills, exhaustion, and rashes.
• Probable Complications: Bacterial superinfection, corneal infection, sepsis, dehydration, bronchopneumonia, and respiratory distress.

Case Studies:

• 2003 Outbreak (U.S.): A hospitalized child with severe symptoms including fever, headaches, muscle aches, fatigue, chills, swollen lymph nodes, and rashes. Symptoms progressed to include lesions on the trunk, extremities, and other body parts. The patient eventually recovered after symptoms started to crust.
• 2016 Case (Democratic Republic of Congo): A four-year-old boy presented with fever, rhinitis, conjunctivitis, cough, and vesiculopapular rashes. Despite supportive treatment, the child passed away on day 12, and measles tests were negative.
• 2017-2018 Nigeria Outbreak: 122 confirmed cases with vesiculopustular rashes across the body, fever, pruritus, headache, and lymphadenopathy.

2022 Outbreak Observations:

London HCID Center Report:

• 197 reported cases, all males, with 196 being gay, bisexual, or having sexual intercourse with other men.
• Symptoms: Mucocutaneous lesions primarily in genital and perianal regions. Non-specific symptoms and new symptoms such as rectal pain and penile edema were reported.
• Comparison to Previous Outbreaks: Previous cases focused on trunk, face, legs, head, and arms. Current outbreaks show more lesions in genital and perianal areas.

Conclusions:

• No conclusive evidence of sexual transmission of MPX, but recent outbreaks show a pattern of symptoms in sexually active populations.
• Clinicians should consider a broad range of symptoms for accurate diagnosis, treatment, and prevention.

Therapeutic Options and Prevention for MPXV

Treatment:

• Supportive Care: For mild cases, supportive care including pain relief, hydration, and symptomatic management is generally sufficient.
• Antiviral Medications: Specific MPXV treatments are not available. However, antiviral drugs effective against smallpox are sometimes used:
• Tecovirimat (TPOXX or ST-246): Approved for smallpox, effective in animal models for MPXV. It inhibits viral envelope VP37. It has been shown to be effective when administered before or after symptom onset.
• Brincidofovir and Cidofovir: DNA polymerase inhibitors, used in severe cases. Brincidofovir has shown effectiveness for Orthopoxvirus infections, while cidofovir's efficacy for MPXV is established in animal studies.
• Vaccinia Immune Globulin (VIG): Used to reduce adverse effects of live-vaccinia vaccines (e.g., ACAM2000). Its efficacy against MPXV is not proven and is used under investigational protocols.

Vaccination:

• Smallpox Vaccines: Effective in cross-protecting against MPXV.
• JYNNEOS (Imvamune/Imvanex): A live-attenuated, non-replicating vaccine, approved in the U.S. and Europe. Provides protection against both smallpox and MPXV. Two doses are required for optimal protection.
• ACAM2000: A live-attenuated, replicating vaccine, approved in the U.S. since 2007. Causes replication of the virus inside cells and may have severe side effects. It is used for individuals at high risk, such as laboratory researchers and military personnel.
• Vaccine Availability and Use:
• Vaccination rates declined after the eradication of smallpox in 1980.
• New smallpox vaccines were produced due to concerns about biological threats and MPXV outbreaks.
• Vaccination post-symptom onset is not recommended by the CDC.
• Aventis Pasteur Smallpox Vaccine (APSV): Available under investigational protocols but considered less significant against MPXV.

Future Directions:

• Investigational Vaccines: Ongoing research into gene and protein subunit vaccines targeting Orthopoxvirus protective elements as safer alternatives.
• Vaccine Programs: WHO and FDA are planning future vaccination programs and evaluating vaccine effectiveness.

Clinical Considerations:

• Antiviral Use: Reserved for severe cases, including those with compromised immune systems, children, pregnant or breastfeeding women, and lesions in sensitive areas (e.g., mouth, eyes, genitals).
• Monitoring and Evaluation: Continuous monitoring of vaccine and antiviral efficacy, and consideration of new therapeutic options are essential for effective MPXV management.

Susceptibility to MPX Disease

1. Vaccination Status:

• Historical Vaccination: Smallpox vaccination provides cross-protection against MPXV. With smallpox eradicated in 1980, vaccination rates have dropped. Studies show nearly zero vaccination rates in people born after 1979, while those born before 1966 had high vaccination rates (about 90%).
• Current Vaccines: There are two smallpox vaccines approved for MPXV: JYNNEOS (non-replicating) and ACAM2000 (replicating). The efficacy of these vaccines in preventing MPX infection depends on the vaccination status and timing relative to exposure.

2. Age:

• Historical Data: Older individuals who were vaccinated against smallpox might have some level of immunity. For example, in the 2003 outbreak, a vaccinated individual had milder symptoms compared to those who were not vaccinated.
• Current Outbreaks: Younger individuals, who are less likely to have been vaccinated, may be more susceptible to severe MPX symptoms.

3. Sex and Risk Groups:

• Recent Trends: In the 2022 outbreak, most cases were among men, particularly those engaging in sexual contact with other men. This demographic showed higher susceptibility and severity.
• Sexual Transmission: While the exact mechanism of sexual transmission is not fully understood, it appears to play a significant role in the spread among this group.

4. Co-infections and Immunosuppression:

• HIV Co-infection: Individuals with HIV or other forms of immunosuppression experience more severe symptoms and higher mortality rates due to MPX.
• Other Health Conditions: Immunocompromised individuals are at increased risk of severe disease outcomes.

5. Animal Reservoirs and Vectors:

• Animal Contact: Exposure to animals that may harbor MPXV increases susceptibility. Identifying and managing animal reservoirs and vectors is crucial for preventing human infection.

6. Socioeconomic and Environmental Factors:

• Displacement and Refugee Crises: Refugee situations and large-scale displacements increase the spread of infectious diseases, including MPX. The lack of proper healthcare and living conditions exacerbates the risk.
• Crowd Management: Events that involve large crowds, such as the FIFA World Cup 2022, can facilitate the spread of MPX and other infectious diseases. Effective crowd management and preventive measures are essential to minimize risks.

7. Public Immunity and Social Factors:

• Population Immunity: General low immunity in populations, especially in regions where vaccination rates have declined, increases susceptibility.
• Social Behavior: Social interactions and practices, including those related to sexual activity and public gatherings, impact the spread and susceptibility to MPX.

Recommendations for Prevention and Management:

• Vaccination Programs: Increase vaccination coverage, especially in high-risk groups and regions with low immunity.
• Public Awareness: Educate populations about MPX symptoms, transmission routes, and preventive measures.
• Health and Safety Measures: Improve healthcare access, especially for refugees and displaced individuals, and implement robust public health measures during large gatherings.
• Research and Monitoring: Continue studying MPXV’s transmission mechanisms, vaccine efficacy, and socio-environmental factors affecting susceptibility.

Diagnostic Assays for MPXV

1. Viral Culture/Isolation:

• Description: Cultivates live virus from patient specimens to identify and characterize the virus.
• Pros: Provides a pure culture for accurate species identification.
• Cons: Time-consuming (takes several days), requires skilled technicians, and is susceptible to bacterial contamination.

2. Electron Microscopy:

• Description: Visualizes viral particles in specimens like scabs or vesicular fluid using negative staining.
• Pros: Direct visualization of poxvirus particles.
• Cons: Requires specialized equipment and highly skilled personnel, and may not be available in all laboratories.

3. Immunohistochemistry:

• Description: Detects orthopoxvirus-specific antigens in biopsy specimens.
• Pros: Helps identify the presence of the virus in tissue samples.
• Cons: Not specific to MPXV alone; requires high-level laboratory expertise.

4. Serology (Anti-Orthopoxvirus IgG and IgM):

• Description: Measures antibodies against orthopoxviruses using immunofluorescence or neutralization assays.
• Pros: Can detect exposure to orthopoxviruses.
• Cons: Antibody testing alone is not recommended due to potential interference from previous vaccinations; more useful for retrospective analysis.

5. Conventional and Real-Time PCR (RT-PCR):

• Description: Amplifies and detects MPXV DNA in lesion material. Real-time PCR provides quantitative data.
• Pros: Highly sensitive and specific for detecting viral DNA; RT-PCR protocols can be adapted for different strains.
• Cons: Requires expensive equipment and reagents, and is sensitive to contamination. Specific RT-PCR assays (e.g., for West African MPXV or OPX3) need careful design and updates due to potential mutations.

6. Tetracore Orthopox BioThreat Alert:

• Description: Point-of-care test that detects orthopoxvirus antigens in lesion material.
• Pros: Simple to use and does not require extensive training; quick results.
• Cons: Less accurate than PCR; may not detect all MPXV strains and is more suitable for endemic areas.

Emerging and Advanced Techniques:

7. CRISPR-Cas-based Systems:

• Description: Portable systems combining CRISPR-Cas12 with isothermal amplification for rapid detection.
• Pros: High sensitivity and potential for field deployment.
• Cons: Still in development; requires validation for widespread use.

8. RT-PCR for Specific Genes:

• Description: Targeted RT-PCR assays for specific MPXV genes (e.g., F3L-gene).
• Pros: High sensitivity with low limit of detection (LOD).
• Cons: Requires precise design and implementation; still needs widespread validation.

9. SNP-Based Detection:

• Description: Uses CRISPR-Cas12a to detect single nucleotide polymorphisms (SNPs) in viral DNA.
• Pros: High sensitivity and ability to distinguish MPXV from other orthopoxviruses.
• Cons: Requires specialized knowledge and technology; still under development.

Best Practices for Diagnostic Testing:

• Sample Collection: Use skin lesion material (swabs, exudates, or crusts) for the most accurate results. Follow standard precautions to prevent contamination.
• Combined Approach: Utilize a combination of diagnostic methods, including molecular assays and serological tests, along with clinical and epidemiological data for comprehensive case confirmation.
• Updating Protocols: Regularly update diagnostic protocols and primer sequences based on emerging data and mutations.

Challenges and Considerations:

• Resource Limitations: PCR and advanced techniques may not be accessible in all settings, particularly in resource-limited areas.
• Field Testing: Point-of-care tests like Tetracore Orthopox BioThreat Alert provide rapid results but may have lower accuracy compared to PCR.

Reference

• Karagoz, Aysel, et al. "Monkeypox (mpox) virus: Classification, origin, transmission, genome organization, antiviral drugs, and molecular diagnosis." Journal of infection and public health 16.4 (2023): 531-541.
• “Monkeypox.” World Health Organization, World Health Organization, www.who.int/health-topics/monkeypox#tab=tab_1. Accessed 16 Aug. 2024. 
• “Mpox (Monkeypox).” World Health Organization, World Health Organization, 18 Apr. 2023, www.who.int/news-room/fact-sheets/detail/monkeypox.