*Pathogenesis and Laboratory Diagnosis of Mpox: An Overview*

**Introduction**
Monkeypox (mpox), an emerging zoonotic disease caused by the *Monkeypox virus* (MPXV), has garnered global attention due to its increasing spread, particularly in Sub-Saharan Africa. As of August 2024, Sub-Saharan Africa remains the epicenter of the epidemic, with the Democratic Republic of the Congo (DRC) reporting over 2,500 confirmed cases and more than 150 fatalities this year alone. Neighboring countries, including Central African Republic, South Sudan, and Uganda, have also seen significant case surges, collectively reporting several hundred cases. The emergence of a new sub-lineage of clade I mpox virus (clade 1b), known for its higher virulence, has compounded the public health challenge in these regions, where access to healthcare remains limited. Understanding the pathogenesis and employing accurate laboratory diagnostic techniques are paramount for effective disease management and control.

**Pathogenesis of Mpox**

1. **Viral Entry and Initial Infection**
*MPXV* enters the host through broken skin, the respiratory tract, or mucous membranes. Transmission occurs via close contact with an infected person, contaminated materials, or zoonotic sources. The virus initially replicates at the entry site, with an incubation period ranging from 5 to 21 days. During this phase, the virus remains undetected as it prepares for systemic spread.

2. **Primary Viremia**
Following local replication, *MPXV* spreads through the lymphatic system to regional lymph nodes, entering the bloodstream, leading to primary viremia. This phase is associated with prodromal symptoms such as fever, headache, myalgia, and lymphadenopathy, which are critical for early disease identification. These symptoms precede the development of the characteristic rash, a key diagnostic feature of mpox.

3. **Systemic Spread and Secondary Viremia**
The virus further disseminates to various organs, including the skin, leading to secondary viremia. During this stage, the hallmark lesions of mpox—macules, papules, vesicles, and pustules—emerge, typically in a centrifugal pattern. The lesions are highly infectious, contributing to the spread of the virus within communities.

4. **Host Immune Response and Complications**
The host immune response plays a pivotal role in controlling the infection. Adaptive immunity, characterized by the production of virus-specific antibodies and T-cell responses, is crucial for viral clearance. However, in severe cases—especially those caused by clade I mpox—complications such as secondary bacterial infections, pneumonia, encephalitis, and sepsis may occur, resulting in increased mortality.

5. **Resolution and Viral Persistence**
In most cases, mpox is self-limiting, with the lesions resolving within 2 to 4 weeks. Recovery generally confers immunity, although the duration of this immunity remains under investigation. Notably, viral persistence in specific tissues, such as the oropharynx and genital tract, may contribute to continued viral shedding and transmission even after clinical recovery.

**Laboratory Diagnostic Methods for Mpox**

Accurate and timely diagnosis of mpox is essential for effective clinical management and outbreak control. The following laboratory diagnostic methods are integral to the identification and confirmation of mpox:

1. **Polymerase Chain Reaction (PCR)**
PCR is the gold standard for mpox diagnosis, detecting viral DNA in clinical specimens such as skin lesion swabs, blood, or respiratory secretions. PCR offers a high sensitivity (~98%) and specificity (~99%), making it the most reliable method for confirming mpox, particularly during the acute phase of infection when viral load is highest.

2. **Serological Testing (ELISA)**
ELISA detects antibodies against *MPXV* in blood samples, indicating either a past or ongoing infection. While serological tests are useful for epidemiological studies and cases where PCR is not feasible, their specificity (~95%) may be reduced due to cross-reactivity with other orthopoxviruses, with a sensitivity of approximately 85-90%.

3. **Virus Isolation and Culture**
Virus isolation involves culturing *MPXV* from clinical specimens, offering 100% specificity but lower sensitivity (70-80%). This method requires specialized facilities and is primarily used in research settings or in cases where other diagnostic methods are inconclusive.

4. **Electron Microscopy**
Electron microscopy allows for the direct visualization of viral particles in clinical specimens. While this method provides high specificity (100%), its sensitivity (60-70%) is lower, limiting its use to situations where rapid diagnosis is essential, and other methods are unavailable.

**Conclusion**

The pathogenesis of mpox and the application of robust laboratory diagnostics are crucial for managing this re-emerging viral threat. As new viral clades, such as clade 1b, continue to emerge, it is imperative to refine diagnostic methodologies and improve access to these technologies, particularly in resource-limited settings. Ongoing research and international collaboration are essential to enhance our understanding and response to mpox, ultimately leading to better patient outcomes and containment of the virus.

**References**

1. Bunge EM, Hoet B, Chen L, Lienert F, Weidenthaler H, Baer LR, Steffen R. The changing epidemiology of human monkeypox—A potential threat? A systematic review. PLoS Negl Trop Dis. 2022;16(2):e0010141.
2. Reynolds MG, Yorita KL, Kuehnert MJ, Davidson WB, Huhn GD, Holman RC, Damon IK. Clinical manifestations of human monkeypox influenced by route of infection. J Infect Dis. 2006;194(6):773-780.
3. McCollum AM, Damon IK. Human monkeypox. Clin Infect Dis. 2014;58(2):260-267.
4. Ladnyj ID, Ziegler P, Kima E. A human infection caused by monkeypox virus in Basankusu Territory, Democratic Republic of the Congo. Bull World Health Organ. 1972;46(5):593-597.
5. Karem KL, Reynolds M, Hughes C, Braden Z, Nigam P, Crotty S, et al. Monkeypox-induced immunity and failure of childhood smallpox vaccination to provide complete protection. Clin Vaccine Immunol. 2007;14(10):1318-1327.
6. Petersen BW, Kabamba J, McCollum AM, Lushima RS, Laven J, Karem K, et al. Vaccinating against monkeypox in the Democratic Republic of the Congo. Antiviral Res. 2019;162:171-177.
7. Sklenovská N, Van Ranst M. Emergence of Monkeypox as the most important orthopoxvirus infection in humans. Front Public Health. 2018;6:241.
8. Thornhill JP, Barkati S, Walmsley S, Rockstroh J, Antinori A, Harrison LB, et al. Monkeypox virus infection in humans across 16 countries—April–June 2022. N Engl J Med. 2022;387(8):679-691.
9. Yinka-Ogunleye A, Aruna O, Dalhat M, Ogoina D, McCollum A, Dosunmu E, et al. Outbreak of human monkeypox in Nigeria in 2017–18: A clinical and epidemiological report. Lancet Infect Dis. 2019;19(8):872-879.
10. Jezek Z, Fenner F. Human monkeypox. Karger Medical and Scientific Publishers; 1988.