COVID-19, influenza A H5N1, monkeypox (mpox): is laboratory medicine ready for the next pandemic?

Coronavirus disease 2019 (COVID-19)

The World Health Organization (WHO) may have prematurely declared that the COVID-19 pandemic was no longer a global health emergency, despite the fact that the pandemic is far from over (1). The emergence of new, highly transmissible variants from the so-called “FLiRT” (F→L and R→T polymorphism at positions 456 and 346 of the spike protein) JN.1 lineage, now mainly comprising LB.1, KP.2(.3) and KP.3(.3.1) (2), has led to a significant increase in infection rates, followed by a rise in emergency room admissions and deaths (3). Unlike the early days of the pandemic, especially during the first two waves of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) when the scientific community was largely unprepared, the situation is now more controlled, largely due to advances in laboratory medicine. Enhanced testing capacities and the availability of antigen-detection rapid diagnostic tests (AG-RDTs) enable quick diagnosis of SARS-CoV-2 infection (4), facilitating timely isolation and patient care. Nonetheless, the current status of the COVID-19 pandemic should not lead to complacency, as new threats continue to emerge.

Influenza A strain H5N1

The first of these threats is the highly pathogenic “avian” influenza A H5N1 virus, which has caused significant outbreaks in birds. Commonly known as “bird flu”, this disease is typically transmitted through direct contact with infected animals (sick or dead poultry) or contaminated surfaces (5,6). Over the past 20 years, the WHO has reported 904 cases of H5N1 infection in humans in 24 different countries, with more than half (464; 51%) resulting in death (last update, September 27, 2024). The incubation period is variable, usually ranging from 1 to 5 days, but potentially extending up to 7 days (7). Initial symptoms can resemble those of other common influenza strains and COVID-19, including fever, conjunctivitis, cough, nasal congestion, sore throat, dyspnea, headache, myalgia and body aches, fatigue, and diarrhea (Table 1). In more severe cases, the disease can progress to pneumonia, potentially leading to acute respiratory distress syndrome (ARDS), altered mental status, and multi-organ failure (MOF), requiring hospitalization and emergency care (5). Recent outbreaks in wild birds, domestic birds, minks, dairy cows, and other animals, combined with genetic mutations, have heightened global concerns about the risk of spillover to humans (7). On August 14, 2024, the U.S. Centers for Disease Control and Prevention (CDC) reported that H5N1 bird flu is highly prevalent among wild birds, causing outbreaks in poultry and U.S. dairy cows, and noted several recent human cases among dairy and poultry workers. Accordingly, the CDC is actively monitoring the situation to prevent major outbreaks (8).

The laboratory diagnosis of influenza A H5N1 infection is similar to that of other influenza strains, and generally involves detecting either antiviral antibodies or viral material in body specimens. The most commonly used methods include: (I) serology (which has the major disadvantage of having very low sensitivity in the early phase of the disease, i.e., before antibody formation); (II) molecular biology techniques [including reverse transcription real-time polymerase chain reaction (RT-PCR), loop-mediated isothermal amplification (LAMP) and nuclear acid sequence-based amplification (NASBA)], which remain the gold standard and enable the detection of viral RNA in respiratory specimens (nasal and/or throat swabs) (9); and (III) rapid immunological tests (for detecting viral antigens) (9). As with COVID-19, the availability and validation of such tests are crucial for the management of large outbreaks, as they would allow timely diagnosis of infected and potentially infectious individuals, while easing the burden on routine clinical laboratories. A comprehensive analysis of over 20 influenza AG-RDTs available on the market published by Sakai-Tagawa in 2019 indicated satisfactory accuracy, with detection limits between 103 and 105 50% tissue culture infectious dose (TCID50)/100 µL for H5N1.

However, a significant issue is that most currently available AG-RDTs cannot specifically distinguish H5N1 from other influenza viruses (10). In most cases, these tests can only distinguish between influenza A and influenza B, and, to our knowledge, no AG-RDTs have been validated to specifically detect H5N1 (Table 1). Thus, there is an urgent need to develop widely accessible, cost-effective, user-friendly, and accurate tests to prepare for the potential evolution and person-to-person transmission of H5N1, which could pose a risk of a severe pandemic similar to that of Spanish flu or SARS-CoV-2 (11).

Monkeypox (mpox)

Mpox is an infectious disease caused by a member of the Orthopoxvirus genus, which also includes the smallpox virus. Like SARS-CoV-2 and avian flu, mpox is a zoonotic disease (12). The virus is thought to be carried by a number of small mammals (including nonhuman primates and rodents), although the exact animal reservoir is still unknown. Human-to-human transmission occurs mainly through close contact with infected individuals, by respiratory droplets, contact with skin, lesions, or contaminated materials like clothing or bedding. The incubation period ranges between 5 and 21 days (12). The initial symptoms are again poorly specific, and may include fever, chills, myalgia and body aches, sore throat, nasal congestion, cough, headache, and fatigue, which are followed by appearance of a cutaneous rash that typically originates from the face and then spreads to other parts, including palms and soles, evolving through sequential stages (macules, papules, vesicles, pustules, and finally scabs) (Table 1). The symptoms usually take between 2 and 4 weeks to resolve. Although in most cases there is full clinical resolution, certain high-risk individuals (e.g., children, pregnant women, immunocompromised and frail people) may have higher risk of developing severe disease and complications, which can include bacterial super-infections, pneumonia, and in rare cases, death (mortality rate initially ranged between 0.1% and 3.6% of affected individuals, but are now as high as 5–10% after emergence of Clade 1b) (12,13).

It is still uncertain whether the mpox virus, which was first identified in 1958 and detected in infected humans in 1970, will become a global threat. Nevertheless, the WHO has now declared mpox outbreak a public health emergency of international concern (PHEIC) due to the surge of cases outside the Congo, in some other African countries and even abroad (e.g., Sweden, United Kingdon, Thailand) (14). Again, laboratory testing will be crucial for the timely diagnosis, isolation and treatment of infected individuals. As with COVID-19 and H5N1, the gold standard for diagnosing mpox involves the detection of viral DNA on suspicious body samples (surface lesions, exudates, swabs, roofs, crusts) using molecular biology techniques (mostly with RT-PCR) (15). Research is currently underway to improve rapid testing capabilities, including the use of clustered regularly interspaced short palindromic repeats (CRISPR) technology for faster identification at the point of care (15). Although some AG-RDTs for mpox can be found in the market, extensive clinical validation for most of these tests has not yet been published (Table 1) (16). This is also confirmed by the fact that the WHO states that it is currently unclear how effectively mpox antigens can be detected by AG-RDTs, which samples are best for identification, or whether these tests are accurate enough for large-scale screening (17). Early detection of mpox is crucial for initiating timely treatment with tecovirimat (TPOXX), especially since rapid tests can identify the virus quickly. Starting TPOXX early can improve outcomes, although it less effective against the Clade 1b variant, which is linked to more severe disease (18). This makes rapid diagnosis and prompt intervention even more important.

Conclusions

One of the key lessons we have learned during the ongoing COVID-19 pandemic is that the availability of rapid diagnosis of infectious diseases through AG-RDTs is a cost-effective pillar of any strategy aimed at mitigating the impact of infectious diseases on the population, particularly for individuals at higher risk of developing severe forms of illness (19). AG-RDTs are also valuable for epidemiological purposes, for monitoring infection progression and patient infectivity, as the time to positivity often correlates well with viral load (20). Given this, there is an urgent need to accelerate the development and clinical validation of AG-RDTs for influenza A H5N1 and mpox. These tests must be validated by laboratory experts before they can be deployed for widespread testing, especially because the initial clinical signs and symptoms of these diseases can be quite similar (see Table 1). It is essential for the diagnostics industry and the scientific community to collaborate effectively to address this gap, ensuring preparedness and swift response in the event of future pandemics.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: This article was a standard submission to the journal. The article has undergone external peer review.

Peer Review File: Available at https://jlpm.amegroups.com/article/view/10.21037/jlpm-24-47/prf

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://jlpm.amegroups.com/article/view/10.21037/jlpm-24-47/coif). G.L. serves as the Editor-in-Chief of Journal of Laboratory and Precision Medicine. The other author has no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

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