Overview of the regulatory approval of tecovirimat intravenous formulation for treatment of smallpox: potential impact on smallpox outbreak response capabilities, and future tecovirimat development potential

Human monkeypox virus: Epidemiologic review and research progress in diagnosis and treatment

Monkeypox virus (MPXV) is responsible for causing a zoonotic disease called monkeypox (mpox), which sporadically infects humans in West and Central Africa. It first infected humans in 1970 and, along with the variola virus, belongs to the genus Orthopoxvirus in the poxvirus family. Since the World Health Organization declared the MPXV outbreak a "Public Health Emergency of International Concern" on July 23, 2022, the number of infected patients has increased dramatically. To control this epidemic and address this previously neglected disease, MPXV needs to be better understood and reevaluated. In this review, we cover recent research on MPXV, including its genomic and pathogenic characteristics, transmission, mutations and mechanisms, clinical characteristics, epidemiology, laboratory diagnosis, and treatment measures, as well as prevention of MPXV infection in light of the 2022 and 2023 global outbreaks. The 2022 MPXV outbreak has been primarily associated with close intimate contact, including sexual activity, with most cases diagnosed among men who have sex with men. The incubation period of MPXV infection usually lasts from 6 to 13 days, and symptoms include fever, muscle pains, headache, swollen lymph nodes, and a characteristic painful rash, including several stages, such as macules, papules, blisters, pustules, scabs, and scab shedding involving the genitals and anus. Polymerase chain reaction (PCR) is usually used to detect MPXV in skin lesion material. Treatment includes supportive care, antivirals, and intravenous vaccinia immune globulin. Smallpox vaccines have been designed with four givens emergency approval for use against MPXV infection.

Early administration of tecovirimat shortens the time to mpox clearance in a model of human infection

Despite use of tecovirimat since the beginning of the 2022 outbreak, few data have been published on its antiviral effect in humans. We here predict tecovirimat efficacy using a unique set of data in nonhuman primates (NHPs) and humans. We analyzed tecovirimat antiviral activity on viral kinetics in NHP to characterize its concentration-effect relationship in vivo. Next, we used a pharmacological model developed in healthy volunteers to project its antiviral efficacy in humans. Finally, a viral dynamic model was applied to characterize mpox kinetics in skin lesions from 54 untreated patients, and we used this modeling framework to predict the impact of tecovirimat on viral clearance in skin lesions. At human-recommended doses, tecovirimat could inhibit viral replication from infected cells by more than 90% after 3 to 5 days of drug administration and achieved over 97% efficacy at drug steady state. With an estimated mpox within-host basic reproduction number, R0, equal to 5.6, tecovirimat could therefore shorten the time to viral clearance if given before viral peak. We predicted that initiating treatment at symptom onset, which on average occurred 2 days before viral peak, could reduce the time to viral clearance by about 6 days. Immediate postexposure prophylaxis could not only reduce time to clearance but also lower peak viral load by more than 1.0 log10 copies/mL and shorten the duration of positive viral culture by about 7 to 10 days. These findings support the early administration of tecovirimat against mpox infection, ideally starting from the infection day as a postexposure prophylaxis.

Clinical Predictors of Monkeypox Diagnosis: A Case-Control Study in a Nonendemic Region during the 2022 Outbreak

Monkeypox (Mpox) is an emerging zoonotic disease with the potential for severe complications. Early identification and diagnosis are essential to prompt treatment, control its spread, and reduce the risk of human-to-human transmission. This study aimed to develop a clinical diagnostic tool and describe the clinical and sociodemographic features of 19 PCR-confirmed Mpox cases during an outbreak in a nonendemic region of northwestern Mexico. The median age of patients was 35 years, and most were male. Mpox-positive patients commonly reported symptoms such as fever, lumbago, and asthenia, in addition to experiencing painful ulcers and a high frequency of HIV infection among people living with HIV (PLWH). Two diagnostic models using logistic regression were devised, with the best model exhibiting a prediction accuracy of 0.92 (95% CI: 0.8-1), a sensitivity of 0.86, and a specificity of 0.93. The high predictive values and accuracy of the top-performing model highlight its potential to significantly improve early Mpox diagnosis and treatment in clinical settings, aiding in the control of future outbreaks.

In vitro susceptibility of eighteen clinical isolates of human monkeypox virus to tecovirimat

BACKGROUND

In 2022, an outbreak of mpox that started in European countries spread worldwide through human-to-human transmission. Cases have been mostly mild, but severe clinical presentations have been reported. In these cases, tecovirimat has been the drug of choice to treat patients with aggravated disease.

OBJECTIVES

Here we investigated the tecovirimat susceptibility of 18 clinical isolates of monkeypox virus (MPXV) obtained from different regions of Brazil.

METHODS

Different concentrations of tecovirimat were added to cell monolayers infected with each MPXV isolate. After 72 hours, cells were fixed and stained for plaque visualization, counting, and measurement. The ortholog of F13L gene from each MPXV isolate was polymerase chain reaction (PCR)-amplified, sequenced, and the predicted protein sequences were analyzed.

FINDINGS

The eighteen MPXV isolates generated plaques of different sizes. Although all isolates were highly sensitive to the drug, two showed different response curves and IC50 values. However, the target protein of tecovirimat, F13 (VP37), was 100% conserved in all MPXV isolates and therefore does not explain the difference in sensitivity.

MAIN CONCLUSIONS

Our results support screening different MPXV isolates for tecovirimat susceptibility as an important tool to better use of the restricted number of tecovirimat doses available in low-income countries to treat patients with mpox.