Experimental Infection of Cynomolgus Macaques (Macaca fascicularis) with Aerosolized Monkeypox Virus

Abstract

Monkeypox virus (MPXV) infection in humans results in clinical symptoms very similar to ordinary smallpox. Aerosol is a route of secondary transmission for monkeypox, and a primary route of smallpox transmission in humans. Therefore, an animal model for aerosol exposure to MPXV is needed to test medical countermeasures. To characterize the pathogenesis in cynomolgus macaques (Macaca fascicularis), groups of macaques were exposed to four different doses of aerosolized MPXV. Blood was collected the day before, and every other day after exposure and assessed for complete blood count (CBC), clinical chemistry analysis, and quantitative PCR. Macaques showed mild anorexia, depression, and fever on day 6 post-exposure. Lymphadenopathy, which differentiates monkeypox from smallpox, was observed in exposed macaques around day 6 post-exposure. CBC and clinical chemistries showed abnormalities similar to human monkeypox cases. Whole blood and throat swab viral loads peaked around day 10, and in survivors, gradually decreased until day 28 post-exposure. Survival was not dose dependent. As such, doses of 4×104 PFU, 1×105 PFU, or 1×106 PFU resulted in lethality for 70% of the animals, whereas a dose of 4×105 PFU resulted in 85% lethality. Overall, cynomolgus macaques exposed to aerosolized MPXV develop a clinical disease that resembles that of human monkeypox. These findings provide a strong foundation for the use of aerosolized MPXV exposure of cynomolgus macaques as an animal model to test medical countermeasures against orthopoxviruses.

Assessment of the Protective Effect of Imvamune and Acam2000 Vaccines against Aerosolized Monkeypox Virus in Cynomolgus Macaques

“…Pock lesions began to appear on day 6 postchallenge, and there was a peak in the number of lesions by day 9 (a mean of 51 lesions per animal). These data are in sharp alignment with other natural history and pathology studies conducted at our laboratories, as well as with work performed by Nalca et al (36). In contrast, in other vaccine trials where control animals have been challenged by a different route, such as the intravenous route with a dose 5 ϫ 10 7 PFU (16) or 2 ϫ 10 7 PFU (32), pock lesions ranging from 250 to Ͼ500 per animal appeared from days 3 to 6.…”

“…Thus, a well-defined animal model using monkeypox virus should mimic the natural course of smallpox disease. Macaques have been used at various stages of smallpox vaccine and antiviral research (16,(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36), and in each case the route of infection, dose, and choice of challenge strain have been key factors in determining whether the macaque model of monkeypox resembles human clinical variola virus infection.…”

Sequence of Pathogenic Events in Cynomolgus Macaques Infected with Aerosolized Monkeypox Virus

“…Thus, a mix of animals was studied; some had developed severe disease at the time of euthanasia, while some developed only mild disease. This approach has allowed the detailed study of the early events following challenge that were missing from studies based on animals with severe disease (22,23).…”

“…A deliberate release of variola or monkeypox virus, however, would probably be in aerosol form for rapid dispersion over large areas (21). A limited number of studies have used the aerosol route, characterizing the pathogenic events following aerosol monkeypox virus infection (22)(23)(24)). Zaucha and colleagues described the systemic dissemination of the monkeypox virus in cynomolgus macaques through a monocytic-cell-associated viremia, similar to that of variola in human beings (23).…”

“…Zaucha and colleagues described the systemic dissemination of the monkeypox virus in cynomolgus macaques through a monocytic-cell-associated viremia, similar to that of variola in human beings (23). More recently, two studies described the clinical progression of disease in NHPs following exposure to different doses of aerosolized monkeypox virus (22,24). These three studies described disease progression from 8 to 17 days after exposure.…”