Asymptomatic Orthopoxvirus Circulation in Humans in the Wake of a Monkeypox Outbreak among Chimpanzees in Cameroon.

Sarah Anne J Guagliardo,Mary G Reynolds,Scott Epperson,Benjamin Monroe,Christian Moundjoa,Gordon Okpu,Michael B Townsend,Andrea M Mccollum,Panayampalli S Satheshkumar,Els Mathieu,Georges Alain Etoundi,Jillybeth Burgado,Ateba Athanase,Elisabeth Dibongue,Jeffrey B Doty

doi:10.4269/ajtmh.19-0467

Abstract

.Monkeypox virus is a zoonotic Orthopoxvirus (OPXV) that causes smallpox-like illness in humans. In Cameroon, human monkeypox cases were confirmed in 2018, and outbreaks in captive chimpanzees occurred in 2014 and 2016. We investigated the OPXV serological status among staff at a primate sanctuary (where the 2016 chimpanzee outbreak occurred) and residents from nearby villages, and describe contact with possible monkeypox reservoirs. We focused specifically on Gambian rats (Cricetomys spp.) because they are recognized possible reservoirs and because contact with Gambian rats was common enough to render sufficient statistical power. We collected one 5-mL whole blood specimen from each participant to perform a generic anti-OPXV ELISA test for IgG and IgM antibodies and administered a questionnaire about prior symptoms of monkeypox-like illness and contact with possible reservoirs. Our results showed evidence of OPXV exposures (IgG positive, 6.3%; IgM positive, 1.6%) among some of those too young to have received smallpox vaccination (born after 1980, n = 63). No participants reported prior symptoms consistent with monkeypox. After adjusting for education level, participants who frequently visited the forest were more likely to have recently eaten Gambian rats (OR: 3.36, 95% CI: 1.91–5.92, P < 0.001) and primate sanctuary staff were less likely to have touched or sold Gambian rats (OR: 0.23, 95% CI: 0.19–0.28, P < 0.001). The asymptomatic or undetected circulation of OPXVs in humans in Cameroon is likely, and contact with monkeypox reservoirs is common, raising the need for continued surveillance for human and animal disease.

Highlights

Monkeypox virus (MPXV) belongs to the genus Orthopoxvirus (OPXV), which includes Variola, Cowpox, and Vaccinia viruses
There are several candidate reservoirs for MPXV, we focused on contact with Gambian rats (Cricetomys spp.) because both laboratory and field studies have repeatedly implicated this species as a possible reservoir[20,21,22,23,28] and because contact with this species was common enough to render sufficient statistical power (> 50% of study participants reporting contact)
Participant ages ranged from 18 to 83 years; 50.8% were born after routine smallpox vaccination ceased in 1980

Summary

Introduction

Monkeypox virus (MPXV) belongs to the genus Orthopoxvirus (OPXV), which includes Variola, Cowpox, and Vaccinia viruses. Orthopoxviruses provide immunological cross-protection such that infection with one OPXV or immunization with Vaccinia virus (via smallpox vaccination) provides some degree of protection against the others in the genus.[1,2] Since the eradication of smallpox in 1980, there have been increasing OPXV outbreaks among both animals and humans, suggesting a shift in the ecology and evolution of OPXVs simultaneous with diminishing smallpox vaccine– derived immunity.[3] Monkeypox virus is endemic in West and Central Africa, and human infections are more frequently recognized.[4] In its most severe form, the clinical presentation of monkeypox is similar to that of smallpox, causing rash following a prodromal period of fever, malaise, headache, and lymphadenopathy.[5,6,7] The gravity of monkeypox disease is determined by the exposure route, the strain and dose of the infecting virus, and the baseline health status of the patient. Of the two viral clades, the Congo Basin clade is thought to have more severe disease presentation than the West African clade.[8,9]

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