Vaccinia Virus Natural Infections in Brazil: The Good, the Bad, and the Ugly

Abstract

The orthopoxviruses (OPV) comprise several emerging viruses with great importance to human and veterinary medicine, including vaccinia virus (VACV), which causes outbreaks of bovine vaccinia (BV) in South America. Historically, VACV is the most comprehensively studied virus, however, its origin and natural hosts remain unknown. VACV was the primary component of the smallpox vaccine, largely used during the smallpox eradication campaign. After smallpox was declared eradicated, the vaccination that conferred immunity to OPV was discontinued, favoring a new contingent of susceptible individuals to OPV. VACV infections occur naturally after direct contact with infected dairy cattle, in recently vaccinated individuals, or through alternative routes of exposure. In Brazil, VACV outbreaks are frequently reported in rural areas, affecting mainly farm animals and humans. Recent studies have shown the role of wildlife in the VACV transmission chain, exploring the role of wild rodents as reservoirs that facilitate VACV spread throughout rural areas. Furthermore, VACV circulation in urban environments and the significance of this with respect to public health, have also been explored. In this review, we discuss the history, epidemiological, ecological and clinical aspects of natural VACV infections in Brazil, also highlighting alternative routes of VACV transmission, the factors involved in susceptibility to infection, and the natural history of the disease in humans and animals, and the potential for dissemination to urban environments.

Synanthropic rodents as virus reservoirs and transmitters

“…Besides synanthropic species, other rodents can cocirculate in rural environments and wild and urban interface areas, where they contact other animals and people 10,15 . Wild rodents are reservoirs for hantavirus, vaccinia virus, and Lassa virus, among others [16][17][18][19] . 20 investigated rural settlements in Goiás (Brazil), and found 2.57% (n=12) positive rate for Orthohantavirus, equally distributed between women and men (n=6).…”

Identification of CP77 as the Third Orthopoxvirus SAMD9 and SAMD9L Inhibitor with Unique Specificity for a Rodent SAMD9L

“…MPXV is likely carried by rope squirrels in Africa (11). The spread of VACV in Brazil involves wild rodents as the reservoir or intermediate hosts (12). In contrast to their varied host range in nature, OPXV host ranges in tissue culture cells are almost universally broad (13).…”

Exposure of free‐ranging capybaras ( Hydrochoerus hydrochaeris ) to the vaccinia virus

“…The participation of capybaras in zoonosis transmission cycles as asymptomatic hosts and possible reservoirs have been reported (Valadas, Gennari, Yai, Rosypal, & Lindsay, ; Yai et al, ). The presence of the VACV in capybara blood and stool (Barbosa et al, ; Dutra et al, ) and in peridomestic rodents (Abrahão et al, ; Miranda et al, ; Peres et al, ) indicates that these animals may act as a source of the virus and serve as a link between wild and urban environments (Costa et al, ; Dutra et al, ; Oliveira et al, ). Virus transmission/circulation between different environments is favoured by the biological and behavioural characteristics of rodents, that is they are nocturnal, they live in overpopulated communities, and they practice coprophagia (Soetan, O'Connell, & Jones, ), which may have facilitated the VACV seropositivity found only in capybaras.…”