Ecoepidemiologia do Vaccinia virus: conectando patógeno, hospedeiros e o ambiente

Abstract

The majority of emerging infectious diseases (EID) are caused by zoonotic pathogens. It is suggested that the increasing occurrence of EIDs is due to the lack of surveillance to prevent and control the spread of new pathogens, which has a significant impact on public health and, overall, on local and global economies. Vaccinia virus (VACV) is the causative agent of Bovine Vaccinia (BV), an occupational zoonosis that affects the dairy economy in Brazil since the late of 90s. However, aspects regarding VACV circulation in different environments, susceptibility of mammalian populations, and potentially distribution and dissemination to other hosts, in addition to the risks for public health, remain poorly explored. Thus, the goal of this study was to evaluate the distribution of VACV in different environments, associated risk/exposure factors, as well as the potential for dissemination to susceptible populations and the risks for public health. We evaluated different collections of mammals sampled in several environments, among them: 1) wild rodents and marsupials captured in an extremely preserved region of Amazon Forest; 2) domestic cats of large urban centers in Brazil; and 3) domestic dogs from an urban area in Belo Horizonte City and coatis (Nasua nasua) from Mangabeiras Municipal Park, an important natural area bordering the urban environment located in the South of Belo Horizonte City. To detect anti-Orthopoxvirus (OPV) neutralizing antibodies, a plaque reduction neutralization assay was performed on serum samples. Alternatively, an enzyme-linked immunosorbent assay (ELISA) was performed to detect IgG antibodies in serum samples from wild rodents and marsupial. In addition, VACV DNA was detected by real-time and conventional PCR in serum and annal swab samples, targeting C11R, A56R and A26L genes. Molecular results were confirmed by sequencing. After serological and molecular analyzes, no rodent, marsupial or bats samples tested positive for VACV or OPV, highlighting the absence of VACV circulation in a highly preserved region of Amazon Forest between 2005-2015. However, our results demonstrated the detection of VACV in coatis from wild environments bordering an urban area, with a seroprevalence of 14.4% of anti-OPV neutralizing antibodies. In addition, a seroprevalence of 19.1% was also observed in domestic dogs and 5.8% in domestic cats. Viral DNA was detected in 4 coatis, 5 domestic dogs and 6 domestic cats, demonstrating the circulation of two distinct VACV populations (virulent and non-virulent strains). The results indicate the absence of VACV circulation in the Amazon region, highlighting the possibility of a dilution effect, probably due to the highly preserved natural environment studied, although a great diversity of species were sampled. Another curious fact to be highlighted is the absence or reduced number of cattle herds in the studied environment when compared to Brazil and other South American countries. Certainly, most studies regarding VACV in Brazil were focused on outbreaks involving bovines and humans, and it is speculated that these animals could act as an excellent amplifying hosts, since the cattle are the main impacted hosts during BV due to the nature of infection. On the other hand, the results presented here suggest the circulation of VACV in wild and urban environments in Brazil, correlating with the risks for human health and consequently impact on public health. Our data also suggests that preventive strategies should be included to improve the surveillance in regions of high probability for the occurrence of EID such as VACV. Furthermore, the improvement of pathogens detection to the better understanding of their reservoirs, as well as the evaluation of some exposure factors that could favor emerging pathogens should be also considered. A further investigation of the dynamics between pathogens, environment, and hosts will be of great validity and could help reduce the impact on public health.