The Constant Threat of Zoonotic and Vector-Borne Emerging Tropical Diseases: Living on the Edge

Key Points Severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV) are zoonotic pathogens that can cause severe respiratory disease in humans. Although disease progression is fairly similar for SARS and MERS, the case fatality rate of MERS is much higher than that of SARS. Comorbidities have an important role in SARS and MERS. Several risk factors are associated with progression to acute respiratory distress syndrome (ARDS) in SARS and MERS cases, especially advanced age and male sex. For MERS, additional risk factors that are associated with severe disease include chronic conditions such as diabetes mellitus, hypertension, cancer, renal and lung disease, and co-infections. Although the ancestors of SARS-CoV and MERS-CoV probably circulate in bats, zoonotic transmission of SARS-CoV required an incidental amplifying host. Dromedary camels are the MERS-CoV reservoir from which zoonotic transmission occurs; serological evidence indicates that MERS-CoV-like viruses have been circulating in dromedary camels for at least three decades. Human-to-human transmission of SARS-CoV and MERS-CoV occurs mainly in health care settings. Patients do not shed large amounts of virus until well after the onset of symptoms, when patients are most probably already seeking medical care. Analysis of hospital surfaces after the treatment of patients with MERS showed the ubiquitous presence of infectious virus. Our understanding of the pathogenesis of SARS-CoV and MERS-CoV is still incomplete, but the combination of viral replication in the lower respiratory tract and an aberrant immune response is thought to have a crucial role in the severity of both syndromes. The severity of the diseases that are caused by emerging coronaviruses highlights the need to develop effective therapeutic measures against these viruses. Although several treatments for SARS and MERS (based on inhibition of viral replication with drugs or neutralizing antibodies, or on dampening the host response) have been identified in animal models and in vitro studies, efficacy data from human clinical trials are urgently required. Supplementary information The online version of this article (doi:10.1038/nrmicro.2016.81) contains supplementary material, which is available to authorized users.

Introduction An epidemic of Coronavirus Disease 2019 (COVID-19) began in December 2019 in China leading to a Public Health Emergency of International Concern (PHEIC). Clinical, laboratory, and imaging features have been partially characterized in some observational studies. No systematic reviews on COVID-19 have been published to date. Methods We performed a systematic literature review with meta-analysis, using three databases to assess clinical, laboratory, imaging features, and outcomes of COVID-19 confirmed cases. Observational studies and also case reports, were included, and analyzed separately. We performed a random-effects model meta-analysis to calculate pooled prevalences and 95% confidence intervals (95%CI). Results 660 articles were retrieved for the time frame (1/1/2020-2/23/2020). After screening, 27 articles were selected for full-text assessment, 19 being finally included for qualitative and quantitative analyses. Additionally, 39 case report articles were included and analyzed separately. For 656 patients, fever (88.7%, 95%CI 84.5–92.9%), cough (57.6%, 95%CI 40.8–74.4%) and dyspnea (45.6%, 95%CI 10.9–80.4%) were the most prevalent manifestations. Among the patients, 20.3% (95%CI 10.0–30.6%) required intensive care unit (ICU), 32.8% presented with acute respiratory distress syndrome (ARDS) (95%CI 13.7–51.8), 6.2% (95%CI 3.1–9.3) with shock. Some 13.9% (95%CI 6.2–21.5%) of hospitalized patients had fatal outcomes (case fatality rate, CFR). Conclusion COVID-19 brings a huge burden to healthcare facilities, especially in patients with comorbidities. ICU was required for approximately 20% of polymorbid, COVID-19 infected patients and hospitalization was associated with a CFR of >13%. As this virus spreads globally, countries need to urgently prepare human resources, infrastructure and facilities to treat severe COVID-19.

In recent decades, several new diseases have emerged in different geographical areas, with pathogens including Ebola virus, Zika virus, Nipah virus, and coronaviruses (CoVs). Recently, a new type of viral infection emerged in Wuhan City, China, and initial genomic sequencing data of this virus do not match with previously sequenced CoVs, suggesting a novel CoV strain (2019-nCoV), which has now been termed severe acute respiratory syndrome CoV-2 (SARS-CoV-2). Although coronavirus disease 2019 (COVID-19) is suspected to originate from an animal host (zoonotic origin) followed by human-to-human transmission, the possibility of other routes should not be ruled out.