key: cord-0945674-l957zskw authors: Fernandez-Montero, Jose Vicente; Soriano, Vicente; Barreiro, Pablo; de Mendoza, Carmen; Artacho, Miguel Ángel title: Coronavirus and other airborne agents with pandemic potential date: 2020-09-24 journal: Curr Opin Environ Sci Health DOI: 10.1016/j.coesh.2020.09.001 sha: 2fcf45394b9a1e63851abedb2c72d2efdb48c1f0 doc_id: 945674 cord_uid: l957zskw The recent emergence of a novel coronavirus (SARS-CoV-2) has caused a pandemic, in what is the most severe infectious disease outbreak in many decades. Other infective agents such as Influenza as well as other neglected viruses such as Lassa, Nipah or Poxviruses are also a cause for concern due to its attack rate and potential for global spread. Drug-resistant bacteria, such as Mycobacterium tuberculosis are already a significant public health issue in many countries, and it is expected that they will be expanding in the near future. Finally, airborne bioterrorism agents have high morbidity and mortality rates, and should be looked with concern in the current international unrest. Traditionally, the respiratory transmission of infective agents has been classified in different categories depending on the size of the inhaled particles. Whereas airborne transmission is defined by the inhalation of small particles (<5 µm), droplet transmission involves larger particles 1 . A further route of transmission, aerosols, are defined as the presence of solid or fluid particles in a gas, such as air. This has significant implications in terms of transmission prevention -larger particles tend to travel longer distances-but also in pathophysiological terms, since airborne particles tend to deposit on the lung alveoli and droplet transmission tends to involve contact with mucosae 2 . Aerosol or airborne pathogens are particularly concerning, due to its high infection rate that, if linked with significant mortality rates, can lead to global health crises. The current collusion of several factors (population movements, natural catastrophes, climate change, wars, deprivation, etc) is causing a globalisation of infections and public health issues, with significant clinical, social and economic repercussions, as the current SARS-CoV-2 pandemics is showing. In December 2019 an outbreak of pneumonia of unknown cause was reported in Wuhan, China. Samples from bronchial lavages (BAL) in patients diagnosed with this pneumonia revealed the existence of a new beta-coronavirus (SARS-CoV-2), found to be the causative agent of this respiratory syndrome 3 . In March 2020, the World Health Organisation (WHO) declared the worldwide expansion of SARS-CoV-2 a pandemic, and, as of June 2020, over 26 million cases have been diagnosed, causing over 800.000 deaths in 188 countries 4 . In epidemiological terms, this is the largest outbreak of an infectious disease since the 2009 Influenza H1N1 pandemic 5 . Initial cases of SARS-CoV-2 infections, clinically named CoVid-19, were linked with exposures in wet markets 9 . The genomic characterisation of SARS-CoV-2 showed similarities to that of two bat coronavirus (bat-SL-CoVZC45 and bat-SL-CoVZXC21), and, to a lesser extent, with SARS-CoV and MERS-CoV 7 . Initial reports confirmed an early zoonotic or environmental transmission, followed by sustained person-toperson transmission in the community. Further reports confirmed cluster transmission of SARS-CoV-2 10 , in keeping with droplet transmission. SARS-CoV-2 is considered to be transmitted mostly by small respiratory droplets (<5µm of diameter), through respiratory tract or eye mucosae after close contact (<1 meter) from an infected individual 11 .Transmission through fomites has also been described, since SARS-CoV-2 can remain viable and infective in droplets for over 3 hours, and up to 72 hours in other surfaces 12 . Faecal-oral transmission has also been considered (studies have reported positive faecal SARS-CoV-2 PCR in 36-53% of patients 13 , whereas vertical transmission 14 is less plausible, since there is no solid evidence regarding the presence of SARS-CoV-2 in amniotic fluid, cord blood or breast milk 15 .Parenteral transmission is unlikely due to the low prevalence of detectable viraemia in CoVid-19 patients 16 along with generally low serum viral loads 17 . However, further research in this area is warranted. SARS-CoV-2 has an incubation period of 14 days from exposure, with most patients developing symptoms after 4-5 days 18 . Most patients present with mild coryzal symptoms (mostly fever, fatigue and cough), anosmia, dysgeusia as well as occasional vomiting and diarrhoea. Severe disease occurs in approximately 20% of cases, and admission to intensive care units (ICU) is required in 5% of patients, due to respiratory distress, heart ischemia, arrhythmias or immune hyperreactivity 19 . Mortality rates range from 1.5 to 13% depending on the series 20 Tocilizumab has shown some efficacy in severely ill patients, particularly in those with raised IL-6 levels 27 . Finally, remdesivir, a prodrug of an adenosine analogue has displayed in vitro activity against SARS-CoV and MERS-CoV polymerases 28 . A randomised study in patients with severe CoVid-19 did not show significant differences on mortality, clinical improvement nor length of hospitalisation 29 . Further trials, particularly in patients with milder disease, are warranted. Other treatment strategies, such as the use of interferon, hepatitis C NS5B polymerase inhibitors, ivermectin or plasma from recovered patients are being assessed. Also, several clinical trials on vaccines are ongoing ( Table 1) . In actual pandemic potential, though mutations or transmission between humans in the setting of travels to risk areas could increase its incidence in the future. 39 . Despite being known as a cause of mild respiratory infections in young children, it has also been described as a causative agent in severe respiratory infections in adults, particularly among immunocompromised patients 40 . Hence, besides influenza A and B viruses, Influenza C might be a respiratory pathogen associated with outbreaks, particularly among children and young adults. Hence, the confluence of higher prevalence of MDR and XDR-TB in densely populated countries, deprivation, lack of access to public healthcare along with globalisation and major population movements give MDR-TB a potential for further expansion and seriously putting at risk the achievement of the WHO "End-TB" initiative 46 . Lassa virus (LASV) is the agent responsible for the Lassa haemorrhagic fever, an endemic disease in Western Africa. Its seroprevalence is variable in different areas in that region, ranging from 8-52% depending on the series 47 . Though mostly a rodent-borne virus, LASV has also a potential for human-to-human transmission through contact with body fluids and aerosol droplets, particularly in healthcare settings in some developing countries in Africa. It is estimated that 100000-300000 people are infected with LASV every year in endemic areas 48 . Lassa fever J o u r n a l P r e -p r o o f symptomatology is highly variable, including multiorgan damage, haemorrhage, central nervous system involvement, kidney damage or gastrointestinal symptoms. Mortality rates can be as high as 39% in vulnerable groups 49 .There are no vaccines available against LASV. Ribavirin (RBV) has shown to reduce mortality, and is the treatment of choice along with supportive therapy 50 . Even when being a rodent-borne virus, the risk of human-to-human transmission, particularly in limited-resource settings, along with an increased mobility in the setting of globalisation, confer LASV a potential for severe regional outbreaks and also for further transmission outwith endemic areas 51 . Nipah virus (NiV) is a zoonotic pathogen, prevalent in Asia and the Pacific. Infective agents have been and can be used as weapons of mass destruction. In order to be effective, these agents need to show high morbidity or mortality, be easily transmittable, particularly on a human-to-human manner, cause social disruption and require special actions in terms of preparedness. Anthrax is a potentially airborne disease, cause by Bacillus anthracis, a sporulating, gram positive rod, which can cause a broad spectrum of conditions in humans. Inhalation of spores of anthrax causes a biphasic disease, starting with a prodromic phase, consisting on flu-like symptoms, that 4-5 days later can progress to a bacteriaemic phase, with haemorrhagic mediastinitis, necrotizing pneumonia or shock, with high rates of mortality despite antibiotic therapy 53 after. Though smallpox has been eradicated, it has been found to be a potential agent for bioterrorism due to its high transmission rates and mortality and its stability in the environment. Though not generally included in routine vaccination schemes anymore, there is a potential to escalate the production of smallpox vaccine should an outbreak develop. Furthermore, tecovirimat, a smallpox virion maturation inhibitor has shown its efficacy 55 . Other poxviruses, such as monkeypox, though not having a significant potential for airborne transmission, could also be modified in order to make it a potential bioterrorism agent. The ongoing SARS-CoV-2 pandemic is arguably the most severe health threat the world has faced in decades. The emergence of this new coronavirus, with a high transmission rate and significant mortality rates, has had a significant impact in many public healthcare systems, and has brought the attention to the risk of further pandemics caused by airborne agents. Coronaviruses or Influenza viruses might be the virus species with a higher potential for future pandemics, as has been shown in the past. Though its spread might happen at a slower rate, drug-resistant TB is arguably a major health problem issue, and can be a more common problem in low prevalence areas due to globalisation and population movements. Other viruses, such as MERS-CoV, Lassa, Nipah or Poxviruses, might be present just in some geographical areas, but have shown the potential of causing local outbreaks that can lead to a wider spread of the disease (Table 2) . 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