Even if persons are constantly revealed to a large range of microorganisms in nature, only a small part of such microbes are able of interacting with the host in such a fashion that infection and illness will end in [1] [2] [3]. Disease-causing microorganisms are named pathogens [4] [5] [6]. Infection is the phenomenon by which the microorganism multiplies or grows in or on the host [1] [7] [8]. Infection does not inevitably conduct to illness as it is conceivable for the organism to grow in or on the host without provoking disease [9] [10] [11]. As an example, in the situation of enteric infections (i.e., diarrhea) induced by Salmonella, only half of the persons infected grow symptoms of the disease. An obvious pathogen is a microorganism apt for generating illness in both normal healthy and immunocompromised individuals. Opportunistic pathogens are frequently apt for provoking infections only in immunocompromised persons like burn patients, patients taking antibiotics, those with impaired immune systems, or elderly patients with diabetes. Opportunistic pathogens are current in nature and can occur in the human gut or skin without provoking illness [1].

To occasion disease, the pathogen has frequently first to expand inside or on the host. The period from infection to the manifestation of symptoms (diarrhea, fever, rash, etc.) is the incubation time (Table 1). Such time could extend from 6 to 12 hours in the case of norovirus diarrhea, or up to 30 to 60 days for the hepatitis A virus, which provokes liver disease. At any moment throughout infection, the pathogen may be liberated into nature by the host in feces, urine, or respiratory secretions. Even if the maximum liberation can happen at the highest point of the illness, it may also come before the initial symptoms. In the case of the hepatitis A virus, the maximum excretion in the feces takes place before the onset of signs of clinical disease. The level of organisms liberated into nature changes with the kind of organism and the pathway of transmission (Table 2). The level of enteric viruses throughout gastroenteritis can be as elevated as 10¹⁰ - 10¹² per gram of feces [1].

Pathogenic microorganisms commonly arise from an infected host (either human or either animal), or directly from nature. Numerous human pathogens could only be transmitted via direct or near contact with an infected person or animal. Examples comprise the herpes virus, Neisseria gonorrhoeae (gonorrhea), and Treponema pallidum (syphilis). This is due to their survival period outside the host is quite short. Pathogens transmitted through nature can survive from hours to years outside the host, depending on the organism and nature.

Pathogens could exit a host in respiratory secretions from the nose and mouth, or be shed on dead skin or in feces, urine, saliva, or tears. Therefore, they may pollute the air, water, food, or inanimate objects (fomites). When polluted air is inhaled or food consumed, the organisms are efficiently transmitted to another host, where the infection phenomenon starts again. Airborne transmission could happen through liberation from the host in droplets (i.e., coughing) or via natural (surf at a beach) or human activities (cooling towers, showers). Several organisms could be carried important distances, hundreds of meters (like Legionnaires’ disease and foot-and-mouth disease). Virus transmission via the airborne pathway can be both direct and indirect. The contagion of a host could be by direct inhalation of infectious droplets or via contact with fomites on which the airborne droplets have settled. Hand or mouth contact with the organism on the surface of fomite leads to the transfer of the organism to the portal of entry, i.e., nose, mouth, or eye [1].

Microorganisms transmitted by the fecal-oral pathway are commonly mentioned as enteric pathogens since they spread the disease to the gastrointestinal tract. They are peculiarly stable in water and food, and, in the instance of enteric bacteria, are apt for development outside the host under the suitable ecological conditions [1].

Waterborne diseases (Table 3) are those transmitted via the ingestion of polluted water that works as the passive carrier of the infectious agent. The traditional waterborne diseases, cholera and typhoid fever, which have considerably damaged densely populated regions during human history, have been efficiently dominated via the protection of water sources and via the treatment of polluted water supplies. Indeed, dominating such traditional diseases lights the significance of water supply treatment which greatly contributed to the decrease of infectious illnesses. Additional illnesses provoked by bacteria, viruses, protozoa, and helminths may as well be transmitted via polluted potable water. Nevertheless, it is crucial to keep in mind that waterborne diseases are transmitted by the fecal-oral route, from human to human or animal to human, so that potable water is only one of numerous probable sources of infection [1].

Water-washed illnesses are intimately related to bad hygiene and wrong sanitation. In such a situation, the accessibility of enough amount of water is usually viewed as more significant than the standard of the water. The shortage of water for washing and bathing participates in illnesses that have an effect on the eye and skin, comprising infectious conjunctivitis and trachoma, as well as in diarrhea diseases, which are a prime source of infant mortality and morbidity in poor countries. Diarrheal illnesses could be immediately transmitted via person-to-person contact, or indirectly via contact with infected foods and utensils employed by persons whose hands are fecally polluted. When sufficient water is accessible for hand washing, the happening of diarrheal illnesses has been illustrated to lower considerably, as has the prevalence of enteric pathogens like Shigella [1].

Water-based illnesses are provoked by pathogens that either spend all (or crucial parts) of their lives in water or depend on aquatic organisms for the completion of their life cycles. Instances of these organisms are the parasitic helminth Schistosoma and the bacterium Legionella, which lead to schistosomiasis and Legionnaires’ disease, respectively [1].

Water-related illnesses, like yellow fever, dengue, filariasis, malaria, onchocerciasis, and sleeping sickness, are transmitted via insects that multiply in water (like mosquitoes that transfer malaria) or live near water (e.g., the flies that transmit the filarial infection onchocerciasis). Such insects are known as vectors [1].

This review focuses on the fate and transport of enteric pathogens in nature. A special interest is accorded to viruses and COVID-19. Further, this work discusses the present facts concerning the proof for the emergence of SARS-CoV-2 and related CoVs in wastewater, controlling wastewater for comprehending COVID-19, and endurance and demobilization of CoVs and enveloped surrogate viruses in water and wastewater matrices.

There are numerous possible pathways for the transmission of excreted enteric pathogens [12] [13] [14]. The possibility of an enteric pathogen to be transmitted by any of such pathways relies considerably on its resistance to ecological features [15] [16] [17], which dominate its survival and its capability to be transferred by water or air, as it moves through the environment [18] [19] [20]. Numerous pathways could be categorized as “natural” pathways for the transmission of waterborne illness [21] [22] [23]; however, others (like the usage of urban wastewater for groundwater recharge, large-scale aquaculture projects, or land disposal of disposable diapers) are in fact novel pathways generated by modern human activities [1] [24] [25].

Human and animal excreta are sources of pathogens. Persons become contaminated via pathogens during consumption of polluted foods, like shellfish from infected waters or crops irrigated with wastewater; from potable polluted water; and via vulnerability to polluted surface waters, as may happen throughout bathing or at recreational sites. Moreover, such humans contaminated by the above routes become sources of pollution via their excrement, thereby completing the cycle [1].

In the main, viral and protozoan pathogens survive longer in nature than enteric bacterial pathogens (Table 5). How long a pathogen survives in a specific medium is a function of many complicated characteristics (Table 6). Of all of the elements, the temperature remains likely the most significant. Temperature is a well-defined element with a systematically anticipated impact on enteric pathogen survival in nature. As a rule, the lower the temperature, the longer the survival time. Nevertheless, freezing temperatures usually conduct to the death of

^aTypical average number of organisms/g feces. ^bEstimated average life of infective stage at 20˚C - 30˚C.

enteric bacteria and protozoan parasites. Even so, enteric viruses could stay infectious for months or years at freezing temperatures. Moisture―or lack thereof―could provoke reduced survival, and UV light from the sun is the main element in the demobilization of indicator bacteria in surface waters; therefore, die-off in marine waters could be anticipated by amount of exposure to daylight. Viruses stay much more resistant to demobilization by UV light [1].

Several laboratory investigations have established that the microflorae of natural waters and sewage are hostile to the survival of enteric pathogens [26] [27] [28]. As an illustration, enteric pathogens survive longer in sterile water than in water from lakes, rivers and oceans [29] [30] [31]. Bacteria in natural waters can feed upon indicator bacteria [32]. Suspended matter (clays, organic debris, and the like) and fresh or marine sediments have been shown to prolong their survival time (Figure 5) [1] [33] [34].

At the end of 2019, China announced an eruption of pneumonia of unknown etiology occurring in Wuhan (Hubei Province) [35]. Preliminary investigations affirmed that this eruption was related to a new coronavirus (nCoV) [36]. The nCoV was proved to possess 75% - 80% nucleotide similarity to severe acute respiratory syndrome coronavirus (SARS-CoV) [36] and was formally named as SARS-CoV-2 after being provisionally called as 2019-nCoV [35]. SARS-CoV-2 and SARS-CoV belong to the species Severe Acute Respiratory Syndrome-related Coronavirus in the subgenus Sarbecovirus of the family Coronaviridae that comprises a group of enveloped viruses with a single-stranded, positive-sense ribonucleic acid (RNA) genome. SARS-CoV and SARS-CoV-2 are distantly related to the Middle East respiratory syndrome coronavirus (MERS-CoV), which belongs to the Middle East Respiratory Syndrome-related Coronavirus species within the genus Betacoronavirus [35]. Further, SARS-CoV-2 is distantly linked to “classical” human CoV strains (229E, OC43, NL63, and HKU1) belonging to the genus Alphacoronavirus or Betacoronavirus that have been investigated since the 1960s and are evaluated to rise 15% - 30% of cases of frequent colds through the globe [35].

The illness provoked by SARS-CoV-2 is alluded to as coronavirus disease 2019 (COVID-19). Signs of COVID-19 at the beginning of disease comprise fever, myalgia, fatigue, and dry cough, and more than half of the patients developed dyspnea [35]. On March 11, 2020, it was announced that the present COVID-19 situation a global pandemic on the basis of “alarming levels of spread and severity, and by the alarming levels of inaction” [35].

Both viable SARS-CoV-2 and viral RNA are shed in bodily excreta, comprising saliva, sputum, and feces, which are posteriorly observed in wastewater. Even if it is accepted that the main transmission pathway of such viruses is inhalation via person-to-person and aerosol/droplet transmission and fomite and hand contamination, presently obtainable evidence shows the necessity for better comprehension of the function of wastewater [37] [38] [39] as a possible source of epidemiological data and as an element in the public health hazard. Recently, Kitajima et al. [35] rigorously consulted the actual information linked to the possibility of wastewater monitoring [40] [41] [42] for grasping the epidemiology of COVID-19. Considering the fast germination of SARS-CoV-2, acquired knowledge on human CoVs, SARS-CoV, MERS-CoV, and surrogate viruses could assist to tell prognosis of the probable ecological destiny and following dangers of SARS-CoV-2. Further, they defined important research necessities that will enhance comprehension of the appearance, continuity, and probable public health dangers related to SARS-CoV-2 in wastewater.

In the next sections, a special focus will be accorded to the proof for the emergence of SARS-CoV-2 and related CoVs in wastewater, controlling wastewater for comprehending COVID-19, and endurance and demobilization of CoVs and enveloped surrogate viruses in water and wastewater matrices.

This review focuses on the fate and transport of enteric pathogens in nature. A special interest is accorded to viruses and COVID-19. Further, this work discusses the present facts concerning the proof for the emergence of SARS-CoV-2 and related CoVs in wastewater, controlling wastewater for comprehending COVID-19, and endurance and demobilization of CoVs and enveloped surrogate viruses in water and wastewater matrices. From this work, the following conclusions can be drawn:

1) Now, huge knowledge gaps remain in the crucial contribution of wastewater in the transmission of SARS-CoV-2. Survival of SARS-CoV-2 in ecosystems, comprising wastewater and water, stays mainly obscure. The stability of SARS-CoV-2 is identical to that of SARS-CoV in aerosols and on surfaces. Employing an identical manner, the stability of SARS-CoV-2 in different water matrices has to be studied. The endurance of SARS-CoV-2 requires to be defined in wastewater and environmental water for tropical, subtropical, and temperate climatic zones since the endurance can be considerably changing in diverse temperatures. Further, the endurance of SARS-CoV-2 in wastewater and receiving waters and demobilization pathways, like predation, UV, sunlight [71] [72] [73], and disinfection [74] [75] [76] has to be studied. Information on SARS-CoV-2 reduction and/or demobilization by wastewater and water treatment technologies [77] [78] [79], like activated sludge, membrane filtration [80] [81] [82], coagulation-sedimentation [83] [84] [85], and disinfection (chlorine [86] [87] [88], chloramine, UV [89] [90], ozone [91], etc.) remains rare. If it is hard to estimate log₁₀ removal values of SARS-CoV-2 itself due to the availability of the virus and/or biosafety restrictions, model enveloped viruses such as human CoVs, MHV, or Pseudomonas phage Φ6 could be employed for laboratory- or pilot-scale tests [35].

2) Wastewater control remains crucial because WBE could furnish important data on the spread of contagions in society. Constant and methodical observation of wastewater can give early warning signs and will greatly distinguish undiagnosed or successive disease at the population level, thus alerting public health officials on the ongoing or future viral disease outbreaks. Nationwide and international wastewater surveillance campaigns should be carried out to better understand the temporal and spatial dynamics of disease prevalence, molecular epidemiology and evolution of the virus, and efficacy of public health interventions [35].

This research has been funded by the Research Deanship of University of Ha’il, Saudi Arabia, through the Project RG-191190.

The authors declare no conflicts of interest regarding the publication of this paper.

Ghernaout, D. and Ghernaout, B. (2020) Controlling COVID-19 Pandemic through Wastewater Monitoring. Open Access Library Journal, 7: e6411. https://doi.org/10.4236/oalib.1106411