Transmission Routes Analysis of SARS-CoV-2: A Systematic Review and Case Report

Abstract

The global outbreak of SARS-CoV-2 spread rapidly throughout the world which transmitted among humans through various routes. Asymptomatic (carriers) and possible fecal-oral transmission, resulted into a large-scale spread. These issues pose great challenges to disease diagnosis and epidemic control. We obtained data on 29 cases of COVID-19 patients in Jinan, China, and reported the clinical data of asymptomatic patients confirmed with stool samples positive. Some patients with gastrointestinal infections are secondary to pulmonary infections, and during the patients' recovery period, the virus may still existin the patient's gastrointestinal tract over 7 days. We combined with epidemiological and clinical data of asymptomatic patients to analyze the possible routes of viral transmission and infection, including eyes-nose, hands-eyes, fecal-oral, and eyes-oral, et al., thus first presented the two-way transmission through eyes-oral. Through associating infection symptoms with the transmission routes of virus and the patient course of the disease, we expect to provide guidelines for clinical diagnosis and the basis for suppressing the spread of the virus and antiviral treatment.

Keywords: COVID-19; SARS-CoV-2; asymptomatic patients; eyes-oral transmission; transmission routes.

Figure 1

Symptoms according to day of illness and hospitalization among the cases confirmed SARS-CoV-2. Representative cases were combined the timeline of positive throat and anal swabs. Case07-10 were treated in Jinan infectious disease hospital and the remaining cases were reported in other hospitals. The patients are some particular cases of being discharged. After the throat swab turned to negative, the stool samples of patients became positive again appeared 5–7 days after discharged, or even longer.

Figure 2

Different clinical symptoms reflect different transmission pathways of SARS-CoV-2. Patients with different clinical symptoms may be closely related to the route of the virus during transmission. The infection sites of virus causing different clinical symptoms and directly affects the course of disease.

Figure 3

The routs of SARS-CoV-2 infection and transmission in eyes. Eyes are important portals of entry for virus. After SARS-CoV-2 infected and replicated in eyes, it will be transmitted through two ways: one is outward transmission, eye secretions, or tears with virus contaminate the hands, and then there is a risk of transmission of the virus through hands. Another route is inward transmission. If the virus infected person though eyes, conjunctival secretions, and tears can flow into the mouth through the nasopharyngeal tube then reach the lungs or gastrointestinal tract and more infections occur.

Figure 4

The transmission pathways of the SARS-CoV-2 in vitro and in vivo. Although direct droplet transmission is the main route route of transmission, fecal excretion, environmental contamination, and fomites might contribute to viral transmission. The prevention and control principles of infectious diseases should include the control of spatter and droplet transmission, contact transmission, fecal-eye transmission, nasal-eye transmission, oral-eye transmission, and the transmission of ocular secretions and tears.

Figure 5

Possible mechanisms of blood transmission after viral infection. After SARS-CoV-2 enters into the lung from mouth and throat and infects cells, the virus replicates in the cell and releases more new viruses. Massive accumulation of SARS-CoV-2 leads to a surge of immune cells and pro-inflammatory cytokines, which resulting in a rapid increase in CK levels in the blood, or releasing more virus particles into the blood circulation. The virus and cytokines positively induce high expression of ACE2 in the intestinal epithelium and other organs, which accelerates overexpression of ACE2 and viral binding, causing the systemic infections with the virus.

Figure 6

Systemic transmission pathways and susceptible organs of the SARS-CoV-2. SARS-CoV-2 was transmitted in a more diverse way among human, respiratory transmission, fecal-oral, hand-oral, eye-nose-oral, stool-hands- oral transmission and blood transmission.