How COVID-19 Impacts the Body

When COVID-19 first emerged, it was assumed that the virus induces only lung disease, but more and more studies have shown that the whole body gets affected. The consequences are tremendous. Understanding how the virus impacts the body helps to find and monitor treatment, but as well helps to identify and diagnose patients that have no access to PCR.

The virus enters the body via droplet infection through nose and throat and starts multiplying inside the body [1]. In case the immune system cannot stop the infection, the virus starts to contaminate the lungs [2]. This can lead to acute respiratory distress syndrom (ARDS) [3]. The rapid deterioration in some patients may be caused by cytokine storm, an overreaction of the immune system [4].

But other organs than the lungs can be affected too. How the virus spreads to other organs and if patients that are not critically ill are affected is still unclear.

Studies showed that a significant number of hospitalized patients had heart damage or arrhythmias [5, 6].

Among other organs the virus affects the blood itself. In one study 1/3 of ICU patients had abnormal blood clots, which can lead to pulmonary embolism or stroke [7]. This explains elevated d-dimer levels in COVID-19 patients and why not only patients with lung disease are at high risk, but also individuals with vascular disease, such as diabetes and high blood pressure.

One study showed that 27% of patients had kidney failure. Viral particles were found in the kidney, which suggests direct viral attack of the organ, but kidney injury could also be collateral damage, caused by ventilators and antiviral compounds. Cytokine storm can also reduce blood flow to the kidney. In addition, risk factors such as diabetes can also lead to pre-existing kidney damage. [8]

Affects on the brain are most likel underestimated and more studies are necessary. Patients with brain inflammation encephalitis, seizures, and hyper reaction of the sympathetic nervous system have been identified. One study reported traces of the virus in the cerebrospinal fluid, suggesting it directly infects the central nervous system. [9]

Evidence suggests the virus may infect even the lining of the lower digestive tract. The protein shell of the virus was found in gastric, duodenal and rectal cells, which suggests that the virus replicates in the gastrointestinal tract. [10]

Studies have shown that 1/3 of hospitalized patients have conjunctivitis (pink, watery eyes). It is not clear yet, if the virus infects the eyes directly or if this is a side effect. [11]

Injury of the liver and bile duct were also identified in COVID-19 patients. It is still unclear if the virus affects these organs directly or not. [12, 13]

Only recently, long-term damage of the lungs and blood vessels caused by the virus have been identified in patients that are already cured [14]. Most likely, more long-term damage will be observed, as more and more people get infected.

References

1. Sungnak W, et al. "SARS-CoV-2 entry factors are highly expressed in nasal epithelial cells together with innate immune genes." Nature medicine 26.5 (2020): 681-687.
2. Ziegler GK, et al. "SARS-CoV-2 receptor ACE2 is an interferon-stimulated gene in human airway epithelial cells and is detected in specific cell subsets across tissues." Cell (2020).
3. Xu Z, et al. "Pathological findings of COVID-19 associated with acute respiratory distress syndrome." The Lancet respiratory medicine 8.4 (2020): 420-422.
4. Ye Q, et al. "The pathogenesis and treatment of theCytokine Storm'in COVID-19." Journal of infection 80.6 (2020): 607-613.
5. Shi S, et al. "Association of cardiac injury with mortality in hospitalized patients with COVID-19 in Wuhan, China." JAMA cardiology (2020).
6. Wang D, et al. "Clinical characteristics of 138 hospitalized patients with 2019 novel coronavirus–infected pneumonia in Wuhan, China." Jama 323.11 (2020): 1061-1069.
7. Klok FA, et al. "Incidence of thrombotic complications in critically ill ICU patients with COVID-19." Thrombosis research (2020).
8. Diao, Bo, et al. "Human kidney is a target for novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection." MedRxiv (2020).
9. Moriguchi T, et al. "A first case of meningitis/encephalitis associated with SARS-Coronavirus-2." International Journal of Infectious Diseases (2020).
10. Xiao F, et al. "Evidence for gastrointestinal infection of SARS-CoV-2." Gastroenterology 158.6 (2020): 1831-1833.
11. Wu P, et al. "Characteristics of ocular findings of patients with coronavirus disease 2019 (COVID-19) in Hubei Province, China." JAMA ophthalmology 138.5 (2020): 575-578.
12. Zhang C, et al. "Liver injury in COVID-19: management and challenges." The lancet Gastroenterology & hepatology 5.5 (2020): 428-430. 
13. Fan Z, et al. "Clinical features of COVID-19-related liver damage." Clinical Gastroenterology and Hepatology (2020).
14. Nieß, A. M., et al. "Position Stand: Return to Sport in the Current Coronavirus Pandemic." (2020).