Pathology of Severe Fever with Thrombocytopenia Syndrome

Abstract

Severe fever with thrombocytopenia syndrome (SFTS) is a novel viral infectious disease with high case fatality rate (CFR). SFTS is caused by a novel phlebovirus, SFTS virus (SFTSV). SFTS, a tick-borne viral infection, was reported to be endemic to central and northeastern China and is also endemic to South Korea and western Japan. Patients with SFTS show symptoms of fever, general fatigue, and gastrointestinal symptoms such as diarrhea, whereas those severely ill with SFTS usually show gastrointestinal hemorrhage and deteriorated consciousness. The CFR of SFTS patients ranges from 5 to 40%. Because the time from the discovery of SFTS is short, pathological studies on SFTS remain limited. However, the existing pathological studies revealed that SFTSV replicated mainly in the lymphoreticular organs such as lymph nodes, spleen, and liver. Furthermore, SFTSV antigen-positive cells showed multi-organ infiltration, including to central nervous cells, kidneys, and lungs. Virus infection-related hemophagocytic syndrome associated with cytokine storm is also seen in most severe SFTS patients, suggesting that the mechanisms behind the high CFR may be multi-organ failure induced by hemophagocytic syndrome and coagulopathy due to disseminated intravascular coagulation causing bleeding tendency. To reduce the morbidity and mortality of SFTS, understanding of the pathophysiology of SFTS is required.