## 1 Introduction
### Previous Research Results on the Etiology of Keshan Disease  
The etiology of Keshan disease is currently not clear. There are more than 10 theories about the etiology. Current research on the etiology of Keshan disease focuses on two aspects: biogeochemical etiology and biological etiology.  
1. Biogeochemical etiology A. Environmental element deficiency etiology In the 1960s, the Keshan Disease Research Laboratory of Xi'an Medical University proposed the hypothesis of soil and water etiology and found that the pathological changes in white muscle disease caused by selenium deficiency in animals in Keshan disease areas were similar to those of Keshan disease, so it was suggested that selenium deficiency was the cause of Keshan disease [8]. However, selenium deficiency cannot explain all the epidemiological characteristics of Keshan disease. Keshan disease does not occur in areas with low selenium, and there is also Keshan disease in areas with sufficient selenium [9]. Moreover, selenium deficiency does not change correspondingly with the seasonal and annual high incidence of Keshan disease. There is no significant difference in selenium and blood selenium between children with and without the disease in the disease area, so selenium deficiency is not the only factor [10]. At the same time, epidemiological investigations found that manganese can promote the excretion of selenium, and abundant manganese can further aggravate myocardial damage, suggesting that abundant manganese is related to the onset of Keshan disease [11].  
B. Lack of protein amino acids and vitamins Experiments conducted by [PERSON] and others found that the total weight gain, food utilization rate, and glutathione peroxidase activity in the whole blood of rats fed with low selenium and low protein were lower than those of rats fed with low selenium and high protein, and the detection rate of myocardial lesions was higher [12]. The supplementation of protein has a protective effect on the myocardium of rats. Through a comparative analysis of the amino acid content in the main grain in the disease area and the free amino acid content and antioxidant capacity in the plasma of the residents, it was found that the sulfur amino acid level in the population in the disease area was at a critical deficiency state, which may lead to a decrease in the antioxidant capacity of the body, thereby inducing the onset of Keshan disease [13].  
Studies have shown that the total amount of vitamin E in the plasma of the population in the disease area is significantly lower than that in the non-disease area, and the content of alpha-tocopherol, which has the strongest antioxidant effect in vitamin E, is generally lower than that in the non-disease area. Studies have found that the content of polyunsaturated fatty acids in grain in the disease area is significantly increased, which can lead to a relative lack of vitamin E, thereby reducing the antioxidant capacity of the body and inducing the onset of Keshan disease [1].  
1. Biological etiology Previous studies have suggested that factors such as simple selenium deficiency cannot fully explain the epidemic pattern of Keshan disease, but some characteristics are consistent with the characteristics of biological factor infection, such as the isolation of multiple viruses from the myocardial tissue of Keshan disease, including Cossackie B group virus [14], chlorogenic acid, T-2 toxin [15], and fusarium toxins [16]. It is believed that viruses are also factors that cause Keshan disease.