Table 6.
Key differences between "summer type" and "autumn-winter type" scrub typhus in China
| The summer type | The autumn-winter type | References | |
|---|---|---|---|
| Seasonal distribution of human cases | Between March and November with a peak occurrence in the summer between June and August | Exclusively from September to December with a peak occurrence in October | [5-7] |
| Geographical distribution | Endemic in southern China (south of the Yangtse River), including Guangdong, Hainan, Guangxi, Fujian, Zhejiang, Yunnan, and Hunan province. | Endemic in northern China (north of the Yangtse River), including Shandong, northern Jiangsu, Tianjing, Shanxi, Hebei, and Henan province | [5-7] |
| Key reservoir hosts | Rattus losea, R. flavipectus, and Apodemus agrarius | A. agrarius, Cricetulus triton, and R. norvegicus. | [6,7] |
| Key vector chigger mites | Leptotrombidium deliense | L. scutellare | [5-8] |
| Virulence of O. tsutsugamushi isolates | More virulent, because: (1) Being tested with mice, the median lethal dose (LD50) values of O. tsutsugamushi isolates were 10-5 – 10-8; (2) O. tsutsugamushi could be successfully isolated from cases by normal experimental mice without any treatment | Less virulent, because: (1) Partial O. tsutsugamushi isolates do not lead to death of mice; (2) Being tested with mice, LD50 values of most O. tsutsugamushi isolates were 10-0.5 – 10-3; (3) In order to isolate O. tsutsugamushi successfully from cases, the experimental mice must be treated by cyclophosphamide to suppress immunity | [5,7] |
| Key serotypes | Karp type, Gilliam type, and Kato type | Gilliam type | [5-7,9-11,14,19] |
| Key genotypes* | Karp type | Kawasaki type | [12-14,20-22] |
| Clinical features and complications | Cases have the common clinical features of scrub typhus such as fever, cutaneous rash, eschar and local lympadenopathy. However, the associated complications of this type scrub typhus were severe | Cases also have the common clinical features of scrub typhus such as fever, cutaneous rash, eschar and local lympadenopathy. However, the associated complications of this type of scrub typhus were less severe than those of the summer type | [5-7,15-18,28] |
* Note: In China, the genotypes of scrub typhus have not been systematically studied until now. Data about genotypes of scrub typhus provided in the Table were only based on the primary results obtained in a few of areas in China. Karp types were identified as the key genotypes of the summer scrub typhus in Guangdong, Fujian, Hainan province in southern China [12-14], while Kawasaki types were identified as the key genotypes of the autumn-winter type scrub typhus in Shandong, northern Jiangsu province in northern China [14,20-22]