Revisiting scrub typhus: A neglected tropical disease.

Scrub typhus is an under diagnosed re-emerging vector borne disease caused by an intracellular gram negative bacteria, Orientia. The disease is commonly prevalent in rural and hilly areas of Tsutsugumashi triangle. The diagnosis of the disease is very challenging due to similarity of its early symptoms with other febrile illnesses, like dengue and COVID 19, as well as non-availability of rapid, reliable and cost-effective methods. Moreover, the diverse clinical presentation in severe cases make it significant health problem. The occupational and behavioral risks responsible for the transmission lead to urgent need of vaccine development against the disease. The complete knowledge about its pathogenesis and the interaction with host's immune cells may help the scientists in developing the appropriate diagnostic methods as well as the vaccines.

The Temporal Lagged Relationship Between Meteorological Factors and Scrub Typhus With the Distributed Lag Non-linear Model in Rural Southwest China.

Background: Meteorological factors can affect the emergence of scrub typhus for a period lasting days to weeks after their occurrence. Furthermore, the relationship between meteorological factors and scrub typhus is complicated because of lagged and non-linear patterns. Investigating the lagged correlation patterns between meteorological variables and scrub typhus may promote an understanding of this association and be beneficial for preventing disease outbreaks. Methods: We extracted data on scrub typhus cases in rural areas of Panzhihua in Southwest China every week from 2008 to 2017 from the China Information System for Disease Control and Prevention. The distributed lag non-linear model (DLNM) was used to study the temporal lagged correlation between weekly meteorological factors and weekly scrub typhus. Results: There were obvious lagged associations between some weather factors (rainfall, relative humidity, and air temperature) and scrub typhus with the same overall effect trend, an inverse-U shape; moreover, different meteorological factors had different significant delayed contributions compared with reference values in many cases. In addition, at the same lag time, the relative risk increased with the increase of exposure level for all weather variables when presenting a positive association. Conclusions: The results found that different meteorological factors have different patterns and magnitudes for the lagged correlation between weather factors and scrub typhus. The lag shape and association for meteorological information is applicable for developing an early warning system for scrub typhus.

Clinical characteristics and risk factors for severe scrub typhus in pediatric and elderly patients.

BACKGROUND: Scrub typhus (ST) is a life-threatening infectious disease if appropriate treatment is unavailable. Large discrepancy of clinical severity of ST patients was reported among age groups, and the underlying risk factors for severe disease are unclear. METHODS: Clinical and epidemiological data of ST patients were collected in 55 surveillance hospitals located in Guangzhou City, China, from 2012 to 2018. Severe prognosis and related factors were determined and compared between pediatric and elderly patients. RESULTS: A total of 2,074 ST patients including 209 pediatric patients and 1,865 elderly patients were included, with a comparable disease severity rate of 11.0% (95% CI 7.1%-16.1%) and 10.3% (95% CI 9.0%-11.8%). Different frequencies of clinical characteristics including lymphadenopathy, skin rash, enlarged tonsils, etc. were observed between pediatric and elderly patients. Presence of peripheral edema and decreased hemoglobin were the most important predictors of severe illness in pediatric patients with adjusted ORs by 38.99 (9.96-152.67, p<0.001) and 13.22 (1.54-113.50, p = 0.019), respectively, while presence of dyspnea and increased total bilirubin were the potential determinants of severe disease in elderly patients with adjusted ORs by 11.69 (7.33-18.64, p<0.001) and 3.17 (1.97-5.11, p<0.001), respectively. Compared with pediatric patients, elderly patients were more likely to receive doxycycline (64.8% v.s 9.9%, p<0.001), while less likely to receive azithromycin therapy (5.0% v.s 41.1%, p<0.001). CONCLUSION: The disease severity rate is comparable between pediatric and elderly ST patients, while different clinical features and laboratory indicators were associated with development of severe complications for pediatric and elderly patients, which is helpful for diagnosis and progress assessment of disease for ST patients.

Ecological and behavioural risk factors of scrub typhus in central Vietnam: a case-control study.

BACKGROUND: The risk factors for scrub typhus in Vietnam remain unknown. Scrub typhus caused by Orientia tsutsugamushi often presents as an undifferentiated febrile illness and remains under appreciated due to the limited availability of diagnostic tests. This tropical rickettsial illness is increasingly recognized as an important cause of non-malaria acute undifferentiated fever in Asia. This study aimed to investigate behavioural and ecological related risk factors of scrub typhus to prevent this potentially life-threatening disease in Vietnam. METHODS: We conducted a clinical hospital-based active surveillance study, and a retrospective residence-enrolment date-age-matched case-control study in Khanh Hoa province, Vietnam, from August 2018 to March 2020. Clinical examinations, polymerase chain reaction and enzyme-linked immunosorbent assay IgM tests were applied to define cases and controls. All enrolled participants filled out a questionnaire including demographic socio-economic status, personal behaviors/protective equipment, habitat connections, land use, and possible exposure to the vector. Multivariable conditional logistic regression was used to define the scrub typhus associated risk factors. RESULTS: We identified 44 confirmed cases and matched them with 152 controls. Among cases and controls, the largest age group was the 41-50 years old and males accounted for 61.4% and 42.8%, respectively. There were similarities in demographic characteristics between the two groups, with the exception of occupation. Several factors were significantly associated with acquisition of scrub typhus, including sitting/laying directly on household floor [adjusted OR (aOR) = 4.9, 95% CI: 1.6-15.1, P = 0.006], household with poor sanitation/conditions (aOR = 7.9, 95% CI: 1.9-32.9, P = 0.005), workplace environment with risk (aOR = 3.0, 95% CI: 1.2-7.6, P = 0.020), always observing mice around home (aOR = 3.7, 95% CI: 1.4-9.9, P = 0.008), and use of personal protective equipment in the field (aOR = 0.4, 95% CI: 0.1-1.1, P = 0.076). CONCLUSIONS: Ecological and household hygiene-related factors were more associated with scrub typhus infection, than individual-level exposure activities in the hyper-endemic area. These findings support local education and allow people to protect themselves from scrub typhus, especially in areas with limitations in diagnostic capacity.