Epidemiology and Risk Factors for Notifiable Scrub Typhus in Taiwan during the Period 2010-2019

Association of scrub typhus with the risk of venous thromboembolism and long-term mortality: a population-based cohort study

BACKGROUND

The existing literature lacks studies examining the epidemiological link between scrub typhus and deep vein thrombosis (DVT) or pulmonary embolism (PE), and the long-term outcomes. The objective of this study is to explore the potential association between scrub typhus and the subsequent risk of venous thromboembolism, and long-term mortality.

METHOD

This nationwide cohort study identified 10,121 patients who were newly diagnosed with scrub typhus. Patients with a prior DVT or PE diagnosis before the scrub typhus infection were excluded. A comparison cohort of 101,210 patients was established from the general population using a propensity score matching technique. The cumulative survival HRs for the two cohorts were calculated by the Cox proportional hazards model.

RESULT

After adjusting for sex, age, and comorbidities, the scrub typhus group had an adjusted HR (95% CI) of 1.02 (0.80-1.30) for DVT, 1.11 (0.63-1.93) for PE, and 1.16 (1.08-1.25) for mortality compared to the control group. The post hoc subgroup analysis revealed that individuals younger than 55 years with a prior scrub typhus infection had a significantly higher risk of DVT (HR: 1.59; 95% CI: 1.12-2.25) and long-term mortality (HR: 1.75; 95% CI, 1.54-1.99).

CONCLUSION

The scrub typhus patients showed a 16% higher risk of long-term mortality. For those in scrub typhus cohort below 55 years of age, the risk of developing DVT was 1.59 times higher, and the risk of mortality was 1.75 times higher. Age acted as an effect modifier influencing the relationship between scrub typhus and risk of new-onset DVT and death.

Climate influences scrub typhus occurrence in Vellore, Tamil Nadu, India: analysis of a 15-year dataset

Climate is one of the major factors determining the prevalence and seasonality of vector borne diseases like scrub typhus (ST). We analyzed, the association of the meteorological factors like temperature, rainfall and humidity with scrub typhus using the 15 years scrub typhus data from a tertiary care hospital in Vellore, South India. Demographic data of permanent residents of Vellore, who had IgM ELISA results for scrub typhus for the time period of May 2005 to April 2020 were included. Meteorological data was correlated with the monthly scrub typhus cases; negative binomial regression model was used to predict the relation between scrub typhus occurrence and climate factors. Maximum number of ST cases were reported between the months August and February with October recording the highest number of cases. Elderly people, farmers, agricultural workers and housewives were at higher risk for scrub typhus. For an increase of 1 °C in mean temperature, the monthly ST cases reduced by 18.8% (95% CI - 24.1, - 13.2%). On the contrary, for 1 percent increase in mean relative humidity (RH), there is an increase of 7.6% (95% CI 5.4, 9.9%) of monthly ST cases. Similarly, an increase of 1 mm of rainfall contributed to 0.5 to 0.7% of monthly ST cases (after 2 months) depending on the variables included in the analysis. This study provides information that meteorological factors influence ST occurrence in Vellore. The rise of scrub typhus cases is maximal 2 months post rainfall. Whereas a rise in relative humidity, causes a rise in scrub typhus cases in same month, while rise in temperature has a negative impact on scrub typhus during the same month. These findings based on a retrospective analysis need validation by prospective studies.

Infestation of Oriental House Rat (Rattus tanezumi) with Chigger Mites Varies along Environmental Gradients across Five Provincial Regions of Southwest China

Chigger mites are the exclusive vector of scrub typhus. Based on field investigations of 91 survey sites in 5 provincial regions of Southwest China, this paper reported variations of chigger infestation on the oriental house rat (Rattus tanezumi) along various environmental gradients. A total of 149 chigger species were identified from 2919 R. tanezumi in the 5 provincial regions, and Leptotrombidium deliense (a major vector of scrub typhus in China) was the first dominant chigger species, followed by Ascoschoengastia indica and Walchia ewingi. Rattus tanezumi had a stable overall prevalence (PM = 21.10%), mean abundance (MA = 7.01), and mean intensity (MI = 33.20) of chiggers with the same dominant mites in the whole Southwest China in comparison with a previous report in Yunnan Province, but chigger infestations on R. tanezumi varied along different environmental gradients. Rattus tanezumi in mountainous landscape had a higher infestation load of chiggers with higher species diversity than in flatland landscape. The infestation was higher at lower altitudes and latitudes. A high intensity of vegetation coverage was associated with high infestations. The results reflect the environmental heterogeneity of chiggers on the same host species. Warm climate and high relative humidity are beneficial to chigger infestation on R. tanezumi.

Scrub typhus seroprevalence from an eastern state of India: findings from the state-wide serosurvey

BACKGROUND

Scrub typhus is a mite-borne infectious disease caused primarily by the obligate intracellular bacteria Orientia tsutsugamushi, which is transmitted by chigger mites. The objective of this study was to determine the prevalence of scrub typhus among adults in Odisha, an eastern state of India.

METHODS

A descriptive cross-sectional study was conducted to analyse 1840 serum samples from five districts (Khordha, Cuttack, Ganjam, Malkangiri and Sundargarh) of Odisha collected during 2020-2021. Both immunoglobulin G (IgG) and IgM antibodies against scrub typhus were tested using commercial enzyme-linked immunosorbent assay kits. Point estimates of the 95% confidence interval and adjusted odds ratio were calculated.

RESULTS

Of 1840 participants, the prevalence of IgG positivity was 1034 (56.19%) and that of IgM was 523 (28.42%). The majority of participants were in the 18-45 y age group (53.7%). Cuttack had the highest IgG positivity (64.54%) and Malkangiri had the lowest (29.32%). The highest and lowest positivity for IgM were found in Malkangiri (40.84%) and Cuttack (25.30%), respectively.

CONCLUSIONS

With an increasing number of infections detected in the state, scrub typhus is emerging as a public health threat. Increasing awareness among the general public and healthcare professionals through health education campaigns regarding scrub typhus is essential. Early detection of the disease through the establishment of a laboratory surveillance system is required to control the transmission of scrub typhus.