Trends in Nationally Notifiable Infectious Diseases in Humans and Animals during COVID-19 Pandemic, South Korea.

We investigated trends in notifiable infectious diseases in both humans and animals during the COVID-19 pandemic in South Korea and compared those data against expected trends had nonpharmaceutical interventions (NPIs) not been implemented. We found that human respiratory infectious diseases other than COVID-19 decreased by an average of 54.7% after NPIs were introduced. On the basis of that trend, we estimated that annual medical expenses associated with respiratory infections other than COVID-19 also decreased by 3.8% in 2020 and 18.9% in 2021. However, human gastrointestinal infectious diseases and livestock diseases exhibited similar or even higher incidence rates after NPIs were instituted. Our investigation revealed that the preventive effect of NPIs varied among diseases and that NPIs might have had limited effectiveness in reducing the spread of certain types of infectious diseases. These findings suggest the need for future, novel public health interventions to compensate for such limitations.

Associations of meteorological factors and dynamics of scrub typhus incidence in South Korea: A nationwide time-series study.

Scrub typhus, also known as Tsutsugamushi disease, is a climate-sensitive vector-borne disease that poses a growing public health threat. However, studies on the association between scrub typhus epidemics and meteorological factors in South Korea need to be complemented. Therefore, we aimed to analyze the association among ambient temperature, precipitation, and the incidence of scrub typhus in South Korea. First, we obtained data on the weekly number of scrub typhus cases and concurrent meteorological variables at the city-county level (Si-Gun) in South Korea between 2001 and 2019. Subsequently, a two-stage meta-regression analysis was conducted. In the first stage, we conducted time-series regression analyses using a distributed lag nonlinear model (DLNM) to investigate the association between temperature, precipitation, and scrub typhus incidence at each location. In the second stage, we employed a multivariate meta-regression model to combine the association estimates from all municipalities, considering regional indicators, such as mite species distribution, Normalized Difference Vegetation Index (NDVI), and urban-rural classification. Weekly mean temperature and weekly total precipitation exhibited a reversed U-shaped nonlinear association with the incidence of scrub typhus. The overall cumulative association with scrub typhus incidence peaked at 18.7 C° (with RRs of 9.73, 95% CI: 5.54-17.10) of ambient temperature (reference 9.7 C°) and 162.0 mm (with RRs of 1.87, 95% CI: 1.02-3.83) of precipitation (reference 2.8 mm), respectively. These findings suggest that meteorological factors contribute to scrub typhus epidemics by interacting with vectors, reservoir hosts, and human behaviors. This information serves as a reference for future public health policies and epidemiological research aimed at controlling scrub typhus infections.

Fine-Scale Spatial Prediction on the Risk of Plasmodium vivax Infection in the Republic of Korea.

BACKGROUND: Malaria elimination strategies in the Republic of Korea (ROK) have decreased malaria incidence but face challenges due to delayed case detection and response. To improve this, machine learning models for predicting malaria, focusing on high-risk areas, have been developed. METHODS: The study targeted the northern region of ROK, near the demilitarized zone, using a 1-km grid to identify areas for prediction. Grid cells without residential buildings were excluded, leaving 8,425 cells. The prediction was based on whether at least one malaria case was reported in each grid cell per month, using spatial data of patient locations. Four algorithms were used: gradient boosted (GBM), generalized linear (GLM), extreme gradient boosted (XGB), and ensemble models, incorporating environmental, sociodemographic, and meteorological data as predictors. The models were trained with data from May to October (2019-2021) and tested with data from May to October 2022. Model performance was evaluated using the area under the receiver operating characteristic curve (AUROC). RESULTS: The AUROC of the prediction models performed excellently (GBM = 0.9243, GLM = 0.9060, XGB = 0.9180, and ensemble model = 0.9301). Previous malaria risk, population size, and meteorological factors influenced the model most in GBM and XGB. CONCLUSION: Machine-learning models with properly preprocessed malaria case data can provide reliable predictions. Additional predictors, such as mosquito density, should be included in future studies to improve the performance of models.

A single-blind randomised study comparing the efficacy of fluconazole and itraconazole for the treatment of Malassezia dermatitis in client-owned dogs.

BACKGROUND: No reports have compared the clinical therapeutic efficacy of fluconazole and itraconazole in canine Malassezia dermatitis. OBJECTIVES: The study aimed to compare the clinical therapeutic efficacy of fluconazole and itraconazole and to evaluate the adverse effects of fluconazole in canine Malassezia dermatitis. ANIMALS: Sixty-one client-owned dogs with Malassezia dermatitis. MATERIALS AND METHODS: The enrolled animals were randomly divided into groups receiving 5 mg/kg fluconazole (5FZ), 10 mg/kg fluconazole (10FZ) or 5 mg/kg itraconazole (5IZ). The drugs were orally administered once daily for 28 days. Cytological examination, clinical index score (CIS), pruritus Visual Analog Scale (PVAS) evaluation and blood analysis (for 5FZ only) were performed on Day (D)0, D14 and D28. RESULTS: On D14, significant reductions in mean yeast count (MYC), CIS and PVAS were observed in the 5FZ (n = 20, p < 0.01), 10FZ (n = 17, p < 0.01) and 5IZ (n = 16, p < 0.05) groups. In all three groups, a significant reduction (p < 0.001) in MYC, CIS and PVAS expression was observed on D28. There was no significant difference in the percentage reduction of MYC, CIS and PVAS among the groups. Moreover, there was a significant difference (p < 0.05) in each group between D14 and D28, except for the percentage reduction in MYC in the 10FZ and 5IZ groups. No adverse effects of fluconazole were observed in the 5FZ or 10FZ groups. CONCLUSIONS AND CLINICAL RELEVANCE: This study indicates that 5FZ and 10FZ are as effective as itraconazole in canine Malassezia dermatitis.

Association of Deforestation With Severe Fever With Thrombocytopenia Syndrome.

BACKGROUND: Severe fever with thrombocytopenia syndrome (SFTS) virus was first isolated in China in 2009 and has since spread to several Asian countries. SFTS is closely related to environmental factors that accelerate vector growth. We evaluated the associations of SFTS and deforestation with environmental variables. METHODS: For this observational study, we generated multiple Poisson models using national SFTS outbreak data (2013-2018) and official environmental data for Korea. We included established risk factors as variables. Deforestation was used as the main variable. All variables were analyzed according to their spatial characteristics using the R-INLA package. RESULTS: SFTS cases increased over time and peaked in 2017, at 272, followed by a decrease in 2018. Disease mapping showed a high incidence of SFTS nationwide, with particular risks in Gangwon and Gyeonggi Provinces in the north, and Jeju in the south of South Korea. Deforestation was significantly associated with a higher risk of SFTS in the final model (relative risk, 1.751 [95% confidence interval, 1.125-2.743]). CONCLUSIONS: SFTS outbreaks are associated with deforestation. Therefore, deforestation in Gyeonggi, Gangwon, and Jeju provinces of South Korea needs to be considered in vector-control strategies and active surveillance of SFTS occurrence.

The Cancer Therapy-Related Clonal Hematopoiesis Driver Gene Ppm1d Promotes Inflammation and Non-Ischemic Heart Failure in Mice.

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Analysis of the effectiveness of non-pharmaceutical interventions on influenza during the Coronavirus disease 2019 pandemic by time-series forecasting.

BACKGROUND: Coronavirus disease 2019 (COVID-19) was first identified in South Korea during the 2019-2020 seasonal influenza epidemic. The social distancing measures, as effective non-pharmaceutical interventions (NPIs), adopted to mitigate the spread of COVID-19 might have influenced influenza activity. We evaluated IFV(influenza virus) activity during the COVID-19 pandemic and the effect of NPI intensity on influenza transmission. METHODS: IFV activity and epidemic duration during COVID-19 pandemic were predicted under a counterfactual scenario with no NPIs against COVID-19. The Seasonal Autoregressive Integrated Moving Average Model was used to quantify the effects of NPIs on the transmission of influenza virus. Influenza-like illness/1000 outpatients and IFV positivity rate from the 2011-2012 to 2021-2022 seasons were used in this study. RESULTS: Comparison of the 2020-2021 and 2021-2022 seasonal influenza activities with those in 2013-2019 showed that COVID-19 outbreaks and associated NPIs such as face mask use, school closures, and travel restrictions reduced the influenza incidence by 91%. Without NPIs against COVID-19, the rates of influenza-like illness and IFV positivity would have been high during the influenza epidemic season, as in previous seasons. NPI intensity decreased the transmission of influenza; the magnitude of the reduction increased as the intensity of social-distancing measures increased (weak social distancing; step-by-step daily recovery: 58.10%, strong social distancing; special quarantine measures: 95.12%). CONCLUSIONS: Our results suggest that NPIs and personal hygiene can be used to suppress influenza transmission. NPIs against COVID-19 may be useful strategies for the prevention and control of influenza epidemics.

Mean pulmonary artery pressure estimated by echocardiogram rapidly exceeds 20 mmHg from the normal range in patients with connective tissue disease.

Earlier intervention for pulmonary hypertension (PH) has been reported to improve the prognosis of patients with connective tissue disease (CTD). However, it is not fully elucidated how rapidly PH develops in patients showing normal mean pulmonary arterial pressure (mPAP) at the index investigation. We evaluated 191 CTD patients with normal mPAP retrospectively. The mPAP was estimated by the formerly defined method employing echocardiography (mPAPecho). We investigated predictive factors that predict increasing mPAPecho at follow-up transthoracic echocardiography (TTE) using uni- and multi variable analysis. The mean age was 61.5 years old, and 160 patients were female. The percentage of patients in whom mPAPecho exceeded 20 mmHg at follow-up TTE was 38%. Multivariable analysis revealed that acceleration time/ejection time (AcT/ET) measured at the right ventricular outflow tract at initial TTE was independently associated with the consequent increase of mPAPecho at the follow-up TTE. When using 0.43 of best cutoff value in AcT/ET calculated by receiver operating characteristic analysis, the change in mPAPecho in patients with low AcT/ET was significantly higher than in those with high AcT/ET (3.05 mmHg in patients with AcT/ET < 0.43 and 1.00 mmHg in patients with AcT/ET ≥ 0.43, p < 0.001). Thirty-eight percent of CTD patients who show the normal estimated mPAP by TTE develop gradual elevation of mPAP to the level to consider early intervention within 2 years. AcT/ET at initial TTE can predict increasing mPAP at follow-up TTE.

Potential applicability of the importation risk index for predicting the risk of rarely imported infectious diseases.

BACKGROUND: There have been many prediction studies for imported infectious diseases, employing air-travel volume or the importation risk (IR) index, which is the product of travel-volume and disease burden in the source countries, as major predictors. However, there is a lack of studies validating the predictability of the variables especially for infectious diseases that have rarely been reported. In this study, we analyzed the prediction performance of the IR index and air-travel volume to predict disease importation. METHODS: Rabies and African trypanosomiasis were used as target diseases. The list of rabies and African trypanosomiasis importation events, annual air-travel volume between two specific countries, and incidence of rabies and African trypanosomiasis in the source countries were obtained from various databases. RESULTS: Logistic regression analysis showed that IR index was significantly associated with rabies importation risk (p value < 0.001), but the association with African trypanosomiasis was not significant (p value = 0.923). The univariable logistic regression models showed reasonable prediction performance for rabies (area under curve for Receiver operating characteristic [AUC] = 0.734) but poor performance for African trypanosomiasis (AUC = 0.641). CONCLUSIONS: Our study found that the IR index cannot be generally applicable for predicting rare importation events. However, it showed the potential utility of the IR index by suggesting acceptable performance in rabies models. Further studies are recommended to explore the generalizability of the IR index's applicability and to propose disease-specific prediction models.

Outbreak of severe diarrhea due to zoonotic Cryptosporidium parvum and C. xiaoi in goat kids in Chungcheongbuk-do, Korea.

Severe diarrhea was reported in goat kids in Chungcheongbuk-do, Korea, from 2021 to 2023, and Cryptosporidium infection was suspected. To confirm the cause of this outbreak, fecal samples were collected from goat farms where diarrhea had been reported and analyzed for Cryptosporidium infection using a molecular assay. A total of 65 fecal samples, including 37 from goats with diarrhea and 28 from goats without diarrhea, were collected from six goat farms. Forty-eight of the goats were kids (<2 months) and 17 were adults (>1 year). Cryptosporidium was identified in 53.8% (35/65) of total samples. Overall, 86.5% (32/37) of the diarrheic fecal samples tested positive; however, Cryptosporidium was not detected in any fecal sample from non-diarrheic adult goats. Therefore, cryptosporidiosis was significantly associated with diarrhea in goat kids, and adult goats were not responsible for transmission of Cryptosporidium to them. Phylogenetic analysis and molecular characterization revealed two Cryptosporidium species, namely, C. parvum (n = 28) and C. xiaoi (n = 7). In the C. parvum-positive samples, gp60 gene analysis revealed three zoonotic subtypes-IIaA18G3R1, IIdA15G1, and IIdA16G1. To the best of our knowledge, this study is the first to identify C. parvum IIaA18G3R1 and IIdA16G1 in goats, as well as the first to identify C. xiaoi in goats in Korea. These results suggest that goat kids play an important role as reservoir hosts for different Cryptosporidium species and that continuous monitoring with biosecurity measures is necessary to control cryptosporidiosis outbreaks.

Ambient PM2.5 exposures could increase risk of tuberculosis recurrence.

BACKGROUND: The effect of ambient PM2.5 on the incidence of tuberculosis (TB) has been investigated in epidemiological studies. However, they did not separately study new and relapsed TB infection and focused on relatively short-term effects of PM2.5. In this regard, we examined the associations of long-term PM2.5 exposures with both new and relapsed TB incidences in South Korea, where the disease burden of TB is greatest among high-income countries. METHODS: An area-level ecological study of 250 districts was conducted from 2015 to 2019. Age- and sex-standardized TB incidence ratios for each district and year were used as outcome variables, and their associations with PM2.5 concentrations for one to five-year average were examined. Negative binomial regression models incorporating spatiotemporal autocorrelation were employed using integrated nested Laplace approximations. Stratified analyses were conducted by type of TB (total, new, and relapsed cases). RESULTS: Districts with higher PM2.5 concentrations tended to have significantly higher TB recurrence rate. The relative risks per 10 µg/m3 PM2.5 increase were 1.218 (95% credible interval 1.051-1.411), 1.260 (1.039-1.527) and 1.473 (1.015-2.137) using the two, three and five-year average PM2.5 exposures, respectively. CONCLUSIONS: The results imply that interventions for reducing air pollution might help prevent TB recurrence.

Urine albumin-to-creatinine ratio on admission predicts early rehospitalization in patients with acute decompensated heart failure.

Detecting high-risk patients for early rehospitalization is crucial in heart failure patient care. An association of albuminuria with cardiovascular events is well known. However, its predictive impact on rehospitalization for acute decompensated heart failure (ADHF) remains unknown. In this study, 190 consecutive patients admitted due to ADHF between 2017 and April 2019 who underwent urinalysis were enrolled. Among them, 140 patients from whom urine albumin-to-creatinine ratio (UACR) was measured with spot urine samples on admission were further analyzed. The association between UACR and rehospitalization due to HF during 1 year after discharge was evaluated. The mean age of 140 participants was 77.6 years and 55% were men. Only 18% (n = 25) of patients presented with normoalbuminuria (UACR < 30 mg/g∙creatinine), whereas 59% (n = 83) and 23% (n = 32) showed microalbuminuria (UACR 30-300 mg/g·creatinine) and macroalbuminuria (UACR > 300 mg/g·creatinine), respectively. The level of UACR on admission was correlated with the risk of subsequent rehospitalization due to HF (p = 0.017). The receiver operating characteristic analysis indicated that the best cut-off values for the UACR and B-type natriuretic peptide (BNP) levels to predict ADHF rehospitalization were 50 mg/g·creatinine and 824 pg/ml, respectively. When the patients were divided into four groups using both cut-off values, the individual predictive impacts of UACR and BNP on rehospitalization were comparable. Patients with both elevated UACR and BNP levels had a higher rate of HF rehospitalization than those with elevated BNP levels alone (p < 0.05). The combination of both values enabled more accurate prediction of HF rehospitalization than BNP levels alone. In conclusion, UACR could be a new useful biomarker to predict HF rehospitalization in patients with ADHF, especially in combination with the levels of BNP, and should be further evaluated in a prospective study.

Association between exposure to traffic-related air pollution and pediatric allergic diseases based on modeled air pollution concentrations and traffic measures in Seoul, Korea: a comparative analysis.

BACKGROUND: Pediatric allergic diseases are a major public health concern, and previous studies have suggested that exposure to traffic-related air pollution (TRAP) exposure is a risk factor. These studies have typically assessed TRAP exposure using traffic measures, such as distance to major roads, or by modeling air pollutant concentrations; however inconsistent associations with pediatric allergic diseases have often been found. Using road proximity and density, we previously found an association between TRAP and atopic eczema among approximately 15,000 children living in Seoul, Korea, heavily populated and highly polluted city in which traffic is a major emission source. We aimed to conduct a parallel analysis using modeled air pollution concentrations and thus examine the consistency of the association. Specifically, we examined the associations of individual-level annual-average concentrations of NO2, PM10, and PM2.5 with symptoms and diagnoses of three pediatric allergic diseases including asthma, allergic rhinitis, and atopic eczema. METHODS: The study population included 14,614 children from the Seoul Atopy Friendly School Project Survey in Seoul, Korea, in 2010. To assess individual exposures to TRAP among these children, we predicted annual-average concentrations of NO2, PM10, and PM2.5 at the children's home addresses in 2010 using universal kriging and land use regression models along with regulatory air quality monitoring data and geographic characteristics. Then, we estimated odds ratios (ORs) of the three allergic diseases for interquartile increases in air pollution concentrations after adjusting for individual risk factors in mixed effects logistic regression. RESULTS: Symptoms and diagnoses of atopic eczema symptoms showed an association with NO2 (OR = 1.07, 95% confidence interval = 1.02-1.13; 1.08, 1.03-1.14) and PM10 (1.06, 1.01-1.12; 1.07, 1.01-1.13). ORs of PM2.5 were positive but not statistically significant (1.01, 0.95-1.07; 1.04, 0.98-1.10). No association was found between asthma and allergic rhinitis, although PM2.5 showed a marginal association with allergic rhinitis. CONCLUSIONS: Our consistent findings regarding the association between TRAP and the prevalence of atopic eczema using traffic measures and surrogate air pollutants suggested the effect of TRAP on children's health. Follow-up studies should elucidate the causal link, to support subsequent policy considerations and minimize adverse health effects in children.

Estimating the Effectiveness of Non-Pharmaceutical Interventions on COVID-19 Control in Korea.

BACKGROUND: The coronavirus disease 2019 (COVID-19) pandemic has posed significant global public health challenges and created a substantial economic burden. Korea has experienced an extensive outbreak, which was linked to a religion-related super-spreading event. However, the implementation of various non-pharmaceutical interventions (NPIs), including social distancing, spring semester postponing, and extensive testing and contact tracing controlled the epidemic. Herein, we estimated the effectiveness of each NPI using a simulation model. METHODS: A compartment model with a susceptible-exposed-infectious-quarantined-hospitalized structure was employed. Using the Monte-Carlo-Markov-Chain algorithm with Gibbs' sampling method, we estimated the time-varying effective contact rate to calibrate the model with the reported daily new confirmed cases from February 12th to March 31st (7 weeks). Moreover, we conducted scenario analyses by adjusting the parameters to estimate the effectiveness of NPI. RESULTS: Relaxed social distancing among adults would have increased the number of cases 27.4-fold until the end of March. Spring semester non-postponement would have increased the number of cases 1.7-fold among individuals aged 0-19, while lower quarantine and detection rates would have increased the number of cases 1.4-fold. CONCLUSION: Among the three NPI measures, social distancing in adults showed the highest effectiveness. The substantial effect of social distancing should be considered when preparing for the 2nd wave of COVID-19.

A dipeptidyl peptidase-IV inhibitor improves diastolic dysfunction in Dahl salt-sensitive rats.

To date, there is no established treatment for heart failure with preserved ejection fraction (HFpEF). Dipeptidyl peptidase-IV (DPP-IV) inhibitors reportedly have improved not only diabetes mellitus but also heart failure with systolic dysfunction in experimental models. We investigated the effects of a DPP-IV inhibitor on HFpEF in rats. Dahl salt-sensitive rats were fed either high-salt (high-salt diet (HSD): 8% NaCl) or low-salt diets (0.3% NaCl) from 6.5 weeks of age. They were then treated with or without a DPP-IV inhibitor, vildagliptin (10 mg/kg/day, orally), from 11 weeks of age for 9 weeks and analyzed at the age of 20 weeks. HSD rats mimicked the pathophysiology of HFpEF. There were no differences in heart rate, blood pressure, left ventricular (LV) systolic function, or the extent of LV hypertrophy between HSD rats with or without vildagliptin. However, vildagliptin decreased LV end-diastolic pressure, the most reliable hemodynamic parameter of HFpEF in HSD rats. Vildagliptin also decreased the LV distensibility index, a sensitive marker of LV diastolic function in HSD rats. Vildagliptin decreased the expression of collagen genes in HSD hearts and attenuated LV interstitial fibrosis (HSD with vehicle and vildagliptin, 2.9% vs. 1.9%; P < 0.05). Furthermore, vildagliptin administration reduced both plasma renin activity and aldosterone concentrations in HSD rats. A DPP-IV inhibitor, vildagliptin, improved the severity of LV fibrosis, and thus, diastolic dysfunction of HFpEF in Dahl salt-sensitive hypertensive rats. DPP-IV inhibitors are promising medicines for treatment of HFpEF in patients with diabetes mellitus.

AST-120, an Adsorbent of Uremic Toxins, Improves the Pathophysiology of Heart Failure in Conscious Dogs.

PURPOSE: Several lines of evidence suggest that renal dysfunction is associated with cardiovascular toxicity through the action of uremic toxins. The levels of those uremic toxins can be reportedly reduced by the spherical carbon adsorbent AST-120. Because heart failure (HF) causes renal dysfunction by low cardiac output and renal edema, the removal of uremic toxins could be cardioprotective. METHOD: To determine whether blood levels of the uremic toxin indoxyl sulfate (IS) increase in HF and whether AST-120 can reduce those levels and improve HF. We induced HF in 12 beagle dogs by 6 weeks of rapid right ventricular pacing at 230 beats per min. We treated six dogs with a 1-g/kg/day oral dosage of AST-120 for 14 days from week 4 after the start of rapid ventricular pacing. The other six dogs did not receive any treatment (control group). RESULTS: In the untreated dogs, IS levels increased as cardiac function deteriorated. In contrast, plasma IS levels in the treated dogs decreased to baseline levels, with both left ventricular fractional shortening and pulmonary capillary wedge pressure also improving when compared with untreated dogs. Finally, AST-120 treatment was shown to reduce both myocardial apoptosis and fibrosis along with decreases in extracellular signal-regulated kinase phosphorylation, the Bax/Bcl-2 ratio, and TGF-ß1 expression and increases in AKT phosphorylation. CONCLUSIONS: IS levels are increased in HF. AST-120 treatment reduces the levels of IS and improves the pathophysiology of HF in a canine model. AST-120 could be a novel candidate for the treatment of HF.

Validating a single-question depression measure among older adults.

BACKGROUND: A single-item depression measure may not be adequate in capturing the complex entity of mental health, despite wide use of this indicator in community studies. This study evaluated the accuracy of a single-question depression measure in comparison to two composite indices-the Center for Epidemiologic Studies Depression Scale (CESD) and the Geriatric Depression Scale (GDS). MATERIALS AND METHODS: A total of 800 elderly participants ranging from 60 to 89 years of age and residing in Seoul were recruited using a multistage sampling scheme in 2015. The survey was conducted by trained interviewers with a constructed questionnaire. Reliability and validity measures such as the Kappa index, sensitivity, specificity, PPV, NPV, and AUC were used to evaluate the accuracy of the single question measure. Socio-demographic group differences in accuracy were compared by age, sex, marital status, education, employment, and financial status. RESULTS: The prevalence of depression by a single-question measure was much lower than those of CESD and GDS (5.5%, 12.3%, and 12.1%, respectively). The sensitivity of the single-item measure, based on CESD and GDS, was extremely low at 30.6% and 36.1%. In the subgroup analysis, however, there was a marked educational discrepancy in all accuracy measures; in sensitivity, people with a university degree or higher showed about 2.4 times higher sensitivity than those having only a primary school education. CONCLUSIONS: The results show that a single-question depression measure should be used with caution. In addition, the single-question measure could substantially underestimate depression among the risk group of older adults.

Mathematical Modeling for Scrub Typhus and Its Implications for Disease Control.

BACKGROUND: The incidence rate of scrub typhus has been increasing in the Republic of Korea. Previous studies have suggested that this trend may have resulted from the effects of climate change on the transmission dynamics among vectors and hosts, but a clear explanation of the process is still lacking. In this study, we applied mathematical models to explore the potential factors that influence the epidemiology of tsutsugamushi disease. METHODS: We developed mathematical models of ordinary differential equations including human, rodent and mite groups. Two models, including simple and complex models, were developed, and all parameters employed in the models were adopted from previous articles that represent epidemiological situations in the Republic of Korea. RESULTS: The simulation results showed that the force of infection at the equilibrium state under the simple model was 0.236 (per 100,000 person-months), and that in the complex model was 26.796 (per 100,000 person-months). Sensitivity analyses indicated that the most influential parameters were rodent and mite populations and contact rate between them for the simple model, and trans-ovarian transmission for the complex model. In both models, contact rate between humans and mites is more influential than morality rate of rodent and mite group. CONCLUSION: The results indicate that the effect of controlling either rodents or mites could be limited, and reducing the contact rate between humans and mites is more practical and effective strategy. However, the current level of control would be insufficient relative to the growing mite population.

Exploring preventive factors against insufficient antibody positivity rate for foot-and-mouth disease in pig farms in South Korea: a preliminary ecological study.

BACKGROUND: Foot-and-mouth disease (FMD) is a highly contagious viral disease in livestock that has tremendous economic impact nationally. After multiple FMD outbreaks, the South Korean government implemented a vaccination policy for efficient disease control. However, during active surveillance by quarantine authorities, pig farms have reported an insufficient antibody positivity rate to FMD. OBJECTIVE: In this study, the spatial and temporal trends of insufficiency among pig farms were analyzed, and the effect of the number of government veterinary officers was explored as a potential preventive factor. METHODS: Various data were acquired, including national-level surveillance data for antibody insufficiency from the Korea Animal Health Integrated System, the number of veterinary officers, and the number of local pig farms. Temporal and geographical descriptive analyses were conducted to overview spatial and temporal trends. Additionally, logistic regression models were employed to investigate the association between the number of officers per pig farm with antibody insufficiency. Spatial cluster analysis was conducted to detect spatial clusters. RESULTS: The results showed that the incidence of insufficiency tended to decrease in recent years (odds ratio [OR], 0.803; 95% confidence interval [95% CIs], 0.721-0.893), and regions with a higher density of governmental veterinary officers (OR, 0.942; 95% CIs, 0.918-0.965) were associated with a lower incidence. CONCLUSIONS: This study implies that previously conducted national interventions would be effective, and the quality of government-provided veterinary care could play an important role in addressing the insufficient positivity rate of antibodies.