Studies on Dengue Epidem Iology and Biological Control of Its Vector

Abstract

The first large scale outbreak of dengue fever was reported in Southeastern port city of Karachi, Pakistan in 1994 which remained the epicenter for the disease afterward. However, heavy rainfall and frequent floods in 2010 provided breeding sites for the proliferation of Aedes aegypti the dengue virus vector, thus biggest outbreak in the history of Pakistan erupted in the Northeastern province of Punjab (n = 21,685) in 2011, with most cases from Lahore (80.8%) followed by Faisalabad (4.2%) and Rawalpindi (2.1%). Now, dengue is endemic in Pakistan, with numerous outbreaks being reported from various cities of Punjab and other provinces. Therefore, the objective of this study was to conduct a comprehensive epidemiology study of dengue in various cities of Pakistan. Further, crude extracts from Actinobacterial isolates and plants were evaluated for their larvicidal potential against the local strain of the dengue virus vector, Aedes aegypti mosquito. In this direction, a two years hospital-based cross-sectional study was carried out to determine the epidemiological and clinical features of dengue fever in Faisalabad city, Pakistan in 2011 and 2012. Out of total 299 anti-dengue IgM positive patients (male 218 and female 81); there were 239 dengue fever (DF) and 60 dengue hemorrhagic fever (DHF) patients. DHF patients were considerably younger (24.5 years) as compared to DF patients (30 years, p-value=0.05). There was a decrease in the median age of dengue patients from 31 years in 2011 to 21.5 years in 2012 (p-value<0.001). Abdominal pain was seen in 35% DHF patients followed by nausea in 28.3%, epistaxis in 25%, and rash in 20% of patients (p-value<0.05). An increase in the levels of liver enzymes (AST, ALT, and ALP) was most commonly associated with DHF. ALT levels were raised in 74.2% (p-value=0.032), while AST levels were raised in all DHF patients (p-value=0.077). The mean length of the stay at the hospital increased substantially (p-value<0.001) in DHF (4.9 days) as compared to DF (3.8 days). A two years hospital-based study was also carried out in Faisalabad to find out the association of co-morbidities with the severity of the disease. A total of 91 patients (69 males and 22 females) with single or multiple comorbidities were enrolled in the study. DF was diagnosed in 68.1% while, DHF was diagnosed in 31.9% of patients. Among 91 cases, xii 80.2% were diagnosed with single comorbidity, 15.3% with two comorbidities while 3.3% were diagnosed with three comorbidities. Additionally, a single case (1.1%) was also diagnosed with 6 comorbidities. The frequency of severe dengue fever (DHF/DSS) was noticeably higher (p-value=0.01) among dengue patients reported with comorbidities (32%) than without comorbidities (20%). The odds to develop DHF in concurrent denguemalaria infection were significantly higher than in the dengue infection alone (OR 5.6, 95% CI 1.7 to 18.2, p-value=0.005). Similarly, odds to develop DHF was significantly higher (OR 2.1, 95% CI 1.1 to 4, p-value=0.03) in patients with HCV co-infection than in dengue infection alone. Socioeconomic disparities in the community make some groups more vulnerable to dengue infection, therefore, a community-based study was carried in Faisalabad. Orthogonal comparisons showed that socioeconomic factors play a significant role in the prevalence of dengue. Socioeconomic factors play an important role in the spread of dengue infection among the community. Therefore, an integrated approach is required to control the menace through vector control strategies and the improvement of the socioeconomic condition of masses. Fourteen dengue cases (IgM positive) served as index cases for positive geographic cluster investigations. Of 292 individuals, the overall dengue seroprevalence was 22.9% (IgM positive 4.8%; IgG positive 18.1%). The highest (45%) seroprevalence was reported in the most socioeconomically vulnerable lower class, followed by the middle class (39%). Orthogonal comparisons showed that socioeconomic factors play a significant role in the prevalence of dengue. After a major outbreak in 2011, a steady increase in the number of cases was recorded in Rawalpindi. Afterward, a major outbreak erupted in Northwestern city Peshawar in the province of Khyber Pakhtunkhwa in 2017. Therefore, a cross-sectional study was carried out to determine the circulating dengue virus serotypes in Lahore, Rawalpindi, and Peshawar Pakistan during 2016-18. Among 6291 samples collected 6.5% were NS1 positive while 2.4% were PCR positive. DENV-2 was the most common (75.5%) serotype followed by DENV-1 (16.1%), DENV-3 (3.9%) and DENV-4 (0.6%) while DENV-1 and DENV-4 concurrent infections were detected in 3.9% samples. DENV-1 was the most common serotype (62.5%) circulating in Punjab province in Lahore and Rawalpindi while DENV-2 was the only serotype detected from Peshawar, Khyber xiii Pakhtunkhwa. Further, Chikungunya virus co-infection was also detected in samples collected from Peshawar. Currently, there is no truly effective dengue vaccine available in the market, therefore, vector control remains the most practical method in controlling dengue transmission. Further, the rapid development of resistance against synthetic pesticides, it is justified to search for new pesticides possibly with different modes of action then the existing ones. In this direction, the true potential of actinobacteria has not been explored. Therefore, a mosquito rearing facility was established as well as the potential of various actinobacterial isolates and plant extracts were evaluated against 4th instar Aedes aegypti mosquito larvae. A total of 154 actinobacterial isolates were screened for larvicidal potential, among them 5.2% showing 90-100% activity were selected for concentrationresponse assays. Besides, 05 plant extracts were also screened while 3 of them including Solanum xanthocarpum, Solanum nigrum, and Commiphora gileadensis were chosen for concentration-response assays. A slight (50<LC<100) to very slight (LC>100) larvicidal potential was demonstrated by actinobacterial isolates including AGRS12, H23 (Streptomyces puniceus), AGRS17, AGRS13A, DD25, AD7 (Streptomyces fradiae), AD12w (Streptomyces albaduncus) and AGRS13B with LC50 values of 56.26, 63.25, 69.83, 159.01, 165.54, 166.81, 199.82 and 1113.58ppm respectively after 24 hours of exposure. While moderate (10<LC<50) to very slight (LC>100) larvicidal potential was demonstrated by H23 (Streptomyces puniceus), AGRS17, AGRS12, AD7 (Streptomyces fradiae), AGRS13A, DD25, AD12w (Streptomyces albaduncus) and AGRS13B with LC50 values of 22.86, 24.8, 32.42, 83.75, 86.03, 91.25, 97.35 and 500.07ppm respectively after 48 hours of exposure. Chemical profiling through TLC, HPLC, and LC-MS was also carried out for H23, AD7, and AD12w. The LC-MS analysis of H23 (Streptomyces puniceus) extracts showed no clear mass although HPLC-UV/Vis analysis generated an interesting profile. The data for AD7, when compared in AntiBase, resulted in close matches with 17 different compounds including antimicrobials (Fibrostatin B, Xanthine, A9145 A, Hatomamicin and Pentenomycin I), antitumor and anticancer agents. Similarly, LC-MS data on comparison with AntiBase data showed 18 matching compounds including various antimicrobials including Boxazomycin A and Dihydroabikoviromycin Emimycin. Two plant extracts including Solanum xanthocarpum and Commiphora gileadensis showed xiv very slight larvicidal potential with LC50 values of 165.67 and 113.43 ppm respectively after 24 hours of exposure in this study. Overall the findings of these studies describes original knowledge that provide a significant advancement in the comprehensive understanding of the public health burden and potential use of findings to overcome the challenges of dengue in Pakistan. As an example, demographic, clinical, and laboratory features of dengue cases studied could be used for the early diagnosis and treatment of the patients at risk of severe dengue fever. Especially, abdominal pain, nausea, rash, cold/clammy skin, periorbital puffiness, elevated liver enzymes, and visceromegaly could be used as early predictors of DHF. The areas identified in this study from which dengue cases were reported more frequently, could be focused by policymakers, educationists, and health professionals for the control of dengue fever in the city. Moreover, HCV and malarial coinfections in dengue patients are significantly associated with the development of severe dengue fever. Co-circulation of all four serotypes in Pakistan is an alarming situation that could result in outbreaks of severe dengue fever in the future. Socioeconomic determinants play a significant role in the spread of dengue infection in the society, therefore, an integrated approach is required for the control of the menace through vector control strategies and improvement of socioeconomic conditions of the masses. Further, various extracts from actinobacteria demonstrated promising larvicidal potential, therefore, could be used for vector control in the future after further characterization and testing of the compounds in the field trials.