Dengue Fever: A Continuous Threat

Dengue fever is a vector borne disease and is caused by DEN Virus. This virus has four different serotypes. The vectors are two mosquitoes known as Aedesaegypti (the yellow fever mosquito) and Aedesalbopictus(the Asian tiger mosquito).  First case of dengue fever was reported back in 1994 in Karachi. A complete outbreak of this epidemic shook the whole nation in 2012. Uptill now, Lahore a city full of culture, witnessed about 16,580 confirmed cases and 257 deaths. About 5000 confirmed cases with 60 deaths were reported from the rest of the provinces. Under guidelines of WHO, Government has made efforts to combat this epidemic. Although the overall efforts have minimized the outbreak on controllable levels but dengue fever is a continuous threat. Since no permanent cure is available, the transmission of DEN virus is controlled indirectly. So the prime focus is to control mosquito population and decrease the possible hot spots i.e. Mosquito breeding sites in human habitations. Every year, the country witnesses monsoon season which brings vast areas full of clear standing waters providing breeding sites for mosquitoes which ultimately leads to increased number of patients suffering from dengue fever. Efforts have been made to fight against dengue including formation of dengue wards in hospitals, vector surveillance, community education, reactive vector control etc. A study has shown prevalence of four mosquito genera in Pakistan including Aedes, Culex, Armigeresand Anopheles. All of the above mentioned genera are associated with disease transmissions as they are the vectors of different viruses and parasites. It is the need of hour to do a collaborative effort stressing the community mobilization and management in war against dengue.

Postharvest Pericarp Browning and Quality Management of Litchi Litchi Chinensis Sonn.

Litchi (Litchi chinensis Sonn.) is an important emerging fruit crop of Pakistan with good production potential. Rapid pericarp browning is the main postharvest issue which reduces its cosmetic and market value, limits its extended storage life and causes losses during its transportation and marketing. This integrated research was planned to check the influence of cultivars, harvest locations, exogenous application of chemicals such as oxalic acid, ascorbic acid, hexanal on pericarp browning and fruit quality of litchi under cold storage conditions. The experiments accordingly followed the experimental designs with factorial arrangements. The fruit were stored for 28 days with 7 days sampling interval to determine fruit weight loss (%), pericarp browning index; whereas, soluble solid concentrations (SSC), titratable acidity (TA), SSC: TA ratio and ascorbic acid were determined from juice samples obtained from pulp tissues. Moreover, total phenolics (TP), total antioxidants, activities of peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD) enzymes were also determined at 7 days interval during cold storage in both peel as well as pulp tissues of litchi fruit. However, activities of polyphenol oxidase (PPO) enzyme and anthocyanin contents were determined only from peel tissues. The results of first experiment suggested that the cultivars and harvest locations significantly influenced pericarp browning and physico-chemical quality attributes along with the activities of antioxidative enzymes in litchi fruit. Fruit of litchi cultivar ‘Gola’ exhibited superior quality characteristics than ‘Serai’; while, litchi fruit harvested from Haripur location showed better quality than Lahore. Based on the results of the first experiment, litchi cv. ‘Gola’ fruit produced at Haripur location were selected for rest of the experiments. In second experiment, postharvest application of oxalic acid was tested on pericarp browning and fruit quality of litchi cv. ‘Gola’ fruit. Exogenous application of 2 mM oxalic acid delayed pericarp browning, maintained better physico-chemical attributes along with the higher activities of antioxidative enzymes (SOD and CAT) in litchi cv. ‘Gola’ fruit during cold storage. Third experiment was carried out to investigate the effect of postharvest application of ascorbic acid on pericarp browning and fruit quality of litchi cv. ‘Gola’ fruit. Application of 45 mM ascorbic acid improved fruit quality by maintaining better physico-chemical attributes and delayed pericarp browning along with higher activities of antioxidative enzymes (SOD and Abstract XX CAT) in litchi cv. ‘Gola’ fruit during cold storage. In fourth experiment, influence of hexanal fumigation on the storage life and pericarp browning of litchi cv. ‘Gola’ fruit was investigated. Hexanal fumigation could not control browning during cold storage period. Even control fruit showed less pericarp browning than hexanal fumigated fruit. However, among hexanal treatments, 250 μL treatment showed better fruit quality attributes by maintaining higher activities of antioxidative (CAT and SOD) and lower activities of PPO and POD enzymes. From above trials, best concentrations of different chemicals (2 mM oxalic acid, 45 mM ascorbic acid or 2 mM oxalic acid + 45 mM ascorbic acid + 250 μL hexanal) were screened and these were re-confirmed on cv. ‘Gola’ along with another commercial litchi cv. ‘Bedana’. Evidently, 2 mM oxalic acid was more effective in controlling pericarp browning, improving fruit quality and storage life of ‘Gola’ and ‘Bedana’ litchi fruits, as compared to other chemical treatments. Application of 2 mM oxalic acid suppressed the activities of pericarp browning enzymes (PPO and POD) and increased the activities of antioxidative enzymes (CAT and POD). In conclusion, 2 mM oxalic acid or 45 mM ascorbic acid were most effective in delaying pericarp browning and improving quality of litchi fruit (cvs. ‘Gola’ and ‘Bedana’) under cold storage conditions.