Production of tetravalent dengue virus envelope protein domain III based antigens in lettuce chloroplasts and immunologic analysis for future oral vaccine development

Dengue fever is a mosquito (Aedes aegypti) ‐transmitted viral disease that is endemic in more than 125 countries around the world. There are four serotypes of the dengue virus (DENV 1‐4) and a safe and effective dengue vaccine must provide protection against all four serotypes. To date, the first vaccine, Dengvaxia (CYD‐TDV), is available after many decades’ efforts, but only has moderate efficacy. More effective and affordable vaccines are hence required. Plants offer promising vaccine production platforms and food crops offer additional advantages for the production of edible human and animal vaccines, thus eliminating the need for expensive fermentation, purification, cold storage and sterile delivery. Oral vaccines can elicit humoural and cellular immunity via both the mucosal and humoral immune systems. Here, we report the production of tetravalent EDIII antigen (EDIII‐1‐4) in stably transformed lettuce chloroplasts. Transplastomic EDIII‐1‐4‐expressing lettuce lines were obtained and homoplasmy was verified by Southern blot analysis. Expression of EDIII‐1‐4 antigens was demonstrated by immunoblotting, with the EDIII‐1‐4 antigen accumulating to 3.45% of the total protein content. Immunological assays in rabbits showed immunogenicity of EDIII‐1‐4. Our in vitro gastrointestinal digestion analysis revealed that EDIII‐1‐4 antigens are well protected when passing through the oral and gastric digestion phases but underwent degradation during the intestinal phase. Our results demonstrate that lettuce chloroplast engineering is a promising approach for future production of an affordable oral dengue vaccine.     

Population dynamics of anthropophilic mosquitoes during the northeast monsoon season in the malaria epidemic zone of Sri Lanka

Abstract. Mosquito-borne diseases are a major health problem in Sri Lanka. Human biting mosquitoes were collected during the night (18.00–06.00 hours) at Nikawehera village, in the malaria endemic intermediate rainfall zone of the country. Collections were made at monthly intervals in the period October 1991 to April 1992, which included the main rainy season due to the northeast monsoon (October-January). Thirteen Anopheles , eleven Culex , three Aedes , three Mansonia and one Armigeres species were identified, including known vectors of malaria, Bancroftian filariasis, Japanese encephalitis and dengue fever. Mosquito human-biting rates were highest in December. The main malaria vector Anopheles culicifacies showed peak biting between 18.00 and 23.00 hours whereas the predominant culicines Culex fuscocephala and Cx quinquefasciatus preferred to bite after midnight. In 1991-92 the prevalence of some species of anophelines at Nikawehera differed markedly from that observed in 1990-91 and the possible reasons are discussed.     

Heritable strategies for controlling insect vectors of disease

Mosquito-borne diseases are causing a substantial burden of mortality, morbidity and economic loss in many parts of the world, despite current control efforts, and new complementary approaches to controlling these diseases are needed. One promising class of new interventions under development involves the heritable modification of the mosquito by insertion of novel genes into the nucleus or of Wolbachia endosymbionts into the cytoplasm. Once released into a target population, these modifications can act to reduce one or more components of the mosquito population''s vectorial capacity (e.g. the number of female mosquitoes, their longevity or their ability to support development and transmission of the pathogen). Some of the modifications under development are designed to be self-limiting, in that they will tend to disappear over time in the absence of recurrent releases (and hence are similar to the sterile insect technique, SIT), whereas other modifications are designed to be self-sustaining, spreading through populations even after releases stop (and hence are similar to traditional biological control). Several successful field trials have now been performed with Aedes mosquitoes, and such trials are helping to define the appropriate developmental pathway for this new class of intervention.     

Field evaluation of the response of Aedes albopictus (Stegomyia albopicta) to three oviposition attractants and different ovitrap placements using black and clear autocidal ovitraps in a rural area of Same,Timor‐Leste

Known oviposition attractants or stimulants were compared, singly and in combination, using inexpensive autocidal ovitraps designed to trap emerging adults, in a rural area of Timor‐Leste during the dry season. In this area, the dengue vector Aedes albopictus (Stegomyia albopicta) Skuse (Diptera: Culicidae) was abundant, but Aedes aegypti (Stegomyia aegypti) L. was not detected. The attractants were: (a) a compound found in Aedes eggs (dodecanoic acid); (b) components of nitrogen, phosphorous and potassium‐based (NPK) fertilizer, and (c) infusions of discarded cigarette butts. A solution of ammonium phosphate and potassium nitrate was significantly more attractive to gravid Ae. albopictus than water only. Dodecanoic acid and cigarette butt infusions were not significantly more attractive than the control; however, they attracted various other Diptera and many non‐culicid larvae developed in ovitraps in which these substances were used; thus, the presence of eggs or larvae of other species may have deterred Aedes oviposition. Significantly more Aedes eggs were found in ovitraps under vegetation than in ovitraps placed inside houses or against external walls. Clear‐sided ovitraps in which black mesh was placed over a black ring floating on the water surface collected significantly fewer eggs than black ovitraps with identically placed mesh and rings.