Zoonotic malaria transmission and land use change in Southeast Asia: what is known about the vectors.

Zoonotic Plasmodium infections in humans in many Southeast Asian countries have been increasing, including in countries approaching elimination of human-only malaria transmission. Most simian malarias in humans are caused by Plasmodium knowlesi, but recent research shows that humans are at risk of many different simian Plasmodium species. In Southeast Asia, simian Plasmodium species are mainly transmitted by mosquitoes in the Anopheles leucosphyrus and Anopheles dirus complexes. Although there is some evidence of species outside the Leucosphyrus Group transmitting simian Plasmodium species, these await confirmation of transmission to humans. The vectors of monkey malarias are mostly found in forests and forest fringes, where they readily bite long-tailed and pig-tailed macaques (the natural reservoir hosts) and humans. How changing land-uses influence zoonotic malaria vectors is still poorly understood. Fragmentation of forests from logging, agriculture and other human activities is associated with increased zoonotic Plasmodium vector exposure. This is thought to occur through altered macaque and mosquito distributions and behaviours, and importantly, increased proximity of humans, macaques, and mosquito vectors. Underlying the increase in vector densities is the issue that the land-use change and human activities create more oviposition sites and, in correlation, increases availably of human blood hosts. The current understanding of zoonotic malaria vector species is largely based on a small number of studies in geographically restricted areas. What is known about the vectors is limited: the data is strongest for distribution and density with only weak evidence for a limited number of species in the Leucosphyrus Group for resting habits, insecticide resistance, blood feeding habits and larval habitats. More data are needed on vector diversity and bionomics in additional geographic areas to understand both the impacts on transmission of anthropogenic land-use change and how this significant disease in humans might be controlled.

Homogeneity and Possible Replacement of Populations of the Dengue Vectors Aedes aegypti and Aedes albopictus in Indonesia.

Currently, Aedes aegypti, the principal vector of dengue virus in Indonesia, has spread throughout the archipelago. Aedes albopictus is also present. Invasion and high adaptability of the Aedes mosquitoes to all of these areas are closely related to their ecology and biology. Between June 2016 and July 2017, larval and adult mosquito collections were conducted in 43 locations in 25 provinces of Indonesia using standardized sampling methods for dengue vector surveillance. The samples collected were analyzed for polymorphism and phylogenetic relationship using the mitochondrial cox1 gene and the nuclear ribosomal internal transcribed spacer 2 (ITS2). Almost all Ae. aegypti samples collected in this study (89%) belonged to the same haplotype. A similar situation is observed with the nuclear ITS2 marker. Populations of Ae. aegypti characterized few years ago were genetically different. A closely related observation was made with Aedes albopictus for which the current populations are different from those described earlier. Ae. aegypti populations were found to be highly homogenous all over Indonesia with all samples belonging to the same maternal lineage. Although difficult to demonstrate formally, there is a possibility of population replacement. Although to a lower extent, a similar conclusion was reached with Ae. albopictus.

Assessment of Mosquito Collection Methods for Dengue Surveillance.

Several methods exist to collect and assess the abundance of dengue vector mosquitoes, i.e., morning adult collection, pupal collection, ovitraps, human landing, and larval collection. Several of these methods are officially implemented to monitor mosquito density and make decisions on treatments for dengue control. This monitoring is also constrained by the need to conduct this assessment on a "one point/one day" process, meaning that once the threshold of 100 households is reached, the assessment is made, and the collectors teams move to another place, thus preventing the use of long-term sampling methods. This diversity of methods might be a source of variability and lack of statistical significance. There is also a lack of published data regarding the efficacy of these methods. Furthermore, the Stegomyia indices are shown to be not reliable for assessing the risk of dengue outbreaks. A mosquito survey was, thus, conducted in 39 locations corresponding to 15 dengue endemic provinces in Indonesia by using the different adult and larval collection methods recommended nationwide. A total of 44,675 mosquitoes were collected. The single larva method was the most efficient. Out of a total of 89 dengue-positive pools, the most frequently encountered virus was DENV2, which made up half of the positive samples, followed by DENV3 and DENV1, respectively. Factor analysis of mixed data showed that no correlation could be found between any methods and the presence of dengue virus in mosquitoes. Moreover, no correlation could be found between any methods and the incidence of dengue. There was no consistency in the efficacy of a given method from one site to another. There was no correlation between any of the parameters considered, i.e., method, incidence of dengue, location, and the presence of dengue virus in mosquitoes.

Fast Expansion of the Asian-Pacific Genotype of the Chikungunya Virus in Indonesia.

Chikungunya is repeatedly affecting Indonesia through successive outbreaks. The Asian genotype has been present in Asia since the late 1950s while the ECSA-IOL (East/Central/South Africa - Indian Ocean Lineage) genotype invaded Asia in 2005. In order to determine the extension of the circulation of the chikungunya virus (CHIKV) in Indonesia, mosquitoes were collected in 28 different sites from 12 Indonesian provinces in 2016-2017. The E1 subunit of the CHIKV envelope gene was sequenced while mosquitoes were genotyped using the mitochondrial cox1 (cytochrome C oxidase subunit 1) gene to determine whether a specific population was involved in the vectoring of CHIKV. A total of 37 CHIKV samples were found in 28 Aedes aegypti, 8 Aedes albopictus and 1 Aedes butleri out of 15,362 samples collected and tested. These viruses, like all Indonesian CHIKV since 2000, belonged to a genotype we propose to call the Asian-Pacific genotype. It also comprises the Yap isolates and viruses having emerged in Polynesia, the Caribbean and South America. They differ from the CHIKV of the Asian genotype found earlier in Indonesia indicating a replacement. These results raise the question of the mechanisms behind this fast and massive replacement.

Original Article: Decline of notified dengue infections in Indonesia in 2017: Discussion of the possible determinants.

This study was conducted to quantify the trend in dengue notifications in the country in 2017 and to explore the possible determinants. Annual nation-wide dengue notification data were obtained from the National Disease Surveillance of Ministry of Health of Indonesia. Annual incidence rate (IR) and case fatality rate (CFR) in 2017 and the previous years were quantified and compared. Correlations between annual larva free index (LFI), implementation coverage of integrated vector management (IVM), El Niño Southern Oscillation (Niño3.4), Dipole Mode Index (DMI), Zika virus seropositivity and the percent change in IR and CFR of dengue were examined. The change of dengue IR and CFRs were mapped. In 2017, dengue IR was declined by 71% (22.55 per 100,000 population) compared to 2016 (77.96 per 100,000 population) while the CFR was slightly reduced from 0.79% to 0.75%. Reduction in IR and CFR occurred in 94.1% and 70.1% out of 34 provinces, respectively. The trend of dengue IR seems to be influenced by Niño3.4 but there is no clear evidence that Niño3.4 is the main reason for dengue reduction in 2017. It is difficult to elucidate that the reduction of dengue in 2017 was associated with previous Zika outbreaks. In conclusion, there was a significant reduction on dengue notifications in Indonesia in 2017. Further investigation is needed to look at the role of climate on the decline of dengue IR at finer temporal scale. In addition, study on the role of cross-protective immunity generated by Zika infection on dengue incidence is also warranted.

Stegomyia Indices and Risk of Dengue Transmission: A Lack of Correlation.

Dengue is present in 128 countries worldwide and is still expanding. There is currently no treatment or universally approved vaccine available. Therefore, prevention and control of mosquito vectors remain the most efficient ways of managing the risk of dengue outbreaks. The Stegomyia indices have been developed as quantitative indicators of the risk of dengue outbreaks. However, conflictual data are circulating about their reliability. We report in this article the first extensive study on Stegomyia indices, covering 78 locations of differing environmental and socio-economic conditions, climate, and population density across Indonesia, from West Sumatra to Papua. A total of 65,876 mosquito larvae and pupae were collected for the study. A correlation was found between incidence and human population density. No correlation was found between the incidence of dengue and the Stegomyia indices.

Genetic homogeneity of Anopheles maculatus in Indonesia and origin of a novel species present in Central Java.

BACKGROUND: Anopheles maculatus (s.s.) is an important vector of malaria in Indonesia. Previously it was considered the only member of the Maculatus Group present in Indonesia. A novel species was recently identified in the Kulon Progo District in Central Java. Until recently, few investigations have been conducted looking at An. maculatus genetic diversity in Indonesia, including allopatric island populations. METHODS: Indonesian An. maculatus (s.l.) samples were collected in several locations in Java, Lesser Sunda Island group, Sumatra and in Kulon Progo (Yogyakarta, central Java) where a novel species has been identified. Samples from a 30-year-old colony of the Kulon Progo population were also included in the analysis. Maximum-likelihood analysis established the phylogenies of the ITS2 (nuclear) and cox1 (mitochondrial) markers. Putative times of separation were based on cox1 genetic distances. RESULTS: Two species of the Maculatus Group are present in Indonesia. The novel sibling species is more closely related to Anopheles dispar than to An. maculatus (s.s.). Anopheles maculatus (s.s.) samples are homogeneous based on the ITS2 sequences. Indonesian samples and An. dispar belong to the same cox1 maternal lineage and differ from all other known members of the Maculatus Group. Divergence time between the different populations found in Java was estimated using an established cox1 mutation rate. CONCLUSIONS: A novel species within the Maculatus Group, most closely related to An. dispar, is confirmed present in the Kulon Progo area of Central Java. The divergence of this species from An. maculatus (s.s.) is explained by the stable refugia in the Kulon Progo area during the quaternary period of intense volcanic activity throughout most of Java. This novel species awaits detailed morphological description before applying a formal species name. For the interim, it is proposed that the Kulon Progo population be designated An. maculatus var. menoreh to distinguish it from An. maculatus (s.s.).

First evidence of the presence of genotype-1 of Japanese encephalitis virus in Culex gelidus in Indonesia.

BACKGROUND: Japanese encephalitis has become a public health threat in Indonesia. Three genotypes have been recorded in Indonesia, i.e. genotype II (GII), genotype III (GIII) and genotype IV (GIV). Genotype I (GI) and genotype V (GV) have never been reported in Indonesia. RESULTS: A Japanese encephalitis virus (JEV) belonging to the genotype I-a (GI-a) has been isolated for the first time from a Culex gelidus mosquito in the Province of Jambi, Indonesia. This virus is related to a 1983 isolate from Thailand whereas the infected Cx. gelidus mosquito belonged to a Chinese haplotype. CONCLUSIONS: Surveillance of JEV and mosquito dissemination is recommended.

Japanese encephalitis in Indonesia: An update on epidemiology and transmission ecology.

The Japanese Encephalitis (JE) virus circulation in Indonesia was first documented in Lombok in 1960, and the virus was first isolated in 1972 from Culex tritaeniorhynchus in Bekasi, West Java and Kapuk, West Jakarta. Since then, Indonesia has been recognized as an endemic country for JE transmission. Up to now, JE cases have been found in at least 29 provinces, with Bali, West Kalimantan, East Nusa Tenggara, West Java and East Java, being the areas of highest incidence. However, routine surveillance on JE has not been established at the national level even though many surveys were conducted. JEV has been isolated from 10 mosquito species: Culex tritaeniorhynchus, Cx. gelidus, Cx. vishnui, Cx. fuscocephala, Cx. bitaeniorhynchus, Cx. quinquefasciatus, Anopheles vagus, An. kochi, An. annularis, and Armigeres subalbatus. Culex tritaeniorhynchus is the main JE vector in Indonesia. JE has been detected throughout the Indonesian archipelago from West to East. However, due to a lack of routine, systematic and standardized diagnostic approaches, the JE burden has still not been clearly established yet. Long term and systematic JE surveillance across Indonesia is a priority, the burden needs to be better assessed and appropriate control measures must be implemented.

Schistosomiasis in Indonesia: past and present.

Schistosomiasis is endemic in Indonesia in two isolated areas, Lindu valley and Napu valley, both located in the Province of Central Sulawesi. In 1940, a prevalence survey was initiated in Lake Lindu, which indicated a Schistosoma japonicum infection prevalence of 56% among the population of Anca, Tomado and Langko villages. Another survey was conducted in 1973 in Napu valley and very high infection prevalences of up to 72% were found among the population in Winowanga village. Since then, comprehensive studies on the epidemiology and the effects of control have been carried out in 24 endemic villages in both areas. Over the past six decades, schistosomiasis control has been implemented and the average prevalence is now much lower than before the control programme was launched. In 2006, it was 0.49% in 7 villages in Lindu valley. In Napu valley, the average infection prevalence among the population of 17 villages was 1.08% in the same year. Again in 2006, the prevalence of infection in snails ranged from 0 to 13.4% and from 0 to 9.1% in Napu and Lindu valleys, respectively. The highest prevalence among snails was found in Dodolo village. The prevalence of S. japonicum in the reservoir host Rattus spp. ranged from 0 to 20% and the highest prevalence was again found in Dodolo village. Contemporary data suggest that transmission of schistosomiasis is still ongoing in Indonesia despite regular surveillance and control activities covering the whole endemic area.