Mosquito species composition and Plasmodium vivax infection rates on Baengnyeong-do (island), Republic of Korea

Vivax malaria is a significant military and civilian health threat in the north of the Republic of Korea (ROK). The island of Baengnyeong-do is the westernmost point of the ROK and is located close to the southwestern coast of the Democratic People's Republic of Korea (DPRK). Mosquitoes were collected using a black light trap on Baengnyeong-do, and Anopheles spp. were assayed by PCR, to identify the species, and screened for sporozoites of Plasmodium vivax. Of a subsample of 257 mosquitoes, Anopheles lesteri was the most frequently collected (49.8%), followed by Anopheles sinensis (22.6%), Anopheles pullus (18.7%), Anopheles kleini (7.8%), and Anopheles belenrae (1.2%). The overall sporozoite rate was 3.1%, with the highest rates observed in An. kleini (15.0%), An. sinensis (5.2%), and An. lesteri (1.6%). No sporozoite positive An. pullus or An. belenrae were observed. The results extend our knowledge of the distribution and potential role in malaria transmission of An. kleini, An. lesteri, and An. sinensis, for an area previously considered to be at a low risk for contracting vivax malaria.     

Population dynamics of five anopheles species of the Hyrcanus group in northern Gyeonggi-do, Korea

To investigate the population densities of potential malaria vectors, Anopheles species were collected by light traps in malaria endemic areas, Paju and Gimpo, Gyeonggi-do of Korea. Five Anopheles Hyrcanus sibling species (An. sinensis, An. pullus, An. lesteri, An. kleini, and An. belenrae) were identified by PCR. The predominant species, An. pullus was collected during the late spring and mid-summer, while higher population consists of An. sinensis were collected from late summer to early autumn. These 2 species accounted for 92.1% of all Anopheles mosquitoes collected, while the other 3 species accounted for 7.9%. Taking into account of these population densities, late seasonal prevalence, and long-term incubation period (9-13 months) of the Korean Plasmodium vivax strain, An. sinensis s.s is thought to play an important role in the transmission of vivax malaria in the study areas.     

The Identification of Plasmodium vivax Infected Anopheles sinensis by Enzyme-Linked Immunosorbent Assay, Republic of Korea, 1998

ABSTRACT To figure out how far spread the malaria parasite infected mosquitoes from Demilitarized Zone (DMZ). We investigated the sporozoite-infected mosquitoes in Chosan-ri and Hajiseok-ri of Paju-shi, Tonae-dong of Koyang-shi, Mudeung-ri of Yonchon-gun, Soyo-dong of Tongduchon-shi, and Tukjeong-ri of Yangju-gun, Kyonggi-do province in 1998. They were known as highly epidemic areas in the Republic of Korea. Anopheline mosquitoes were collected by human biting collection method from the 2nd week of June to the 5th week of August. A total of 3,256 anopheles mosquitoes were captured in these areas. A sandwich enzyme-linked immununosorbent assay (ELISA) for identifying Plasmodium vivax sporozoites in mosquitoes was used in this survey. Only one mosquito which was captured in Chosan-ri, on 2nd week of July showed positive reaction in this test. This mosquito was identified as Anopheles sinensis. This showed a 0.068% (1/1,465) positive rate in Chosan-ri on 2nd week of July. We could not detect positive mosquitoes the other areas. So we concluded the parasite infected mosquitoes may be highly limited near the DMZ.     

Vector competence of Anopheles lesteri Baisas and Hu (Diptera: Culicidae) to Plasmodium vivax in Korea

Three anopheline mosquitoes in Korea were studied for their abilities as vectors for Plasmodium vivax. The female mosquitoes of Anopheles lesteri, An. pullus and An. sinensis were allowed to suck malaria patient blood until fully fed, and they were then bred for 2 weeks to develop from malaria parasites to sporozoites. The result from the above confirmed the sporozoites in one An. lesteri of one individual and five An. sinensis of six individuals. We also confirmed that An. sinensis was the main vector to transmit malaria and An. lesteri as well as An. sinensis were able to carry Korean malaria parasites. Therefore, we propose that diversified study is needed to manage malaria projects.     

Re-emerging Plasmodium vivax malaria in the Republic of Korea.

Plasmodium vivax malaria, which was highly prevalent in the Republic of Korea, disappeared rapidly since 1970s. However, malaria re-emerged with the first occurrence of a patient in 1993 near the demilitarized zone (DMZ), the border between South Korea and North Korea. Thereafter, the number of cases increased exponentially year after year, totaling 6,142 cases (6,249 if United States Army personnels were included) by the end of 1998. Interestingly enough, the majority of cases (3,743; 61%) was soldiers aged 20-25, camping around the northern parts of Kyonggi-do or Gangwon-do (Province) just facing the DMZ. Among 2,399 civilian cases, 1,144 (47.7%) were those who have recently retired from their military services in the northern parts of the two Provinces. The re-emerging malaria characteristically revealed a combination type of short and long incubation periods with predominance of the long type. The course of illness was relatively mild, and the treatment was successful in most patients. Vector mosquitoes are Anopheles sinensis and possibly A. yatsushiroensis. Wide-scale preventive and control measures should be operated to eradicate this re-emerging disease. It has been suggested by many authors that the initial source of the re-emerging malaria was infected mosquitoes which had flown from the northern part of the DMZ.     

Detection of vivax malaria sporozoites naturally infected in Anopheline mosquitoes from endemic areas of northern parts of Gyeonggi-do (Province) in Korea

We investigated population densities of mosquitoes infected with sporozoites in three highly epidemic areas of Josan-ri and Jangpa-ri (Paju City) and Dongjung-ri (Yeoncheon County) in Korea. Anopheline mosquitoes were collected from both indoors and outdoors by human baiting collection method during the period of the first week of June to the second week of September 1999. Total 13,296 female mosquitoes were collected and 8,650 (65.1%) were Anophelines. Thirty seven percent (3,199) of the Anopheline mosquitoes were captured outdoors and 63.9% (5,531) indoors. Employing a sandwich enzyme-linked immunosorbent assay (ELISA), we analyzed a total of 7,820 Anopheline mosquitoes and found that 7 Anopheline mosquitoes were infected with sporozoites. The positive rate in Josan-ri was 0.14% (5/3,500) and 0.15% (2/1,370) in Jangpa-ri. The total positive rate in all three surveyed areas was 0.09% (7/7,820). The mosquitoes infected with the sporozoites were detected on June 28th (n = 2), July 5th (n = 1), July 19th (n = 1), August 9th (n = 1), September 6th (n = 1), and the last one on September 13th (n = 1). They were all classified as Anopheles sinensis, which showed positive reaction in ELISA test. Therefore it might be concluded that Anopheles sinensis plays an important role in re-emerging malaria transmission in Korea.     

Evidence for a conspecific relationship between two morphologically and cytologically different forms of Korean Anopheles pullus mosquito

Despite the medical importance of anopheline mosquitoes as vectors of Korean vivax malaria, differentiation between Korean anopheline mosquitoes by traditional morphological taxonomic criteria is difficult. An. yatsushiroensis is the second most common Anopheles mosquito species in Korea and a possible vector of Korean vivax malaria together with An. sinensis, the predominant anopheline species. Recently, An. yatsushiroensis has been declared a synonym of An. pullus, based on comparisons of egg morphology and adult progeny, although they differ in ecology and morphology. To verify the species status of these two ambiguous forms, we established isofemale lines of Korean An. pullus and An. yatsushiroensis (An. pullus form yatsushiroensis) mosquitoes and investigated their genetic relationship by metaphase karyotype analysis, comparing the DNA sequences of rDNA internal transcribed spacer 2 (ITS2) and mitochondrial cytochrome c oxidase subunits I (COI) and II (COII), and by hybridization experiments. Two isofemale lines had differently shaped X and Y chromosomes. However reciprocal crosses between them yielded viable progeny with completely synaptic salivary gland polytene chromosomes. DNA analyses also strongly supported their conspecificity. The two strains also showed great sequence similarity in the ITS2, COI and COII regions (variation rate = 0.0 to 0.8%). Based on these findings, we conclude that the two forms, though differing distinctly in morphological, cytological and ecological traits, remain interfertile.     

Studies on Anopheles sinensis, the vector species of vivax malaria in Korea

Extensive previous studies on taxonomy, behavior/bionomics and control of Anopheles sinensis are reviewed and summarized. Recent molecular identification revealed that the population of An. sinensis complex includes An. sinensis, An. pullus, An. lesteri and at least two new species, and An. yatsushiroensis is synonmy of An. pullus. An. sinensis is the main vector species of vivax malaria in Korea. Larvae of An. sinensis breed in wide range of habitats which are naturally-made clean water, stagnant or flowing; main habitats include rice fields, ditches, streams, irrigation canals, marshes, ponds, ground pools, etc. Their host preferences are highly zoophilic. Human blood rate is very low (0.7-1.7%); nevertheless An. sinensis readily feeds on man when domestic animals are not found near by. They feed on hosts throughout the night from dusk to dawn with a peak period of 02:00-04:00 hours; they are slightly more exophagic (biting outdoors); much larger numbers come into the room when light is on. Main resting places are outdoors such as grasses, vegetable fields and rice fields. A mark-release-recapture study resulted that 37.1% was recaptured within 1 km, 29.4% at 1-3 km, 21.1% at 3-6 km, 10.3% at 6-9 km and 2.1% at 9-12 km distance. An. sinensis hibernate outdoors (mostly under part of dense grasses) during October-March. At the end of the hibernation period (March-April) they feed on cows at daytime. Until today any single measure to effectively control An. sinensis population has not been found. Indoor residual spray with a long-lasting insecticide can not reduce vector population densities, but shorten their life spans in some degree, so contributes to malaria control.     

Distribution and larval habitats of Anopheles species in northern Gyeonggi Province,Republic of Korea

A total of 180 larval collection sites (e.g., rice paddies, marshes, ground pools, ponds, stream margins, and irrigation and drainage ditches) was surveyed within a 2 km radius from Warrior Base training area, 5 km south of Panmunjeom (Joint Security Area, demilitarized zone), Gyeonggi Province, Republic of Korea (ROK), from May through October, 2007 to characterize larval habitat distributions of members of the Anopheles Hyrcanus Group (An. sinensis, An. lesteri, An. pullus, An. belenrae, An. kleini, and An. sineroides). A total of 5,859 anopheline larvae was collected from 84.4% of the sites surveyed, of which 4,071 were identified to species by polymerase chain reaction (PCR) using the ribosomal DNA internal transcribed spacer 2 (rDNA ITS2). Anopheles sinensis (52.6%) was the most frequently collected, followed by An. kleini (29.4%), An. sineroides (9.8%), An. pullus (6.7%), An. belenrae (1.1%), and An. lesteri (0.5%). Anopheles pullus and An. kleini were collected in greater proportions in May and from May – July, respectively. Few An. sinensis were collected from May – June, but it was the predominant species collected by August, and accounted for >80% of all larvae from September – October. Anopheles kleini was found in all habitats sampled; however, it was collected most frequently in young growth rice paddies, while An. sinensis was collected more frequently in mature and post‐harvest paddies. Anopheles pullus was associated with pre‐cultivated rice paddies, including water‐filled tire ruts left from the previous fall's harvest.     

Black light trap collections in Wangging county and Yanji city,Jilin Province,China, August 2006–2007

Adult mosquito surveillance was conducted using black light traps in August of 2006 and 2007 at Wangging county and Yanji city, Jilin Province, China to identify the distribution of anopheline mosquitoes in northern China. A total of 2459 female mosquitoes comprising three genera and eight species including Anopheles (Anopheles) lesteri, An. (Ano.) kleini, An. (Ano.) pullus, Culex inatomii, Cx. orientalis, Cx. pipiens, Cx. bitaeniorhynchus and Aedes vexans nipponii were collected. The most commonly collected species was An. kleini which had not been previously reported from China. Anopheles sinensis sensu stricto is commonly collected throughout China, but was not collected from these areas.     

A mark-release-recapture experiment with Anopheles sinensis in the northern part of Gyeonggi-do,Korea

In order to study the range of flight and feeding activity of Anopheles sinensis, the dispersal experiment was conducted in Paju city, located in the northern part of Gyeonggi-do, Republic of Korea, during the period of 7th to 28th September 1998. Unfed females An. sinensis were collected in cowshed and released after being marked with fluorescent dye at 23:00 hours on the same day. Released female mosquitoes were recaptured everyday during 21 days using light traps, which were set at 10 sites in the cowsheds located 1, 3, 6, 9 and 12 km north-northwest and north-northeast and at 3 sites located 1, 6 and 9 km toward south-west from the release point. In addition, to study the longest flight distance in one night, we set the light traps at 16 and 20 km toward north-northeast from the release site. All the collected mosquitoes were placed on filter papers and observed on UV transilluminator after treatment with one drop of 100% ethanol. Out of 12,773 females of An. sinensis released, 194 marked females mosquitoes were recaptured, giving 1.52% recapture rate. Of 194, 72 mosquitoes (37.1%) were recaptured in light traps from three places set at 1 km from the release point, 57 mosquitoes (29.4%) from two places at 1-3 km, 41 mosquitoes (21.1%) from three places at 3-6 km, 20 mosquitoes (10.3%) from three places at 6-9 km, and 4 mosquitoes (2.1%) from two places at 9-12 km. Since 170 female mosquitoes (87.6%) out of 194 marked mosquitoes were captured within 6 km from the release point, this flight radius represents the main activity area. An sinensis was found to be able to fly at least 12 km during one night.     

Seasonal population density and daily survival of anopheline mosquitoes (Diptera: Culicidae) in a malaria endemic area, Republic of Korea.

Mosquito surveillance was conducted near the Korean Demilitarized Zone (Paju County, Gyeonggi Province) from April to October, 1999, where malaria cases were reported. Adult mosquito surveillance, using black light and CDC UV light traps, was conducted at five and two sites, respectively. Weekly larval collections were made at five rice paddies located adjacent to the adult collection sites. Anopheles sinensis was the most abundant mosquito of 11 species collected throughout the surveillance period in 1999, comprising 47 - 48% of the total number of mosquitoes collected at cow sheds and residence. At all five sites surveyed by CDC UV light traps, anophelines appeared early in the year (May 3) and were most abundant in the cow sheds followed by the hillside forest, residence, stream/river bank, and were least abundant in rice fields. The population density of the larvae and the adults of An. sinensis increased steadily in June and reached their peaks during the second week of July (mean 112 females/trap/night). The parity rates were higher in July and September, when populations were highest. The probabilities of daily survival of An. sinensis were 0.804 in June to 0.895 in July. Cross-correlation showed a significant relationship between the number of adult anopheline mosquitoes and the number of larvae collected on the previous day, the same day, and also three and seven days later, which may be useful for determining treatment thresholds.     

DIFFERENCES IN SEQUENCES OF RIBOSOMAL DNA SECOND INTERNAL TRANSCRIBED SPACER AMONG THREE MEMBERS OF ANOPHELES HYRCANUS COMPLEX FROM THE REPUBLIC OF KOREA

Abstract  Differences in sequences of ribosomal DNA second internal transcribed spacer (ITS) among Anopheles sinensis, An. lesteri and An. yatsushiroensis from Korea were compared. The PCR amplified rDNA-ITS2 fragments were sequenced directly. Three samples of each species were individually determined.
Lengths of the ITS2 regions were 468bp in An sinensis , 451bp in An lesteri and 453bp in An yatsushiroenesis and GC contents were 44.87 % 46.2 % and 45.7 % respectively. Variations of the sequences ranged from 12.16 % to 30.7 % among the three species. The differences of the rDNA-ITS2 sequences would be useful for molecular identification of the three members of Anopheles hycanus complex from Korea.     

Seasonal prevalence of mosquitoes collected from light traps in the Republic of Korea, 2005

Adult mosquito surveillance was conducted during 2005 at 22 US military installations and two training sites located in six provinces in the Republic of Korea. Adult mosquitoes were collected in New Jersey light traps from 1 May to 15 October to determine threshold levels to initiate pesticide applications based on trap indices. A total of 27 363 adult mosquitoes (22 368 [81.7%] females and 4995 [18.3%] males) comprising 15 species (including five members of the Anopheles sinensis group) belonging to seven genera were collected. The most common species collected were members of the Anopheles sinensis Wiedemann group (50.2%), followed by Culex tritaeniorhynchus Giles (30.6%), Aedes vexans nipponii (Theobald) (11.8%), and Culex pipiens Coquillett (6.3%) females. Trap indices varied widely for species over their range, due in part to geographical distribution and degree of association with urban or rural communities.     

Seasonal prevalence of mosquitoes collected from light traps in the Republic of Korea, 2006

Adult mosquito surveillance was conducted during 2006 at 22 US Army and Air Force installations and two training sites located in six provinces in the Republic of Korea. Adult mosquitoes were collected in New Jersey light traps from 1 May through 15 October 2006 to determine threshold levels to initiate pesticide applications based on trap indices. In total 16 217 adult mosquitoes [13 612 (83.9%) females and 2605 (16.1%) males] comprising 16 species (including five members of the Anopheles sinensis Group) belonging to eight genera were collected. Females of the most commonly collected species were members of the Anopheles sinensis Wiedemann Group (58.9%), followed by Aedes vexans nipponii (Theobald) (21.3%), Culex tritaeniorhynchus Giles (11.8%) and Culex pipiens Coquillett (5.2%). Trap indices varied widely for species over their range, due in part, to their geographical distribution and degree of association with urban or rural communities.     

韩国赫坎按蚊复合体3成员种核糖体DNA内转录间隔2区的比较(英文)

本文对韩国中华按蚊、雷氏按蚊和八代按蚊核糖体DNA (rDNA)内转录间隔 2区 (ITS2 )序列进行了比较研究。用PCR扩增的rDNA ITS2片段直接测序 ,每种蚊测定 3个个体 ,结果显示 :韩国中华按蚊、雷氏按蚊和八代按蚊的rDNA ITS2序列长度分别为 4 6 8bp、 4 51bp和 4 53bp ,GC含量分别为 4 4 .87%、 4 6 .2 %和 4 5.7% ,3种按蚊序列差异范围为 12 .16 %— 30 .74 %。研究表明 ,rDNA ITS2序列差异可用于韩国中华按蚊、雷氏按蚊和八代按蚊的分子鉴别。     

Seasonal Prevalence of Mosquitoes Collected from Light Traps in the Republic of Korea, 2001

ABSTRACT Adult mosquito surveillance was conducted during 2001 at 28 US military installations and training sites located in five provinces in the Republic of Korea (ROK). Adult mosquitoes were collected in New Jersey and dry ice-baited CDC-type light traps from 1 May through 15 October. Mosquito surveillance was conducted to determine threshold levels to initiate pesticide applications and identify malaria infection rates at selected Army installations and training sites. A total of 61,584 adults [45,814 (74.4%) females and 15,770 (25.6%) males] comprising 17 species and 7 genera were collected during 2001. The most common species collected were Anopheles sinensis Wiedemann (36.3%), Aedes vexans nipponii (Theobald) (23.1%), Culex tritaeniorhynchus Giles (22.3%) and Culex pipiens Coquillett (17.6%). Trap indices (TIs) varied widely for species over their range, due in part, to geographical distribution and degree of association with urban communities. During 2001, the TI for An. sinensis was 19.6 females/trap night compared to years 1999 and 2000, when the TI for the Munsan area was 1.4 and 2.9 times (27.7 and 57.4 TI) greater, respectively. The weekly population densities for some species were variable for each of the years, apparently as a result of variable annual weather conditions. None of the 16,302 Anopheles sinensis assayed for plasmodium vivax (Pv) malaria infections by Enzyme Linked Immunosorbent Assay (ELISA) were positive.     

Unstable vivax malaria in Korea

Korean vivax malaria had been prevalent for longtime throughout the country with low endemicity. As a result of the Korean war (1950-1953), malaria became epidemic. In 1959-1969 when the National Malaria Eradication Service (NMES) was implemented, malaria rates declined, with low endemicity in the south-west and south plain areas and high endemic foci in north Kyongsangbuk-do (province) and north and east Kyonggi-do. NMES activities greatly contributed in accelerating the control and later eradication of malaria. The Republic of Korea (South Korea) was designated malaria free in 1979. However, malaria re-emerged in 1993 and an outbreak occurred in north Kyonggi-do and north-west Kangwon-do (in and/or near the Demilitarized Zone, DMZ), bordering North Korea. It has been postulated that most of the malaria cases resulted from bites of sporozoite-infected females of An. sinensis dispersed from North Korea across the DMZ. Judging from epidemiological and socio-ecological factors, vivax malaria would not be possible to be endemic in South Korea. Historical data show that vivax malaria in Korea is a typical unstable malaria. Epidemics may occur when environmental, socio-economical, and/or political factors change in favor to malaria transmission, and when such factors change to normal conditions malaria rates become low and may disappear. Passive case detection is a most feasible and recommendable control measure against the unstable vivax malaria in Korea in cost-effect point of view.     

Malaria Vector Surveillance in Ganghwa-do, a Malaria-Endemic Area in the Republic of Korea

We investigated the seasonality of Anopheles mosquitoes, including its species composition, density, parity, and population densities of mosquitoes infected with the parasite in Ganghwa-do (Island), a vivax malaria endemic area in the Republic of Korea. Mosquitoes were collected periodically with a dry-ice-tent trap and a blacklight trap during the mosquito season (April-October) in 2008. Anopheles sinensis (94.9%) was the most abundant species collected, followed by Anopheles belenrae (3.8%), Anopheles pullus (1.2%), and Anopheles lesteri (0.1%). Hibernating Anopheles mosquitoes were also collected from December 2007 to March 2008. An. pullus (72.1%) was the most frequently collected, followed by An. sinensis (18.4%) and An. belenrae (9.5%). The composition of Anopheles species differed between the mosquito season and hibernation seasons. The parous rate fluctuated from 0% to 92.9%, and the highest rate was recorded on 10 September 2008. Sporozoite infections were detected by PCR in the head and thorax of female Anopheles mosquitoes. The annual sporozoite rate of mosquitoes was 0.11% (2 of 1,845 mosquitoes). The 2 mosquitoes that tested positive for sporozoites were An. sinensis. Malarial infections in anopheline mosquitoes from a population pool were also tried irrespective of the mosquito species. Nine of 2,331 pools of Anopheles mosquitoes were positive. From our study, it can be concluded that An. sinensis, which was the predominant vector species and confirmed as sporozoite-infected, plays an important role in malaria transmission in Ganghwa-do.     

Seasonal Prevalence of Mosquitoes Collected from Light Traps in Korea (1999-2000)

ABSTRACT Adult mosquito collections were conducted from 1999 through 2000 at 29 US military installations located in six provinces in the Republic of Korea (ROK). Adult mosquitoes were collected in New Jersey light traps from 15 May to 15 October each year. Adult mosquito surveillance was conducted to determine the appropriate time for pesticide applications at each of the Army installations. A total of 68,051 and 62,526 adults were collected in 1999 and 2000 respectively, comprising 53,983 (79.3%) females and 14,068 (20.7%) males in 1999, and 50,274 (80.4%) females and 12,252 (19.6%) males in 2000. A total of 19 species from 7 genera were collected. The most common species collected were Anopheles sinensis (34.2%), Culex tritaeniorhynchus (29.4%), Aedes vexans nipponii (18.2%) and Culex pipiens (16.8%). Anopheles sinensis were collected at the same level while Culex tritaeniorhynchus decreased by 6.2% in 2000. The weekly population densities for some species were variable for each of the years, apparently as a result of changing weather conditions.