Dirofilaria repens from the eyelid of a woman in Thailand.

An immature male Dirofilaria repens was removed from a cystic mass in the eyelid of a 51-year-old woman employee of a rubber plantation in Phangnga Province, southern Thailand.

Experimental transmission of subperiodic Wuchereria bancrofti to the leaf monkey (Presbytis melalophos), and its periodicity.

Infective larvae of nocturnally subperiodic Wuchereria bancrofti were obtained from laboratory-raised Aedes togoi mosquitoes which had fed on an infected human volunteer from Kanchanaburi, Thailand, and 471 of them were inoculated subcutaneously into the inguinal regions of an immunosuppressed Presbytis melalophos. Microfilaremia was first detected 287 days after inoculation, and 77 days later, at 364 days of infection, the number of microfilariae determined at 2-hour intervals reached a maximum of 619/20 mm3 at 4 hours past midnight, and the daytime levels were 11-35/20 mm3; the corresponding levels in the human volunteer were 121 and 13-32/20 mm3. Thus the nocturnal periodicity was relatively greater in the monkey than it was in the human host. Eight days after the periodicity study the monkey died and 77 adult worms were recovered from the popliteal (4), inguinal (58), iliac (6) and para-aortic (9) lymph nodes and 1 each from the ovary and liver. Of 56 females, only half were gravid.

Anthropophilic and zoophilic phlebotomine sand flies (Diptera, Psychodidae) from Thailand.

As a result of extensive surveys of sand flies carried out during 1987-90 in Thailand, species including a man-biter, Phlebotomus hoepplii, and cattle-biters, P. argentipes and P. major major, were discovered in Kanchanaburi Province. The human-baited catches revealed a low density of P. hoepplii and the biting occurred during 2100-2300 hours. Phlebotomus hoepplii was also found feeding on buffalo and inhabiting Pha-Thai Cave, Lampang Province. Phlebotomus argentipes was also a common cave-dweller and therefore had a wider distribution than P. major major, which was only collected in Sara Buri and Kanchanaburi provinces. The 3 species inhabited forest environments close to foothills and on stream banks. Although there is yet no evidence that they are involved in leishmaniasis transmission, the bionomics of the species are of importance and should be studied further.

Morphological differentiation in Anopheles maculatus of Thailand accompanied with genetical divergence assessed by hybridization.

Anopheles maculatus of Thailand were distinguished morphologically into densely and sparsely scaled types and cross-mating experiments between these types revealed a substantial amount of genetic divergence. Progeny of wild females of An. maculatus collected throughout Thailand from north to south were examined morphologically with respect to adult tergal pale scales. Northern progeny broods could be separated into densely scaled (willmori) and sparsely scaled (maculatus) types, or W and M types, respectively. Using these two types of An. maculatus from Chiang Rai and Nakhon Phanom, cross-mating experiments were conducted, which resulted in sterile F1 male hybrids in one direction of cross and very low survival rate of F1 male hybrids in the reciprocal cross. However, southern broods could not be separated clearly because of intergradation of scaling. These results indicate that Thai An. maculatus involves at least 2 forms differentiated morphologically, as well as by incomplete reproductive isolation.

Laboratory bionomics of Tripteroides aranoides.

Tripteroides aranoides was colonized in the laboratory. Total duration of the immature stages was ca. 3 weeks at 28 degrees C, L:D = 15.5:8.5 with an ample food supply. Retardation of 4th instar development was observed in larvae fed on insufficient food. Females were autogenous for the first clutch of eggs and required a blood meal for maturation of the second clutch. Mating was initiated in flight and copulation occurred on the cage wall. Gravid females hovered in small oblique loops above water in bamboo cups, whereupon a white egg appeared at the abdominal tip, which was propelled by the swing of the abdomen towards water surface. The females propelled eggs in the same manner into small apertures (11 x 4 mm) bored in bamboo.

Recent advances in vector control in filariasis.

Three factors are involved when vector control is incorporated into an integrated control program for filariasis: (1) the vector species or species complex of each filarial worm; (2) type of control measures employed; (3) pesticide application. Recent advances in vector control in filariasis include the use of bed nets, environmental manipulation, insecticides and biological control. Three promising advances in vectrol control are the use of pathogenic bacteria such as Bacillus thuringiensis H-14 and B. sphaericus, juvenile hormone mimics or insect growth regulator (IGR) and predatory crustaceans.

Observation on the reduction of the prevalence of malayan filariasis in Chumphon Province of South Thailand.

Further studies on malayan filariasis were made at Bangluke canton of Chumphon province of South Thailand, where mass drug treatment was not applied. It was found after 9 years that there was a marked reduction in filariasis in the area. The filariasis infection rate being decreased from 14.1 to 1.9 per cent, the microfilarial rate from 10.8 to 0.9 per cent, and the elephantiasis rate from 3.3 to 1.0 per cent, and the mean microfilarial density among positive cases being decreased from 27.6 to 6.6 per 20 c.mm blood. Dissection of 1,893 Mansonia mosquitoes revealed the finding of only stage I and stage II larvae of B. malayi in seven M. annulifera and M. indiana. The reduction in the filariasis infection was assumed to be due to the interruption of transmission of filariasis cycle in the mosquitoes resulting from DDT spraying operation of the Malaria Eradication Programme of the Thai Government. There were also some positive cases moving out of the area. The rural development programme of the Thai Government also played another important role in the reduction in the prevalence of malayan filariasis in this area.

Experiments in crossing two strains of Anopheles barbirostris van der Wulp 1884 (Diptera: Culicidae) in Thailand.

Crossing experiments between two strains of Anopheles (Anopheles) barbirostris from Chumphon and Chon Buri provinces in Thailand were done by induced copulation in order to determine the genetic relationship. On comparison of the F1 hybrids and those of their parent species as the control, there was a difference in the number of eggs laid, hatchability and viability. The low viability of the F1 hybrids with high larval and pupal mortalities, producing only a few F hybrids, and the fact that F1 hybrids' salivary chromosome showed asynapsis suggest there exists reproductive isolations between both strains. The data presented suggest that these two strains exhibit possible presence of a species complex in An. barbirostris.

Biology of the snail-killing fly, Sepedon spangleri Beaver (Diptera: Sciomyzidae). II. Ability of the larvae to kill snails of medical importance in Thailand.

S. spangleri larvae preferred five species of non-operculate snails; Gyraulus convexiusculus Hutton, Segmentina hemisphaerula Benson, Hippeutis umbilicalis Benson, Indoplanorbis exustus Larambergue, and Trochobis trochoideus Benson. They occasionally consumed the operculate snails: Melanoides tuberculata Muller, Lithoglyphopsis aperta, Hubendickia siamensis Brandt, Lacunopis munensis Brandt, Tarebia granifera, Lamarch and Viviparus sp. but were innocuous to Bithynia laevis Lea.

A survey of houseflies in bangkok and neighboring provinces.

A survey of flies in Bangkok and neighboring province revelaed that among 8,675 flies collected there were 10 genera and 18 species of flies, eg. Musca domestica, M. bezzii, M. conducens, M. nebulo, Chrysomyia megacephala, C. rufifacies, Phaenicia sericata, P. cuprina, Sarcophaga ruficornis, S. peregrina, S. orchidae, S. albiceps, Megaselia scalaris, Lispe orientalis, Anaclysta flexa, Morellia hortensia, Hemipyrellia ligurriens and Orthellia coeruleifrons. Musca mostly bred in low-protein content media, eg., garbage piles of vegetable and rice, and was predominant in the morning while Chrysomyia and Phaenicia mostly bred in high-protein content media, eg., animal carcasses, and were predominant in the afternoon. Female flies were bigger than male and they were more predominant than males in or around breeding places. The density of flies was correlated with the relative humidity but not with rainfall or temperature. The density of flies was correlated with the occurrence of gastrointestinal diseases. Some cases of myiasis have been reported from Thailand.

Residual effectiveness of insecticidal deposits on various wall surfaces.

The effectiveness of three chemicals DDT, malathion and Dursban was evaluated against larvae and adults of C. p. fatigans. When larvae and adult mosquitoes were tested for susceptibility, they were susceptible to malathion and Dursban. These insecticides were sprayed onto various wall surfaces at a dose of 2 gm per square metre and the residual effect on C. p. fatigans were studied. Dursban residue was superior on all sufaces, giving effective kill for 10-30 weeks, malathion gave satisfactory result on thatch, plywood and galvanized iron while DDT residue failed to produce effective kills.

Studies on the life history of Megaselia scalaris (Loew) in Thailand.

The morphological, life-cycle, and experimental studies of Megaselia scalaris were reported. This fly is commonly found both in urban and rural areas in Thailand. It is easily identified and the humped thorax was the most distinct characteristic of the adult. The egg to the adult stage and the life span required 15 to 20 days for the male and 16 to 22 days for the female. Experimental attempts to induce myiasis infection in laboratory animals were unsuccessful.

Descriptions of odonate nymphs from Thailand.

The descriptions of odonate nymphs from Thailand are presented. The insects of the Order Odonata both naiads and adults may serve as the second intermediate host of some intestinal parasites in Thailand.

DDT-resistant Culex quinquefasciatus: the effect of DDT on the mosquito's size, fecundity and survival.

Resistant strains of Culex quinquefasciatus were selected in the larval stage by exposure to sublethal doses of DDT. The size, body weight and fecundity of DDT-resistant mosquitoes were significantly decreased. There was no significant difference between the longevity of females in the original strain and the DDT selected strains, however, there was a significant difference in the males of the DDT-resistant strains than those of the original strain.

Plasmodium falciparum infection in Bisazir chemosterilized Anopheles dirus in laboratory studies.

Bisazir, at a 0.5% solution induced sterility in males and at a 1.5% solution in female A. dirus. These sterilizing doses reduced P. falciparum infection in mosquitoes, however, they can still transmit malaria. It is concluded that by the concentration of 1.5 and 2.0% that induced complete sterility in males and females are not safe in sterile-male release programme for the control of A. dirus, unless all females were eliminated prior to release.

Biology of the snail-killing fly, Sepedon spangleri Beaver (Diptera: Sciomyzidae). I. Life history.

One complete generation of the sciomyzid fly, S. spangleri, was on the average 27.90 days at 25 +/- 3 degrees C. The egg stage lasted 3.55 days. The first, second and third instar larvae lasted 4.35, 2.95 and 4.45 respectively when fed with live snails, Australorbis glabratus. Pupae floated on the water surface for 8 days until they emerged as adults. The longevity of adults fed with crushed snails, dried milk, brewer's yeast and honey average 199.95 days for females and 136.80 days for males. Under these conditions the average number of eggs laid per female was 414.70.

The differentiation of brugia malayi, B. pahangi, B. tupaiae and Wuchereria bancrofti.

During studies on filariasis in Thailand, attempts were made to differentiate Wuchereria bancrofti and Brugia spp. by morphological characteristics, as well as by vector species.

Vectors of Japanese encephalitis virus (JEV): species complexes of the vectors.

The vectors of JEV are Cx. tritaeniorhynchus, Cx. vishnui, Cx. pseudovishnui, Cx. gelidus, Cx. fuscocephala, Cx. quinquefasciatus, Cx. pipiens pallens, Cx. bitaeniorhynchus, Cx. annulirostris, Aedes togoi, Ae. japonicus, Ae. vexans nipponii, Anopheles annularis and An. vagus. Cx. tritaeniorhynchus is in the tritaeniorhynchus complex, breeds in rice fields, ground pools in vast areas. Two types of mating behavior, eurygamy and moderate stenogamy were detected. In the case of the eurygamy type, the mosquitoes were from Southern Thailand and hilly areas near Kanchanaburi, Thailand. Female mosquitoes are usually dark in color, the cibarial armature has rod teeth and the posterior end of the cibarial armature is bowl shaped with a typical rim. The rim of the bowl is everted. The moderate stenogamy type were mosquitoes from the plain areas such as Bangkok, Ayutthaya, Suphan Buri and Saraburi. The posterior end of the cibarial armature is bowl shaped with a stout rim. The larvae were characteristic in their siphon index, antennal index, hair O of prothoracic segment, and comb scale number and arrangement. Cx. tritaeniorhynchus summorosus from Japan, Los Banos and Luzon, Philippines, differed from Cx. tritaeniorhynchus in that on the lateral plate of the phallosome tritaeniorhynchus teeth are somewhat weakly developed and only gently curved whereas in tritaeniorhynchus summorosus they are strongly developed, considerably longer, and sharply recurved. The siphons of larvae are short, the sides parallel and the apex truncate in tritaeniorhynchus whereas in tritaeniorhynchus summorosus they are long and slender. Cx. tritaeniorhynchus var. siamensis is possibly present. Colonies have been maintained in the Department of Medical Entomology for 31 generations. The characteristics are in hair O (short, less than 20 branches, and without secondary branching and the larval siphon (short and broad where the others are long). Cx. vishnui and Cx. pseudovishnui are in the vishnui complex. Cx. quinquefasciatus and Cx. pipiens pallens are in the Cx. pipiens complex comprising: (1) Cx. pipiens; (2) Cx. quinquefasciatus Say; (3) Cx. molestus Forskal; (4) Cx. pipiens pallens; (5) Cx. australicus; (6) Cx. globocoxitus. Anopheles annularis is a species complex evidenced by two types of polytene chromosomes.

Alteration in Aedes togoi susceptibility to Brugia pahangi microfilariae induced by Aedes albopictus thoracic homogenate.

Refractoriness to Brugia pahangi microfilarial infection could be induced in the normally susceptible Aedes togoi mosquitoes by intrathoracic injection with crude thoracic homogenate of the refractory Aedes albopictus mosquitoes. The crude thoracic homogenate contained three Sephadex G-200 protein profiles of which the first profile showed strongest inhibition to the parasite development.

Investigation of malaria sporozoites by immunoradiometric assay.

Two-site immunoradiometric assay (IRMA) (Zavala et al., 1982) using monoclonal antibodies to P. falciparum and P. vivax was applied to detect sporozoites in laboratory-maintained An. dirus and also mosquitoes collected from endemic areas of malaria in Thailand. Study in P. falciparum infected mosquitoes revealed that the circumsporozoite (CS) antigen was first found in the abdominal portion on day 10 post-infection, while it could be observed in the salivary glands from day 15 onwards. The head-thorax portion of wild-caught mosquitoes were investigated by IRMA compared with the dissection technique. The results showed that none of the mosquitoes collected from Phrae was positive for malaria. The mosquitoes collected from Chantaburi showed 4 out of 1243 An. dirus that were positive for P. falciparum by IRMA, with sporozoites ranging from 207 to 3875. Among 3123 An. minimus collected from Kanchanaburi, 3 were positive by IRMA, 2 for P. falciparum and one P. vivax with sporozoites found in head-thorax portion were 1880, 2380 and 1026 respectively. Not a single sporozoite was found in the mosquitoes collected from these areas by the dissection technique. However 7 out of 1219 An. minimus from Kanchanaburi were found to possess undeveloped oocysts in the stomach wall. It is evident that the IRMA is efficient, convenient and suitable for the investigation of sporozoites in this region. The application of this technique in further epidemiological study of malaria is in progress.