Short Communication: First report of canine cutaneous myiasis caused by Chrysomya bezziana Villeneuve (Diptera: Calliphoridae) in Thailand

@#Although myiasis caused by the blow fly, Chrysomya bezziana Villeneuve (Diptera: Calliphoridae), has been reported in Thailand, all of the cases were human. This study described three cutaneous myiasis cases caused by C. bezziana in dogs in Chiang Mai province, northern Thailand. The removal of fly larvae together with specific treatment to cure all cases in this study was represented.

Polygamy: the possibly significant behavior of Aedes aegypti and Aedes albopictus in relation to the efficient transmission of dengue virus.

The polygamous behavior of male Aedes aegypti (L.) and Ae. albopictus (Skuse) was investigated by co-habiting a newly-emerged male and females in a 30 cm3 cage (1 male: 20 females) for up to 5 consecutive days. As determined by insemination rates, the results indicated that one Ae. aegypti and Ae. albopictus male could successfully mate with 1.10 (0-4), 4.10 (1-8), 5.40 (4-8), 5.10 (2-8), 5.15 (3-9) and 0.20 (0-3), 1.70 (0-3), 2.35 (1-4), 2.30 (0-4), 2.35 (1-4) Ae. aegypti and Ae. albopictus females, respectively on day 1,2,3,4 and 5 consecutively. The possibly significant role of their polygamy in relation to dengue virus transmission is discussed.

Aedes albolateralis, a potential vector of nocturnally subperiodic Wuchereria bancrofti and dengue type 2 virus.

The susceptibility of Aedes albolateralis to nocturnally subperiodic Wuchereria bancrofti and dengue type 2 virus was investigated by using artificial membrane feeding and intrathoracic inoculation techniques, respectively. The results indicated that Ae. albolateralis was susceptible to nocturnally subperiodic W. bancrofti (susceptibility rate = 9.43%) and dengue type 2 virus (susceptibility rate = 100%), suggesting the potential vector of the two pathogens.

Intensity of trematode metacercariae in cyprinoid fish in Chiang Mal Province, northern Thailand.

The intensity of infection of trematode metacercariae was determined in five species of cyprinoid fish collected from Mae Ngud reservoir, Chiang Mai Province. These species were Thynnichthys thynnoides, Puntioplites proctozysron, Hampala macrolepidota, Puntius leiacanthus and Puntius gonionotus. T. thynnoides contained the highest number (83.0%) of metacercariae, whereas P. gonionotus had the fewest (0.19%). The caudal fin was the area of highest infection of metacercariae (49.39%), with the anal fin having the fewest (5.93%). Most metacercariae was isolated from Haplorchis taichui (63.27%), with an intensity variation of 0.3-165.2 metacercariae/fish.

Prevalence of Opisthorchis viverrini infection among villagers harboring Opisthorchis-like eggs.

The precise occurrence of Opisthochis viverrini infection in humans, who were positive for Opisthorchis-like eggs in a stool examination, was determined using the potassium permanganate staining method. In the 68 specimens examined, there were more individual O. viverrini eggs (38.24%) than singular Haplorchis taichui eggs (29.41%). One-fourth of the total specimens contained a mixed infection of O. viverrini and H. taichi eggs. The median ratio of O. viverrini: H. taichui eggs in mixed infection cases was 2.29 (min = 1, max = 17.5). It is suggested that chemotherapy with praziquentel treatment should be given to patients who are positive for O. viverrini-like eggs.

Development of Haplorchis taichui (Trematoda: Heterophyidae) in Mus musculus mice.

The development of Haplorchis taichui was studied in sixteen mice, Mus musculus. Metacercarial cysts of H. taichui were obtained from the freshwater fish, Thynnichthys thynnoides, collected in Chiang Mai Province, north Thailand. Approximately 200 active metacercariae were orally introduced into each mouse. Two mice were randomly sacrificed and necropsied daily from day 2-9 postinfection (pi). Two peaks of increment in the length and width of worms were found at day 3 and 7 pi. H. taichui was rapid in maturation, similar to other minute intestinal flukes. Rudimentary sex organs were found at day 2 pi. Spermatozoa in a seminal receptacle, vitellaria and eggs were seen as early as 3 days pi. The number of eggs increased daily to approximately 50-60 eggs thereafter. Mice can serve as a suitable experimental definitive host for harvesting adult H. taichui, especially in 1-week pi.

Experimental infection of Gnathostoma spinigerum larvae in prawns and tadpoles.

Naturally captured Lanchester's freshwater prawns (Macrobrachium lanchesteri) and farm-bred Rana regulosa tadpoles were assessed for their capability of being the first or second intermediate hosts of Gnathostoma spinigerum. Seventy specimens from each animal group were randomized into a control group and investigated for larvae of G. spinigerum by pressing them between two pieces of glass and examination under stereomicroscope. No Gnathostoma larvae were found in the entire control group. Another 120 specimens of each animal were used in two treatment groups; 60 being exposed to the first-stage larvae, G. spinigerum, and 60 exposed to cyclops containing the third-stage larvae for 7 days. No larvae of G. spinigerum were found in the prawns of both treatment groups that resembled tadpoles exposed to the first-stage larvae. In contrast, 18.3% of tadpoles, which were exposed to cyclops containing third-stage larvae, were infected. Lanchester's freshwater prawns cannot serve as intermediate host of G. spinigerum, while R. regulosa can serve as the second intermediate host.

In vitro excystation of Haplorchis taichui (Trematoda: Heterophyidae).

The effects of trypsin, bile extract, temperature and acid-based condition for the in vitro excystation of Haplorchis taichui metacercariae were studied. At 37 degrees C, approximately half the number of metacercariae excysted when exposed to 1% trypsin for 15 minutes with no more excystation found beyond this time. Increasing trypsin concentration seemed to reduce the excystation rate while bile extract was, however, unlikely to be an absolute requirement. A temperature of 37 degrees-41 degrees C yielded a similar excystation result in combination with 1% trypsin; however, less excystation occurred at a lower temperature of 35 degrees C. The acid-based environment of pH 8 gave the best excystation result in association with 1% trypsin at a temperature of 39 degrees C. Higher and lower basicity produced a smaller excystation rate. An environmental condition of 1% trypsin at pH 8 and a temperature of between 37 degrees-41 degrees C was recommended for the in vitro excystation of H. taichui metacercariae. The relatively broad temperature and pH range condition for the excystation of H. taichui corresponded with various definitive hosts that were infected naturally by this fluke.

In vitro development of Haplorchis taichui (Trematoda: Heterophyidae).

Newly excysted metacercariae of Haplorchis taichui were cultured in a candle jar set at 37 degrees C. Both monophasic culture media [0.85% NaCl, RPMI 1640, RPMI 1640+10% fetal calf serum (FCS)] and diphasic culture media [RPMI 1640 + egg yolk agar, RPMI 1640 + 5%, 10% or 15% blood in blood agar (BA), RMPI 1640 + 5%, 10% and 15% FCS with 5% blood in BA] were used in vitro. Parasites survived for only 1 day in 0.85% NaCl without any development. In RPMI 1640 with egg yolk agar and RMPI 1640 + 5%, 10% FCS, the parasite survived for 3-5 days. In contrast, worms survived for 12-14 days in RPMI 1640 with blood agar without any change in result in a different concentration of blood in BA. The ovary and testes were observed after 3 days incubation in this media. Nevertheless, only 1 parasite in RPMI 1640 with 15% blood in BA had vitellaria and eggs at day 6. RPMI 1640 with blood agar can be used as short-term maintenance for the in vitro culture of H. taichui. However, further studies are needed.

Surface ultrastructure of excysted metacercariae of Haplorchis taichui (Trematoda: Heterophyidae).

The morphology of newly excysted juvenile Haplorchis taichui was studied using a light and a scanning electron microscope (SEM). The reproductive organs were well developed. The whole body surface was covered with numerous transverse rows of scale-like spines, which had 3-11 points at the tip. The spines on the dorsal were similar with those on the ventral surfaces in shape, size and number of points. The spines in anterior were digitated into 10-11 points, then 8-9 points and 7 points. The presence of 3 points in each spine was observed in the area adjacent to the excretory pore. Two types of sensory papillae existed throughout the body: type I, ciliated knob-like swellings and type II, round swellings of the tegument. The rapid maturation of H. taichui results from the development of both internal and external organs during the newly excysted stage.