HOUSEFLIES WITH HELMINTHIC OBJECTS, GOOD INDICATOR OF AN UNSANITARY ENVIRONMENT Wanna Maipanich, Paron Dekumyoy, Surapol Sa-nguankiat, Somchit Pubampen, Akkarin Poodeepiyasawat, Teera Kusolsuk, Urusa Thaenkham, and Dorn Watthanakulpanich Department of Helminthology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand Abstract The housefly is a mechanical vector of helminthic infections, and it is common to find all stages (egg-larvaadult) of helminths in flies. In communities where the prevalence of worm infection is high, and where the use of outside latrines is common, houseflies may play an important role in the mode of disease transmission. In areas highly contaminated with flies, people are at risk of many helminth infections, such as Ascaris, Trichuris, Taenia and Angiostrongylus. For this study, helminth objects from two study areas were compared: Tak and Yasothon provinces, in Thailand. In Tak Province (western Thailand) where defecating in external latrines or in the open is common, the prevalence of helminthiasis was 55.2%. The majority of infections were Ascaris (47.8%), and some villagers were diagnosed with heavy Ascaris infestations. Upon examination of 622 houseflies captured in this area, the number of eggs detected was as follows: 1,951 (Ascaris), 369 (Taenia), 147 (Trichuris), 52 (hookworm), and 1 (Toxocara). In Yasothon Province (northeastern Thailand), indiscriminate defecation is rare, and the prevalence of helminthic infections was low; no Ascaris infections were noted among this population. The examination of houseflies showed that Dicrocoelium eggs were common, and other eggs, such as Strongylid, Trichuris, and Opisthorchis, were also present. These eggs are commonly found in dogs and cats, so it is possible that they belonged to animal parasites. We found that each fly carried 4.1 and 0.3 helminth eggs in poor and good sanitation communities, respectively. Helminthic objects on the body surfaces of houseflies can be detected easily, and the agents can be examined using a light microscope. This simple method can provide an indicator of an environment s sanitary status, and its relation to human and animal waste. Keywords: helminth objects, houseflies, indicator of unsanitary environment INTRODUCTION The housefly is a pest to humans. They dart around the air, knock and buzz at windows and lights, walk all over our food and persistently land on the same spot, despite being shooed away (Burkley, 2010). Besides being a nuisance, they are also unsanitary bearers of disease. They act as mechanical transmitters Correspondence: Wanna Maipanich, Department of Helminthology, Faculty of Tropical Medicine, Mahidol University, 420/6 Ratchawithi Road, Ratchathewi, Bangkok 10400, Thailand. Tel; Fax: 66 (0) 2643 5600 E-mail: wanna.mai@mahidol.ac.th of many pathogenic microorganisms, such as bacteria, viruses, fungi, protozoa, and helminthes (Suntaravitun, 2012). Houseflies favor open garbage cans and waste. They carry pathogens which are picked up on their hairy legs and in their mouths after landing on waste. Contamination occurs when they land on our food, water, utensils, clothes and even our bodies (Burkley, 2010). In unsanitary communities, houseflies were reported to carry eggs, larvae, and adults of several helminthes (Maipanich et al, 2008, 2010, 2011, 2012). Therefore, we can deduce that an environment with appropriate fecal-disposal practices may reduce the prevalence of helminth pathogens on houseflies, and thereby reduce helminth transmission. 40 Vol 3 2014
OBJECTIVE To demonstrate the role of houseflies in helminth transmission, two areas one with a sanitary, and one with an unsanitary, environment were examined. The different types and numbers of helminthic objects obtained from the houseflies in these locations were compared and discussed. MATERIALS AND METHODS Study areas The study areas are two provinces in Thailand: Ban Nongbua, in Thasongyang District, Tak Province (western Thailand), and Ban Khum-ngern, Meuang District & Ban Thungmon, Khumkuenkaew District, Yasothon Province (northeastern Thailand) (Fig 1). It was noted that the defecation habits of the people in the two study areas differed. The use of outside latrines was common for villagers residing in Tak Province, since most had no latrine in the home. However, in Yasothon Province, people practiced good toilet-use habits, using latrines built specifically for each household. Houseflies Houseflies were collected with fly traps using rotten shrimp as bait. The traps were placed near food shops in the villages, and the flies collected were stored in a cooler box. Thirty flies were kept in a capped bottle containing 15 ml formalin-detergent (FD) solution (10 ml formalin and 50 ml detergent dissolved in 440 ml water) and transported to the laboratory for examination. In the laboratory, the preserved flies, in their preservative solution, were washed in an ultrasonic cleaner (Elma Transsonic Digital D-7700) at level 5 for 15 minutes at room temperature (RT). The flies were then isolated for identification and sediments in the washing solution were collected and examined for helminthic objects (3). Records were maintained of the houseflies and parasites found in each area. Fig. 1- The two study areas, Tak and Yasothon Provinces. Vol 3 2014 41
Stool samples Stool examinations were conducted among the villagers (67 subjects in Tak Province and 1,040 in Yasothon Province) using Kato- Katz s thick-smear technique, to determine the prevalence of helminthiases. RESULTS Ban Nongbua, in Tak Province, is near the mountainous Thai-Myanmar border where the Moei River marks the border between the two countries. Cross-border human migration is frequent, but is neglected by government authorities. Over 90% of villagers are Karen people who collect herbs and plants, and hunt in the forest. Their houses are made of wood, and there is always an animal house nearby. The villagers had a habit of defecating in the open, near their houses, and thus external latrines were uncommon. The few latrines that were observed in the village were unsanitary (Fig 2 and 3). Flies and vegetables were contaminated by exposure to human waste in the environment. Stool examinations showed the prevalence of helminth infections in Ban Nongbua to be high (55.2%). The most prevalent was Ascaris, at 47.8%, with 12.5% of cases being heavy infestations. Other infections were caused by Trichuris (10.5%), hookworm (5.9%), and Taenia (1.5%) (Table 1). Fig. 2-0An unsanitary latrine was seen in the study area. Fig. 3- Deposited waste from the latrine contaminates the surrounding environment. Table 1 Prevalence of helminthic infections among the population at Ban Nongbua, Thasongyang District, Tak Province (January, 2013). Number examined Villagers 67 37 (55.2) Number of positive cases (%) Prevalence Ascariasis Trichuriasis Hookworm infection 32* (47.8) 7 (10.5) 4 (5.9) Taeniasis 1** (1.5) * with 4 cases of heavy infestation (12.5%) ** eggs found in feces 42 Vol 3 2014
A total of 622 houseflies were trapped, comprising common houseflies, blow flies, and stable flies (Table 2). The captured houseflies carried many helminthic objects. The highest number of eggs found was Ascaris (1,951), which were then classified according to stage of development; 1 cell = 455, multicellular = 735, embryonate = 654, unfertile = 66 and degenerate = 41. This finding indicated that 33.5% (654/1,951) of Ascaris eggs were infective, i.e., capable of immediately causing Ascaris infection after ingestion. Those that were in developing stages (1 cell and multicellular stage), i.e., they could cause infection later, accounted for 61.0%. The total count of live Ascaris eggs was 1,844/1,951 (94.5%). Almost all Trichuris eggs found were in the multicellular stage (99.3%), and all hookworm eggs were degenerated. Many Taenia eggs were isolated from houseflies, but their medical importance depends on the species. One Toxocara egg was obtained from the sediment, and was possibly T. canis, due to the presence of a finely pitted eggshell (Table 3 and Fig 4). The two study areas in Yasothon Province are situated on plateaus. Most villagers are Buddhists and the main occupation is farming; Table 2 Houseflies captured in Ban Nongbua, Thasongyang District, Tak Province (February, 2013). Areas Entry point of Thai- Myanmar people residing along Moei River Houseflies Blow flies Common houseflies Stable flies Total 542 30 13 585 Official border check point 12 7 18 37 Total 554 37 31 622 Table 3 Helminthic objects detected from houseflies at Ban Nongbua, Thasongyang District, Tak Province. Entry point of Thai-Myanmar people residing along Moei River Official border check point Helminth eggs Total Ascaris Taenia Trichuris hookworm Toxocara Unidentified Nematode larvae 2,520 1,951* 369 147** 52*** 1 53 0 0 0 0 0 0 1 * various stages: 1 cell = 455, multicellular = 735, embryonate = 654, unfertile = 66, degenerate = 41 ** multicellular = 146, degenerate = 1 *** all degenerate Vol 3 2014 43
they grow rice, fruits, and herbs. The people are of medium economic status. Their houses are of solid construction, and made of wood/ concrete; each had its own latrine. Human excretion outside the latrines was not evident. Stool examinations revealed that the prevalence of helminth infections was low (14.0%). The presence of small eggs in fecal samples, possibly O. viverrini, is likely due to the habit of eating improperly cooked fish, which are intermediate hosts of Opisthorchis. Their prevalence was prominent (9.7%) (Table 4). Houseflies collected from the two study areas were blow flies, common houseflies, and stable flies (Table 5). The helminth eggs isolated from the flies were Dicrocoelium, Opisthorchis, Trichuris and Strongylid (Table 6 and Fig.4). Since Ascaris eggs were not observed in human infections or houseflies, it appears the eggs discovered were animal parasites from dog and cat infections. There were also a number of unidentified nematode larvae and mites found in the washed sediments of the houseflies. The results showed that, in the area with poor community sanitation, each fly carried an average of 4.1 eggs (2520/622), while in the area with good sanitation, the number was 0.3 (130/477). DISCUSSION In tropical countries, houseflies are difficult to exterminate and have a close association with the presence of humans particularly in unsanitary areas; the helminthic objects Table 4 Prevalence of helminthic infection in villagers at Ban Khum-ngern, Meuang District and Ban Thungmon, Kumkuenkaew District, Yasothon Province (September, 2013). Study sites Ban Khumngern No. exam 507 86 (17.0) Number of positive eggs/larvae (%) prevalence Trichuris Hookworm Opisthorchis Echinostoma Taenia* Strongyloides stercoralis 1 (0.2) 8 (1.6) 67 (13.2) 0 (0) 5 (1.0) 5 (1.0) Ban Thungmon 533 60 (11.3) 0 (0) 6 (1.1) 34 (6.4) 6 (1.1) 9 (1.7) 5 (0.9) Total 1,040 146 (14.0) 1 (0.1) 14 (1.3) 101 (9.7) 6 (0.6) 14 (1.3) 10 (1.0) * eggs found in feces Table 5 Houseflies captured in Ban Khum-ngern, Meuang District and Ban Thungmon, Kumkuenkaew District, Yasothon Province (September, 2013). Study sites Blow flies Common houseflies Houseflies Stable flies Total Ban Khum-ngern 44 45 5 91 Ban Thungmon 323 41 22 386 Total 367 86 24 477 44 Vol 3 2014
Table 6 Helminthic objects discovered from houseflies Ban Khum-ngern, Meuang District and Ban Thungmon, Kumkuenkaew District, Yasothon Province. Study sites Helminth eggs Total Trichuris Opisthorchis Dicrocoelium Strongylid Unidentified nematode larvae Ban Khum-ngern 1 0 0 0 1 19 Ban Thungmon 130 1 1 125 3 9 Fig. 4- Helminth eggs isolated from houseflies. isolated from the houseflies matched those found in fecal samples (Maipanich et al, 2008). The present study demonstrated a high degree of fly contamination (4.1 eggs per fly) in the unsanitary community, as previously reported from southern Thailand (Maipanich et al, 2008). In rural areas, most pets are kept outdoors; they excrete around houses and nearby woods. Animal dung with houseflies was evident everywhere, until the waste was eventually washed away with water/rain. To avoid human zoonotic infections, greater attention should be given to animal excreta in the surrounding area, since it contains the causative agents of the diseases (Maipanich et al, 2011). This study also demonstrated that the community with poor sanitation had more contaminated houseflies with helminth objects than those with good conditions. Houseflies are disease transmitters, and helminthic objects from flies can be easily examined in a laboratory without complex or expensive equipment. Thus, housefly contamination can be used as a good indicator of unsanitary environments caused by human and animal waste. Vol 3 2014 45
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