Detection of adult Brugia malayi filariae by ultrasonography in humans in India and Indonesia

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1 Tropical Medicine and International Health doi: /j x volume 11 no 9 pp september 2006 in humans in India and Indonesia S. Mand 1, T. Supali 2, J. Djuardi 2, S. Kar 3, B. Ravindran 3 and A. Hoerauf 1 1 Institute of Medical Parasitology, Faculty of Medicine, Bonn University, Bonn, Germany 2 Department of Parasitology, Faculty of Medicine, University of Indonesia, Jakarta, Indonesia 3 Department of Immunology, Regional Medical Research Center, Bhubaneswar, India Summary In bancroftian filariasis, ultrasonography (USG) is a suitable tool to monitor infection by the detection of adult filariae in addition to antigen detection tests (ICT, Og4C3). However, in brugian filariasis, ultrasound examinations in humans have so far failed to detect adult worms and no antigen test is available to verify infections in patients who are carriers of adult worms but amicrofilaraemic. In this study, we describe the feasibility of detection of adult Brugia malayi filariae by USG. Worm nests were detected in 4 of 32 patients in India and Indonesia, located in the breast, the thigh, the calf and an inguinal lymph node. The study shows that adult filariae of B. malayi in humans can be detected by USG, but the technique is limited by the fact that worm nests seem not to be stable over time in humans, as is the case in bancroftian filariasis. keywords Brugia malayi, ultrasonography, filaria dance sign, adult filariae Introduction Lymphatic filariasis is still endemic in 83 countries. One hundred twenty million humans are infected, and it is estimated that 1 billion are at risk worldwide to acquire the mosquito-transmitted disease (Global Alliance to Eliminate Lymphatic Filariasis). Besides lymphatic filariasis because of Wuchereria bancrofti, infections with Brugia malayi account for about 10% of the world s burden of lymphatic filariasis and the resulting disabilities. To date, lymphatic filariasis has been mainly diagnosed by direct microscopic demonstration of the microfilariae (mf) in peripheral night blood of infected people. However, this method does not detect those individuals who have adult worm infection but are amicrofilaraemic. For W. bancrofti infections, assessment by the determination of 1antigenaemia using ICT Ò or TropBio ELISA test kit is available to detect amicrofilaremic infections, which offers the convenience of any-time-of-day testing (Lammie 22004). Ultrasonography (USG), an additional tool to diagnose infections in lymphatic filariasis because of W. bancrofti, is useful to detect adult filarial worms by their typical movement pattern, called filaria dance sign (FDS) (Amaral et al. 1994). The worms are found in adult men mainly within the intrascrotal lymphatic vessels (Dreyer et al. 1996; Faris et al. 1998; Mand et al. 2003; Hussein et al. 2004). Recently, in women, adult filariae were detected by USG in lymph nodes, the inguinal channel, between fibres 3 of the muscles in the thigh and in the female breast (Mand et al. 2004). This technique allows diagnosis of amicrofilaremic bancroftian filariasis, measurement of pathological enlargement of lymphatic vessels, detection of filarial associated hydrocoele (Tobian et al. 2003; Hussein et al. 2004), differentiation between hydrocoele, lymphocoele and chylocoele and evaluation of potential macrofilaricidal 4 effects after treatment (Dreyer et al. 1999; Noroes et al ; Hussein et al. 2004; Taylor et al. 2005). In brugian filariasis, ultrasound examinations so far have failed to identify adult filariae (Shenoy et al. 2000). Shenoy et al. examined the scrotal area including regional lymph nodes in 22 male patients without using the pulse wave Doppler (PWD) technique. However, this technique has proved essential for the differentiation of small worm nests from fluid flow in vessels (Faris et al. 1998; Dreyer et al. 2001; Mand et al. 2003; Hussein et al. 2004). Therefore, without PWD, a cautious examiner may tend to misinterpret a small doubtful worm nest as a vessel. The present study was carried out to re-evaluate the potential value of USG, using additional options such as the PWD technique in the diagnosis of brugian filariasis, first in an animal model (Mand et al. 2006), followed by USG examinations in infected adults and children in India and Indonesia. The aim of the study is consistent with main research priorities for additional diagnostic tools in the detection of brugian filariasis, identified and described as one of the needs and ª 2006 Blackwell Publishing Ltd 1375

2 opportunities for research on infections because of B. malayi by the Filariasis Community of Scientists in Association with an LF Research Forum convened in Philadelphia, December 2003 (Addiss & Mackenzie 2004). Material and methods Patients Five patients (three women, two men), years old, were examined by USG in Chudamani village (Basalore District), India in order to detect adult filariae of B. malayi in human tissues. Co-infection because of bancroftian filariasis, which is also endemic in Orissa, was excluded in these patients by polymerase chain reaction (PCR). All patients were negative for W. bancrofti primers and positive for B. malayi-specific primers. To avoid coinfections with W. bancrofti in general, subsequently a larger study was carried out in Gorontalo, Sulawesi, Indonesia in the Primary Health Center of the Bonebolango District, which is endemic for brugian filariasis but not bancroftian filariasis. Twenty-seven participants (15 males and 12 females) aged 8 73 (mean 27.3 years), who were recruited from the nearby villages Innomata, Monano, Mootayu and Tombolilato, met the following criteria: they were mf carriers of B. malayi, antigen negative (ICT card test) for W. bancrofti and residents in the villages for at least 5 years. The study was approved by the ethics research committees of the Indian Medical Research Council, Delhi, India, the University of Indonesia, Faculty of Medicine, Jakarta, Indonesia and the Ethics Committee of the University of Liverpool, UK. We received funds from European Union (ICA4-CT ) and the Federal Ministry of Education and Research (DLR-IND 02/010). Determination of microfilariae and exclusion of co-infection with Wuchereria bancrofti Blood samples were obtained from recruited individuals in EDTA tubes between 10 and 12 pm. One millilitre blood was filtered through a Whatman Ò Membrane Polycarbonate 25 mm Nucleopore 5 lm filter (Eurolab Merck, Darmstadt, Germany). The filters were Giemsa stained for later mf counting. Polymerase chain reaction Brugian and bancroftian filariasis are co-endemic in Orissa, India. To identify and exclude patients who had bancroftian filariasis, PCR was used to amplify species-specific genes from gdna extracted from patient blood. PCR using primers for the HhaI repeat from B. malayi and primers for the SspI repeat from W. bancrofti was performed as described by Lizotte et al. (1994) and Ramzy et al. (1997). Amplified products were separated on a 2% agarose gel and stained with ethidium bromide. Ultrasound equipment Ultrasonography examinations were carried out using a SonoSite 180 Plus hand-carried ultrasound system (Sono- 6 Site Ò Inc., Washington, USA), equipped with an L 38 mm 5 10 MHz linear array transducer. For the present study, a frequency of MHz was used. Worm nests were detected by a typical pattern for filarial worm movements in the two-dimensional b-mode search (Amaral et al. 1994). The additional use of the PWD technique served for confirmation of potential worm nests detected in the twodimensional b-mode presenting the typical irregular sharp peaks induced by the worm movements (Mand et al. 2003; Hussein et al. 2004). For documentation of worm nests, a Handycam Ò (SONY Corporation, Tokyo, Japan) was directly connected to the ultrasound machine via video plug. Findings were recorded on mini digital video (DV) tapes and DV sequences edited using the programme Final Cut Pro Ò (Apple Computer Inc., California, USA). Videos were exported as avi files (Mand et al. 2003). Ultrasound examination Patients were examined in a supine position to avoid artefacts and interferences by muscle contractions and movements of themselves. We conducted the USG examinations in darkened rooms using ultrasound gel kept at room temperature. In each patient, we scanned the breast or thorax, including the intercostal area between all ribs up to the pleura, lungs, heart, diaphragm, axillary lymph nodes and the inguinal and femoral region, including lymph nodes. The limbs were scanned following the main lymphatic vessels. The scrotal area was scanned in three male patients. The remaining male patients were not willing to agree to this examination because of the reasons associated with religion. All participants received a single dose of diethylcarbamazine 7 (DEC) (6 mg/kg) after USG examination. Results Detection of living adult filariae of Brugia malayi in a female patient in India Within the scope of a larger study in lymphatic filariasis in Orissa, India, we examined five patients (three women, two men) by USG who were known to be mf positive for 1376 ª 2006 Blackwell Publishing Ltd

3 brugian filariasis only ( mf/ml, geometric mean 439 mf/ml). We were able to detect one worm nest in a 24-year-old woman by USG in the right breast, lateral of the acromastium. The adult filaria(e) was detected by their movement pattern, similar to the signals caused by W. bancrofti, in an echo-free area of a lymphatic vessel or a ductus lactiferus (Figure 1a). The sample volume window was positioned where the movements were detected. After switch to the one-dimensional PWD mode, irregular sharp peaks on top and beneath the neutral line could be seen as confirmation of a worm nest (Figure 1b). The amplitude (a) (b) KIT L cm KIT L38 TIW 0,2 9 cm/s Figure 1 (a) Oblique scan of the patient s right breast. An echofree area containing adult moving filarial(e) is presented in the b-mode image. The sample volume window is positioned where the worm nest is located. (b) The pulse wave Doppler mode confirms the clinical finding of a worm nest by the irregular sharp peaks caused by the movements of the adult worm(s). was not as high as is usually seen in bancroftian infections. This is due to the smaller size of the adult filariae of B. malayi and matched with the size of the amplitudes seen in the PWD mode after worm nest detection in rodents. It is remarkable that the finding of the worm nest in the breast was only seen for 10 min. After detection of the adult worm(s), the finding could be confirmed three times using the PWD mode within the 10 min before the adult filaria(e) was no longer visible in the b-mode. USG was repeated after 30 and 60 min without success to observe the worm(s) again. The echo-free areas where the adult filaria(e) were detected before remained empty. In the other four patients, no worm nests could be detected. Further detection of living adult filariae of Brugia malayi in patients in Indonesia To facilitate the exclusion of co-infection with W. bancrofti, a larger study was carried out in Sulawesi, Indonesia, endemic for brugian, but not for bancroftian filariasis. The group consisted of 27 participants in the age of 8 73 years (mean 27.3 years). All patients were mf positive and untreated for lymphatic filariasis before USG examination. The mf load ranged from 32 to 4026 mf/ml (geometric mean 388 mf/ml). Patients were asked about the frequency of acute attacks of lymphangitis during the past year. Particulars ranged from 0 to 48 acute attacks/ year (mean 6.62 attacks/year, median 0.5 attacks/year). The thorough USG examinations, conducted as described earlier, lasted min. We detected worm nests of adult B. malayi filariae in 3 of the 27 patients. One worm nest was found in the subcutaneous tissue of the medial region of the thigh above the musculus adductor magnus in a 16 year-old female patient with 72 mf/ml (Figure 2a, video image). A second worm nest, detected in a 16-yearold female patient (1853 mf/ml), was found in the subcutaneous tissue of the calf, in the area of the caput medialis of the musculus gastrocnemius. The third worm nest was detected next to an inguinal lymph node in a 23-year-old male patient with 2139 mf/ml. These three worm nests could be clearly differentiated from blood flow in small arteries or veins in the PWD mode. While arteries appear as pulsating signals and veins as spindle-shaped signals, motile filariae can be confirmed by their typical irregular signals seen as sharp peaks on top and beneath the neutral line (Figures 1b and 2b). As described earlier for the Indian patient, the three worm nests in patients in Indonesia could be observed in the PWD mode three to four times, but again the signals could only be seen for min each. In the three patients in Indonesia, all areas where adult filariae could be located were observed for 45 more minutes in the first session and the three patients were re-examined after ª 2006 Blackwell Publishing Ltd 1377

4 (a) (b) 24 h in an attempt to depict the worm signals again. In no case was it possible to observe the adult filariae detected before, either in the region where the moving adult filariae were detected before or in the regional lymph nodes (femoral, inguinal). It was also impossible to redisplay the worm signals after DEC provocation (2 mg/kg) given to these three patients during the second USG examination. Discussion This is the first study about the detection of adult filariae by USG including the PWD technique in humans infected with Figure 2 (a) Transverse scan of the patient s left upper thigh. The sample volume window marks the position of the detected worm nest in the subcutaneous tissue. (b) The pulse wave Doppler confirms the finding of a worm nest by the undulating band with irregular sharp peaks caused by the adult filaria(e). B. malayi. About 10% of the 120 million infections of lymphatic filariasis worldwide are due to brugian filariasis, but the number of unknown cases is estimated to be higher. At present, there is no tool available to detect non-patent infections with B. malayi, while there are two antigen tests available to detect circulating filaria antigen (TropBio Ò ELISA, ICT card test) in W. bancrofti-infected subjects (Weil et al. 1997; Lalitha et al. 1998; Nguyen et al. 1999). Consequently, it is not possible to give a statement about the real epidemiology of infection in brugian filariasis, although accurate mapping of endemic areas would be one of the pre-requisites for successful elimination. Lack of data in the group of amicrofilaraemic patients may lead to a false too low prevalence in brugian filariasis. Thus, it is important that a suitable diagnostic tool be employed to detect occult infections in patients with brugian filariasis who are amicrofilaraemic but who may be carriers of adult filariae. In bancroftian filariasis, USG is accepted as a suitable and sensitive diagnostic tool to detect living adult filariae in the lymphatic vessels, mainly in the scrotal region of male patients (Amaral et al. 1994; Dreyer et al. 1996, 1998; Faris et al. 1998; Mand et al. 2003). The adult filariae can be detected by their typical movement pattern, the so-called FDS. The worm nests are stable over time and can be observed at regular intervals under treatment conditions (Dreyer et al. 1994; Hussein et al. 2004; Taylor et al. 2005). The present study was conducted to evaluate the suitability of USG in the diagnosis of B. malayi infections, in particular using the PWD technique. The PWD technique allows for rapid and precise detection of the typical FDS and an exact differentiation from blood flow in vessels, which is often ambiguous in the twodimensional b-mode. Below a dilation of 0.1 cm of lymphatic vessels, detection is impossible in most cases (Noroes et al. 1996). Exclusive use of the two-dimensional b-mode and m-mode, without using the PWD technique, can lead to a wrong judgement by the examiner, as very small blood vessels induce, in the b- and m-modes, signals similar to adult filariae of B. malayi in slightly dilated lymphatic vessels. The PWD technique was especially useful in the present attempt to detect adult B. malayi worms (female worms up to 3 cm) that are smaller than adult W. bancrofti (female worms up to 10 cm). The amplitudes caused by the worm movements of B. malayi (Figures 1b and 2b) were lower than those observed in earlier studies (Mand et al. 2003, 2004; Taylor et al. 2005) with W. bancrofti, because of the smaller length of the adult worms. Nevertheless, in PWD mode sharp peaks could be seen and it was possible to differentiate between flow in small blood vessels and adult moving worms. The PWD technique is the ideal method to validate worm nest detection in B. malayi ª 2006 Blackwell Publishing Ltd

5 As shown in a study in India in 2000, adult filariae could not be detected by thorough USG examinations in a group of 22 male patients infected with B. malayi (Shenoy et al. 2000). Hence, this is the first study on the detection of adult filaria(e) using USG in humans. After demonstrating the feasibility of USG to detect 8 B. malayi in Mastomys coucha (Mand et al. 2006), we carried out further ultrasound examinations in patients in India and Indonesia, using the PWD technique to evaluate the suitability of this tool as a potential method for diagnosis in human brugian filariasis. In the first group, consisting of five patients with brugian filariasis in Orissa, India, we examined within the scope of a larger USG study in a nearby district in patients with bancroftian filariasis, to verify if adult worms of B. malayi can also be detected in humans. In the breast of one woman, a worm nest was detected. This finding was confirmed by the signals induced by worm movements seen in the PWD mode. The small pilot study in India established that it is, in principle, possible to detect living adult filariae of B. malayi in humans. To facilitate exclusion of co-infections with W. bancrofti, subsequently a study in Sulawesi, Indonesia was carried out. The northeast of Sulawesi is non-endemic for W. bancrofti. The aim of this study was to determine the frequency of detection of adult B. malayi filariae in the lymphatic vessels and lymph nodes in a larger group of humans. It was possible by thorough examinations, lasting more than 1 h, to detect living filariae in 15% of the adult patients. However, the sites where living filariae of B. malayi were detected in human tissues were not stable over 9time, as described for W. bancrofti (Dreyer et al. 1994; Mand et al. 2003). In all four human cases where adult worms could be detected, the worm nests were not visible for longer than min each, neither could they be observed the next day. It is assumed that the adult filariae change their location within the lymphatic vessels of the human body. An interesting hypothesis could be that the adult worms also may migrate through lymph nodes. At least one worm was detected in the area of the sinus of an inguinal lymph node. The earlier failure to detect filariae of B. malayi by USG may have been due to the lack of using the PWD technique, as the resolution in the two-dimensional mode using a 7.5 MHz transducer is sufficient to detect worms of 2 3 cm. Thus, a higher resolution would not increase the detection rate. While high resolution can improve the near field, in general the observed area becomes smaller and the deeper tissues would be left out. This would prolong the time of USG examination, without more frequent or even more precise detection. Hence, we conclude that adult filariae of the species B. malayi can be detected by USG. However, USG use is limited for detection of B. malayi because it is not a suitable tool for repeated, consistent observation (e.g. in longitudinal studies) in brugian filariasis in contrast to W. bancrofti infection, as the adult filariae apparently change the location in the lymphatic vessels in humans. This also may lead to false too low prevalence data. Furthermore, the worm nests are very small (dilation cm) in brugian infections and thus not visible in deeper tissues and areas of the body where artefacts because of respiration and heartbeat can mask the signals of worm movements. Using the animal model, the situation is different because the transducer is as broad as the chest and the abdomen of the animal. The penetration depth for USG waves of 4 5 cm is sufficient to observe the whole thorax or abdomen simultaneously in rodents. Therefore, USG can serve as a suitable tool for long-term observation in animal models to observe potential macrofilaricidal effects. In humans, a penetration depth of 4 5 cm is just sufficient to observe the subcutaneous layers and the pleura or the peritoneum, but in deeper tissues worm nests of cm cannot be detected. Thus, this technique has technical limitations. The question whether there are adult worms in the human pleural cavity, abdominal lymph nodes or intracardial remains open. Another limitation is the fact that only three male patients in India and another three male participants in Indonesia were willing to be examined in the scrotal area using USG. The remaining male patients did not give their consent for religious reasons. Thus, we cannot report about the frequency of detection of adult worms of B. malayi in the scrotal area using the PWD technique. As Shenoy et al. thoroughly examined the scrotal areas of 22 men with brugian filariasis without detecting any worm nests; it is unlikely that stable worm nests of adult worms occur in the scrotal region, but it might make sense to include the PWD technique for further examinations of the scrotal region in patients with brugian filariasis. Conclusions We detected adult living B. malayi in human tissues using USG. As a result of the availability of an ultrasound system with high resolution and the option to make use of the PWD technique, we were able to observe adult worms of B. malayi far smaller than the frequently detected filariae of W. bancrofti. Brugia malayi worm nest locations in humans appear to change, unlike those of W. bancrofti. This fact limits the use of USG as a diagnostic tool for repeated longitudinal observations under treatment conditions in humans, where consistent, stable findings would be required. Detection of adult filariae in brugian filariasis is possible, but the examination is time consuming and requires an ultrasound system equipped with a PWD. ª 2006 Blackwell Publishing Ltd 1379

6 However, in animal models, USG may serve as a suitable tool for long-term observation of potential macrofilaricidal effects without the need to kill animals. Acknowledgements We thank Hari Wibowo, Siddhard Padhi, the health workers of the Primary Health Center of Basalore District, India and Bonebolango District, Indonesia for their assistance. The trial was funded by the European Commission and the Bundesministerium für Bildung und Forschung, Germany. References Addiss DG & Mackenzie C (2004) LF disease clinical management. The American Journal of Tropical Medicine and Hygiene 71 (Suppl. 3), Amaral F, Dreyer G, Figueredo-Silva J et al. (1994) Live adult worms detected by ultrasonography in human Bancroftian filariasis. The American Journal of Tropical Medicine and Hygiene 50, Dreyer G, Amaral F, Noroes J & Medeiros Z (1994) Ultrasonographic evidence for stability of adult worm location in bancroftian filariasis. Transactions of the Royal Society of Tropical Medicine and Hygiene 88, 558. Dreyer G, Brandao AC, Amaral F, Medeiros Z & Addiss D (1996) Detection by ultrasound of living adult Wuchereria bancrofti in the female breast. Memorias do Instituto Oswaldo Cruz 91, Dreyer G, Addiss D, Santos A, Figueredo-Silva J & Noroes J (1998) Direct assessment in vivo of the efficacy of combined single-dose ivermectin and diethylcarbamazine against adult Wuchereria bancrofti. Transactions of the Royal Society of Tropical Medicine and Hygiene 92, Dreyer G, Noroes J, Addiss D, Santos A, Medeiros Z & Figueredo- Silva J (1999) Bancroftian filariasis in a paediatric population: an ultrasonographic study. Transactions of the Royal Society of Tropical Medicine and Hygiene 93, Dreyer G, Figueredo-Silva J, Carvalho K, Amaral F & Ottesen E (2001) Lymphatic filariasis in children: adenopathy and its evolution in two young girls. The American Journal of Tropical Medicine and Hygiene 65, Faris R, Hussain O, El Setouhy M, Ramzy RM & Weil GJ (1998) Bancroftian filariasis in Egypt: visualization of adult worms and subclinical lymphatic pathology by scrotal ultrasound. The American Journal of Tropical Medicine and Hygiene 59, Global Alliance to Eliminate Lymphatic Filariasis. Available at: 11 Hussein O, Setouhy ME, Ahmed ES et al. (2004) Duplex Doppler sonographic assessment of the effects of diethylcarbamazine and albendazole therapy on adult filarial worms and adjacent host tissues in Bancroftian filariasis. The American Journal of Tropical Medicine and Hygiene 71, Lalitha P, Ravichandran M, Suba S, Narayanan RB & Jayaraman K (1998) Quantitative assessment of circulating antigens in human lymphatic filariasis: a field evaluation of monoclonal antibody-based ELISA using blood collected from filter strips. 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7 Supplementary material The following supplementary material is available for this article online: Video S1: Transverse scan of the patient s left upper thigh. A worm nest is seen in a lymphatic vessel of the subcutaneous tissue. After switch to the Pulse Wave Doppler-mode the filarial movements are seen as an undulating band as a function of time, with sharp, irregular peaks. This material is available as part of the online article from j x (This link will take you to the article abstract) Please note: Blackwell Publishing are not responsible for the content or functionality of any supplementary materials supplied by the authors. Any queries (other than missing material) should be directed to the corresponding author for the article. Corresponding Author Sabine Mand, Institute of Medical Microbiology, Immunology and Parasitology (IMMIP), Faculty of Medicine, Bonn University, Sigmund Freud Str. 25, Bonn, Germany. Tel.: ; Fax: ; mand@parasit.meb.uni-bonn.de Détection échographique chez l homme de filaires adultes de Brugia malayi en Inde et Indonésie Dans les filarioses de Bancroft, l échographie associée aux tests de dosage d antigènes (ICT, Og4C3) est l outil de choix pour surveiller une infection grâce à la détection de filaires adultes. Cependant, dans les filarioses brugiennes l échographie n a pas fait ses preuves pour permettre de détecter les vers adultes et aucun test de dosage d antigènes n est disponible pour dépister des patients infectés amicrofilarémiques qui ne sont pas porteurs de vers d adultes. Dans cet article nous décrivons la possibilité de détecter par échographie des filaires adultes de Brugia malayi. Les nids des vers ont été retrouvés chez 4 des 32 patients indiens et indonésiens. Ils étaient situés au niveau d un sein, une cuisse, un mollet et un ganglion lymphatique inguinal. L étude prouve que des filaires adultes de B. malayi peuvent être détectées chez l homme par échographie, mais la technique est limitée par le fait que l emplacement des nids des vers ne semblent pas être fixes chez l homme, contrairement à ce qui est le cas dans le filariose de bancroft. mots clés Brugia malayi, échographie, signe filarial de danse FDS, filaire adulte Detección de Brugia malayi filariana adulta por ecografía en humanos en India e Indonesia En la filariasis de Bancroft, la ecografía es una herramienta apropiada para monitorear la infección, detectando la filaria adulta en añadidura a las pruebas de detección de antígenos (ICT, Og4C3). No obstante, en la filariosis de Brug los exámenes con ultrasonido en humanos han, de momento, fracasado en detectar gusanos adultos, y no hay pruebas de antígenos disponibles para detectar infecciones en pacientes que son portadores de gusanos adultos, excepto para microfilaremia. En este trabajo describimos la viabilidad de la detección de la Brugia malayi filariana adulta por ecografía. Se detectaron nidos de gusanos en 4 de 32 pacientes en India e Indonesia, localizados en el pecho, muslo, pantorrilla, y un nódulo linfático inguinal. El estudio muestra que la filaria adulta de Brugia malayi en humanos puede ser detectada por ecografía, pero la técnica está limitada por el hecho de que los nidos de gusanos parecen no ser estables en humanos con el correr del tiempo, como si sucede en la filariasis de Bancroft. palabras clave Brugia malayi, ecografía, marca de filaria, filaria adulta ª 2006 Blackwell Publishing Ltd 1381