Veterinary Parasitology 101 (2001) 45–52 Epidemiological aspects of bovine parasitic otitis caused by Rhabditis spp. and/or Raillietia spp. in the state of Minas Gerais, Brazil E.R. Duarte a , M.M. Melo b , J.S. Hamdan a,∗ a Department of Microbiology, Federal University of Minas, Biological Science Institute, ICB/UFMG, Av. Antônio Carlos, 6627, 31270-901, Belo Horizonte, Minas Gerais, Brazil b Medical Veterinary School, Federal University of Minas Gerais, Minas Gerais, Brazil Received 17 January 2001; received in revised form 16 May 2001; accepted 29 June 2001 Abstract The occurrence of bovine external otitis in tropical regions is predominantly assigned to parasitic infections by rhabditiform nematodes and infestations by mites of the genus Raillietia. This research had the purpose of investigating the prevalence of parasitic otitis in the dry and rainy seasons of Minas Gerais and correlating it with variables age, breed and the presence of horns. The secretion or cerumen of 981 cattle was collected with sterile swabs, placed in test tubes and exposed to sunlight for the identification of clinical infections caused by rhabditiform nematodes. The ear canals of 109 animals were flushed to study the occurrence of mites of the genus Raillietia. Clinical otitis caused by rhabditiform nematodes was observed only in animals of the Gyr breed, affecting 169 (60.1%) of the total (278) of these cattle. The prevalence of otitis in this breed was significantly higher for mature adult cows (P < 0.001) and in cows with horns (P < 0.001). In a total of nine animals suspected of raillietiosis, the examinations revealed the presence of Raillietia spp. in two Dutch cows. These results demonstrate that treatment must be focused on adult Gyr cattle with horns. This and future studies with an emphasis on epidemiological aspects may contribute to development of alternative approaches to reduce disease. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Rhabditiform nematodes; Raillietia spp.; Bovine otitis 1. Introduction Parasitic otitis caused by nematodes of the genus Rhabditis has been reported in several Brazilian states. Martins et al. (1971) reported the occurrence of nematodes of the family ∗ Corresponding author. Fax: +51-31-3499-2730. E-mail address: handan@icb.ufmg.br (J.S. Hamdan). 0304-4017/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 4 0 1 7 ( 0 1 ) 0 0 4 9 2 - 7 46 E.R. Duarte et al. / Veterinary Parasitology 101 (2001) 45–52 Rhabditidae in 94% of the 50 cattle with otitis in the Federal District in Brazil. Leite et al. (1993) described the occurrence of disease in the states of Minas Gerais and Goiás (southeast and midwest Brazil, respectively), and only in cattle of the Gyr and Indubrasil breeds (93 and 53% of the adult animals, respectively). The nematodes of the genus Rhabditis are relatively small in size (approximately 1.5 mm for females and 1.2 mm for males of Rhabditis spp. They possess a small buccal cavity with four to six lips, a rhabditiform oesophagus and some can be free-living nematodes (Soulsby, 1982; Martins, 1985; Urquhart et al., 1998). The female possesses two ovaries and can be viviparous or oviparous (Fig. 1). The species identified in Brazil spends from 7 to 8 days completing their life cycle when grown in blood agar at room temperature. The presence of rhabditiform nematodes at different stages of development can be observed in specimens collected from cattle with otitis (Martins, 1974; Vieira, 1998). Bovine otitis caused by Rhabditis bovis has been reported in many African countries with a hot and humid climate (Msolla et al., 1986; Odongo and Souza, 1989). A positive and Fig. 1. Adult female Rhabditis spp. collected from a Gyr cow with otitis, 100×. E.R. Duarte et al. / Veterinary Parasitology 101 (2001) 45–52 47 highly significant association was observed between the increase of the number of flies and the rainy season in Zimbabwe with the occurrence of bovine otitis caused by rhabditiform nematodes (Obatolu et al., 1999). In studies of the epidemiology of these nematodes in Tanzania, dip wash, manure and flies were associated with the transmission of R. bovis nematodes (Msolla et al., 1986, 1993). Infestation of the bovine ear by Raillietia spp., or raillietiosis, was first described more than one century ago. The acarid is a parasite of the internal portion of the external ear canal (EEC) and the external surface of the tympanic membrane. Raillietia auris has worldwide distribution, and, in Brazil, has been reported in the states of Acre, Amapá, Distrito Federal, Mato Grosso do Sul, Minas Gerais, Pará, Paraná, Rio de Janeiro, Rio Grande do Sul and São Paulo (Nunes et al., 1975; Faccini et al., 1992). R. auris has a life span of approximately 21 days and an in vitro life cycle of 78.3 h for the male and 68.7 h for the female (Santos and Faccini, 1996). The clinical significance of the presence of the mites is not well clarified. Some authors have ascribed the etiology of otitis with severe neural complications to this organism (Schlotthauer, 1970; Jubb and Wroth, 1993). Host susceptibility to parasitism by these acarids was shown to be clearly influenced by age and breed. The prevalence of the infestation increased from calves to the adult animal. Animals of the zebu breeds, especially Nellore, were more infested than others. This higher frequency observed in zebu animals may be related to fewer dips with anti-acarid agents (Araújo et al., 1996). A bacteriological study of otitis caused by Raillietia spp. has associated the genera Proteus and Pseudomonas with the chronic inflammatory processes in the bovine ear (Leite et al., 1987). In a recent study, Duarte et al. (1999) suggested the participation of yeasts of the genus Malassezia in the etiology of bovine parasitic otitis caused by rhabditiform nematodes and mites of the genus Raillietia. The purpose of this study was to describe the distribution of bovine otitis caused by rhabditiform nematodes and acarids of the genus Raillietia during the dry and rainy seasons in the state of Minas Gerais, Brazil, correlating it to the variables breed, age and presence of horns. 2. Material and methods To examine clinical infections and external otitis caused by rhabditiform nematodes in the state of Minas Gerais, 981 cattle were sampled, including 278 of the Gyr breed, 27 Indubrasil cows, 43 Nellore cows, 371 hybrid animals (half breed or three quarters Dutch–Gyr), and 262 European breed (Dutch and Brown Swiss). The hybrid and Zebu cattle were raised under pasture management and European cattle were raised under free-stall confinement. The hybrid cattle were controlled for bovine tick in October–May (wet season). The European and Zebu cattle were not controlled for bovine tick with acaricides. The occurrence of clinical otitis caused by rhabditiform nematodes was evaluated among the Gyr cattle of different ages in the central region of Minas Gerais during the dry season. For this study, 56 older cows greater than 8 years of age, 58 adult cows, less than 8 years of age, 46 primiparous cows less than 4 years of age and 35 calves up to 6 months of age were sampled. Subsequently, during the wet season, in the same region, 48 Gyr adult cows 48 E.R. Duarte et al. / Veterinary Parasitology 101 (2001) 45–52 with horns and 35 Gyr adult cows without horns and raised under the same conditions, were examined and compared in relation to the presence of clinical otitis caused by rhabditiform nematodes. To test for climatic influences in the central region, the occurrence of clinical otitis caused by these parasites was evaluated during the dry season and the wet season in 58 and 48 adult Gyr cows with horns, respectively. To carry out the collection, the cattle had their heads immobilised with a rope attached to a bar or a cattle restraint passageway was used. The cerumen or ear secretions from all study animals were collected with the aid of sterile swabs which were reinserted into test tubes, and subsequently exposed to sunlight. This procedure induces the migration of nematodes from the specimen to the wall of the test tube, where they can be easily visualised with the unaided eye (Leite and Faccini, 1994). Subclinical infections of Rhabditis spp. and the presence of mites of the genus Raillietia were evaluated in 40 healthy hybrid cows and 60 healthy Gyr cows from the central region of Minas Gerais. In cattle with otitis (suspected of raillietiosis), these parasites were investigated in five Dutch and four hybrid cows (Dutch–Gyr). To detect the mites of the genus Raillietia and subclinical infections of rhabditiform nematodes, the EEC was flushed with approximately 100 ml of filtered and boiled water. The backflow material was collected in Falcon tubes, then identified and sealed for transport to the laboratory. The parasites were observed and identified with the help of a magnifying glass and stereoscopic microscope (Faccini et al., 1987; Leite and Faccini, 1994). The Chi-square test (χ 2 ) was used to determine the existence or not of statistically significant differences in the occurrence of parasitic infestations in the external ear among the sampled groups. Differences with P < 0.05 were considered significant. 3. Results Acarids of the genus Raillietia were not observed in parasitological examination of lavages from 100 healthy cattle (40 hybrid cows and 60 Gyr cows). However, among the hybrid and European cattle, which were mostly raised on dairy properties, occasionally one or two cases of otitis were reported, which many times provoked the discarding/loss of animals (Table 1). In examination of nine animals with suspected of Raillietia otitis, acarids of the genus Raillietia were observed in the EEC lavage from only two Dutch cows from the south region of the state of Minas Gerais. The presence of Rhabditis spp. nematodes was not observed in specimens collected from these animals with otitis (Table 1). Examination of clinical otitis and subclinical infections for the presence of rhabditiform nematodes in 981 cattle from different geographical regions of the state of Minas Gerais demonstrated positive results only in Gyr cattle. External otitis was diagnosed in all herds of this breed and represents a significant health problem. Many of these animals were considered top class, with high zootechnical characteristics and economic value. Clinical infections and external otitis caused by rhabditiform nematodes in the Gyr breed was found in 169 (60.1%) of 278 animals evaluated. In study of subclinical infections (EEC 49 E.R. Duarte et al. / Veterinary Parasitology 101 (2001) 45–52 Table 1 Occurrence of parasitic otitis in cattle according to season, age, breed and the presence of horns Category Seasona Rhabditis spp. Clinical, (total) Hybrid cows Hybrid calves European cows European cows European calves Nellore cows Indubrasil cows Wet Wet Wet Dry Dry Wet Dry Gyr cows with horns Older cows Adult cows Primiparous cows Dry Dry Dry 56 (56) 42 (58) 17 (46) Gyr calves Dry 5 (35) Adult Gyr cows With horns Without horns Wet Wet Total no.d 0 (271) 0 (100) 0 (103) 0 (80) 0 (79) 0 (43) 0 (27) Subclinical, no.b (total)c Raillietia spp., no.b (total)c 0 (44) – 0 (2) 0 (3) – – – 0 (44) – 0 (2) 2 (3) – – – – 4 (11) 1 (19) – 0 (11) 0 (19) – – 38 (48) 11 (35) 1 (6) 6 (24) 0 (6) 0 (24) 169 (981) 12 (109) 2 (109) a Dry season: May–October, wet season: November–April. Number of positive examinations. c Total number of cattle examined with ear flushing technique (Faccini et al., 1987; Leite and Faccini, 1994). These animals were a sample from the 812 cattle, out of 981, with had negative results for clinical infections of Rhabditis spp. in test tube with swab. d The number of cattle with external otitis and positive results for clinical infections of rhabditiform nematodes (test tube, Leite and Faccini, 1994). b lavage), 12 (20%) out of 60 Gyr cows had positive results for Rhabditis spp.; however, these parasites were not observed in examinations of 40 hybrid cows that were also evaluated (Table 1). In a total of 58 Gyr cows examined during the dry season in Minas Gerais, an otitis prevalence of 72.4% caused by nematodes was observed. In the summer (rainy season), 38 (79.2%) of 48 Gyr cows showed parasitic otitis, with no significant differences between groups. In the study of the influence of age on the Gyr cattle and occurrence of otitis caused by nematodes, examinations revealed the presence of parasitic otitis in the entire group of 56 older cows, in 42 (72.4%) of the 58 adult cows, 17 (37%) of 46 primiparous cows, and in 5 (14.3%) out of 35 calves (Table 1). Statistical analysis confirmed the increasing prevalence of rhabditiform nematodes with age progression of the animals (P < 0.001). Clinical otitis caused by these nematodes was observed in 11 (31.4%) of 35 Gyr cows without horns and 38 (79.2%) of 48 Gyr cows with horns (Table 1). Statistical analysis of these data showed a higher prevalence of otitis caused by rhabditiform nematodes in horned Gyr cows (P < 0.001). 50 E.R. Duarte et al. / Veterinary Parasitology 101 (2001) 45–52 4. Discussion The absence of infestation by acarids of the genus Raillietia in the healthy cattle, raised under pasture management, may have been influenced by the intensive administration of miticidal pour-on products (cypermethrin or ivermectin), used for the control of the bovine tick (Boophilus microplus), as suggested by Araújo et al. (1996). The animals which had been suspected of raillietiosis, in this sample, were raised under a system of confinement and belonged to herds where the bovine tick has been controlled or eradicated. Only in two cases were acarids detected. On the other hand, most cattle suspected of raillietiosis presented the chronic form of disease, where mites and other possible triggering agents could not be found in the infection site (Leite et al., 1987; Msolla et al., 1993). The higher rate of clinical infection and occurrence of otitis by rhabditiform nematodes in the Gyr breed is in agreement with the findings of Leite et al. (1993), who reported that the breeds Gyr, Indubrasil and their hybrids, are more susceptible to the parasite. In the Gyr breed, the anatomical structure of the external ear, long, pendant and gutter-shaped, may create a more favourable environment for nematodes, with temperature, humidity and substrates more adequate for their development. Martins et al. (1971) reported the occurrence of these nematodes in 94% of 50 cattle examined in the Federal District in Brazil. The results of these studies in Brazil revealed that otitis caused by Rhabditis spp. has been reported since the 1970s, and is still present in cattle herds, mainly in the Gyr breed, affecting a great number of animals, demonstrating the enzootic character and difficulty in controlling and treating these infections. In the area studied, climatic changes during the year (with a drier and colder winter, compared to a hotter and wetter summer), did not seem to have influenced the microenvironment established in the ear canal and the presence of rhabditiform nematodes. Obatolu et al. (1999) observed a significant association between the rainy season in Zimbabwe and the higher occurrence of otitis caused by nematodes in cattle; however, the winter is cooler and drier than in Minas Gerais. The prevalence of otitis in the Gyr breed was significantly higher for older cows. Cerumen and other secretion accumulation increases the availability of substrates in the ears of older cattle, which may constitute a positive factor for the growth and multiplication of nematodes. In older animals, the larger horns may compress the ear canal and this could be an explanation for increased parasitism. The most serious signs of disease were observed among these animals, including weight loss, the vestibular syndrome, middle and internal ear otitis, meningitis and paralysis of cranial nerves, which frequently resulted in the death of the animal. Martins et al. (1971) also reported a difference in the clinical manifestations of the disease among adult and young cattle. They observed that the infections in adults were higher, and generally associated to otitis symptoms, while in calves the infections were always mild and asymptomatic. Leite et al. (1993) observed a higher occurrence of parasitosis in cows (93%) than in Gyr heifers (40%). In Gyr cows with horns, the prevalence of otitis caused by nematodes was significantly higher. The presence of horns may be considered a favouring factor for parasitic otitis caused by Rhabditis spp. Although this association has not been confirmed in the literature dealing with parasitic otitis, the results may suggest an auxiliary approach for the control E.R. Duarte et al. / Veterinary Parasitology 101 (2001) 45–52 51 and treatment of this parasitosis, i.e. the non-surgical horn removal of young animals, thus reducing the number of cattle with favourable conditions to host the parasite, and consequently, a reduced population of the nematodes in the herd. Surgical horn removal of adult animals could also contribute to otitis treatment, decompressing the ear canal, favouring aeration of the EEC, reducing humidity, and also improving access to the site for locally applied therapeutics. These results may also point to the necessity of the selection of cattle of this breed with a better shape of the horns, aiming to reduce the compression upon the ear canal. These results demonstrate that the focus for treatment of the disease must be directed towards the Gyr breed and with emphasis on older cattle with horns. This and future studies with an emphasis on epidemiological aspects may contribute to develop alternative approaches to reduce disease which, although studied over many decades, has remained a problem. Acknowledgements To the lecturers in Ruminant Clinical Practice at the Medical Veterinary School, Federal University of Minas Gerais, Dr. Antônio Último de Carvalho and Dr. Elias Jorge Facury Filho, who have given important technical support to this study. This work was supported by CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nı́vel Superior), FAPEMIG (Fundação de Amparo à Pesquisa do Estado de Minas Gerais) and CNPq (Conselho Nacional de Desenvolvimento Cientı́fico e Tecnológico). References Araújo, F.R.S., Vianna, S.S.S., Pereira, J.R., 1996. 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