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Evidence of Onchocerca fasciata (Filaroidea: Onchocercidae) in camels (Camelus dromedarius): I- prevalence, nodular lesions appearance and parasite morphology
Veterinary Parasitology 88 (2000) 305–312
Short communication
Evidence of Onchocerca fasciata (Filaroidea: Onchocercidae) in camels (Camelus dromedarius): I- prevalence, nodular lesions appearance and parasite morphology Aida A. El-Massry a , A.A Derbala b,∗ a
b
Parasitology Department, Faculty of Veterinary Medicine, Cairo University, Giza, Egypt Parasitology and Animal Diseases Department, National Research Center, P.O. Box 12311, Tahreer St., Dokki, Giza, Egypt Received 27 October 1998; accepted 5 August 1999
Abstract Examination of 3376 imported and 200 local Egyptian camels was carried out during the period extending between September 1997 and August, 1998. These animals were carefully examined for the presence of Onchocerca fasciata nodules and subsequently for O. fasciata adult parasites. Results of this study revealed that imported camels had the higher infection rate (2.75%), while those of local origin showed no palpable or detected Onchocerca nodules. Distribution of these nodules was mainly on the two sides of abdomen, hind limbs (concentrated in thigh region) and fore limbs particularly on the shoulders and nuchal ligament. This distribution varied according to the degree of infection. Searches for microfilariae were also performed using either blood samples, or in the subcutis and fascial sheath near or around the detected nodules. ©2000 Elsevier Science B.V. All rights reserved. Keywords: Onchocerca fasciata; Camel; Epidemiology-Nematoda; Pathology
1. Introduction The filarial nematode Onchocerca fasciata lives as an adult worm, forming well developed fibrous tissue nodules within the fascial sheath of various parts of the camel body. The ∗
Corresponding author. Fax: +202-3370931.
0304-4017/00/$ – see front matter ©2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 4 0 1 7 ( 9 9 ) 0 0 2 0 3 - 4
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parasite was first found in Australisan camels by Cleland (1909). It was first described by Railliet and Henry (1910) and redescribed by Bain and Nasher (1981). Morphological studies of this nematode were based on the examination of worm portions and the cuticle (Henery and Masson, 1933a, b; Badanine, 1938; Bain and Nasher, 1981). Different stages of camel onchocercosis, histopathological findings and ultra structures were investigated by Cheema et al., 1984; Nasher, 1986; Ghandour et al., 1991 and Determann et al., 1997. Despite these studies, the insect vector(s) of O. fasciata remains unknown (Cheema et al., 1984; Determann et al., 1997). In Egypt, no contributions have dealt with camel onchocercosis before. However, O. fasciata is probably a self limiting disease in dromedaries (Cheema et al., 1984). Moreover, heavily infected animals may not be suitable for sale as they resemble tuberculous infected camels. Therefore, a prevalent study was conducted to determine the infection rate of the parasite among local and imported camels. Typical nodular lesions were also examined either grossly or histopathologically.
2. Materials and methods 2.1. Camels Three thousand three hundred and seventy-six imported camels as well as 200 locally bred ones (older than 5 years old) were examined immediately after slaughter to determine the occurrence of adult O. fasciata nematode. The imported camels originated from Sudan and Somalia. These animals were investigated at the main Cairo abattoir during the period between September 1997 and August 1998. The camels both male and female, were subjected to careful palpation for the presence of Onchocerca nodules. Young camels were also examined for Onchocerca lesions. The number of these camels was one or two from both camel breeds in each visit/week (total 50 camels in 1 year). 2.2. Parasites Adult worms were surrounded with fibrous tissue nodules. These nodules were digested in a 2.0% acidic solution of pepsin (HCl pepsin). The volume of digesting solution depended on the size of examined nodules. Materials were incubated at 37◦ C in a water-bath for 4–8 h. Digested nodules were examined under a dissecting microscope for detection of adult parasites (Cheema et al., 1984). 2.3. Microfilariae Searches for microfilariae were carried out on nodular lesions and various localities of fascial sheaths near or around these nodules. This search was the modified method of Ferenc et al. (1986). Briefly, the specimens were incubated in physiological saline at 25◦ C for 24 h. Specimens were removed. The contents were centrifuged at 1000 rpm for 10 min and the recovered microfilariae of the sediment were examined microscopically.
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To exclude other filarial larvae, sufficient numbers of microfilaria fasciata were obtained from the uteri of female worms. Teased parts of gravid females were placed in petri-dishes containing physiological saline for 30 min to 1 h at 25◦ C, followed by removal of female remnants. The sediment was examined microscopically after centrifugation at 1000 rpm for 10 min. These microfilariae were examined either as fresh or after staining with Leishman or Giemsa stain (Hussein et al., 1975). The obtained microfilariae were measured and morphologically described. Blood samples of infected camels were examined for detection of Onchocerca filariae according to the method described by Selim and Fouad (1965). 2.4. Gross appearance and histopathological findings The subcutaneous fascial sheath of nuchal ligaments as well as other parts of slaughtered camels were examined for presence of Onchocerca nodules. The number, distribution and size of these nodules were noted for each animal.
3. Results 3.1. Rate of prevalence infection Results of the present study indicated that age, sex and geographic origins of examined camels were important determinants of O. fasciata infection rate. Onchocercal lesions were observed in 93 of 3376 (2.75%) of imported camels. However, two hundred local breed camels had no nodular lesions (Table 1). Female animals were found to be infected more than males. All months recorded positive infection rate, but with varied levels. Monthly prevalence of O. fasciata infection revealed that July (5.76%) and August (6.25%) were of the highest infection rate, while, January (1.36%) and February (0.99%) were of the lowest prevalence of infection (Table 1). The number of young camels in both breeds was small (50 camels). Examination of such camels for O. fasciata nodules was usually negative. 3.2. Distribution of Onchocerca nodules The existence of nodular lesions were mainly on the two sides of the abdomen, hind limbs (especially concentrated on the lateral sides of the thigh) and fore limbs, particularly on the regions of elbow and shoulders. The nodules were rarely found on the back region of infected animals. The intensity of infection,varied between 27 nodules and one nodule. It was noted that percentage of degenerating worms in nodular lesions was low. Measurements of 50 Onchocerca nodules revealed the ranges of 9–23 mm length, 6–11 mm width and 3–7 mm height. The means were 15–6±2.69 mm, 8.08±1.34 mm and 4.84± 0.76 mm, respectively.
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Table 1 Prevalence of O. fasciata infection in camels by survey dates Date 1997–1998
Number of examined — origin of camels Imported breed
Number of Posit.a Male
September October November December January February March April May June July August
285 270 291 276 293 302 294 240 279 296 278 272
Total (No. & %)
3376
5 2 2 2 2 1 2 2 3 4 7 7 39 (1.15%)
Total Female
Numbers
Local origin
No. of positivesb
Positive %c
% posit.
6 4 2 3 2 2 3 3 4 6 9 10
11 6 4 5 4 3 5 5 7 10 16 17
3.86 2.22 1.37 1.81 1.36 0.99 1.70 2.08 2.51 3.38 5.76 6.25
18 17 16 17 16 17 17 16 18 15 17 16
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
54 (1.60%)
93
2.75
200
0.0
0.0
a
Posit.=Positive. No.=Number. c %=Percentage. b
3.3. Macroscopical appearance of Onchocerca lesions Adult parasites inside O. fasciata nodules produced a spectrum of gross pathogenic changes. The nodules were located mainly within the fascial sheath or slightly pedunculated from it. They were detected in the head, nuchal ligament and other parts of infected camels. The fascia was thickened to form the nodules. The nodules were raised, tactile or hard in their texture, ovoid, flattened and of a button appearance resembling small lymph nodes. Heavily infected animals contained more extensive groups of these nodules (often like a cluster of grapes). The parasites were surrounded by a smooth fibrous tissue capsules. On cutting specimens revealed tangled masses of thin filarial worms (Fig. 1). This capsule may increase in thickness as the lesion grows older. Older nodules showed a grayish core of necrotic tissues in which portions of the worms were found embeded. Sometimes, the parasites appeared thicker than normal as a result of tissue reactions. Calcified worms were also commonly encountered and were easily recognized by their whitish calcareous appearance. 3.4. Microfilariae Microfilariae were recovered from the subcutis and entire hides near the onchocercal lesions. The location of microfilariae was generally parallel to the location of nodules containing adult parasite. In heavily infected animals, the nodules and microfilariae were observed
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Fig. 1. Nodular lesion in fascial sheath of infected camels showing adult parasites of O. fasciata.
in fascial sheaths and subcutis of positive examined areas. However, the microfilariae were not recovered from positive blood samples. Microfilariae are relatively long and thin without a sheath. They have a blunt cephalic end but, the tail tapers to a fine pointed tip (Fig. 2). The filarial larvae measured 297–415.5 in length (mean 350.72±44.52 ) and 3–6 width (mean 4.54±0.95 ). Coiled and straight forms may be found within the uterus of gravid females and Onchocerca nodules.
Fig. 2. Microfilaria having a blunt head-end and sharply pointed tail. Relatively small circular eggs were noticed (×400).
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3.5. Histopathological findings Adult worms in tissues evoked a wide range of histopathological alterations in relation to duration and previous exposure to the parasite. The fibrous connective tissue spreading from the capsule formed the nodular matrix and several cavities, containing worm fragments. The bicornuate uterus filled with embryonated eggs and microfilariae were often observed with inflammatory cell infiltration. These cells were lymphocytes, eosinophils, histiocytes and plasma cells. In later stages of infection, the worms may produce a more intensive granulomatous response with many histiocytes and a dense outer zone. This zone comprised of lymphocytes, multinucleated giant cells and eosinphils. Heavy infiltration by neutrophils occurred in Onchocerca nodules, containing degenerated or dead worms. The continuous resolution of the adult parasites resulted in formation of granulation tissue with fibrosis and calcification of these nodules. 4. Discussion In the present study O. fasciata was detected in 2.75% of imported camels. However, a higher occurrence (15.5%) was reported by Cheema et al., 1984 in Saudi Arabia. A significant difference was observed between the prevalence rate of onchocercosis among local and imported camels. This variation in prevalence may be due to either their exposure to the insect vector(s) or to greater transmission rate of O. fasciata in imported countries than in Egypt. In spite of the examination of large number of imported camels, the infection rate was still lower than that detected in Saudi Arabia by Cheema et al. (1984). That may be due to the veterinary quarantine measures applied on the borders between Egypt and the adjacent or exported countries. These measures allow entrance of healthy animals only. Furthermore, freedom of local camels from O. fasciata infection means that Egypt is still free from the insect vector(s) which is essential in transmission of this filarial nematodes. The vector(s) of O. fasciata are presently unknown (Determann et al., 1997). The prevalence of onchocercosis in young camels could not be assessed because the number of encountered animals were too few. Moreover, all young examined camels were negative for Onchocerca lesions. Sex-related effects on prevalence of infection were evaluated. A higher infection rate in female camels was observed than in males. However, Beveridge et al. (1979) found that bulls had a higher rate of infection with O. lienalis than did the cows. Furthermore, Ladds et al. (1979) and Ferenc et al. (1986) mentioned that this higher infection rate in bulls was observed only in temperate regions, in which the prevalence was low or moderate. They did not find a difference between bulls and cows in tropical regions, where prevalence of infection with O. guttarosa was high. Therefore, a host sex-related factor may be the best indicator when levels of infection are low or moderate. Such data may reflect on the prevalence of infection. It was interesting to note that O. fasciata nodules were confined to the fascial sheath of the ligamentum nuchae and subcutis of other locations of infected camels. The filarial
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nematodes usually were not visible but could be palpable. In the later stages these nodular lesions were caseated or partly calcified. These results were relatively similar to that of cattle infected with O. lienalis (Scholten et al., 1977) and O. ochengi (Cross et al., 1997) but in some instances, the adult worm of O. ochengi forms intradermal nodules which can be easily palpated and removed. The proportion of old or degenerating worms inside Onchocerca nodules was low. This result was similar to that recorded by Schulz-Key (1990) in case of O. volvulus infection. The Onchocerca females were very rarely surrounded by some males in detected nodules. Ghandour et al. (1991) did not find any males in the nodules, but contrasting this finding Bwangamoi (1969) found that O. ochengi females were often surrounded with some male worms in nodules. Our results indicated that the location of microfilariae fasciata is generally parallel to the location of nodules containing adult parasites. Thus, the existence of microfilariae in mildly infected camels is probably a reflection of nodular distribution in these animals. These results agree to that obtained by Cheema et al. (1984) but this data was unlike the microfilariae localization of O. guttarosa infection in cattle (Eichler, 1973) and was most probably influenced by the biting habit of the insect vector (Muller, 1979). Onchocerca nodules particularly in heavily infected camels are sometimes mistaken as tuberculous infection of lymph nodes. This mistake resulted in confused condemnation of some carcasses. The two conditions can be distinguished by cutting these nodules. If the nodules reveal filarial nematodes, it could be easily differentiated from suspected lymph nodes that were free upon cutting. It is concluded that Egypt is still free from the insect vector(s). This vector(s) is essential for transmission of the infective stage of O. fasciata. Despite that intermediate host is still unknown, it is possible that camels of local origin may be infected when this vector(s) had been introduced from the exported and adjacent countries. References Badanine, N.V., 1938. Sur la question d’helminthofaune du chameau en Turkmnie, Vol. 3. Livro Jubilar do Professor Lauro Travassos, Rio de Janeiro, pp. 61–73. Bain, O., Nasher, E., 1981. Redescription de l’onchocerquedu dromadaire, O. fasciata (Railliet and Henry 1910). Ann. Paraist (Paris) 56, 401–406. Beveridge, I., Kummerow, E., Wilkinson, P., 1979. The prevalance of Onchocerca lienalis in the gastro-splenic ligament of cattle in north Queensland. Aust. Vet. J. 55, 204–205. Bwangamoi, O., 1969. Onchocerca ochengi new species, an intradermal parasite of cattle in east Africa. Bull. Epizoot. Dis. Afr. 17, 321–335. Cheema, A.H., El-Bihari, S., Ashour, N.A., Ali, A.S., 1984. Onchocercosis in camels (Camelus dromedarius) in Saudi Arabia. J. Helminth. 58, 279–285. Cleland, J.B., 1909. Trypanosomiasis and other diseases in camels. Transaction of the 8th session of the Australian Medical Congress. J. Trop. Vet. 1909, 324. Cross, H.F., Bronsvoort, B.M., Wahl, G., Renz, A., Achu-Kwi, D., Trees, A.J., 1997. The entry of ivermectin and suramin into Onchocerca ochengi nodules. Ann. Trop. Med. Parasitol. 91, 393–401. Determann, A., Mehlhorn, H., Ghaffar, F.A., 1997. Electron microscope observation on Onchocerca ochengi and O. fasciata (Nematoda: Filarioidea). Parasit. Res. 83, 591–603. Eichler, D.A., 1973. Studies in Onchocerca gutturosa (Neumann, 1910) and its development in Simulium ornatum (Meigen, 1818). 4- Systematics of O. gutturosa. J. Helminth. 47, 89–96.
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Ferenc, S.A., Copeman, D.B., Turk, S.R., Courtney, C.H., 1986. Onchocerca gutturosa and Onchocerca lienalis in cattle: effect of age, sex and origin on prevalence of onchocercosis in subtropical and temperate regions of Florida and Georgia. Am. J. Vet. Res. 47, 2266–2268. Ghandour, A.M., Al-Amoudi, A.A., Banaja, A.A., 1991. Onchocerca fasciata (Railliet and Henry, 1910) and its nodule development in camels in Saudi Arabia. Vet. Parasitol. 39, 67–77. Henery, A., Masson, G., 1933a. Onchocercose du dromadaire (1). Bull. Acad. Vet. France 6, 208–213. Henery, A., Masson, G., 1933b. Onchocercose du dromadaire. Bull. Acad. Vet. 45, 231–241. Hussein, M.F., Abdel Nur, O., Gassouma, M.S., Nelson, G.S., 1975. Onchocerca gutturosa (Neumann, 1910) infection in Sudanese cattle. Br. Vet. J. 131, 76–84. Ladds, P.W., Copeman, D.B., Goddard, M., 1979. The occurrence of Onchocerca guttarosa infection in the nuchal ligament in relation to breed, sex and age of slaughtered cattle. Aust. Vet. J. 56, 445–446. Muller, R., 1979. The identification of Onchocerca. In: Taylor, A.E.R., Muller, E. (Eds.), Problems in the identification of parasites and their vectors. 17th Symp. Br. Soc. Parasitol. Blackwell, Oxford, pp. 175–206. Nasher, A.K., 1986. Incidence and intensity of Onchocerca fasciata Railliet and Henry, 1910 in local camels in Saudi Arabia. Ann. Parasitol. Hum. Comp. 61, 77–80. Railliet, A., Henry, A., 1910. Le onchocerques, nematodes parasites due tissu conjonctif. C. R. Soc. Biol. Paris 151, 248–251. Scholten, R.G., Adams, S.R., Broderson, J.R., 1977. Evidence of onchocercosis in Georgia cattle: prevalence at slaughter. Am. J. Vet. Res. 38, 1093–1097. Schulz-Key, H., 1990. Observation on the reproductive biology of Onchocerca volvulus. Acta Leidensia 59, 27–43. Selim, .K., Fouad, .A., 1965. Incidence of equine filariasis in Egypt. Vet. Med. J. 10, 113–118.
Short communication
Evidence of Onchocerca fasciata (Filaroidea: Onchocercidae) in camels (Camelus dromedarius): I- prevalence, nodular lesions appearance and parasite morphology Aida A. El-Massry a , A.A Derbala b,∗ a
b
Parasitology Department, Faculty of Veterinary Medicine, Cairo University, Giza, Egypt Parasitology and Animal Diseases Department, National Research Center, P.O. Box 12311, Tahreer St., Dokki, Giza, Egypt Received 27 October 1998; accepted 5 August 1999
Abstract Examination of 3376 imported and 200 local Egyptian camels was carried out during the period extending between September 1997 and August, 1998. These animals were carefully examined for the presence of Onchocerca fasciata nodules and subsequently for O. fasciata adult parasites. Results of this study revealed that imported camels had the higher infection rate (2.75%), while those of local origin showed no palpable or detected Onchocerca nodules. Distribution of these nodules was mainly on the two sides of abdomen, hind limbs (concentrated in thigh region) and fore limbs particularly on the shoulders and nuchal ligament. This distribution varied according to the degree of infection. Searches for microfilariae were also performed using either blood samples, or in the subcutis and fascial sheath near or around the detected nodules. ©2000 Elsevier Science B.V. All rights reserved. Keywords: Onchocerca fasciata; Camel; Epidemiology-Nematoda; Pathology
1. Introduction The filarial nematode Onchocerca fasciata lives as an adult worm, forming well developed fibrous tissue nodules within the fascial sheath of various parts of the camel body. The ∗
Corresponding author. Fax: +202-3370931.
0304-4017/00/$ – see front matter ©2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 4 0 1 7 ( 9 9 ) 0 0 2 0 3 - 4
306
A.A. El-Massry, A.A Derbala / Veterinary Parasitology 88 (2000) 305–312
parasite was first found in Australisan camels by Cleland (1909). It was first described by Railliet and Henry (1910) and redescribed by Bain and Nasher (1981). Morphological studies of this nematode were based on the examination of worm portions and the cuticle (Henery and Masson, 1933a, b; Badanine, 1938; Bain and Nasher, 1981). Different stages of camel onchocercosis, histopathological findings and ultra structures were investigated by Cheema et al., 1984; Nasher, 1986; Ghandour et al., 1991 and Determann et al., 1997. Despite these studies, the insect vector(s) of O. fasciata remains unknown (Cheema et al., 1984; Determann et al., 1997). In Egypt, no contributions have dealt with camel onchocercosis before. However, O. fasciata is probably a self limiting disease in dromedaries (Cheema et al., 1984). Moreover, heavily infected animals may not be suitable for sale as they resemble tuberculous infected camels. Therefore, a prevalent study was conducted to determine the infection rate of the parasite among local and imported camels. Typical nodular lesions were also examined either grossly or histopathologically.
2. Materials and methods 2.1. Camels Three thousand three hundred and seventy-six imported camels as well as 200 locally bred ones (older than 5 years old) were examined immediately after slaughter to determine the occurrence of adult O. fasciata nematode. The imported camels originated from Sudan and Somalia. These animals were investigated at the main Cairo abattoir during the period between September 1997 and August 1998. The camels both male and female, were subjected to careful palpation for the presence of Onchocerca nodules. Young camels were also examined for Onchocerca lesions. The number of these camels was one or two from both camel breeds in each visit/week (total 50 camels in 1 year). 2.2. Parasites Adult worms were surrounded with fibrous tissue nodules. These nodules were digested in a 2.0% acidic solution of pepsin (HCl pepsin). The volume of digesting solution depended on the size of examined nodules. Materials were incubated at 37◦ C in a water-bath for 4–8 h. Digested nodules were examined under a dissecting microscope for detection of adult parasites (Cheema et al., 1984). 2.3. Microfilariae Searches for microfilariae were carried out on nodular lesions and various localities of fascial sheaths near or around these nodules. This search was the modified method of Ferenc et al. (1986). Briefly, the specimens were incubated in physiological saline at 25◦ C for 24 h. Specimens were removed. The contents were centrifuged at 1000 rpm for 10 min and the recovered microfilariae of the sediment were examined microscopically.
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To exclude other filarial larvae, sufficient numbers of microfilaria fasciata were obtained from the uteri of female worms. Teased parts of gravid females were placed in petri-dishes containing physiological saline for 30 min to 1 h at 25◦ C, followed by removal of female remnants. The sediment was examined microscopically after centrifugation at 1000 rpm for 10 min. These microfilariae were examined either as fresh or after staining with Leishman or Giemsa stain (Hussein et al., 1975). The obtained microfilariae were measured and morphologically described. Blood samples of infected camels were examined for detection of Onchocerca filariae according to the method described by Selim and Fouad (1965). 2.4. Gross appearance and histopathological findings The subcutaneous fascial sheath of nuchal ligaments as well as other parts of slaughtered camels were examined for presence of Onchocerca nodules. The number, distribution and size of these nodules were noted for each animal.
3. Results 3.1. Rate of prevalence infection Results of the present study indicated that age, sex and geographic origins of examined camels were important determinants of O. fasciata infection rate. Onchocercal lesions were observed in 93 of 3376 (2.75%) of imported camels. However, two hundred local breed camels had no nodular lesions (Table 1). Female animals were found to be infected more than males. All months recorded positive infection rate, but with varied levels. Monthly prevalence of O. fasciata infection revealed that July (5.76%) and August (6.25%) were of the highest infection rate, while, January (1.36%) and February (0.99%) were of the lowest prevalence of infection (Table 1). The number of young camels in both breeds was small (50 camels). Examination of such camels for O. fasciata nodules was usually negative. 3.2. Distribution of Onchocerca nodules The existence of nodular lesions were mainly on the two sides of the abdomen, hind limbs (especially concentrated on the lateral sides of the thigh) and fore limbs, particularly on the regions of elbow and shoulders. The nodules were rarely found on the back region of infected animals. The intensity of infection,varied between 27 nodules and one nodule. It was noted that percentage of degenerating worms in nodular lesions was low. Measurements of 50 Onchocerca nodules revealed the ranges of 9–23 mm length, 6–11 mm width and 3–7 mm height. The means were 15–6±2.69 mm, 8.08±1.34 mm and 4.84± 0.76 mm, respectively.
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Table 1 Prevalence of O. fasciata infection in camels by survey dates Date 1997–1998
Number of examined — origin of camels Imported breed
Number of Posit.a Male
September October November December January February March April May June July August
285 270 291 276 293 302 294 240 279 296 278 272
Total (No. & %)
3376
5 2 2 2 2 1 2 2 3 4 7 7 39 (1.15%)
Total Female
Numbers
Local origin
No. of positivesb
Positive %c
% posit.
6 4 2 3 2 2 3 3 4 6 9 10
11 6 4 5 4 3 5 5 7 10 16 17
3.86 2.22 1.37 1.81 1.36 0.99 1.70 2.08 2.51 3.38 5.76 6.25
18 17 16 17 16 17 17 16 18 15 17 16
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
54 (1.60%)
93
2.75
200
0.0
0.0
a
Posit.=Positive. No.=Number. c %=Percentage. b
3.3. Macroscopical appearance of Onchocerca lesions Adult parasites inside O. fasciata nodules produced a spectrum of gross pathogenic changes. The nodules were located mainly within the fascial sheath or slightly pedunculated from it. They were detected in the head, nuchal ligament and other parts of infected camels. The fascia was thickened to form the nodules. The nodules were raised, tactile or hard in their texture, ovoid, flattened and of a button appearance resembling small lymph nodes. Heavily infected animals contained more extensive groups of these nodules (often like a cluster of grapes). The parasites were surrounded by a smooth fibrous tissue capsules. On cutting specimens revealed tangled masses of thin filarial worms (Fig. 1). This capsule may increase in thickness as the lesion grows older. Older nodules showed a grayish core of necrotic tissues in which portions of the worms were found embeded. Sometimes, the parasites appeared thicker than normal as a result of tissue reactions. Calcified worms were also commonly encountered and were easily recognized by their whitish calcareous appearance. 3.4. Microfilariae Microfilariae were recovered from the subcutis and entire hides near the onchocercal lesions. The location of microfilariae was generally parallel to the location of nodules containing adult parasite. In heavily infected animals, the nodules and microfilariae were observed
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Fig. 1. Nodular lesion in fascial sheath of infected camels showing adult parasites of O. fasciata.
in fascial sheaths and subcutis of positive examined areas. However, the microfilariae were not recovered from positive blood samples. Microfilariae are relatively long and thin without a sheath. They have a blunt cephalic end but, the tail tapers to a fine pointed tip (Fig. 2). The filarial larvae measured 297–415.5 in length (mean 350.72±44.52 ) and 3–6 width (mean 4.54±0.95 ). Coiled and straight forms may be found within the uterus of gravid females and Onchocerca nodules.
Fig. 2. Microfilaria having a blunt head-end and sharply pointed tail. Relatively small circular eggs were noticed (×400).
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3.5. Histopathological findings Adult worms in tissues evoked a wide range of histopathological alterations in relation to duration and previous exposure to the parasite. The fibrous connective tissue spreading from the capsule formed the nodular matrix and several cavities, containing worm fragments. The bicornuate uterus filled with embryonated eggs and microfilariae were often observed with inflammatory cell infiltration. These cells were lymphocytes, eosinophils, histiocytes and plasma cells. In later stages of infection, the worms may produce a more intensive granulomatous response with many histiocytes and a dense outer zone. This zone comprised of lymphocytes, multinucleated giant cells and eosinphils. Heavy infiltration by neutrophils occurred in Onchocerca nodules, containing degenerated or dead worms. The continuous resolution of the adult parasites resulted in formation of granulation tissue with fibrosis and calcification of these nodules. 4. Discussion In the present study O. fasciata was detected in 2.75% of imported camels. However, a higher occurrence (15.5%) was reported by Cheema et al., 1984 in Saudi Arabia. A significant difference was observed between the prevalence rate of onchocercosis among local and imported camels. This variation in prevalence may be due to either their exposure to the insect vector(s) or to greater transmission rate of O. fasciata in imported countries than in Egypt. In spite of the examination of large number of imported camels, the infection rate was still lower than that detected in Saudi Arabia by Cheema et al. (1984). That may be due to the veterinary quarantine measures applied on the borders between Egypt and the adjacent or exported countries. These measures allow entrance of healthy animals only. Furthermore, freedom of local camels from O. fasciata infection means that Egypt is still free from the insect vector(s) which is essential in transmission of this filarial nematodes. The vector(s) of O. fasciata are presently unknown (Determann et al., 1997). The prevalence of onchocercosis in young camels could not be assessed because the number of encountered animals were too few. Moreover, all young examined camels were negative for Onchocerca lesions. Sex-related effects on prevalence of infection were evaluated. A higher infection rate in female camels was observed than in males. However, Beveridge et al. (1979) found that bulls had a higher rate of infection with O. lienalis than did the cows. Furthermore, Ladds et al. (1979) and Ferenc et al. (1986) mentioned that this higher infection rate in bulls was observed only in temperate regions, in which the prevalence was low or moderate. They did not find a difference between bulls and cows in tropical regions, where prevalence of infection with O. guttarosa was high. Therefore, a host sex-related factor may be the best indicator when levels of infection are low or moderate. Such data may reflect on the prevalence of infection. It was interesting to note that O. fasciata nodules were confined to the fascial sheath of the ligamentum nuchae and subcutis of other locations of infected camels. The filarial
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nematodes usually were not visible but could be palpable. In the later stages these nodular lesions were caseated or partly calcified. These results were relatively similar to that of cattle infected with O. lienalis (Scholten et al., 1977) and O. ochengi (Cross et al., 1997) but in some instances, the adult worm of O. ochengi forms intradermal nodules which can be easily palpated and removed. The proportion of old or degenerating worms inside Onchocerca nodules was low. This result was similar to that recorded by Schulz-Key (1990) in case of O. volvulus infection. The Onchocerca females were very rarely surrounded by some males in detected nodules. Ghandour et al. (1991) did not find any males in the nodules, but contrasting this finding Bwangamoi (1969) found that O. ochengi females were often surrounded with some male worms in nodules. Our results indicated that the location of microfilariae fasciata is generally parallel to the location of nodules containing adult parasites. Thus, the existence of microfilariae in mildly infected camels is probably a reflection of nodular distribution in these animals. These results agree to that obtained by Cheema et al. (1984) but this data was unlike the microfilariae localization of O. guttarosa infection in cattle (Eichler, 1973) and was most probably influenced by the biting habit of the insect vector (Muller, 1979). Onchocerca nodules particularly in heavily infected camels are sometimes mistaken as tuberculous infection of lymph nodes. This mistake resulted in confused condemnation of some carcasses. The two conditions can be distinguished by cutting these nodules. If the nodules reveal filarial nematodes, it could be easily differentiated from suspected lymph nodes that were free upon cutting. It is concluded that Egypt is still free from the insect vector(s). This vector(s) is essential for transmission of the infective stage of O. fasciata. Despite that intermediate host is still unknown, it is possible that camels of local origin may be infected when this vector(s) had been introduced from the exported and adjacent countries. References Badanine, N.V., 1938. Sur la question d’helminthofaune du chameau en Turkmnie, Vol. 3. Livro Jubilar do Professor Lauro Travassos, Rio de Janeiro, pp. 61–73. Bain, O., Nasher, E., 1981. Redescription de l’onchocerquedu dromadaire, O. fasciata (Railliet and Henry 1910). Ann. Paraist (Paris) 56, 401–406. Beveridge, I., Kummerow, E., Wilkinson, P., 1979. The prevalance of Onchocerca lienalis in the gastro-splenic ligament of cattle in north Queensland. Aust. Vet. J. 55, 204–205. Bwangamoi, O., 1969. Onchocerca ochengi new species, an intradermal parasite of cattle in east Africa. Bull. Epizoot. Dis. Afr. 17, 321–335. Cheema, A.H., El-Bihari, S., Ashour, N.A., Ali, A.S., 1984. Onchocercosis in camels (Camelus dromedarius) in Saudi Arabia. J. Helminth. 58, 279–285. Cleland, J.B., 1909. Trypanosomiasis and other diseases in camels. Transaction of the 8th session of the Australian Medical Congress. J. Trop. Vet. 1909, 324. Cross, H.F., Bronsvoort, B.M., Wahl, G., Renz, A., Achu-Kwi, D., Trees, A.J., 1997. The entry of ivermectin and suramin into Onchocerca ochengi nodules. Ann. Trop. Med. Parasitol. 91, 393–401. Determann, A., Mehlhorn, H., Ghaffar, F.A., 1997. Electron microscope observation on Onchocerca ochengi and O. fasciata (Nematoda: Filarioidea). Parasit. Res. 83, 591–603. Eichler, D.A., 1973. Studies in Onchocerca gutturosa (Neumann, 1910) and its development in Simulium ornatum (Meigen, 1818). 4- Systematics of O. gutturosa. J. Helminth. 47, 89–96.
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Ferenc, S.A., Copeman, D.B., Turk, S.R., Courtney, C.H., 1986. Onchocerca gutturosa and Onchocerca lienalis in cattle: effect of age, sex and origin on prevalence of onchocercosis in subtropical and temperate regions of Florida and Georgia. Am. J. Vet. Res. 47, 2266–2268. Ghandour, A.M., Al-Amoudi, A.A., Banaja, A.A., 1991. Onchocerca fasciata (Railliet and Henry, 1910) and its nodule development in camels in Saudi Arabia. Vet. Parasitol. 39, 67–77. Henery, A., Masson, G., 1933a. Onchocercose du dromadaire (1). Bull. Acad. Vet. France 6, 208–213. Henery, A., Masson, G., 1933b. Onchocercose du dromadaire. Bull. Acad. Vet. 45, 231–241. Hussein, M.F., Abdel Nur, O., Gassouma, M.S., Nelson, G.S., 1975. Onchocerca gutturosa (Neumann, 1910) infection in Sudanese cattle. Br. Vet. J. 131, 76–84. Ladds, P.W., Copeman, D.B., Goddard, M., 1979. The occurrence of Onchocerca guttarosa infection in the nuchal ligament in relation to breed, sex and age of slaughtered cattle. Aust. Vet. J. 56, 445–446. Muller, R., 1979. The identification of Onchocerca. In: Taylor, A.E.R., Muller, E. (Eds.), Problems in the identification of parasites and their vectors. 17th Symp. Br. Soc. Parasitol. Blackwell, Oxford, pp. 175–206. Nasher, A.K., 1986. Incidence and intensity of Onchocerca fasciata Railliet and Henry, 1910 in local camels in Saudi Arabia. Ann. Parasitol. Hum. Comp. 61, 77–80. Railliet, A., Henry, A., 1910. Le onchocerques, nematodes parasites due tissu conjonctif. C. R. Soc. Biol. Paris 151, 248–251. Scholten, R.G., Adams, S.R., Broderson, J.R., 1977. Evidence of onchocercosis in Georgia cattle: prevalence at slaughter. Am. J. Vet. Res. 38, 1093–1097. Schulz-Key, H., 1990. Observation on the reproductive biology of Onchocerca volvulus. Acta Leidensia 59, 27–43. Selim, .K., Fouad, .A., 1965. Incidence of equine filariasis in Egypt. Vet. Med. J. 10, 113–118.