Epidemiological observations on Gasterophilus intestinalis and G. nasalis in donkeys from Morocco.

During a 24 month period, 198 donkeys were examined for Gasterophilus intestinalis and Gasterophilus nasalis larvae. Gasterophilus intestinalis was found in 97.5% and G. nasalis in 95.5% of donkeys. The third instars (L3) of both species occurred during all months of the year and so did the second instars (L2), except in April (G. nasalis) and May (G. intestinalis). Over 75% of the animals had up to 200 larvae and 1.5% had over 600 larvae. The maximum number of both L2 and L3 larvae found in any animal was 418 G. intestinalis, 433 G. nasalis and 715 of both species combined. The seasonal variation in the numbers and development status of larvae indicated that the period of greatest activity of adult flies of G. intestinalis was from August/September to November, and that of G. nasalis from May to September. Consequently, the L2 larvae in the stomachs were in peak numbers between November and January for G. intestinalis and between July and September for G. nasalis. The L3 larvae of G. intestinalis had peak numbers between December and July, and those of G. nasalis between October and March. During January-March, most of the L2 larvae of G. nasalis were trapped in polypous nodules near the pyloric end of the stomach. It is concluded that the high-risk period for infection is during late spring and autumn, leading to the heavy larval burden of Gasterophilus in the stomach of donkeys during winter.     

Seasonal occurrence and distribution of Gasterophilus intestinalis and Gasterophilus nasalis in the stomachs of equids in Texas

Stomachs of 271 horses and ponies from 2 sources were evaluated for the presence of Gasterophilus intestinalis and G nasalis larvae, through 2 overlapping 12-month periods of bot fly activity in southern Texas. Equids (n = 140) from one source had nearly 96% of their stomachs infected, whereas equids (n = 131) from another source had 44% of their stomachs infected by Gasterophilus spp. Seasonal dynamics of the bot infection indicated the highest average number of bot larvae per infected stomach occurred in the winter and spring. The smallest average number of bots per infected stomach occurred in the fall. Higher percentages of early (2nd instar plus young 3rd instar) larvae of G intestinalis were observed in the fall in equids from both sources. The late (more fully developed older 3rd instar) G intestinalis larvae outnumbered the early larvae in the winter, spring, and summer. Seasonal variation in numbers and development status of the larvae was consistent with the largest period of adult bot fly activity occurring during the fall. The 2 species of bots had different predilection sites of attachment. Gasterophilus intestinalis larvae concentrated in the nonglandular portions of the stomach near the margo plicatus on the cranial (parietal) surface of the stomach and in the most dorsal extent of the saccus cecus. Gasterophilus nasalis larvae attached almost exclusively in the first ampulla of the duodenum. Predilection sites for both Gasterophilus spp occurred in dorsally positioned areas in the alimentary tract favoring increased availability of oxygen.     

Efficacy of moxidectin equine oral gel against endoscopically-confirmed Gasterophilus nasalis and Gasterophilus intestinalis (Diptera: Oestridae) infections in horses

A 3 m, video gastroscope was used to screen 47 horses suspected of being naturally infected with equine bot larvae. 17 of 47 (36.2%) candidate horses harbored Gasterophilus nasalis larvae in the proximal duodenum and 46 of 47 (97.9%) had G. intestinalis larvae in the stomach. All horses infected with G. nasalis had concurrent infections with G. intestinalis. 14 horses with dual infections were allocated randomly to two treatment groups. Seven horses in Group 1 received 2% moxidectin oral gel once at a dosage of 0.4 mg/kg bodyweight (BW), and seven horses in Group 2 were untreated controls. 14 days after treatment, all horses were necropsied and the stomach and proximal duodenum harvested from each. Bot larvae were recovered, identified to species and instar, and counted. At the label dosage, moxidectin oral gel was 100 and 97.6% effective (P < 0.05) against third-instar G. nasalis and G. intestinalis, respectively. In addition to demonstrating the boticidal efficacy of moxidectin, this trial illustrated that gastroscopy/duodenoscopy is a feasible method for confirming infections with different species of bot larvae in the horse.     

Prevalence and intensity of non-strongyle intestinal parasites of horses in northern Queensland

A quantitative post-mortem study of 57 horses from northern Queensland was done to determine the prevalence and intensity of non-strongyle intestinal parasites. The following species (% prevalence) were found: Draschia megastoma (39%); Habronema muscae (43%); Gasterophilus intestinalis (34%), G. nasalis (30%); Parascaris equorum (15%); Strongyloides westeri (6%); Probstmayria vivipara (2%); Oxyuris equi (26%); Anoplocephala magna (2%); A. perfoliata (32%). Mean parasite numbers of individual species ranged from 10 to 1310. Prevalence and intensity data were compared to recent studies in Western Australia and in the United States of America. Differences between stabled and paddocked horses were noted, particularly for botfly larvae and spiruroids. Climatic and seasonal changes in prevalence were restricted to H. muscae, G. nasalis and P. equorum with highest prevalence in the wet season or in horses from wet coastal areas. Only P. equorum showed any age effect being restricted to horses less than 5 years old. Breed and sex of horses was not important. The likelihood of changing parasite population dynamics with improved anthelmintic regimen is discussed.     

Species composition of Gasterophilus spp. (Diptera, Oestridae) causing equine gastric myiasis in southern Italy: parasite biodiversity and risks for extinction

Horse gastrointestinal myiasis caused by larvae of Gasterophilus spp. (Diptera, Oestridae) flies has a worldwide distribution and, where present, it is primarily caused by larvae of Gasterophilus intestinalis and Gasterophilus nasalis. Other species, i.e., Gasterophilus inermis, Gasterophilus pecorum and Gasterophilus haemorrhoidalis, present in different or in the same regions of the gastrointestinal tract, were only occasionally reported in very limited areas of eastern European Countries and in central Italy. With the aim to contribute data on the species composition of Gasterophilus and on the seasonal variation of the infection pattern in southern Italy, 152 native horses were necropsied from January to December 2003 and Gasterophilus larvae were collected from the stomach, the small intestine and the rectum of each of them. On the whole, 125 (82.2%) horses were infected by larvae of Gasterophilus spp. and 214 second stage larvae (L2) and 13,342 third stage larvae (L3) collected. Five species of Gasterophilus were identified with the following prevalence: G. intestinalis=95.2%, G. nasalis=44.8%, G. inermis=15.2%, G. pecorum=2.6% and G. haemorrhoidalis=0.8%. L3 were retrieved throughout the observation period with the highest mean burdens from January to August 2003 while the lowest mean was registered from September to November 2003. L2 were collected in February-March 2003 and from September to December 2003. The majority of the animals (n=66, 43.4%) were infected with a single Gasterophilus species, however, 45 animals (29.6%) harboured 2 species, 12 animals (7.9%) 3 species and 2 animals (1.3%) 4 species. The trend of abundance in the L3 of G. intestinalis and G. nasalis, the most represented species, was highly concordant (r=0.5, p<0.001). A retrospective comparison of our results and of other data from four seasons of observation (1983-1986) in central Italy showed that the number of G. inermis, G. pecorum and G. haemorrhoidalis have been decreasing relative to G. intestinalis and G. nasalis which may suggest tendency toward the extinction of the three former species of Gasterophilus.     

Occurrence of second and third instars of Gasterophilus intestinalis and Gasterophilus nasalis in stomachs of horses in Kentucky.

The occurrence of 2nd and 3rd instars of Gasterophilus intestinalis and Gasterophilus nasalis was determined in 476 horses during the 22-year period from 1951 to 1973. Overall, G intestinalis infected 98.7% of the horses and averaged 168/horse; whereas G nasalis infected 80.7% of the horses and averaged 52/horse. Aggregate average total numbers for G intestinalis ranged from a low of 50 in September to a high of 229 in March, and for G nasalis, from a low of 14 in September to a high of 82 in February. Horses were infected by 2nd or 3rd instars of both species on a year-round basis. Differentiation between the instars provided insight into the dynamics of the infections. For G intestinalis, the data indicated (1) 2nd instars from the previous year's generation of flies continue to arrive in the stomach until April; (2) arrival of the current year's crop of 2nd instars starts in July; and (3) 3rd instars from the previous year's generation of flies are not voided in appreciable numbers until August, when numbers of the current year's crop of 3rd instars appear in the stomach. For G nasalis, the data indicated (1) arrival in the stomach of the current year's generation of 2nd instars starts in July and terminates in January and (2) 3rd instars from the previous year's generation of flies are voided over a period beginning in March and extending into August, when the current year's crop of 3rd instars begin to appear. Acquisition of infections of horses with G intestinalis is nearly a year-round process, except for April, because of the persistence of viable larvae in eggs for a prolonged period after development and fly activity has ceased in the fall. In contrast, infection with G nasalis is interrupted between December and May, because eggs hatch naturally after a short period of development, and fly activity ceases in the fall.     

An epidemiological study of summer eczema in Icelandic horses in Norway

A survey of summer eczema was conducted on 391 Icelandic horses in Norway. The study showed a prevalence of summer eczema of 17.6 per cent in the horses investigated. Icelandic horses born in Norway where shown to be less affected with summer eczema than imported horses, 8.2 per cent and 26.9 per cent respectively (P less than 0.001). There was no difference in the prevalence of summer eczema relative to gender or colour of the horse. The number of horses affected with summer eczema rose with increasing age and the number of years which had elapsed since importation. On average, Icelandic horses born in Norway developed summer eczema at the age of 5.3 years. The onset of disease for imported horses was, on average, 4.1 years after importation. The study also revealed that a significantly greater number of horses imported from Iceland to Norway during the period October to April, which has a minimal or low activity of insects (32.3 per cent), had developed summer eczema, compared with horses imported during the period May to September, when insects are more active (16.7 per cent), (P = 0.044). Horses with summer eczema were shown to be significantly more affected by respiratory disease than non-affected horses (P = 0.0086). The most common sites and clinical signs of summer eczema are also described.     

Incidence and monthly prevalence of Gasterophilus spp. larvae (Diptera: Gasterophilidae) in the stomach of donkeys (Equus asinus) in Egypt

The stomachs of 118 donkeys were examined at postmortem during the period from March 1982 to February 1983 for Gasterophilus spp. larvae. G. intestinalis larvae clustered in groups near the boundary of the glandular and non-glandular epithelium of the stomach and infested 98.3% of the donkeys with highest numbers in July and lowest numbers in October. G. nasalis larvae were mainly attached near the pylorus and first part of the duodenum and infested 87.3% of donkeys with highest incidence in December and lowest in October. The ratio of the second and third instars of G. intestinalis to G. nasalis ranged from 71% to 29%. The percentage of donkeys infested with 1-100, 101-200 and 201-300 larvae was 72.0, 18.6 and 4.3% for G. intestinalis and 76.3, 8.5 and 0.8% for G. nasalis.     

Critical tests of morantel-trichlorfon paste formulation against internal parasites of the horse

Critical tests were completed on six horses to evaluate the antiparasitic activity of a paste formulation mixture of morantel citrate and trichlorfon, administered intraorally at the dose rate of 6 mg morantel base kg-1 and trichlorfon at 30 mg kg-1. Aggregate average removals were: 78% for two horses infected with 2nd instar Gasterophilus intestinalis; 100% for one infected with 2nd instar G. nasalis; 96% for six infected with 3rd instar G. intestinalis; 100% for four infected with 3rd instar G. nasalis; 100% for five infected with Parascaris equorum; 100% for one infected with mature Oxyuris equi; 100% for five infected with Strongylus vulgaris; 72% for five infected with S. edentatus; and partial removal (25%) of Anoplocephala perfoliata infection from one infected animal. Pre- and post-treatment EPG and LPG data indicated a reduction of 97% of the mature small strongyle infections. Evidence of toxicosis was not observed in any of the horses.     

Parasites of the stomach in donkeys of the highveld of Zimbabwe

Fourteen donkeys from a communal area of the Zimbabwean highveld were examined for stomach parasites during July and November of 1986 and January and April of 1987. All 14 animals were infected. Habronema muscae occurred in 12, Draschia megastoma in 11, H. majus in 9, Trichostrongylus axei in 9, Gasterophilus intestinalis in 14 and G. nasalis in 1 donkey. The lowest level of infection was in January for the helminths and in April for Gasterophilus larvae. The peak burdens of parasites were in July for Habronema spp. and in November for D. megastoma and Gasterophilus larvae. Infections with spirurid worms and Gasterophilus develop mainly from the middle of the rainy season to the beginning of the dry season (January to May/June). G. intestinalis seems to have an annual cycle.     

The prevalence of Gasterophilus intestinalis and G nasalis in horses in Ireland.

During the months October-May inclusive 90-8% of horses slaughtered at an abattoir near Dublin and 66-9% of those at an abattoir near Belfast were infected with Gasterophilus intestinalis; 28-6% of horses at the former abattoir harboured G nasalis while none of the horses examined at the latter abattoir was found to be infected with this species.     

Classification of the main macroscopic lesions produced by larvae of Gasterophilus spp. (Diptera:Gasterophilidae) in free-ranging horses in Umbria

Listed and described herein are the main macroscopic lesions produced along the whole digestive tract of free-ranging horses by larvae of the five Gasterophilus spp., occurring in Umbria, a region of central Italy: Gasterophilus intestinalis, Gasterophilus nasalis, Gasterophilus pecorum, Gasterophilus inermis, Gasterophilus haemorrhoidalis. Lesions are classified on the basis of their sizes and shapes and the host's anatomic sites infested, and they are examined in relation to the developmental stages of larvae causing them. The examination of the lesions shows that it is very difficult to differentiate the hemorrhagic impressions caused by migrating 1st and 2nd instar larvae of all the species in the absence of the specific parasite. It is also difficult to differentiate between the gastric lesions caused by Gasterophilus intestinalis and Gasterophilus pecorum. It has been found that an easy identification is possible even in the absence of parasites for gum lesions and for lesions on the soft palate produced respectively by Gasterophilus intestinalis and Gasterophilus pecorum, for duodenal lesions caused by Gasterophilus nasalis, for rectal lesions caused by Gasterophilus inermis and for duodenal and rectal lesions produced by Gasterophilus haemorrhoidalis.     

Efficacy of ivermectin (22,23-dihydroavermectin B1) against gastrointestinal parasites in ponies

The controlled test method was used to evaluate the antiparasitic efficacy of IM inoculated 22,23-dihydroavermectin B1 (ivermectin) against gastrointestinal parasites of horses (ponies). Parasite infections were naturally acquired in southern Louisiana. Dose levels of the drug tested were 0.2 mg/kg, 0.3 mg/kg, and 0.5 mg/kg. Ivermectin at all dose levels tested had an efficacy greater than 97% (P less than 0.05) against Gasterophilus intestinalis larvae, Trichostrongylus axei, Oxyuris equi larvae, Strongylus vulgaris, S edentatus, 15 species of small strongyles, and small strongyle larvae. Ponies were less uniformly infected with Habronema sp larvae, G nasalis larvae, Parascaris equorum, O equi adults, Anoplocephala perfoliata, S equinus, and 11 small strongyle species, and statistical analysis was not possible to do. However, observations indicate that the drug was also highly effective against these species. There were no gross or clinical reactions observed in treated animals. Dissections of the injection sites revealed spindle-shaped lesions, 3 to 5 cm long, in a few ponies in all treatment groups, including those given the placebo injection.     

Efficacy of an oxibendazole-trichlorfon paste formulation against third stage larvae of Gasterophilus intestinalis and its safety in horses

A paste formulation containing 14.3 per cent of oxibendazole and 44 per cent of trichlorfon was administered to 33 ponies and horses. The dose rate used was equivalent to 10 mg and 30 mg/kg bodyweight, of oxibendazole and trichlorfon respectively. After treatment 25 animals passed between one and 82 third stage larvae of Gasterophilus intestinalis in their faeces. Dosing with 0.2 mg ivermectin/kg bodyweight three weeks later resulted in six animals expelling between one and four bots. The efficacy of the oxibendazole-trichlorfon paste was on average 96.2 per cent. This drug combination given to 52 ponies and horses at the indicated dose rate and to six ponies at twice that dose was tolerated without side effects except transient softening of the faeces in several animals and mild symptoms of colic in two horses.     

Prevalence of selected species of internal parasites in equids at necropsy in central Kentucky (1995-1999)

A survey to determine current prevalence of several species of endoparasites in equids (n=350) at necropsy was conducted at the Livestock Disease Diagnostic Center in central Kentucky (1995-1999). Thelazia lacrymalis were found in 42% of the 1- to 4-year olds (n=132), which was the only age group examined for these parasites. Five- to 30-year olds (n=157), examined for Onchocerca spp. worms/lesions, had a prevalence of 24%. In > or =1-year olds (n=324), the infection rate for Gasterophilus intestinalis was 12% for second instars and 14% for third instars and for Gasterophilus nasalis was 2% for second instars and 2% for third instars. For Anoplocephala perfoliata (n=268 equids), prevalence was 52%. Data were compiled for the equids according to breed, age, sex, month of necropsy, and number of parasites. Arterial lesions caused by migrating Strongylus vulgaris larvae were observed in a low number (3 of 52) of equids. Specific examination for Parascaris equorum revealed that 46% of 13 weanlings and 10% of 20 older horses were infected. Anoplocephala magna were found in one of the weanlings. Compared to previous studies (about 15-25 years ago) in Kentucky, the present survey indicated the genera Onchocerca and Gasterophilus greatly declined but Thelazia, Anoplocephala, and Parascaris did not.     

Observations on the epizootiology of gasterophilus intestinalis and G. nasalis in horses in morocco

Ninety four horses from the Settat region of Morocco were examined for Gasterophilus intestinalis and G. nasalis larvae. All the horses were infected with G. intestinalis and 89 with G. nasalis; the mean larval burdens were 219 and 153, respectively. Third instar larvae of both species were present throughout the year. Second instar larvae of G. intestinalis were absent in April and May and those of G. nasalis in April only. More than 50% of horses had total burdens of more than 300 larvae and 4% harboured more than 1000 larvae. Young horses had higher infections than older animals. The period of adult activity of G. intestinalis is from April to October, with a maximum in summer. Second instar larvae of G. intestinalis are present in peak numbers from July to January and the third instars are voided in the faeces mainly in spring and summer.Infection with G. nasalis starts sooner than that with G. intestinalis. Second instar larvae are present from May to December in peak numbers. During January to March, many second instars of G. nasalis were found trapped in nodules.     

Prevalence of benzimidazole-resistance in equine cyathostome populations in south east England.

In order to study the prevalence of benzimidazole-resistance in equine cyathostomes, 30 stables in south east England were selected according to strict criteria but with minimum bias to provide three matched groups of 100 horses. One group was treated with fenbendazole, one with pyrantel embonate and the third was left untreated. The overall efficacies of fenbendazole and pyrantel embonate, as judged by the faecal egg-count reduction test, were 56.3 and 95.8 per cent, respectively. The numbers of horses at individual stables were too small to draw conclusions at each stable, but whereas efficacies greater than 85 per cent were recorded for pyrantel at 26 of 27 stables, the corresponding figure for fenbendazole was five of 27. Cyathostomes accounted for more than 90 per cent of the larvae cultured from faeces before and after treatment. Trichostrongylus axei was detected on 20 sites, but Strongylus species were present on only five. In the area of the survey, benzimidazole-resistance was very widespread in stables which used benzimidazole anthelmintics regularly and had more than nine horses per stable, but the benzimidazole-resistant cyathostome strains were adequately controlled with the non-benzimidazole anthelmintic pyrantel embonate.     

Prevalence and macro- and microscopic lesions produced by Gasterophilus nasalis (Diptera: Oestridae) in the Botucatu Region, SP, Brazil.

The objective of the present study was to investigate the prevalence of Gasterophilus nasalis larvae in Botucatu, the central west region of S?o Paulo State, Brazil, and to describe the lesions caused by the parasite. The climate of Botucatu is warm and rainy during the months of December through March and cool and dry during the months of May through August. The prevalence of G. nasalis was 16.84%, and the period of peak infestation corresponded to the months of cold and dry weather. The lesions detected at the sites of larval attachment were examined macro- and microscopically. Erosions and ulcerations of the gastric mucosa and proximal duodenum were the major macroscopic lesions detected. Microscopically, the lesion spectrum ranged from mild inflammatory reactions to extensive necrosis and ulceration.     

Inter-relationship between Gasterophilus larvae and the horse's gastric and duodenal wall with special reference to penetration.

The degree of penetration into the stomach and duodenum of the horse by bot fly larvae, Gasterophilus intestinalis (De Geer) and G. nasalis (Linnaeus) (Diptera : Gasterophilidae) was evaluated. Evidence of larval perforation of the stomach or duodenum was not found on gross inspection. Palpation of the intact stomach and duodenum was not effective in establishing the existence of Gasterophilus larvae within the organs. Findings suggest that larvae of both species produce an ulcer of similar depth within the gastrointestinal wall. The ulcer depth produced by larvae did not correlate with the normal, unaffected thickness of the particular stomach or duodenum. Tissue proliferation beneath ulcers of the stomach and duodenum was not correlated with the depth of the ulcer. Proliferation of the tissue beneath the ulcers of the stomach generally exceeded that found under duodenal ulcers. Gastric wall beneath the G. intestinalis ulcer frequently attained a thickness equal to or greater than the normal stomach wall. Histopathological examinations below the ulcer revealed intense fibrosis. Duodenal thickness below the G. nasalis ulcer was typically less than normal and resulted in an attenuated wall. Histopathological analysis of the affected duodenum revealed severe loss of submucosal glands in a sharply demarcated area below and surrounding the lesion. Fibrosis of the underlying lamina propria mucosae and tunica submucosa was appreciable but failed to restore the original thickness of the duodenal wall. Host tissue response and moderation of the parasite' s behavior reduce the chances of direct perforation of the gastrointestinal tissue.     

Allergic dermatitis (sweet itch) of Icelandic horses in Sweden: an epidemiological study

A survey of allergic dermatitis (sweet itch) in Sweden contained information on 441 Icelandic horses. Results of a questionnaire indicated that approximately 15 per cent of the country's Icelandic horses suffered from the disease. The prevalence of allergic dermatitis was significantly higher among horses imported from Iceland (26.2 per cent) compared to that of Swedish-born animals (6.7 per cent). In addition, horses born in Iceland were significantly more severely affected than horses born in Sweden. The risk of allergic dermatitis in Sweden appeared to be more than six times higher for horses exported from Iceland to Sweden relative to that of horses originally born in Sweden. The prevalence of disease for horses of seven years or older was 30 per cent for Icelandic-born individuals as compared to 7.3 per cent for horses born in Sweden. Similarly, the risk of allergic dermatitis in Sweden for horses of seven years or older appeared to be nearly 10 times higher for horses imported from Iceland relative to that of horses born in Sweden. Allergic dermatitis usually appeared during the third grazing season for imported horses and during the fourth season for horses born in Sweden. Furthermore, the course of the disease tended to become worse with time. Analysis of the prevalence of allergic dermatitis relative to gender revealed no significant differences. Certain geographical variations in the prevalence of the disease was also found.