Ph. Dorchies

Epidemiology of Oestrus ovis in southwest France

From July 1989 to June 1990, 555 heads of adult sheep obtained from Pamiers slaughterhouse (southwest France) were examined for infestation by Oestrus ovis. Infestation was present in 65% of the heads and the mean larval burden per positive case over the year was 24.8. The monthly prevalence rate varied from 44% in April to 88.2% in November. There are usually three generations of O. ovis each year: the first in March-April, the second in June-July and the last in September-October. There was no fly activity in winter and during the hottest months of summer. On the other hand, nearly all the larvae overwintered as the first stage. This study emphasizes the seriousness of the problem in the region and the authors recommend three strategic treatments per year during periods of high fly activity.

Pathophysiology of Oestrus ovis infection in sheep and goats: a review

Oestrus ovis is a very common parasite of sheep and goats in many countries. Its pathological effects are often underestimated because owners and veterinarians are used to seeing the infection. The study of natural and experimental infections has provided information about the evolution of the disease and its pathophysiology. Hypersensitivity is involved; the numbers of mast cells and eosinophils increase but changes in IgE have only recently been examined. Little is known about the development of immunity but it is possible that some animals are immunodeficient.

Prevalence and larval burden of Oestrus ovis (Linné 1761) in sheep and goats in northern mediterranean region of France

A slaughterhouse survey to determine prevalence and larval burden of Oestrus ovis larvae in sheep and goats was performed monthly during one year in Pézenas, South of France, northern mediterranean region. A total of 1303 sheep and goat heads were selected at random. O. ovis larvae were found in 274 sheep out of 631 (43.4%), and the prevalence rate varied from 14.3% in February to 65% in October. The mean number of larvae in infected sheep heads was 10.86 with 9.24 L1, 0.91 L2 and 0.71 L3. One hundred and ninety-one goats out of 672 were infected (28.4%), and the prevalence rate varied from 6.25% in September to 47.1% in April. In infected goat heads, the mean parasitic burden was 5.35 with 4.04 L1, 0.73 L2 and 0.58 L3. These results confirm worldwide observations indicating that the prevalence and the parasitic burdens are less in goats than in sheep.

Serine protease activity in excretory-secretory products of Oestrus ovis (Diptera: Oestridae) larvae.

The sheep bot fly, Oestrus ovis, is a very common myiasis of nasal and sinus cavities of sheep and goats causing severe welfare and production implications. As the viability of O. ovis adult flies strictly depends on larval abilities to assimilate and to stock nutrients from the host, it was necessary to investigate proteolytic activities in larval excretory/secretory products (ESP). ESP of O. ovis larvae degrade mucosal and plasmatic components such as mucin, albumin or immunoglobulin G. A preliminary biochemical characterization, using substrate gel analysis and inhibitor sensitivity, demonstrated the presence of at least six major serine proteases (molecular weights from 20 to 100 kDa), mainly trypsin-like, secreted in the digestive tube of larvae. Their involvement in larval trophic activity and evasion from the host immune response is further discussed as O. ovis excretory/secretory serine proteases could represent potential vaccinal targets.

Disturbances of digestive motility in horses associated with strongyle infection

Abstract Motility disturbances of the ileo-caeco-colic region resulting from natural and experimental strongyle infection were studied by electromyography in six ponies, before and after treatment. Compared with control animals regulary treated by mebendazole (10 mg/kg), naturally infected animals exhibited a low level of ileal motility and a reduction by 50% of the caeco-colic motor response to feeding. Complete disorganization of the motility patterns occured during the 48 h following the anthelmintic treatment. A marked decrease in motility and/or disorganization of the motility patterns accompanied by intermittent diarrhoea occurred 40–50 days after an experimental infection of the ponies with 70,000–300,000 small strongyle larvae. The results showed that strongyle infection resulted in changes in motility patterns associated with both the lower rate of weight gain and the digestive disturbances.

Oestrus ovis (Diptera: Oestridae): sheep humoral immune response to purified excreted/secreted salivary gland 28 kDa antigen complex from second and third instar larvae.

The potential of Oestrus ovis larvae excretory-secretory products (ESP), crude extract, salivary gland contents (SGc) and digestive tube contents (DTc) proteins from O. ovis larvae as antigens in serological assay were analyzed and compared. This study demonstrated that excretory-secretory proteins were produced mainly by digestive tube and salivary gland. The main antigenic component of ESP was a 28kDa protein complex (pc28) synthesized by the salivary gland ring. After purification, its diagnostic value was estimated by an ELISA using sheep sera sampled in summer (n=30) and winter (n=69) in order to investigate the relative importance of wintering hypobiotic first instar larvae on animal responsiveness. ELISA test based on pc28 antigen was compared to a reference ELISA test based on second instar larvae crude extract. After comparison it appeared that the pc28 test was much more specific (87%) and more sensitive (90%) in summer. Anti-pc28 antibody titers were significantly higher in summer than in winter demonstrating the impact of summer developing larvae on the humoral systemic immune response. This data was correlated to the maturation of larvae in summer as the number of larvae at necropsy was significantly higher in winter, when the larval population is only represented by first instar larvae, than in summer. No correlation was observed between the mean antibody titers and the number of larvae.

Estimation of the growth patterns of Oestrus ovis L. larvae hosted by goats in Baja California Sur, Mexico

To estimate parameters for the variation in larval weight and dimension in Oestrus ovis L. and to describe the approximate pattern of growth, 2041 larvae were collected from 431 slaughtered goats and classified on a scale of 12 identified physiological ages, according to spiracular and integumental pigmentation. Larval live weight and measures of length, width, and thickness at the seventh segment were obtained. Weight increased from 0.23 mg in L1 larvae to 49 mg in late L2 larvae; however, the highest increases in weight were found to occur after the L2-L3 molt, especially during the early L3 period, when larvae acquired about 45% of the average mature weight (518 mg). Average larval length increased almost linearly from about 2 mm in L1 larvae to reach full length (21.3 mm) just before initiating integumental pigmentation, then it tended to stabilize until full maturation. Except for higher increases during the early L3 period, larval width and thickness increased linearly to reach mean maximum values (6.0 and 5.0 mm, respectively) at full maturity. Weight and measurement data were fitted by monophasic, s-shaped growth functions. The y = 0.25 [1 + tanh[0.504 (12-6.65)]] function (R2 = 0.99) indicated that L3 larvae began to have a decrease in weight gain rates before the beginning of integumental pigmentation. The patterns of growth of O. ovis described from individual measurements in larvae may be suitable for descriptive purposes.

Seasonal variation of Oestrus ovis-specific antibodies in sheep and goats mixed flocks in Greece.

The aim of this survey was to investigate the year-round epidemiological patterns of Oestrus ovis ELISA sero-prevalence in sheep and goats kept together under the same husbandry system in an endemic area of Greece. Twenty-five adult female sheep and 25 adult female goats, coming from a large mixed flock, were randomly selected, eartaged and monthly blood sampled during 1 year period (November 1998-October 1999). Serological prevalence in sheep was 100% all around the year. Mean intensities of specific O. ovis antibodies follow a seasonal evolution with higher mean titers between March and July than in winter. In contrast, the serological prevalences in goats were low specially in winter months (from October to January). No significant difference were noticed in goats antibody levels during the year period. The possible reasons of this difference of O. ovis sero-prevalence between sheep and goats are discussed.

The relationship between nasal myiasis and the prevalence of enzootic nasal tumours and the effects of treatment of Oestrus ovis and milk production in dairy ewes of Roquefort cheese area

Infection by Oestrus ovis is common in Lacaune dairy ewes of Roquefort cheese area (Aveyron, France). It is believed by local breeders that there is a close relationship between nasal myiasis and the incidence of enzootic nasal tumour. In order to check these anecdotal reports, a serological survey was done on 658 breeding ewes before turn-out and 897 breeding and primiparous (hoggets) ewes at the end of the grazing season. By the time of sampling, it was clear whether the sheep were infected at the end of the winter or had been re-infected over summer. In April and September, 40.7 and 26.3%, respectively, were free of O. ovis infection, indicating that the autumn treatment was not completely effective and that O. ovis adult flies were circulating during the summer in many flocks. There were no differences in the incidence of adenocarcinoma between the groups indicating that there is no relationship between O. ovis infection and the presence of the cancer. Differences in milk production between the three groups were not statistically significant (Anova test P>0.05). In flocks where 1-5% of the ewes were infected or in non-infected flocks, ewes produced 3.6 and 8.56%, respectively, more milk than ewes from flocks where more than 5% of animals were infected. For primiparous ewes, the differences were of 8.5 and 12.24%.

Expected effects of reducing Oestrus ovis L. mature larval weight on adult populations.

In order to estimate the effects of eventual reductions in larval weight (LW) of Oestrus ovis L. as a measure of control, the correlation between mature LW and adult fly length (AL) in laboratory specimens (n=150) was calculated. The regression equation AL=5.62+10.65LW (r(2)=0.76) was obtained. This equation was then applied to estimate the mature LW of wild larvipositing females (n=51) to predict the minimum mature LW at which fly viability would be compromised. The critical weight, 0.28 g (standard error limits 0. 235, 0.323), was obtained from a small fly measuring 8.6mm in length. Data from 383 mature third instars were used to estimate, by statistical analysis, the expected effects of decreasing the mature LW on subsequent fly population size. A considerable mean reduction (38%) in adult populations might be achieved by a 40% reduction of mature LW, but this eventual reduction may be temporary due to the high reproductive rate in this species. Sex differences in mature LW and fly size are also reported.