Survey for antibodies to respiratory viruses in two groups of sheep in Northern Ireland

Two hundred serum samples from Texel and Texel crossbred sheep (non-indigenous breeds) and 200 from indigenous Northern Ireland breeds (mainly Blackface, Cheviot and Border Leicester crosses) were tested for antibodies to parainfluenza virus types 1, 2 and 3, respiratory syncytial virus, bovine adenovirus (subgroups 1 and 2), influenza type A, maedi-visna virus and bovine virus diarrhoea virus. The percentage of animals with antibodies to parainfluenza virus 3 (50 to 56 per cent) and adenovirus subgroups 1 and 2 (70 to 90 per cent) was comparable in both groups. Infection of sheep with subgroup 2 adenoviruses has not previously been reported. In the case of respiratory syncytial virus and bovine virus diarrhoea virus, the percentage of animals positive was higher in the non-indigenous group (55.5 and 53 per cent, respectively) than in indigenous breeds (18.5 and 11 per cent, respectively). No antibodies were detected to parainfluenza virus 1 or 2, influenza A or maedivisna virus.     

Failure of a single treatment with ivermectin to control sheep scab (Psoroptes ovis) on artificially infested sheep

Ivermectin at 200 micrograms/kg bodyweight given either as a single subcutaneous injection or as an oral drench failed to eradicate Psoroptes ovis from artificially infested sheep. The oral drench reduced the mite populations by 43 per cent within 24 hours but no further significant decline was recorded over 38 days. The subcutaneous injection reduced the mite populations by 90 per cent after 10 days but live P ovis were present on all the treated animals 84 days after treatment. The efficacy of treatment was less the higher the initial mite burden. The injection had no effect on clinical sheep scab, and the disease continued to progress despite the mite mortality.     

Within-flock transmission of sheep scab in naive sheep housed with single infested sheep.

The within flock transmission of sheep scab was studied in two trials, which lasted 14 and 12 weeks, respectively. A total of 40 non-infested, scab-naive sheep were divided into six groups of between 6 and 20 individuals. Each group was subsequently housed with a single infested index case, carrying scab lesions of different ages. The groups of sheep in both trials were video recorded continuously and all the sheep were individually examined on a weekly basis. The occurrence of transmission was measured in two ways: first, by the detection of early scab lesions during clinical examination and, second, by an increase in the rubbing of individual sheep as noted from the analysis of the video recordings. These two methods complemented each other in predicting the week on which transmission occurred. Overall, transmission was detected in 34 of the 40 scab-naive sheep. Transmission was shown to occur at about the time when the population of adult mites in lesions on index cases reached their peak numbers. The highest number of mites at this time, however, differed markedly between index sheep. There was no obvious relationship between the incidence of transmission and the time index sheep spent rubbing each day or other index sheep variables, including the age of the lesion or the time since the introduction to the scab free sheep.     

Incidence of Mycobacterium paratuberculosis in raw sheep and goats' milk in England, Wales and Northern Ireland

A blind survey of 104 raw sheep and goats' milk samples (90 goat, 14 sheeps) from bulk tanks on farms throughout England, Wales and Northern Ireland was carried out over a 5-month period (January-May 1998) in order to determine the incidence of Mycobacterium paratuberculosis. Each milk sample (100 ml) was divided into two 50ml portions. One portion was decontaminated with 0.75% hexadecylpyridinium chloride for 5h before culture on slopes of Herrold's egg yolk medium and in BACTEC radiometric medium. The second portion was subjected to immunomagnetic separation followed by IS900 PCR (IMS-PCR). The IMS-PCR assay was employed in order to provide a more rapid indication of the presence of M. paratuberculosis in each milk sample than is possible by culture. Information on the Johne's disease status of the sheep and goat herds that took part in the survey was not sought at the time of milk sampling. However, it subsequently emerged that at least some of the herds whose bulk milk was tested during this study were previously or currently infected with Johne's disease. Overall, during this survey one raw goats' milk sample tested positive for the presence of M. paratuberculosis by IMS-PCR (<1% of milk samples tested) but no viable M. paratuberculosis were isolated by culture. The results of this study suggest that bulk raw sheep and goats' milk from these regions of the UK may not represent significant vehicles of transmission of M. paratuberculosis to humans.     

The in vitro response of sheep scab mites to pyrethroid insecticides.

The response of sheep scab mites to pyrethroid insecticides and organophosphate compounds was studied in vitro with the objective of finding a simple test for detecting insecticide resistance in scab mites. Psoroptes cuniculi from rabbits or P. ovis from sheep were enclosed in small 'tea bags' made from heat sealable paper prior to dipping in insecticide. Mites failed to die 24 h after a 1 min dip in working concentrations of insecticidal sheep dips. With flumethrin a variety of different conditions were tested but most failed to improve the efficacy of flumethrin. It is suggested with freshly collected mites pyrethroids may be taken up by ingestion.     

Serological cross-sectional survey of psoroptic sheep scab in Switzerland

Sheep scab, caused by the mite Psoroptes ovis, is a notifiable disease in Switzerland. Mandatory prophylactic treatments are carried out in spring for all sheep grazing on common alpine pastures. Despite these strict control measures the number of outbreaks has been increasing in recent years, raising questions on the spread of this epizootic disease. To improve the traditional microscopic diagnosis, we developed an ELISA for the specific determination of antibodies against psoroptic antigens with sensitivity and specificity of 93.7 and 96.5%, respectively. Using this test, a serum bank, representative of the sheep population in Switzerland (approximately 15% of registered sheep flocks, randomly chosen, collected between February and May 1998), was screened. The prevalence using 16,404 sera was 10.4, and 11.9% of the 2083 flocks were diagnosed as positive. Additionally, there was a significant increase found for mean seropositivity relative to the flock size (P<0.001, linear regression). Therefore, larger flocks had a higher risk of sheep scab, which may be caused by more frequent animal movement. Spatial analysis of the results revealed a region with significantly higher risk (relative risk = 3.5, P<0.001) of seropositivity, where no cases have officially been notified in the period between 1997 and 1999. The next goal is to establish an efficient control strategy based on serological monitoring of the total sheep population.     

Endemic sheep scab: risk factors and the behaviour of upland sheep flocks

Since the deregulation of sheep scab in 1992, the number of scab outbreaks per year in the UK has increased rapidly; there has been an estimated 60-fold increase in outbreak incidence between 1992 and 2007. How best to focus management or eradication efforts has therefore been an issue of ongoing debate. Previous work has shown that scab outbreaks occur repeatedly on some farms whereas others never or rarely experience outbreaks. Here, to consider why this pattern occurs, and to quantify the risk of scab associated with different husbandry practices, face-to-face interviews with farmers at 16, randomly selected, repeat-outbreak farms and 16 matched farms with no or little history of scab over the previous 10 years, were used to identify associated risk factors. This showed that farms using common grazing were at significantly higher risk of infestation than farms not using common grazing, as were farms that had direct contact with neighbours' sheep and that had neighbours with scab. To further demonstrate the risk of common grazing, a survey of sheep on one common in south Wales showed that there was significant mixing of sheep from three farms, highlighting the potential for scab transmission between flocks. Common grazing, associated with upland regions, would appear to be the largest single obstacle to effective national scab control in the UK. The results suggest that a cost-effective approach to scab control may be to consider upland and lowland farms as separate epidemiological systems, with upland regions requiring a co-ordinated, systematic approach to achieve any significant management of the problem. In contrast, on lowland farms outbreaks are already largely contained effectively through good biosecurity and treated on a case-by-case basis if they occur.     

Immune responses to Staphylococcus aureus and Psoroptes ovis in sheep infected with P. ovis--the sheep scab mite

In sheep, lesions caused by Psoroptes ovis, the sheep scab mite, may become colonized by Staphylococcus aureus. The present study compares clinical signs, lesional area and the immune response to P. ovis and S. aureus in P. ovis-infested sheep with and without secondary S. aureus infection. No differences were detected in the clinical signs or lesional areas in the S. aureus-positive and -negative sheep. However, 6 weeks after infestation an IgG but not IgE isotype antibody response to S. aureus was detected in the S. aureus-positive but not the S. aureus-negative group of sheep. This response targeted S. aureus antigens with molecular weights of approximately 36, 38, 50 and 65 kDa. In addition, 6 weeks after infestation an IgE response to P. ovis was detected in the S. aureus-positive but not the S. aureus-negative group of sheep.     

A strategic dosing scheme for the control of fasciolosis in cattle and sheep in Ireland

This study examined the effectiveness of a strategic dosing scheme in lowering the incidence of fasciolosis on a mixed dry-stock farm and in maintaining the reduced incidence following a reduction in dosing intensity. Two neighbouring farms with a history of chronic fluke disease were selected, the strategic dosing scheme being implemented on one (the trial farm) while the other (the control farm) continued to treat according to its normal practice. The strategic dosing scheme was designed to suppress the faecal egg output of Fasciola hepatica at critical times of the year in order to limit infection of the intermediate host snail population and thus reduce the subsequent contamination of the pasture with metacercariae. On the trial farm cattle and sheep were treated three times per year for the first 2 years at approximately 8 week intervals, starting in March of each year. A fourth treatment was given when the cattle were housed and out-wintered sheep received an additional treatment in January. In Years 3 and 4 the dosing intensity was reduced. By the end of Year 2, data from faecal egg counts, tracer-sheep fluke burdens and snail infection levels indicated that the treatment strategy had succeeded in suppressing the fluke population and eliminating the occurrence of clinical fasciolosis. The decrease in dosing intensity in Years 3 and 4 maintained both stock and snail infections at low levels and there was no re-emergence of the disease.     

Some observations on the biology and control of the sheep scab mite Psoroptes ovis (Hering) in Britain

Sheep scab was eradicated from Britain in 1952 but reappeared in 1973. The host specificity of the sheep scab mite is discussed; sheep are the only reservoir of the disease in Britain. Control is by single dipping in the approved acaricides, HCH, diazinon or propetamphos. Acaricides are approved only if the minimum use rate (Maintenance level) will give at least 4 weeks' protection. The method of testing is described. Traditionally, compulsory dipping has been in the winter when the disease is most active. Although the mites were originally thought to enter a latent phase during the summer, new observations indicate that there is little difference between their summer and winter behaviour. In Britain, dipping is now compulsory in both the summer and winter.     

Gastrointestinal nematode control practices on lowland sheep farms in Ireland with reference to selection for anthelmintic resistance

Gastrointestinal parasitism is a widely recognised problem in sheep production, particularly for lambs. While anthelmintics have a pivotal role in controlling the effects of parasites, there is a paucity of data on how farmers use anthelmintics. A representative sample of Irish lowland farmers were surveyed regarding their parasite control practices and risk factors that may contribute to the development of anthelmintic resistance. Questionnaires were distributed to 166 lowland Irish sheep producers. The vast majority of respondents treated their sheep with anthelmintics. Lambs were the cohort treated most frequently, the majority of farmers followed a set programme as opposed to treating at sign of disease. A substantial proportion (61%) administered four or more treatments to lambs in a 'normal' year. Departures from best practice in anthelmintic administration that would encourage the development of anthelmintic resistance were observed. In conclusion, in the light of anthelmintic resistance, there is a need for a greater awareness of the principles that underpin the sustainable use of anthelmintics and practices that preserve anthelmintic efficacy should be given a very high priority in the design of helminth control programmes on each farm. To this end, given that veterinary practitioners and agricultural advisors were considered to be the farmer's most popular information resource, the capacity of these professions to communicate information relating to best practice in parasite control should be targeted.     

Fertility of dairy cows in Northern Ireland

A comprehensive database was established on the milk production and reproductive performance of dairy cows in 19 selected herds in Northern Ireland, varying in size, management system and genetic merit. Data were obtained for 2471 cows, 1775 of which calved in a second year, and 693 were culled from the herd for specific reasons. The estimated mean rate of heat detection (assessed by the interheat interval during the main breeding season) in all the herds was 71 per cent, with a range from 53 to 92 per cent The average conception rate to first insemination was 37.1 per cent (range 21 to 66 per cent). The average calving interval for the retained cows was 407.2 days (range 359 to 448 days). Twenty-eight per cent of the cows that calved were culled, with infertility being the largest single reason (26.8 per cent of the cows culled). There were major differences in reproductive performance between the herds, but heat detection rate, conception rate and calving interval did not appear to be affeded by a herd's genetic merit. The herds with shorter calving intervals were characterised by better heat detection efficiency (83 v 61 per cent, P<0.01), a shorter interval from calving to first insemination (74 v 97 days; P<0.05), a higher conception rate to first insemination (45 v 34 per cent, P>0.10) and a lower removal rate (23 v 37 per cent, P<0.01). Furthermore, the cows in these herds had lower body condition scores (BCS) in the dry period (3.0 v 3.3; P<0.05) but lost less body condition in early lactation (0.3 v 0.6 BCS units, P<0.05). These results show that dairy herd fertility in Northern Ireland is generally low and similar to that previously reported for England and the USA, but that in some herds changes in herd management practices improved the cows' fertility.     

Haematological and immunological response of unrestrained cattle to Psoroptes ovis, the sheep scab mite

Cows were infected twice with 600 and 500 nymphs and adults of a bovine strain of Psoroptes ovis with a nine-week interval. The haematological response and the non-specific mitogen- and antigen-induced responsiveness of the peripheral blood lymphocytes of the animals was followed. Dermal reactivity to P ovis antigen injection was studied five weeks after reinfection. After the first infection with 600 mites none of the infected animals developed clinical psoroptic mange but a leucocytosis developed, contributed to primarily by an eosinophilia and by a slight lymphocytosis. Antigen-induced lymphocyte blastogenesis was used to measure the antigen-sensitive cell population in peripheral blood and this population showed a maximum increase 10 days after infection; however, antigen-sensitive cells remained above normal levels until reinfection. Upon challenge infection with 500 mites the infected animals showed an immediate hypersensitivity type reaction with a marked pruritus, scratching and exudation. Thereafter the lesions healed rapidly and none of the animals developed clinical mange. This clinical reaction was accompanied by a secondary eosinophilia but no change was apparent in the other blood elements. A marked increase in the blastogenic response of the peripheral blood lymphocytes was also apparent and this peaked three weeks after challenge. Following the intradermal injection of P ovis antigen there was an immediate swelling of the injection site in all infected and control animals and skin thickness was maximal one hour after injection. Thereafter there was a clear distinction in dermal reactions between P ovis infected and control animals; after 48 hours reactions were not seen in the control animals while marked dermal reactions were still present in the P ovis infected group.     

Cutaneous hypersensitivity reactions to Psoroptes ovis and Der p 1 in sheep previously infested with P. ovis--the sheep scab mite

We have previously shown that infestation with Psoroptes ovis induces an IgE response and intense tissue eosinophilia, typical of a Type I hypersensitivity response [Parasite Immunol. 22 (2000) 407]. Intradermal tests (IDSTs) suggest that there are also delayed and Arthus-type responses to this parasite. In order to study the nature of ovine cutaneous reactions to P. ovis, na?ve controls and experimentally infested sheep (n = 5) were challenged intradermally with mite antigen. Challenge elicited immediate (P < 0.001) and delayed (P < 0.005) wheal reactions in sensitised sheep. At 6 (P < 0.02) and 30 h (P < 0.001) the predominant infiltrating cells were eosinophils. To explore the role of circulating antibodies, na?ve sheep (n = 5) were subjected to Prausnitz-Kustner (PK) tests. These elicited immediate (P < 0.02) but not delayed wheal reactions. At 6 h eosinophils (P < 0.001) dominated the infiltrate. These results suggest that P. ovis allergens provoke an IgE-dependent immediate and late phase response and a cell-mediated eosinophil-rich delayed-type hypersensitivity response (ER-DTH).     

On-host ecology and off-host survival of the sheep scab mite Psoroptes ovis

These studies were conducted to investigate the possible role of certain aspects of the on-host ecology and off-host survival of the sheep scab mite, Psoroptes ovis, in the dissemination of infestation. All developmental stages of the mite occurred in the fleece both proximally or distal to the skin of infested Merino and Dorper sheep. A larger proportion of mites was present in the fleece of Dorper sheep distal to the skin in the late afternoon and early morning than at other times during the day. Immature and adult mites readily transferred to tufts of wool or hair placed on infested sheep of both breeds. No mites could be found on wool or hair rubbed off onto tree trunks or branches or other structures in enclosures housing heavily infested sheep, nor could any mites be collected from the soil of these enclosures, whereas more than 80% of mites artificially seeded onto soil samples were recovered. The longest mean off-host survival times for larvae, nymphs, and male and ovigerous female mites were recorded at 10 degrees C, and were 9.25 days (RH = 90%), 15 days (RH = 33% and 75%), 10.5 days (RH = 75% and 90%) and 11.25 days (RH = 90%) respectively. Under natural climatic conditions ovigerous females in glass vials containing Merino wool survived for 17 days compared to 15 days for females in vials without wool; this difference was, however, not significant. The mean off-host pre-hatch period for eggs varied between 5.9 days (T = 25 degrees C and RH = 33%) and 22.1 days (T = 10 degrees C and RH = 75%), while the longest time individual eggs took to hatch at the latter temperature and RH was 31 days.