The epidermal location and possible feeding site of Psorergates ovis, the sheep itch mite

Skin biopsies from two Merino sheep heavily infested with Psorergates ovis were immersed in liquid nitrogen and cut into vertical frozen sections stained with lipophilic Sudan IV or Oil Red O and haematoxylin. A survey of the lateral distribution of mite sections showed a majority (ca 80%) were in or within 0.2 mm of the follicle mouth. A survey of vertical distribution showed no mite penetration deeper than inner stratum corneum where 57% of mite sections were seen; 30% were within outer stratum corneum or scurf; 13% were on the outer surface and less than 1% were detached. Lipid was the only material seen within stained mites at a location considered to be gut. This was supported by dosing sheep with quinacrine, taking biopsies at Day 6 and Day 14 and examining frozen sections under blue light. Fluorescent lipid was seen at a location considered to be mite gut. From these results it was recommended that acaricide treatments against P. ovis be lipophilic and administered transepidermally because less than 15% of mites were at a superficial location likely to be reached by topical application.     

Feeding of the chewing louse Damalinia ovis (Schrank) (Phthiraptera:Trichodectidae) on sheep

The possibility that Damalinia ovis ingests intact epidermis could explain economically important irritation behaviour by infested sheep. To test this, feeding lice were observed on sheep by hand lens and macrophotography and on light and scanning electron microscope preparations. Aspects of feeding behaviour were described, particularly an epidermal ingestion posture. Louse ingesta were examined in paraffin and frozen sections. Lipid-covered stratum corneum squames were identified in crop, midgut, rectum and faeces. Nucleated keratinocytes from inner epidermal strata were not seen, neither were wool fibres. Vertical frozen sheep skin sections, with feeding lice cryofixed by liquid nitrogen, showed mandibles engaged in the outer stratum corneum of the epidermis. The epidermal origin of some ingesta was confirmed by confirming lice over sheep whose skin was stained with Oil Red O, whose colour was seen in crop, midgut, rectum and faeces of harvested lice. Lipase was found in louse midgut. It was concluded that sebaceous secretions may form an important component of the D. ovis diet. The relative contribution from loose scurf or from stratum corneum squames was not determined. Mechanical stimuli by feeding lice did not seem to be the source of host irritation. The role of sensitising agents in louse brei filtrates was investigated with inconclusive results. Intradermal injections of louse faeces did not elicit a demonstrable response.     

Comparison of cryofixation methods for skin biopsies from sheep infested with Psoroptes ovis (Acari: Psoroptidae)

Two methods of cryofixing skin samples from sheep infested with Psoroptes ovis were compared. In one method the skin biopsy was placed in a capped vial before immersion, while the other allowed direct contact with liquid nitrogen. No statistically significant differences were found between the cryofixation methods with regard to location of P. ovis sections or engaged mouthparts. Direct contact with liquid nitrogen is recommended as the preferred method for cryofixing epidermal feeding ectoparasites on skin samples.     

Clinical development and serological antibody responses in sheep and rabbits experimentally infested with Psoroptes ovis and Psoroptes cuniculi

Psoroptes ovis of sheep origin, and Psoroptes cuniculi of rabbit origin were used in experimental infestations. In experiment I, groups of four rabbits and four sheep were infested with 50-100 mites of each isolate on the skin of the back (skin infestation, SI) or in the external auditory canal (aural infestation, AI). In rabbits, SI and AI with P. cuniculi and AI with P. ovis induced in all animals typical ear lesions and pronounced antibody reactions to P. cuniculi antigens in ELISA. After SI of rabbits with P. ovis no clinical signs were detected, no mites could be reisolated and no specific antibodies were detected. In sheep, P. ovis SI induced mange whereas AI did not induce typical clinical signs and mites could not be reisolated. In both these animal groups, ELISA revealed pronounced and comparable specific antibody reactions. After SI and AI with P. cuniculi no clinical symptoms were observed and no mites could be reisolated. Nevertheless, low levels of specific antibody were detected. In experiment II, clinical progression and antibody reactions to P. ovis SI in naive sheep were compared with sheep previously exposed to P. ovis or P. cuniculi. In both pre-exposed groups of animals, clinical signs appeared within 2 days after challenge infestation and three days earlier than in primarily infested sheep. Subsequently, no obvious difference in the clinical progression was observed between the three groups of animals. The results of this study document antigenetic crossreactivity of the two morphologically and genetically distinguishable Psoroptes species but differences in their biological behaviour and virulence which both are of epidemiological and taxonomic relevance.     

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.     

The effects of temperature and humidity on the off-host survival of Psoroptes ovis and Psoroptes cuniculi.

The effects of both temperature and humidity on the survival of the mites Psoroptes ovis and Psoroptes cuniculi were considered in laboratory assays. When P. ovis and P. cuniculi were maintained at 95% humidity, maximum survival decreased linearly with increasing temperature, from approximately 15 days at 9 degrees C to 5 days at 30 degrees C. There was no significant difference between P. ovis and P. cuniculi in the effects of temperature on maximum survival. Adult male P. ovis and P. cuniculi had lower mean maximum survival than any of the other life cycle stages. There was a small but significant effect of humidity on survival for P. cuniculi; LT50 values were greater at 75-85% r.h. than at 55-65% r.h. The influence of off-host survival and the infestation of naive sheep from mites in the environment on the epidemiology of sheep scab are discussed.     

A simple pump-assisted method for collecting live,undamaged Psoroptes ovis from sheep using circulating saline

The availability of large numbers of undamaged sheep scab mites, Psoroptes ovis, would be beneficial for discovery screening and development trials. There are several reported procedures for removing scab mites from sheep but they have limitations. To overcome this, a simple but versatile method employing the use of pumped saline was developed to remove all stages of the P. ovis mite from sheep. The method takes no more than 2 min to remove mites from the selected site with relative ease and is not affected by the condition of the fleece or lesion. The number of mites removed with the new method was 5-10 times more than detected by visual examination. These mites were undamaged and survived off-host for up to 16 days. The robust, portable equipment is easy to use under field conditions, making this method suitable for use as a diagnostic tool for early detection and monitoring of scab mites thus providing opportunities for development of novel alternative control strategies.     

Ectoparasites are the major causes of various types of skin lesions in small ruminants in Ethiopia

Ectoparasites are the major causes of skin lesions in animals. Clinical, skin scraping examination, and histopathological studies were conducted to identify and characterize skin lesions in small ruminants caused by ectoparasites. Mange mites, lice, sheep keds, and ticks were collected from the skin of affected animals for species identification. Skin biopsies were collected from affected part of the skin and fixed in 10% neutral buffered formalin for histopathology. Of 1,000 sheep and 600 goats examined, 815 (81.50%) sheep and 327 (54.5%) goats were infested with one or more types of ectoparasites. Sarcoptes scabiei var ovis, Demodex ovis, Psoroptes ovis, Bovicola ovis, Melophagus ovinus, and Amblyomma variegatum and other tick species were identified from sheep. S. scabiei var caprae, Demodex caprae, Linognathus stenopsis, and A. variegatum and other tick species were identified from goats. Gross skin lesions or defects observed on the skin include stained and ragged wool, loss of wool/hair, nodules, crusts, lichenification, and fissuring. Microscopic evaluation of H and E stained skin sections revealed lesions in the epidermal layer such as hyperkeratosis, acanthosis, and melanin inconsistency on the basal cells of the epidermis. Follicular keratosis, perifolliculitis, frunculosis, perivasculitis, and aggregates of inflammatory cells (of acute and chronic type) with fibrosis were experiential in the dermal layer of the skin. Most of the skin lesions caused by ectoparasites are overlapping. Thus, ectoparasites control program should be executed to reduce skin lesions as skins are the major export commodity of the country.     

Treatment and control of sheep scab (Psoroptes ovis) with ivermectin under field conditions in South Africa.

Four trials including 11,266 sheep were conducted in South Africa to evaluate the efficacy of the systemic parasiticide ivermectin against field outbreaks of sheep scab (Psoroptes ovis) when two doses of approximately 200 micrograms/kg were administered subcutaneously seven days apart (days 0 and 7). As sheep scab is a notifiable disease in South Africa, it was not possible to include an untreated control group. The prevalence of clinically affected animals in the four treated flocks varied from 0.4 per cent to 99 per cent before the two treatments. After the treatments, there were no signs of active clinical infection in any of the sheep between days 28 and 30, or at subsequent examinations. P ovis mites were recovered from scrapings from 114 of 127 indicator sheep before the treatment but no mites were recovered from them between days 28 and 30 or 42 and 58 after the treatments.     

Pathogenesis of psoroptic scabies in Hereford heifer calves

Hereford heifer calves were experimentally infested with Psoroptes ovis. Histologic examination of skin specimens was conducted at weekly intervals before and after treatment with ivermectin on postinfestation week 7. Electron microscopy revealed numerous degranulating mast cells in the skin of infested but not in control calves. many active, as well as degenerate, neutrophils were in the scab on infested calves. Microscopic epidermal ulcers developed on infested calves when live mites were present but not after treatment. Numbers of dermal neutrophils and plasma cells decreased and numbers of circulating neutrophils increased 1 week after treatment. Numbers of dermal eosinophils and mast cells in calves with eosinophilia increased for several weeks after treatment. Statistical analysis indicated significant correlations (P less than 0.05) among numbers of dermal inflammatory cells, hemogram values, and changes in dermal thickness. Seemingly, mite-induced epidermal damage was the key pathogenic event in psoroptic scabies in calves. Mast cell degranulation contributed to the pathogenesis of the dermatitis, and neutropenia was caused by sustained, poorly compensated efflux of neutrophils into the scab through mite-induced breaks in the epidermis.     

不同温湿度和培养环境对离体绵羊痒螨生存活力的影响

目的 测不同温度及培养环境对离体绵羊痒螨生存能力的影响,进一步了解痒螨的传播机制,为制定防治瘁螨的有效措施提供理论基础。方法 置室内外自然温度和实验室恒温条件,以及5种相对湿度：50、60、70、80及90％RH,培养观察绵羊痒螨不同虫态（卵、幼虫、幼虫静止期、若虫、若虫静止期、雌虫、雄虫）的生存发育情况;同时观察痒螨在水、痂皮屑、羊毛、羊粪、土壤、皮组织等6种条件下的生存活力。结果 痒螨的最适生长发育温度及繁殖期在21℃-28℃范围内,随着温度的升高,痒螨存活时间缩短,绵羊痒螨对4℃低温有一定耐受力,但对35℃以上的高温耐受力较弱。在同一温度下,相对湿度越高,各虫态存活时间越长。结论 体外观察实验表明痒螨对外界环境有较强的适应能力,在缺乏营养的条件下仍能存活较长一段时间。     

The prevalence of itchmite, Psorergates ovis, among sheep flocks with a history of fleece derangement

An investigation of sheep flocks in the main sheep raising areas of New South Wales showed that the itchmite Psorergates ovis was frequently associated with fleece derangement. In 26 of the 41 flocks examined, P. ovis was the only ectoparasite detected. P. ovis and the sheep body louse Damalinia ovis, were found in 5 flocks. No external parasites were found on sheep examined from the 10 remaining flocks. The type of fleece derangement most frequently recorded was rubbing which in some cases was combined with areas of chewed fleece. Among flocks, there were positive relations between the prevalence of fleece derangement and prevalence of itchmite or scurf and between itchmite count and mean scurf score. Within flocks, itchmite infested sheep or sheep with scurf had higher prevalences of fleece derangement than sheep on which no mites or no scurf were found. Itchmite infested sheep had a higher prevalence of scurf than those with no detectable mite infestation. There were no significant differences in itchmite populations or fleece derangement between untreated flocks and flocks treated with synthetic pyrethroids, organophosphates or arsenic and rotenone.     

Diagnosis of psoroptic sheep scab with an improved enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay (ELISA) was developed for the detection of specific antibodies against crude Psoroptes antigen. The diagnostic sensitivity was 93.7% in 191 sheep with clinical signs associated with mange. These animals originated from 29 flocks in which psoroptic mites were detected. All of 59 sheep infested with Psoroptes ovis were seropositive. Additionally, in 49% of 70 clinically unaffected sheep originating from P. ovis-infested flocks, specific antibodies could be detected, suggesting that asymptomatic infestations can be diagnosed by serology. The specificity of the ELISA was 96.5% as determined with 254 sheep originating from 44 flocks without clinical mange. Cross-reactivity in a low range was detected with selected sera of sheep with clinical chorioptic or forage mite infestations. Four sheep seroconverted 2 weeks after experimental P. ovis infestation, i.e. 2 weeks before clinical signs became obvious. After successful doramectin treatment of 14 sheep with naturally acquired P. ovis infestation, the ELISA values declined slowly but remained positive in seven cases beyond 17 weeks.     

5%AVM预防绵羊疥癣病的长效试验

目的检测5%AVM对绵羊疥癣病的预防效果。方法通过痒螨检查确定试验羊,设Ⅰ、Ⅱ、Ⅲ5%AVM三个剂量组,Ⅳ为1%阿维菌素注射液组,Ⅴ为螨净组,Ⅵ为空白对照组,每个组7只试验羊;Ⅶ为传染源组。按羊的体重皮下注射或药浴,观察近90d。结果Ⅰ组61d发病;Ⅱ、Ⅲ组92d发病;Ⅳ组35d发病;Ⅴ组没有发病;Ⅵ组21d发病。结论5%AVM有效预防绵羊疥癣病近90d。     

Control of the sheep scab mite Psoroptes ovis in vivo and in vitro using fungal pathogens

As part of a research programme designed to identify biological agents for the control of sheep scab, the pathogenicity of the fungus Metarhizium anisopliae to Psoroptes mites in the presence of sheepskin and wool was examined in the laboratory. No inhibitory effects of skin and wool were observed and high levels of infection were recorded. Subsequently the pathogenicity of formulations of both M. anisopliae and Beauveria bassiana to Psoroptes ovis was studied in vivo. For this, 36 batches of 20 adult female Psoroptes mites were confined in 25 mm diameter chambers which were attached to the backs of 6 scab-naive sheep. In some treatments, mites were exposed to the fungal pathogens for 48 h in vitro prior to being placed on the host, while other treatments involved mites with no prior exposure placed directly onto the skin of a host treated with a fungal pathogen. After 48 h on the host, mites were removed, incubated individually and all fungal infections were recorded. Fungal infection was observed in all treatments, except untreated controls. However, B. bassiana infected a significantly greater number of mites than M. anisopliae with all the formulations examined. Infection rates were highest when mites were exposed to dry conidia (>90%) and lowest with M. anisopliae in diatomaceous earth. Overall, the infection rate was not affected by whether or not the mites were given prior exposure to the conidia, before being placed on the sheep. The results demonstrate that Psoroptes mites can become infected by entomopathogenic fungi on the skin of sheep and provides a first demonstration of the potential of this technology for the control of sheep scab.     

Host preference of the sheep scab mite,Psoroptes ovis

Sheep scab mites, Psoroptes ovis, collected from a Merino donor sheep, were used to infest Merino and Dorper sheep, and Angora and Boer goats. Mites were placed on the sheep on 1 or 2 occasions and on 5 occasions on the goats. All the animals were examined at regular intervals for the presence of scab lesions and living mites. Both sheep breeds developed lesions, but those on the Merino sheep were always larger than those on the Dorper sheep at the same intervals after infestation. None of the goats developed lesions or showed signs of irritation, or harboured any mites.     

Use of Oil Red O stain in the cytologic diagnosis of canine liposarcoma

BACKGROUND: Oil Red O, a stain commonly used to demonstrate lipid in frozen tissue, also may be used to stain air-dried cytologic specimens. OBJECTIVE: The purpose of this study was to prospectively evaluate the value of Oil Red O in identifying lipid to aid in the differentiation of liposarcomas from other types of sarcoma. METHODS: Twelve tumor specimens from dogs were evaluated. The tumors were included in the study if initial cytologic evaluation indicated a sarcoma, and if histologic confirmation was available. Oil Red O was applied to all cytologic specimens. RESULTS: Tumor specimens were diagnosed histologically as liposarcoma (3 well-differentiated, 1 pleomorphic), hemangiopericytoma (n = 3), fibrosarcoma (n = 3), malignant fibrous histiocytoma (n = 1), and undifferentiated sarcoma (n = 1). Cytologic specimens from all liposarcomas showed strong positive staining of cytoplasmic vacuoles for lipid. Specimens from other sarcomas stained negative for Oil Red O, with the exception of weak, irregular positive staining in 1 hemangiopericytoma. CONCLUSION: Our results suggest that Oil Red O staining may be an easy, inexpensive, and useful diagnostic tool for the differentiation of liposarcoma from other mesenchymal neoplasms.     

Study on skin diseases in sheep from northern Ethiopia

A study was conducted to determine the cause and prevalence of skin diseases in local sheep from northern Ethiopia. Of 520 sheep examined 174 (33%) had skin diseases of different causes. The identified causes were lice infestation due to Damalina ovis and Linognatus africanus (21%), sheep pox (8%), sarcoptic mange (Sarcoptic Scab. var. ovis) (4%), dermatophilosis due to Dermatophilus congolensis (3%), and orf (contagious ecthyma) (3%). There was no statistically significant (P > 0.05) association of any of the skin diseases with age and sex of the sheep examined. The occurrence and spread of the diseases were associated with poor management, climatic factors, feed scarcity and inadequate veterinary services. The increasing threat of skin diseases to the development of sheep production warranting an urgent control intervention is indicated.     

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.     

Simulation analysis of the population dynamics of the mite, Psoroptes ovis, infesting sheep.

The pattern of population growth of the ectoparasitic mite, Psoroptes ovis (Acari: Psoroptidae), on its ovine host is considered through the development of a Leslie matrix-based, simulation model. The model is parameterised using experimental data in conjunction with reanalysis of published data. The model shows that on sheep P. ovis populations grow at a rate of approximately 11% per day and the population doubles every 6.3 days. Additional rates of adult mortality, in excess of 50% per day, need to be imposed to prevent population growth. The predictions of the model are tested by comparison of the expected numbers of mites with the numbers recorded in lesions either on naturally infested sheep where the date of infestation can be estimated or on one artificially infested animal, where the initial number of mites and date of infestation are known precisely. In both cases the observed number of mites in lesions relate closely to the numbers expected from the simulations. The model simulations do not support the concept of a 'lag' phase as distinct from the 'growth' phase in the changing pattern of mite abundance on an infested sheep and suggests that the observed pattern of growth is a natural function of an exponential increase in numbers. The development of such models and their use in explaining the demographic processes which drive mite population dynamics are discussed.