Therapeutic use of Bacillus thuringiensis in the treatment of psoroptic mange in naturally infested New Zealand rabbits.

Bacillus thuringiensis is a bacteria known for its bioinsecticidal toxins and it has been proposed as an alternative in the treatment of several parasites that infect domestic animals (helminths, ticks, mites). In this work, we evaluated the clinical efficiency of the Bacillus thuringiensis GP532 strain in the treatment of six rabbits naturally infested with the P. cuniculi mite. GP532 extract (10mg/ml) was applied by aspersion in both pinna, with a second application after seven days, and the therapeutic effect was measured in both qualitative and quantitative manner. GP532 application resulted in a decreased infestation rate, which was observed as early as 3days post-treatment. At day 14, a decrease from 4.66±0.61 to 0.50±0.10 in the left pinna and from 1.66±0.21 to 0.66±0.16 (P<0.05) in the right pinna was observed. This response was comparable to the commercial drug Ivermectin, which induced a decreased infestation rate from 4.00±0.51 to 0.16±0.10 in the left pinna and from 4.66±0.80 to 0.25±0.11 in the right pinna (P<0.05). At day 30 post-treatment, GP532 decreased the total infested area by 76.80±16.06%, whereas Ivermectin resulted in a 97.41±0.99% decrease. Neither treatment produced irritation or macroscopic lesions. Our results show that the B. thuringiensis GP532 strain has a therapeutic potential in the treatment of psoroptic mange in rabbits.

Identification and disruption of bacteria associated with sheep scab mites-novel means of control?

Psoroptes ovis mites, which cause psoroptic mange (sheep scab), were investigated to identify potential bacterial targets for endosymbiont control of sheep scab. In addition, transmission of bacteria to the sheep skin was investigated through the characterisation of bacteria present in P. ovis faecal trails and on the fleece environment by internal transcribed spacer (ITS) sequencing. A diverse range of bacteria was identified in addition to a potential endosymbiont candidate, Comamonas sp, which was detected in P. ovis by both ITS PCR and endosymbiont-specific PCR. Disruption of these bacteria within P. ovis, through the use of antibiotics, was explored; with significant reduction in mean mite survival when administered antibiotic diets compared with controls (LR4 = 23.12, P < 0.001). The antibiotic treatments also significantly affected the bacterial density (CFU/mite) within P. ovis, indicating that mite survival may be linked to the bacterial communities that they harbour. Although antibiotics are not suitable for practical application, these results suggest disrupting bacteria associated with P. ovis should be further investigated for novel control.

Pathogenicity and thermotolerance of entomopathogenic fungi for the control of the scab mite, Psoroptes ovis.

Psoroptes ovis is responsible for a highly contagious skin condition, both in sheep and cattle. This parasite has a marked economical impact in the sheep and cattle industry. Biological control is considered as a realistic alternative to chemotherapeutic control. Laboratory experiments were carried out to evaluate the pathogenicity and the thermotolerance of twelve isolates of entomopathogenic fungi from four genera (Beauveria Vuillemin, Metarhizium Sorokin, Paecilomyces Bainier and Verticillium Nees). The pathogenicity was evaluated by the survival of P. ovis females after exposure to 10(6) to 10(8) conidia ml(-1) in humidity chambers. Results revealed intra- and interspecies differences. All isolates with the exception of B. bassiana IHEM3558 and V. lecanii MUCL8672 induced 50% mortality within 2 days at the highest concentration. At this concentration the entire mite population became infected with all isolates but B. bassiana IHEM3558; however, only four isolates gave rise to 100% infected cadavers at the lowest concentration. The thermotolerance of each isolate was evaluated by measuring its growth on an artificial medium kept between 25 and 37.5 degrees C. All isolates were able to grow up to 30 degrees C but only two, M. anisopliae IHEM18027 and Paecilomyces farinosus MUCL18885, tolerated temperatures up to 35 degrees C. These two isolates could be considered as good candidates for further use as biopesticide taking into account their virulence and thermotolerance. Other critical factors linked with the implementation of this type of biocontrol in P. ovis infected animals are discussed.

Isolation of Scopulariopsis spp. fungi from Psoroptes cuniculi body surface and evaluation of their entomopathogenic role.

In this study, some in vitro trials were carried out to evaluate the association between Scopulariopsis spp. fungi with Psoroptes cuniculi (Acari: Psoroptidae) and their potential pathogenicity to this mite species. After cultivation on Sabouraud dextrose agar with chloroamphenicol at 26 degrees C for 20 days and macro- and microscopical examinations, from P. cuniculi mites taken from some infested rabbits fungi belonging to the genus Scopulariopsis were isolated. Investigations were carried out to evaluate in vitro the potential pathogenic role of Scopulariopsis to P. cuniculi; to this aim, Scopulariopsis brevicaulis isolated from a cat was tested. In several culture media, the dose-dependent P. cuniculi mortality with different concentrations of S. brevicaulis and the ability of S. brevicaulis to penetrate inside the body of infected mites were evaluated. Results obtained demonstrated that, in the rabbit, Scopulariopsis fungi can be associated with P. cuniculi, and that S. brevicaulis can be an entomopathogen for P. cuniculi in a dose-dependent manner. A more rapid mortality of the mites and a quicker S. brevicaulis growth in plates containing rabbit serum with respect to all other media used were also found. S. brevicaulis demonstrated the ability to invade the body of P. cuniculi.

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.

In vitro entomopathogenic activity of Beauveria bassiana against Psoroptes spp. (Acari: Psoroptidae).

An indigenous strain (IHEM 18747) of Beauveria bassiana (Balsamo) Vuillemin (Deuteromycetes) was evaluated for its in vitro entomopathogenic activity against the parasitic mite Psoroptes ovis Hering (Acari: Psoroptidae) from rabbits. The following aspects were evaluated: (1) effects of conidial concentration on the viability of adult females; (2) influence of the infection on the fertility, and on the hatchability of eggs; (3) and transmission of infection between mites, and from contaminated surface. Adult females immersed into increasing concentrations of conidia (10(4)-10(9)conidia ml(-1)) showed a dose-related susceptibility. At the highest concentration of conidia, LT50 was 1.6 days while LT50 of the controls reached 5.8 days. The fungus was able to sporulate on the body surface and 100% of the mites were covered with mycelium after immersion in solutions containing 10(7)-10(9)conidia ml(-1). One hundred percent of healthy mites exposed to infected cadavers or surfaces acquired the infection (LT50 reached 1.9 and 1.73 days, respectively, versus 6.1 and 5.1 days in controls, respectively). Egg laying was not reduced by the fungal infection but both the hatchability of the eggs and the life span of the emerging larvae were significantly reduced. Eggs directly infected with the fungus did not show reduced hatchability but the life span of the larvae was shortened. It is concluded that B. bassiana has a high entomopathogenic activity against Psoroptes spp. The in vivo use of this biocontrol agent against Psoroptes spp. in rabbit, sheep and cattle deserves further attention.

Relationship between Psoroptes cuniculi and the internal bacterium Serratia marcescens.

The bacterium Serratia marcescens isolated from surface-sterilised Psoroptes cuniculi was found sensitive to the antibiotic Amikacin. Mites placed in this antibiotic for 48-72 h and then washed by centrifugation were found to be alive and S. marcescens-free. Two experimental infestations were undertaken in order to verify the ability of the S. marcescens-free mites to infect and to give ear skin lesions in healthy rabbits and to evaluate the differential ability of the S. marcescens-free and S. marcescens-infected mites to give ear skin lesions. All rabbits were found to be infested, but only rabbits infested with S. marcescens-free mites presented crusts in their ears, whereas mites and/or eggs were only detected in the ear cerumen of all rabbits infested with S. marcescens-infected mites. S. marcescens was isolated only from P. cuniculi mites taken from these latter rabbits. Results indicate that P. cuniculi mites do not need S. marcescens to live and to be able to infest a healthy rabbit. In addition, S. marcescens was not isolated from eggs and newly born larvae of S. marcescens-infected P. cuniculi, demonstrating that in a population of P. cuniculi this bacterium is not transmitted transovarially.

Aerobic and microaerophilic bacteria isolated from Psoroptes cuniculi.

The bacterial flora of Psoroptes cuniculi removed from nine naturally infested rabbits was investigated. Mites were collected in sterile glass tubes; half of the mites were surface sterilised, the others were not. All mites were crushed using sterile glass pestles, placed in Buffered Peptone Broth, smeared on to several culture media, by glass rods, and incubated at 37 degrees C for 48 hours, aerobically and/or in 5% CO2. Representative colonies were removed and streaked on to several selective media. Different colour changes of the selective media used, macro and microscopic morphology, ability to grow aerobically, Gram staining, and several biochemical tests evaluated with API test strips, were used for bacterial identification. Staphylococcus aureus, Serratia marcescens and S. odorifera were the bacteria isolated from surface sterilised mites.

Infection of Psoroptes mites with the fungus Metarhizium anisopliae.

The astigmatid mite, Psoroptes ovis (Hering) (Acari: Psoroptidae), is an obligatory ectoparasite that causes psoroptic mange in a range of domesticated animals, particularly sheep, where the clinical disease is known as sheep scab. A series of laboratory assays were used to assess the use of the fungus, Metarhizium anisopliae (Metchnikoff) (Deuteromycotina: Hyphomycetes) as a biocontrol agent for P. ovis derived from rabbits (syn. P. cuniculi). The immersion of mites in a suspension of conidia of M. anisopliae resulted in the acquisition of fatal infections. The number of mites which developed infections increased significantly with the increasing concentration of the conidial suspension to which they were exposed; 77% of mites developed infections when exposed to the highest concentration used (1 x 10(8) conidia ml(-1)). Controls developed no fungal infections. Mites allowed simply to walk across a surface which had been treated with a suspension of conidia also acquired fungal infections; the number infected was again related to the concentration of conidia present. After contact for 24 h with a surface treated with 1 x 10(8) conidia ml(-1), 73% of the mites became infected. To determine whether dead infected mites could act as sources of infection, infected cadavers were placed in chambers with live uninfected mites. The uninfected mites acquired fatal infections from the cadavers; a higher ratio of infected cadavers to uninfected mites resulted in greater transmission of infection. The time after death of the infected cadaver was also an important factor influencing the number infected, 5-day-old cadavers were the most infective and 18-day-old cadavers the least infective. The results indicate that M. anisopliae is a good candidate control agent for Psoroptes mites.