Ectoparasites: future challenges in a changing world

Ectoparasites are ubiquitous, often highly damaging and in most cases cannot be permanently eradicated; hence, they must usually be managed at a local scale with insecticides or endectocides. However, the growth in resistance, the slow rate of development of new actives, coupled with environmental and health concerns associated with the continued use of some of the existing neurotoxic insecticides, suggest that more sophisticated approaches to their management need to be identified. These approaches need to allow ectoparasite populations to be maintained at acceptable levels, while conserving the compounds that remain available. The development of integrated approaches, in which cascades of management tactics are deployed, with parasiticides available as one component to be used in requisite circumstances, may be the most appropriate route to achieving this aim. An essential element of such an approach is the clear articulation of the purpose of intervention and rational justification of the time-point and manner in which it is attempted. However, for this to be possible, considerably better information is required about the effects of ectoparasite abundance on animal welfare and productivity, in addition to the greater availability of effective alternative control tools. To this end, recent work undertaken at the School of Biological Sciences at the University of Bristol, into the use of biological control agents, off-host trapping and the selective treatment of more highly susceptible individuals or classes of host, is reviewed here.     

Serology of Campylobacter fetus fetus strains from four outbreaks of ovine abortion

As a result of a Ministry of Agriculture & Fisheries survey on ovine abortions, 76 isolates of Campylobacterfetus fetus were obtained. These isolates were from four farms in the southern Hawkes Bay, with an abortion incidence of 2.8% to 9.1%. Antisera to eight different strains of C. fetus fetus were made in rabbits. Strains were then examined using whole cell tube agglutination tests and sensitised Staphylococcal Protein A slide agglutination tests. Heat labile antigens were examined by absorbing antisera with heat-treated bacteria. Two broad serogroups were found, but within-group variation was demonstrated by cross-absorbing antisera. The isolates from one farm were all of a single broad serogroup. Both serogroups were found on the remaining three farms. Evidence for the presence of two major serogroups was also obtained by immobilisation tests and antigen analysis by gel diffusion.     

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.     

Estimation of the number of exposed people during highly pathogenic avian influenza virus outbreaks in EU/EEA countries,October 2016–September 2018

We estimated that more than 11,000 people were exposed to highly pathogenic avian influenza viruses in EU/EEA countries over the outbreak period October 2016–September 2018 by cross‐linking data submitted by Member States to European Food Safety Authority and EMPRES‐i. A stronger framework for collecting human exposure data is required.     

Correlated inheritance of sex expression and fruit shape in Cucumis

Genetic control of sex expression in particular strains of Cucumis melo and C. sativus is under the control of a single locus. A dominant allele, A, is responsible for monoecious sex expression; the recessive allele, a, is responsible for andromonoecious sex expression. The evidence suggests that in C. melo fruit shape is determined by a single gene with incomplete dominance plus minor modifying genes, linked in coupling phase with the gene for determination of sex expression. In C. sativus the evidence does not completely exclude the possibility that the alleles for sex determination are pleiotropic and, therefore, are also the major determiners of fruit shape. However, evidence in favor of close linkage between genes determining sex and fruit shape is given and the author favors an interpretation of close linkage between two subunits of a complex gene. Evolutionary significance is seen in the presence of correlated inheritance of sex expression and fruit shape in three species of two genera of the Cucurbitaceae.     

Toxicity and efficacy of cisplatin and doxorubicin combination chemotherapy for the treatment of canine osteosarcoma

Thirty-five dogs with appendicular osteosarcoma underwent amputation and chemotherapy with cisplatin and doxorubicin every 21 days for up to four cycles. Sixteen dogs completed all four cycles. Two dogs had therapy discontinued because of metastases. The remaining 17 dogs experienced toxicities necessitating protocol alteration or discontinuation. The median survival time of 300 days was not improved over previously reported single-agent protocols, but the 10 dogs that survived to a year lived a median of 510 days.     

Non-equivalence of canine tissue and intraluminal PCO2 responses at different sites during hemorrhage and during resuscitation

Objective: The purpose of this study was to measure and compare the hemorrhage and resuscitation partial pressure of CO₂ (PCO₂) responses at a variety of sites, predominantly intraluminal gastrointestinal, in the same dog and among different dogs. Design: Observational study. Setting: Association for Assessment and Accreditation of Laboratory Animal Care accredited research laboratory. Animals: Pound source mongrel dogs being used in 4 separate hemorrhage and resuscitation studies, the objectives of which were unaffected by the PCO₂ monitoring. Interventions: Fiber‐optic PCO₂ monitoring systems were used to simultaneously monitor subcutaneous (n=8), sublingual (n=8) PCO₂, and intraluminal esophageal (n=10), gastric (n=27), duodenal (n=16), jejunal (n=8), and ileal (n=7) PCO₂ of 28 dogs used in 4 hemorrhage and resuscitation studies. Measurements and main results: The tissue or intraluminal PCO₂ at all sites increased in response to hemorrhage. The rate and magnitude of esophageal, gastric, duodenal, jejeunal, and ileal intraluminal PCO₂ varied widely between dogs for the same site and between sites in the same dog. Different gastrointestinal sites also responded differently to resuscitation. The rate and magnitude of changes in subcutaneous and sublingual PCO₂ values were lower than those in the other tissues examined. The mean and maximum coefficients of variation for each site were as follows: subcutaneous 9%, 31%; sublingual 10%, 23%; esophageal 15%, 40%; gastric 26%, 90%; duodenal 25%, 70%; jejunal 25%, 95%; and ileal 34%, 87%. Conclusions: At different tissue sites, PCO₂ values do not respond equivalently to either hemorrhage or resuscitation. One site cannot, therefore, be reliably used to indicate the energy status of an alternate site.     

Growth and pathogenicity of isolates of the fungus Metarhizium anisopliae against the parasitic mite, Psoroptes ovis: effects of temperature and formulation

Psoroptes mites (Acari: Psoroptidae) are important ectoparasites of mammals, and are of particular economic significance as the agents of mange in sheep. To be effective against mites, putative fungal biocontrol agents must be able to operate at the relatively high temperatures and humidities found at the sheep skin surface. To consider this, the growth rates of different isolates of the entomopathogenic fungus Metarhizium anisopliae (Metschnikoff) Sorokin (Deuteromycotina: Hyphomycetes) were compared and the pathogenicity of these isolates against Psoroptes derived from rabbits (Psoroptes ovis Hering, syn P cuniculi) were evaluated at temperatures between 28 degrees C and 40 degrees C, and when formulated in either Tween 80 or silicone oil. For this study four multi-conidia, arthropod-derived, isolates of M anisopliae were used: from the USA, France, Denmark and Brazil. One single-conidia culture derived from the US isolate was also included in the investigation. Fungal growth was higher at the lower temperatures and none of the isolates grew at 40 degrees C. The growth of the US and single-conidia isolate declined markedly with temperature. In contrast, the Danish, French and Brazilian isolates grew almost as well at 32 degrees C and 35 degrees C as at 28 degrees C and 30 degrees C. The French and Brazilian isolates showed some growth at 37.5 degrees C but the Danish and US isolates did not. The number of fatal infections which resulted from exposure of mites to the fungal isolates was also strongly influenced by temperature. At 30 degrees C all isolates gave between 70 and 90% infection. The number of infections declined with increasing temperature and no infections were seen at 40 degrees C. However, the French and Danish isolates of M anisopliae gave higher numbers of infections than the other isolates at elevated temperatures. When formulated in silicone oil, significantly higher levels of infection were obtained than when formulated in Tween 80, even at the relatively high temperature of 37.5 degrees C. It is suggested that high-temperature adapted isolates of M anisopliae formulated in silicone oil offer good candidates as control agents under the conditions found at the sheep skin surface.     

One Mars year: viking lander imaging observations

Throughout the complete Mars year during which they have been on the planet, the imaging systems aboard the two Viking landers have documented a variety of surface changes. Surface condensates, consisting of both solid H(2)O and CO(2), formed at the Viking 2 lander site during the winter. Additional observations suggest that surface erosion rates due to dust redistribution may be substantially less than those predicted on the basis of pre-Viking observations. The Viking 1 lander will continue to acquire and transmit a predetermined sequence of imaging and meteorology data as long as it is operative.