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M Baylis

Publications and source records attributed to M Baylis.

At least 19 recordsLinked to original sources
PubMed2001

Prediction of areas around the Mediterranean at risk of bluetongue by modelling the distribution of its vector using satellite imaging.

Bluetongue is an infectious disease of ruminants caused by a virus transmitted by biting midges, one species of which, Culicoides imicola, is the major vector in the Old World. Following an epizootic of African horse sickness,a related disease, in Iberia and Morocco between 1987 and 1991, C imicola was trapped for two years at 44 sites in the affected region and models were developed for predicting the abundance of C imicola at these sites. Discriminant analysis was applied to identify the best model of three levels of abundance from 40 Fourier-processed remotely sensed variables and a digital elevation model. The best model correctly predicted the abundance level at 41 of the 44 sites. The single most important variable was the phase of the annual cycle of the normalised difference vegetation index. The model was used to predict the abundances of C imicola elsewhere around the Mediterranean and predicted high levels of abundance in many areas recently affected by bluetongue, including the Balearics, Sardinia, Sicily, eastern Greece, western Turkey, Tunisia and northern Algeria. The model suggests that eastern Spain, the island of Ibiza, the provinces of Lazio and Puglia in Italy, the Peloponnese and parts of northern Algeria and Libya may be at risk of bluetongue in 2001.

Animals↗
PubMed2001

The potential size and duration of an epidemic of bovine spongiform encephalopathy in British sheep.

Because there is a theoretical possibility that the British national sheep flock is infected with bovine spongiform encephalopathy (BSE), we examined the extent of a putative epidemic. An age cohort analysis based on numbers of infected cattle, dose responses of cattle and sheep to BSE, levels of exposure to infected feed, and number of BSE-susceptible sheep in the United Kingdom showed that at the putative epidemic peak in 1990, the number of cases of BSE-infected sheep would have ranged from fewer than 10 to about 1500. The model predicts that fewer than 20 clinical cases of BSE in sheep would be expected in 2001 if maternal transmission occurred at a rate of 10%. Although there are large uncertainties in the parameter estimates, all indications are that current prevalence is low; however, a simple model of flock-to-flock BSE transmission shows that horizontal transmission, if it has occurred, could eventually cause a large epidemic.

Age Factors↗
PubMed2001

Using climate data to map the potential distribution of Culicoides imicola (Diptera: Ceratopogonidae) in Europe.

Culicoides imicola, a vector of bluetongue virus and African horse sickness virus, is principally Afro-Asian in distribution, but has recently been found in parts of Europe. A logistic regression model based on climate data (temperature, saturation deficit, rainfall and altitude) and the published distribution of C. imicola in Iberia was developed and then applied to other countries in Europe, to identify locations where C. imicola could become established. The model identified three temperature variables as significant determinants of the distribution of C. imicola in Iberia (minimum of the monthly minimum temperatures, maximum of the monthly maximum temperatures and number of months per year with a mean temperature > or = 12.5 degrees C). The model indicated that under current conditions, the distribution of C. imicola in Spain, Greece and Italy could be extended and the vector could potentially invade parts of Albania, Yugoslavia, Bosnia and Croatia. To simulate the effect of global warming, temperature values in the model were increased by 2 degrees C. Under these conditions, the potential spread of C. imicola in Europe would be even more extensive.

African Horse Sickness↗
PubMed2000

The signature of scrapie: differences in the PrP genotype profile of scrapie-affected and scrapie-free UK sheep flocks.

The amino-acid sequence of the PrP protein plays an important role in determining whether sheep are susceptible to scrapie. Although the genetics of scrapie susceptibility are now well understood, there have been few studies of the PrP gene at the population level, especially in commercially farmed sheep. Here we describe the PrP genetic profiles of the breeding stock of four UK sheep flocks, comprising nearly 650 animals in total. Two flocks had been scrapie affected for about eight years and two were scrapie free. Scrapie-resistant PrP genotypes predominated in all flocks but highly susceptible genotypes were present in each case. The distribution of PrP genotypes was similar in the scrapie-affected and scrapie-free flocks. The former, however, showed a slight but significant skew towards more susceptible genotypes despite their previous losses of susceptible sheep. Surprisingly, this skew was apparent in younger, but not older, sheep. We suggest that these patterns may occur if sheep flocks destined to become scrapie affected are predisposed by a genetic profile skewed towards susceptibility. The age structure of the scrapie-affected flocks suggests that the number of losses attributable directly or indirectly to scrapie considerably exceeds that recognized by the farmers, and also that significant losses may occur even in sheep of a moderately susceptible genotype. Similar patterns were not detected in the scrapie-free flocks, indicating that these losses are associated with scrapie infection as well as genotype.

Age Factors↗
PubMed2000

Stabling and the protection of horses from Culicoides bolitinos (Diptera: Ceratopogonidae), a recently identified vector of African horse sickness.

The stabling of horses at night reportedly offers protection from African horse sickness and the most significant vector of the disease, Culicoides imicola Kieffer, has been shown to be exophilic. In certain high-lying regions of South Africa, however, C. bolitinos Meiswinkel, may be the major vector of the disease but its entry behaviour into stables is unknown. Accordingly, in the eastern Free State province of South Africa, light trap catches of C. bolitinos inside stables and outside, were compared. Two horse-baited stables, one traditional, and one modern, were used and combinations of stable (old/new), ceiling fans (on/off) and accessibility to Culicoides (stable doors open/closed or windows gauzed/ungauzed) were investigated as treatments. A total of 111,452 Culicoides of 26 species was collected on 60 trap nights; C. bolitinos was dominant (89.1% overall) with C. imicola second in abundance (2.9%). Outside catches were greater on warmer, drier, evenings but were suppressed by high wind speeds. Catches of C. imicola inside stables with doors open, or with windows ungauzed, were less than the numbers captured outside. In contrast, more C. bolitinos were caught in open stables than outside, i.e. open structures may protect horses from the exophilic C. imicola, but may increase attack rates from the endophilic C. bolitinos. The closing of doors and the gauzing of windows, however, led to a 14-fold reduction in numbers of C. bolitinos and C. imicola entering stables. A well-gauzed 'traditional' stable was as effective as a closed 'modern' stable. Ceiling fans had no suppressant effect.

African Horse Sickness↗
PubMed2000

Feeding behaviour of Glossina pallidipes and g. morsitans centralis on Boran cattle infected with trypanosoma congolense or T. vivax under laboratory conditions.

In field studies, tsetse flies (Diptera: Glossinidae) feed more successfully on cattle infected with Trypanosoma congolense Broden (Kinetoplastida: Trypanosomatidae) than on cattle infected with T. vivax Ziemann or uninfected cattle. Here we describe the first laboratory investigation of this phenomenon. In the first experiment, caged Glossina pallidipes Austen were fed for 1 and 5 min on a Boran steer infected with T. congolense clone IL 1180 and on an uninfected steer. Feeding success was recorded in this way five times over several weeks. The same protocol was subsequently used in three additional experiments with the following combinations: G. pallidipes and a steer infected with T. vivax stock IL 3913, G. morsitans centralis Machado and a steer infected with T. congolense, and G. morsitans centralis and a steer infected with T. vivax. The four experiments were replicated once, making eight experiments in total. In three experiments there was increased tsetse feeding success, measured at 1 min, after a steer became infected (T. congolense, two experiments and T. vivax, one experiment). Analysis of all data combined found no significant differences in tsetse feeding success on the different groups of cattle prior to infection, but after infection tsetse feeding success was significantly greater on the infected cattle (P< 0.001). Trypanosoma congolense infection led to a greater increase in tsetse feeding success than T. vivax infection. The increase in feeding success was not related to changes in the level of anaemia, skin surface temperature or parasitaemia. A possible explanation is the effects of trypanosome infection on cutaneous vasodilation and/or blood clotting in infected cattle. When allowed to feed for 5 min, nearly all tsetse engorged successfully and effects of cattle infection on feeding success were not found.

Animals↗
PubMed2000

Climate change: effects on culicoides--transmitted viruses and implications for the UK.

Changes in the distribution and abundance of insects are likely to be amongst the most important and immediate effects of climate change. We review here the risk that climate change poses to the UK's livestock industry via effects on Culicoides biting midges, the vectors of several arboviruses, including those that cause bluetongue (BT) and African horse sickness (AHS). The major old-world vector of BT and AHS viruses, C. imicola, occurs in southern Europe and will spread further north as global temperatures increase. It is unlikely, however, that in the foreseeable future it will reach and become established in the UK. As the distribution of C. imicola moves north, however, it may bring BT and AHS viruses into the range of other Culicoides species that are known to be competent vectors and which occur much further north. Once infected via this 'baton effect', these species may be able to spread the viruses over much of Europe, including the UK. Climate change may increase their vector competence further and will also increase the likelihood of viruses surviving from one year to the next. An additional risk is that the predicted increase in the frequency of short periods of hot temperatures may lead to the creation of novel vector species, by removing the barriers that in colder conditions make them refractory to viral infection.

African Horse Sickness↗
PubMed2000

Culicoides biting midges: their role as arbovirus vectors.

Culicoides biting midges are among the most abundant of haematophagous insects, and occur throughout most of the inhabited world. Across this broad range they transmit a great number of assorted pathogens of human, and domestic and wild animals, but it is as vectors of arboviruses, and particularly arboviruses of domestic livestock, that they achieve their prime importance. To date, more than 50 such viruses have been isolated from Culicoides spp. and some of these cause diseases of such international significance that they have been allocated Office International des Epizooties (OIE) List A status. Culicoides are world players in the epidemiology of many important arboviral diseases. In this context this paper deals with those aspects of midge biology facilitating disease transmission, describes the factors controlling insect-virus interactions at the individual insect and population level, and illustrates the far-reaching effects that certain components of climate have upon the midges and, hence, transmission potential.

Animals↗
PubMed1999

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Journal Article↗
PubMed1999

Estimation of survival rates in haematophagous insects.

Estimation of the survival rate through a gonotrophic cycle is an important factor in determining the vectorial capacity of a population of haematophagous insects in a disease cycle. Most methods used to calculate survival rates make stringent assumptions which may not be valid for all species. Birley and colleagues used a time series analysis of samples collected over several consecutive days, the lagged parous rate. Here, we use a simulation model to investigate (i) the length of data series needed and (ii) the consequences of failures in the assumptions of this method for the estimated survival rate. The accuracy of the estimated survival rate per cycle was high with sample periods of 10-100 days. The standard deviation (a measure of precision) decreased with the length of the sample period. When random sampling efficiency was included, the accuracy remained high but the estimates were less precise (larger standard deviations). If the sampling was biased in favour of either nulliparous or parous females, estimates of the survival rate were not accurate. The relationship between estimated survival rate, bias in collection, and true survival rate was non-linear. Thus, correction for the bias requires (i) prior knowledge of the direction and the severity of the bias and (ii) an independent estimate of the survival rate. This method of estimating survival rates is less accurate when the collection method is biased for or against parous females, although robust to other assumptions.

Animals↗
PubMed1999

A preliminary attempt to use climate data and satellite imagery to model the abundance and distribution of Culicoides imicola (Diptera: Ceratopogonidae) in southern Africa.

Abundances of Culicoides imicola, the insect vector of several livestock viruses, including bluetongue and African horse sickness, were recently published for 34 sites in southern Africa, together with associated climate data. Here, these data are analysed statistically in combination with certain satellite-derived variables, with the aim of developing predictive models of C. imicola abundance. Satellite-derived variables were the land surface temperature (LST, a measure of temperature at the earth's surface) and the normalised difference vegetation index (NDVI, a measure of photosynthetic activity). Two models were developed: (1) climatic variables only and (2) satellite-derived and climatic variables. For model I, the best model used a single predictor variable (the mean daily minimum temperature) only, and accounted for nearly 34% of the variance in C. imicola abundance. Two variable climatic models did not perform significantly better. For model II, the best 1-variable model used the annual minimum LST as a predictor of C. imicola abundance, and accounted for nearly 40% of the variance in C. imicola abundance. The best 2-variable model, which gave a significantly better fit than the 1-variable model, combined the minimum LST and minimum NDVI as predictors of C. imicola abundance, and accounted for nearly 67% of variance. A map of predicted C. imicola abundances is produced on the basis of this 2nd model which, despite some anomalies, agrees largely with what is currently known of the prevalence of C. imicola in the region.

Africa, Southern↗
PubMed1998

The Culicoides vectors of African horse sickness virus in Morocco: distribution and epidemiological implications.

African horse sickness (AHS) is a vector-borne, infectious disease of equids caused by African horse sickness virus. The only proven field vector of the virus is the biting midge Culicoides imicola, although C. obsoletus and C. pulicaris are suspected vectors. In 1994-5 a total of 3887 light trap samples were collected from 22 sites distributed over most of Morocco. Culicoides imicola was found to be very widely distributed with the greatest catches in the low-lying north-western areas (between Tangier and Rabat) and at Marrakech. Culicoides imicola was absent at one site only, near Settat. In general, the catch of C. imicola peaked in late summer and autumn, with a smaller peak in spring. Catches of C. obsoletus were greatest in the north-western provinces of Morocco and in the south, while catches of C. pulicaris were greatest in the north. Although both species were widely distributed, trap catches were much lower than those of C. imicola. Peak catches were in spring or late summer and autumn. In general, the findings for C. imicola correspond well with the seasonal and spatial distribution of disease outbreaks during the 1989-1991 epizootic of AHS in Morocco. It is suggested that C. obsoletus and C. pulicaris were probably of little significance in the epidemiology of AHS in Morocco in 1989-91.

African Horse Sickness↗
PubMed1998

Studies of the mortality rate of Culicoides imicola in Morocco.

Daily mortality rates of female Culicoides imicola were found for eight sites in Morocco in 1994 and for six sites in 1995. The mortality rates were found by operating Pirbright-type light traps for a number of consecutive nights in late summer or autumn and finding the parous rate assuming a feeding interval of 3 to 5 days. The mortality rates were calculated according to established methods. In Morocco the daily mortality rates were found to vary from about 5% per day (Arbaoua, 1994, 1995 and Sidi Moussa 1995) up to 20-25% per day (Berkane, Marrakech, Tangier). In general, estimates of daily mortality rate were consistent between the two years of study. Among sites, daily mortality rate was significantly correlated with the average night-time minimum wind speed but not mean or maximum night-time wind speeds, or with temperature, humidity or saturation deficit. The observed mortality rates suggest that at Arbaoua, were 1,000 flies to become infected with African horse sickness virus, at least 330 would live long enough to take 3 or more infective blood meals on hosts. At Berkane, the survival rate per 1,000 is less than 10. In general, the pattern observed for daily mortality rate, combined with the relative population sizes of C. imicola in Morocco, agree well with the observed distribution of African horse sickness in the country during the 1989-1991 epizootic.

Animals↗