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M Baylis

Publications and source records attributed to M Baylis.

At least 19 recordsLinked to original sources
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↗
PubMed1998

Modelling the distribution and abundance of Culicoides imicola in Morocco and Iberia using climatic data and satellite imagery.

Relative abundances of Culicoides imicola at 22 sites in Morocco were compared with climatic variables, altitude and the NDVI (Normalised Difference Vegetation Index, a satellite derived measure of photosynthetic activity) of the same sites. Abundances were negatively correlated with wind speed and positively correlated with the average and minimum NDVI (NDVImin). There were no significant correlations with air or soil temperatures, relative humidity, saturation deficit, rainfall, altitude or mean annual maximum or range of NDVI. The best 2-variable model, which combined wind speed and NDVImin as predictors, explained over 50% of the variance in abundance. It is suggested that wind speed affects the abundance of C. imicola by causing adult mortality while NDVImin provides a measure of the availability of C. imicola breeding sites. Data from 27 sites in Iberia yielded broadly similar results to those found in Morocco although the great abundance of C. imicola at Milfontes (Portugal) could not be accounted for. Several northern sites where the NDVImin is sufficiently high to suggest the presence of C. imicola but where it appears to be absent indicate that there may be a northern limit to the distribution of C. imicola in Iberia that is independent of NDVImin. The potential use of NDVImin to predict the distribution of outbreaks of African horse sickness was investigated using data from the 1989-1990 epizootic in northern Morocco. Within the cluster of outbreaks in Larache province is a corridor of very low NDVImin in which few or no outbreaks were reported.

African Horse Sickness↗
PubMed1998

Effect of temperature on African horse sickness virus infection in Culicoides.

This paper shows that both the infection rate and the rate of virogenesis of African horse sickness virus (AHSV) within vector Culicoides are temperature dependent. As temperature is reduced from permissive levels the lifespan of the vector itself is extended but the rate of virogenesis decreases and infection rate falls dramatically so that at 10 degrees C virtually all midges are free from virus by 13 days post infection (dpi). When vectors that had been kept at this temperature for 35 days were moved to a permissive temperature for 3 days; however, the apparent zero infection rate increased to 15.5%. It therefore appears that at low temperature (< or = 15 degrees C) AHSV does not replicate but virus may persist in some vectors at a level below that detectable by traditional assay systems and when the temperature later rises to permissive levels virus replication is able to commence. On the basis of this information an overwintering mechanism for AHSV is suggested. The temperature at which the immature stages of Culicoides are reared may also influence infection with AHSV. A 5-10 degrees C rise in larval developmental temperature resulted in an increase in oral infection rate of a normally non-vector species of Culicoides, from < 1% to > 10%. A mechanism is suggested.

African Horse Sickness Virus↗
PubMed1998

Use of climatic data and satellite imagery to model the abundance of Culicoides imicola, the vector of African horse sickness virus, in Morocco.

African horse sickness (AHS) is a vector-borne, infectious disease of equids caused by African horse sickness virus (AHSV). The only proven field vector of the virus is the biting midge Culicoides imicola. Following a recent epizootic (1989-91) of AHS in Morocco, light traps and automatic weather stations were operated for 2 years at twenty-two sites distributed over much of the country. The annually-averaged mean daily trap catch of C. imicola at these sites was negatively correlated with wind speed, and positively correlated with the average and mean annual minimum NDVI (Normalized Difference Vegetation Index, a remotely sensed measure of vegetation activity). There were no significant correlations between the mean daily trap catch and air temperature, soil temperature, relative humidity, saturation deficit, rainfall, altitude or the mean annual maximum or range of NDVI. The best two-variable model, which combined WindspeedMnAvMn (the average daily minimum wind speed of the least windy month) and NDVImin (the average annual minimum NDVI) as predictors, explained over 50% of the variance in the annually-averaged mean daily trap catch of C. imicola. There was a significant, positive correlation between minimum wind speed at night and the daily mortality rate of adult female C. imicola and it is suggested that the relationship between wind speed and the abundance of C. imicola arises from effects on adult mortality or dispersal. Considering several climatic variables, in North Africa NDVImin was most significantly correlated with total annual rainfall. It is suggested that the relationship between NDVImin and the abundance of C. imicola arises from the impact of soil moisture on both. It is proposed that areas of Morocco with higher levels of soil moisture in late summer or autumn provide more, larger and/or more enduring breeding sites for C. imicola, as well as supporting more photosynthetically active vegetation and hence having higher NDVI.

African Horse Sickness Virus↗
PubMed1998

Activity patterns in Glossina longipennis: a field study using different sampling methods.

Studies n the daily activity of Glossina longipennis at Galana Ranch using a black odour-baited electrocuting target confirmed its crepuscular activity profile. Activity started at 05.00-05.30 hours and peaked at 06.00-06.30 hours, stopped by 09.00 hours, then started again at 17.00-17.30 hours with a peak at 18.30-19.00 hours, ceasing by 19.30 hours. Females made up 60% of the overall catch, and tended to arrive later than males. Other stationary sampling methods (trap, stationary ox) gave similar results. With the stationary methods, very few flies were caught outside the periods of peak activity (only 1.5% of the total between 09.00 and 17.00 hours); the ox was the only stationary bait to catch any flies between 10.00 and 16.00 hours. More flies were caught throughout the day at mobile baits (8.3% of the male and 2.3% of the female catch was taken between 09.00 and 17.00 hours). Mobile baits caught considerably more males than females (females were 17% of the catch). These males had on average higher fat and haematin reserves. Similar nutritional differences were not observed for females. There were fewer older females (ovarian category 3 or more) in mobile compared to stationary baits, and a lower proportion of the youngest males (wing fray category 1) at natural compared with artificial baits.

Age Factors↗
PubMed1998

Morphological confirmation of the separate species status of Culicoides (Avaritia) nudipalpis Delfinado, 1961 and C. (A.) imicola Kieffer, 1913 (Diptera: Ceratopogonidae).

Ten character states were used to compare five females and two males of two populations of C. nudipalpis from the Philippines and Timor in south-east Asia with 121 females and 167 males of 11 populations of C. imicola collected throughout its Afro-Asiatic range. It is concluded that they are closely related but good species, and together form a subgroup, or species-pair, in the imicola group; currently this Old World group of the subgenus Avaritia comprises seven described species. Culicoides nudipalpis and C. imicola are most reliably separated on the ratio of the length of the proboscis to the height of the head (P/H ratio: 0.66-0.73 in nudipalpis, 0.82-1.02 in imicola). Compared to C. imicola very little is known of the life habits of C. nudipalpis. The latter's close taxonomic relationship to C. imicola, a proven vector of African horse sickness (AHS) and bluetongue (BT), indicates that the capacity of C. nudipalpis to vector these orbiviruses deserves to be investigated.

Animals↗
PubMed1997

The daily feeding rate of tsetse (Diptera: Glossinidae) on cattle at Galana Ranch, Kenya and comparison with trypanosomiasis incidence.

At Galana Ranch, south-eastern Kenya, for 2 days each month from January to May 1993. Glossina pallidipes and G. longipennis were sampled around a heifer for 30 min every hour from 06:00 to 19:00. There was a seasonal decline in tsetse abundance; estimates of the total number attracted to the heifer in 1 day ranged from 556 G. pallidipes in January to 0 in May and 122 G. longipennis in February to 27 in May. The number of tsetse estimated to have fed on the heifer in 1 day during peak months was 260 G. pallidipes and 15 G. longipennis. Trypanosome infection rates of tsetse, obtained from trapped flies, suggest that the heifer received 1.1 T. congolense and 2.2 T. vivax-infected bites per day in January but only 0.007 T. congolense and 0.047 T. vivax-infected bites per day in May. These predictions are compared with the observed incidence of trypanosomiasis in a nearby herd of cattle. There was a linear relationship between the estimated daily rate of infected flies feeding on the heifer and the incidence of trypanosomiasis the following month. The slope of this relationship suggests that the transmission efficiencies of T. congolense and T. vivax from tsetse to cattle are 0.84 and 2.36%, respectively, considerably lower than has been reported elsewhere. Possible reasons for this are discussed and it is suggested that previous estimates may be too high.

Animals↗
PubMed1997

The spatial and seasonal distribution of African horse sickness and its potential Culicoides vectors in Morocco.

African horse sickness (AHS) is a vector-borne, infectious disease of equines that is caused by African horse sickness virus (AHSV). The only proven field vector is the biting midge Culicoides imicola, although C. obsoletus and C. pulicaris are suspected vectors. There was a recent epizootic of AHS in Iberia (1987-90) and Morocco (1989-91). In 1994-45 a total of 3887 light trap samples were taken from twenty-two sites distributed over most of Morocco. Culicoides imicola was found to be very widely dispersed, with the greatest catches in the low-lying northwestern areas (between Tangier and Rabat) and at Marrakech. Culicoides imicola was absent at one site only, near Settat. Culicoides imicola was found at altitudes ranging from 4 to 1275 m and in climatic conditions ranging from subhumid to saharan. In general, the catch of C.imicola peaked in late summer and autumn, with a smaller peak in spring. In areas where the insect appears most abundant at least one adult C.imicola per night may be caught in a light trap at all times of year, thus providing a possible means of viral overwintering. Culicoides obsoletus and C.pulicaris are also widely distributed in Morocco but trap catches were much lower than for C.imicola. Peak catches occurred in spring, and late summer and autumn. Other frequently caught species were C.circumscriptus, C.newsteadi, C.puncticollis and members of the odibilis subgenus. In general, the findings for C.imicola correspond well with the distribution of disease outbreaks during the epizootic. Although disease outbreaks were widespread in the country, the greatest number of reported cases was in the northwest (1989-90); in 1991 there were also significant numbers in Marrakech province. No cases were reported in a large area to the west of the Atlas mountains (including Settat) despite the presence of a large equine population. It is likely that during the epizootic the virus overwintered in the northwest (1989) and in Marrakech province (1990). Disease outbreaks occurred from July to December, with a peak from September to November. An unexplained phenomenon is the large number of reported cases of AHS in mules in Chefchaouen province in 1990, despite the apparent low abundance of C.imicola at a site at Chefchaouen. It is argued that C.obsoletus and C.pulicaris were probably of little significance to the epidemiology of AHS in Morocco in 1989-91.

African Horse Sickness↗
PubMed1996

The role of cattle as hosts of Glossina longipennis at Galana Ranch, south-eastern Kenya.

Glossina longipennis were recorded visiting and engorging on cattle in an enclosure and on a single ox in a crush using transparent electrocuting nets in an incomplete ring. Of the total flies caught, 3-6% of males and 5-6% of females in the total catches were engorged (a feeding success rate of up to 16.6% and 12.6%, respectively, depending on assumptions made about the proportion which had an opportunity to feed). Direct observation of tsetse from an observation pit showed 57% landing on the front legs, 13% on the hind legs, and 11% on the belly of the host. The largest number of bloodmeals was taken from the front legs, although only 14% of landings there terminated in feeding; a higher proportion of the flies alighting on the hind legs and flank succeeded in feeding (28% and 21% respectively). Glossina longipennis were attracted to targets baited with ox odour from an underground pit in a dose-dependent manner. Odour of humans was much less attractive to G. longipennis than that of oxen (for equivalent biomass). Analysis of bloodmeal samples from tsetse caught in two sites on the ranch showed that G. longipennis preferentially feeds on suids, bovids and hippopotamus.

Animals↗
PubMed1995

Feeding behaviour of tsetse flies (Glossina pallidipes Austen) on Trypanosoma-infected oxen in Kenya.

An incomplete ring of electric nets was placed around oxen which were either uninfected, infected with Trypanosoma vivax, or infected with T. congolense. The numbers of fed and unfed Glossina pallidipes caught on the nets were used to estimate the attractiveness of the oxen to tsetse, and the feeding success of the tsetse on the oxen. Oxen infected with T. congolense attracted more G. pallidipes than the other groups of oxen. Taking into consideration daily variation in the abundance or activity of the flies, oxen infected with T. congolense were about 70% more attractive to G. pallidipes than were uninfected oxen or oxen infected with T. vivax. The latter two groups mostly attracted high numbers of G. pallidipes on days when the flies were especially abundant or active. The feeding success of G. pallidipes declined with increase in the rate at which oxen made anti-fly movements. Taking this movement rate into consideration, the feeding success of G. pallidipes on oxen infected with T. congolense was approximately 60% greater than on uninfected oxen or oxen infected with T. vivax. It is suggested that vasodilation induced by T. congolense may account for the difference in feeding success. The level of parasitaemia of T. congolense or T. vivax was not found to affect either the attractiveness of oxen or the feeding success on oxen. There was significant daily variation in the mean fat content of male G. pallidipes caught around the oxen but not effect of mean daily fat content on the proportion of males that fed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗