Zoogeographical distribution amplifier
Figure 1. Horseshoe bats. A, Indonesian horseshoe bat Rhinolophus sp. Indeed, it is a vast country whose varied climates give rise to a great diversity of bats and viruses Table.
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Metrics details. Animal hosts may vary in their attraction and acceptability as components of the host location process for assessing preference, and biting rates of vectors and risk of exposure to pathogens. However, these parameters remain poorly understood for mosquito vectors of the Rift Valley fever RVF , an arboviral disease, and for a community of mosquitoes.
Using three known livestock amplifiers of RVF virus including sheep, goat and cattle as bait in enclosure traps, we investigated the host-feeding patterns for a community of mosquitoes in Naivasha, an endemic area of Rift Valley fever RVF , in a longitudinal study for six months June—November We estimated the incidence rate ratios IRR where mosquitoes chose cow over the other livestock hosts by comparing their attraction total number collected and engorgement rate proportion freshly blood-fed on these hosts.
Despite the overall attractive pattern to feed preferentially on cows, the engorgement rate was clearly independent of the number attracted for certain mosquito species, notably among the flood water Aedes spp.
Our findings suggest that insecticide treated cattle ITC can be exploited in enclosure traps as contact bait in the monitoring and control of disease-causing mosquitoes in RVF endemic areas.
The foraging behaviour of disease vectors controls the opportunities for infection and transmission of pathogens that cause vector-borne diseases [ 1 ]. The emergence of zoonotic arbovirus diseases is intimately linked to the range of blood hosts that may be fed upon by vectors such as mosquitoes [ 2 ]. As such, assessment of host blood feeding preference is of ecologic and epidemiological value for arboviral zoonoses such as Rift Valley fever RVF , a disease of public and veterinary health importance transmitted by mosquitoes.
Despite the isolation of the causative agent, RVF virus, from so many mosquito species [ 3 — 5 ], knowledge of their blood- feeding patterns on potential vertebrate hosts remains poor and is only just beginning to be appreciated. A number of methods have been employed to examine the host preferences of RVF mosquitoes. Earlier studies employed biochemical and molecular identification of host source from blood in naturally engorged mosquitoes sampled using traps [ 6 , 7 ]. Evaluation of host preference based on trap captures of mosquito vectors is limited because certain important species may not be readily collected in traps.
While this points to the inefficiency of traps to representatively sample different species, this observation inadvertently fails to add much to our knowledge of the host feeding patterns of Culex spp. Additionally, earlier studies on host preference have narrowly focused on selected flood water Aedes spp. Aedes mcintoshi and Aedes ochraceus , in a specific geographic area. However, similar data remains wanting for other important species given that mosquito species incriminated in virus transmission vary from region to region [ 5 ] and not necessarily the floodwater Aedes spp.
A number of samples processed for blood meal analyses may largely remain unidentified using biochemical and molecular means likely to be affected by integrity of the sample, quality and quantity of the DNA following blood meal digestion and specificity of the associated gene target [ 8 ].
Behavioural observations using choice assays in the field may provide a more objective tool for assessing host preference [ 9 ]. These competitive experiments may often represent what a mosquito experiences in nature when a host-seeking mosquito encounters more than one potential host source.
Within this context, animal-baited trapping systems may be applicable to examine host associations of animal-biting insects and to determine the seasonal activity or geographic distribution of these insect species [ 10 ]. Animal-baited traps provide olfactory cues from hosts for attraction of mosquitoes [ 10 , 11 ] and often overcome inherent biases from conventional mosquito traps and attractants. Using such methods the possibility of collecting host specific mosquitoes not readily encountered in conventional traps remains high.
For instance, collections of mainly ornithophilic species of Culex or Culiseta has been achieved by baiting traps with birds [ 12 , 13 ], which are not readily collected in conventional traps [ 14 ]. For vector species, animal-baited trapping is also useful for measuring parameters of pathogen transmission, including host feeding preference and host biting rate [ 10 ]. In a related study, animal skin host cues have been used as bait in conventional traps to evaluate host preference of RVF mosquitoes in the field [ 11 , 15 ].
However, this approach is only suitable for host-attraction studies and provides no measure of engorgement. In studies of host preference the final criterion of host selection is taking a blood meal and the most epidemiological significant end point [ 16 , 17 ]. Animal species may vary in attraction and acceptability and the knowledge is important in determining vector biting rates and exposure to pathogens and for risk assessment among farm animals.
These parameters were also not monitored in a study using humans and calves as bait to evaluate the biting habits of mosquitoes associated with flooded dambos with particular interest in flood water Aedes , incriminated as primary RVF vectors [ 18 ]. Although livestock hosts cow, sheep and goat serve as amplifiers for RVF virus [ 19 ], we posit that the feeding parameters, attraction and engorgement, vary for a community of mosquitoes that could likely predispose them to differential risk of or source of infection.
Hence, their assessment may help identify the biting pressure and the mosquito species feeding on these domestic animals and identify those most likely to transmit pathogens. Of epidemiological value, the highly attractive and acceptable host is the individual with the greatest potential exposure to risk of infection with RVF and possibly other mosquito-borne disease agents.
Such an attractive host also serving as amplifier could facilitate enhanced transmission through infection of efficient and inefficient mosquito vectors. This knowledge can potentially be exploited in mitigation strategy against this disease to target the vectors given that effective vaccine or therapeutic treatments are lacking.
Naivasha is located in Nakuru County at an altitude of 1, m above sea level with an estimated , inhabitants as per the census.
The vegetation is characterized by patterns of shrub savannah, shrub and bush land and irrigated cropland. Among the inhabitants are the indigenous Masai who are predominantly pastoralists while the immigrants practice rain-fed and irrigated farming that includes the large multinational owned flower and horticulture farms nestled along the shores of Lake Naivasha, taking advantage of the fertile volcanic soils.
The horticulture farming forms the main agricultural activity in the area, which is also rich in wildlife. We used cow Bos taurus , sheep Ovis aries and goat Capra hircus as bait in an enclosure trap comprising a cage measuring 1. During each experiment, the enclosure trap was placed over each bait animal, which was restrained at the centre in an iron cage that allowed the animal space to freely move around Fig.
Animals were placed in their respective cages at h; thereafter, a side slot was opened, allowing host-seeking mosquitoes access to the animal baits. Experimental set up showing a animal cow restrained inside a cage and b enclosure trap with an opening for access of host-seeking mosquitoes to the animal.
Mosquitoes were then collected with a battery-powered backpack aspirator with the aid of a flashlight from the interior wall of the enclosure netting. Daily experiments comprised of using each animal as bait replicated over 8 days and typically conducted in the last week of every month from June to November During each experimental night, the animal-baited traps were placed at least 50 m apart employing a Latin square design in the trap placement in a uniform area in terms of vegetation cover.
These animals were randomly selected from a herd of the same species usually held in pens throughout the night in the farm after grazing during the day accompanied by 1 or 2 herdsmen after which they returned to their homes 2—3 km away. The animals used were about a year old for goat and sheep just as the case of the calf cow , which was easy to handle.
Experiments were conducted 1 km from the pens where they are normally held at night. Trapped mosquitoes were knocked down using triethylamine TEA and stored in liquid nitrogen. Engorgement was determined by the distended abdomens and appearance of visible red blood coloration of engorged mosquitoes [ 24 ]. Partially engorged individuals were also classified as engorged. Data were analysed using R version 3. Data on the overall mosquito counts were compared using Chi - square test and a Generalized Linear Model GLM by fitting a quasipoisson for all mosquito species combined and separately for select species, with mosquito abundance as the only factor in the model after controlling for sampling period.
We computed the diversity of community of mosquitoes by estimating and comparing the Shannon's diversity index using ANOVA by specifying the sampling period and total counts as explanatory variables. Overall number of engorged mosquitoes and for species fairly represented across the sampling periods out of the total sampled for each month was analysed using a Generalized Linear Model GLM with quasibinomial error and log link.
Incidence rate ratios IRR and corresponding confidence interval CI were estimated against a reference category from a select animal type. Chi - square goodness-of-fit was used to compare the proportion engorged among the animal types for species not represented each sampling month. Informed consent was obtained from the owner of the farm after explaining the background and objectives of the study. A total number of 2, mosquitoes belonging to twenty-seven species in five genera were collected.
Of these, 1, were found to be engorged with an overall engorgement rate of The total number collected and number engorged for each species is presented in Table 1. Aedes dentatus , Culex pipiens , Culex vansomereni , Anopheles gambiae and Anopheles funestus were the most abundant species in their respective genera.
The number of mosquitoes attracted and the percentage engorged from each host showed that overall, most species preferred cattle over sheep or goat Table 1. While the data suggest less preference for the small ruminants goat and sheep , these end points varied depending on the species. Overall, attraction was highest for cow 1, followed by goat and sheep , which was also reflected in the engorgement rate with cow recording the highest Data summary for the total number of mosquitoes attracted and percentage engorged for each sampling period and animal used are presented in Table 2.
In studies of host preference the final criterion of host selection is taking a blood meal [ 16 ]. Our analyses showed significantly higher numbers of An.
An analogous pattern was observed for An. No significant difference among the animals in the proportion of engorged Ae. This was the case for Cx. Among the important Culex spp. Also within the category of flood water Aedes mosquitoes known to contain the primary RVF vectors, Aedes dentatus was dominant with only low occurrence of Aedes mcintoshi and Ae.
Moreover, Ae. Our results show that overall, attraction and engorgement rates were at least three fold higher for cow than goat or sheep. Mosquitoes find their hosts mainly through orientation to olfactory stimuli emanating from the host [ 33 ]. Our data suggest that the relatively larger size of the cow compared to the small ruminants sheep and goat could account for the cow releasing larger emissions of CO 2 , which act as a long distance attractant for host seeking mosquitoes [ 11 , 34 ].
However, we found that the engorgement rate was clearly independent of the number attracted for certain mosquito species. This suggests that other factors such as host specific odours may contribute to the overall attraction of the host as has been shown in related studies [ 11 , 34 ].
This pattern was very evident for most of the flood water Aedes spp. This was the case for the species Ae. Previous observations based on blood meal analysis have documented preferential feeding of flood water species of Aedes Ae. However, a related recent study has shown that some of these flood water Aedes spp. The finding that attraction and feeding success among these hosts did not vary suggest that feeding preference for these flood water Aedes spp.
This behaviour could potentially contribute to reproduction and effective survival of these mosquito species regardless of the local host population. Most Culex spp. While attraction of Culex spp. Among the Culex spp. This clearly indicates that attraction does not always translate into feeding success. Although a number of Culex spp. This could justify the role of some of these species as secondary vectors of RVFV acting as bridge vectors to extend infection even to humans given the commonality in host attractive cues among these mammals [ 15 , 38 ].
The increasing association of Anopheles mosquitoes with arboviruses is of concern. RVFV and other arboviruses of medical importance such as Ngari virus, O'nyong-nyong, have been isolated from species such as Anopheles gambiae and Anopheles funestus , Anopheles coustani , Anopheles squamosus mosquitoes [ 3 , 5 , 39 — 41 ].
The finding confirms their high ability to feed on animals. This result may contrast earlier findings that have suggested high degrees of anthropophily [ 8 , 42 — 44 ], a pattern that is likely biased by collections indoors or outdoors where humans and animals are dominant, respectively. Our findings, however, confirm their high ability to feed on animals especially on cows, although this may be associated with only certain species within the complexes that we did not delineate which is only possible via molecular means.
Our experimental design using animals allowed us to trap certain species in high numbers not readily collected using light traps.
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Origin and cross-species transmission of bat coronaviruses in China
Fragment shape and size, landscape permeability and fragmentation level as predictors of primate occupancy in a region of Brazilian Cerrado. Acta Scientiarum. Biological Sciences , vol. Abstract: Human activities result in the formation of a mosaic of forest patches within a non-habitat matrix. The response of the local biodiversity to changes in land-use may occur at different scales. It is important to evaluate the effects of the attributes of both the patches and the surrounding landscape on the occupancy of forest patches by animal populations. We used playback to survey primate populations in 22 focal patches and assessed the landscape within a m buffer zone around each site. Focal patch size and the permeability of the matrix were the principal determinants of the occupancy of..
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Skip to search form Skip to main content Skip to account menu You are currently offline. Some features of the site may not work correctly. DOI: Sellers Published 1 August Medicine, Biology The Journal of hygiene The spread of insect-borne animal virus diseases is influenced by a number of factors. Hosts migrate, move or are conveyed over long distances: vectors are carried on the wind for varying distances in search of hosts and breeding sites; weather and climate affect hosts and vectors through temperature, moisture and wind.
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Metrics details. Animal hosts may vary in their attraction and acceptability as components of the host location process for assessing preference, and biting rates of vectors and risk of exposure to pathogens. However, these parameters remain poorly understood for mosquito vectors of the Rift Valley fever RVF , an arboviral disease, and for a community of mosquitoes. Using three known livestock amplifiers of RVF virus including sheep, goat and cattle as bait in enclosure traps, we investigated the host-feeding patterns for a community of mosquitoes in Naivasha, an endemic area of Rift Valley fever RVF , in a longitudinal study for six months June—November We estimated the incidence rate ratios IRR where mosquitoes chose cow over the other livestock hosts by comparing their attraction total number collected and engorgement rate proportion freshly blood-fed on these hosts. Despite the overall attractive pattern to feed preferentially on cows, the engorgement rate was clearly independent of the number attracted for certain mosquito species, notably among the flood water Aedes spp. Our findings suggest that insecticide treated cattle ITC can be exploited in enclosure traps as contact bait in the monitoring and control of disease-causing mosquitoes in RVF endemic areas. The foraging behaviour of disease vectors controls the opportunities for infection and transmission of pathogens that cause vector-borne diseases [ 1 ].
discontinuous distribution
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A bipolar distribution is particularly characteristic of marine organisms: several marine invertebrates for example, mussels , marine fish the anchovy, Pacific saury, basking shark, and porbeagle , some mammals southern whale, gray dolphin , and many species of marine algae kelp and fucus. The occurrence of bipolar distribution is caused by the conditions that prevailed in the ice age, when the temperature in the tropics dropped and northern organisms were able to spread to the tropics and reach the southern hemisphere. Later when the temperature rose, these organisms died out in the tropics, thereby giving rise to an interrupted or noncontinuous range. This explanation of bipolar distribution was suggested by the Soviet scientist L.
Such a distribution is thought to indicate the great age of the group, with intermediate populations having become extinct. Collins Dictionary of Biology, 3rd ed. Hale, V. Saunders, J. Margham Mentioned in? References in periodicals archive?
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