Abstract:It is extremely likely that the malaria vaccines currently in development will be used in conjunction with treated bednets and other forms of malaria control. The interaction of different intervention methods is at present poorly understood in a disease such as malaria where immunity is more complex than for other pathogens that have been successfully controlled by vaccination. Here we develop a general mathematical model of malaria transmission to examine the interaction between vaccination and bednets. Count… Show more
“…Age-related shifts in the peak of infection by helminths have been reported for human populations (51,56) and also predicted for malaria under different levels of bednet coverage (57). This feature should also be common in farm and wild animals where host immunity plays an important role in parasite dynamics.…”
Global climate change is predicted to alter the distribution and dynamics of soil-transmitted helminth infections, and yet host immunity can also influence the impact of warming on host-parasite interactions and mitigate the long-term effects. We used time-series data from two helminth species of a natural herbivore and investigated the contribution of climate change and immunity on the longterm and seasonal dynamics of infection. We provide evidence that climate warming increases the availability of infective stages of both helminth species and the proportional increase in the intensity of infection for the helminth not regulated by immunity. In contrast, there is no significant long-term positive trend in the intensity for the immune-controlled helminth, as immunity reduces the net outcome of climate on parasite dynamics. Even so, hosts experienced higher infections of this helminth at an earlier age during critical months in the warmer years. Immunity can alleviate the expected long-term effect of climate on parasite infections but can also shift the seasonal peak of infection toward the younger individuals.long-term climate warming | seasonality | host-parasite interaction | gastrointestinal helminths | European rabbit T he marked progression of climate warming and intensification of extreme climatic events have been implicated in the increased prevalence of infections, epidemic outbreaks, and the geographical shifting of endemic foci of infections (1-3). Experimental manipulations of vectors and infective stages have shown that warming, coupled with increased variability in temperature, can influence the vital rates of the parasite and the immunophysiological characteristics of the host (4-9). Predictive models of infection dynamics have reinforced the importance of these findings by showing that the risk of infection and transmission are likely to increase with the projected temperature changes (10-15) and synchronous, unpredicted weather events (16), although exceptions have been reported (17)(18)(19). Despite these findings, the extent to which climate disruption is in fact having an effect on parasite infections in natural systems is far from clear, as nonlinear effects in the parasite-host relationship and confounding variables can be difficult to disentangle.The way climate change modifies the development and survival of vectors and infective stages, and the consequences for the contact rate between infective and susceptible individuals, has been the central focus of many of the predictions and trials. However, this approach ignores the contribution of variability in the response of the hosts, which we expect to be critical in regulating the parasite abundance and the changes in the transmission rate. Given that immunity to infections is an important source of variation among individuals (20-23), if climate increases exposure to parasites, do we expect a proportional increase in the intensity of infection in hosts that mount an immune response against these parasites? In other words, how does variatio...
“…Age-related shifts in the peak of infection by helminths have been reported for human populations (51,56) and also predicted for malaria under different levels of bednet coverage (57). This feature should also be common in farm and wild animals where host immunity plays an important role in parasite dynamics.…”
Global climate change is predicted to alter the distribution and dynamics of soil-transmitted helminth infections, and yet host immunity can also influence the impact of warming on host-parasite interactions and mitigate the long-term effects. We used time-series data from two helminth species of a natural herbivore and investigated the contribution of climate change and immunity on the longterm and seasonal dynamics of infection. We provide evidence that climate warming increases the availability of infective stages of both helminth species and the proportional increase in the intensity of infection for the helminth not regulated by immunity. In contrast, there is no significant long-term positive trend in the intensity for the immune-controlled helminth, as immunity reduces the net outcome of climate on parasite dynamics. Even so, hosts experienced higher infections of this helminth at an earlier age during critical months in the warmer years. Immunity can alleviate the expected long-term effect of climate on parasite infections but can also shift the seasonal peak of infection toward the younger individuals.long-term climate warming | seasonality | host-parasite interaction | gastrointestinal helminths | European rabbit T he marked progression of climate warming and intensification of extreme climatic events have been implicated in the increased prevalence of infections, epidemic outbreaks, and the geographical shifting of endemic foci of infections (1-3). Experimental manipulations of vectors and infective stages have shown that warming, coupled with increased variability in temperature, can influence the vital rates of the parasite and the immunophysiological characteristics of the host (4-9). Predictive models of infection dynamics have reinforced the importance of these findings by showing that the risk of infection and transmission are likely to increase with the projected temperature changes (10-15) and synchronous, unpredicted weather events (16), although exceptions have been reported (17)(18)(19). Despite these findings, the extent to which climate disruption is in fact having an effect on parasite infections in natural systems is far from clear, as nonlinear effects in the parasite-host relationship and confounding variables can be difficult to disentangle.The way climate change modifies the development and survival of vectors and infective stages, and the consequences for the contact rate between infective and susceptible individuals, has been the central focus of many of the predictions and trials. However, this approach ignores the contribution of variability in the response of the hosts, which we expect to be critical in regulating the parasite abundance and the changes in the transmission rate. Given that immunity to infections is an important source of variation among individuals (20-23), if climate increases exposure to parasites, do we expect a proportional increase in the intensity of infection in hosts that mount an immune response against these parasites? In other words, how does variatio...
“…(Figure 1 shows the compartmental framework for the epidemiological model). This is a simplistic representation of immunity in accordance with many other contemporary models of malaria [33]. If the projected impacts of endectocide-treated cattle on malaria immunity in humans were to be investigated, a significantly more complex model structure would be required.Fig.…”
BackgroundMalaria is spread by mosquitoes that are increasingly recognised to have diverse biting behaviours. How a mosquito in a specific environment responds to differing availability of blood-host species is largely unknown and yet critical to vector control efficacy. A parsimonious mathematical model is proposed that accounts for a diverse range of host-biting behaviours and assesses their impact on combining long-lasting insecticidal nets (LLINs) with a novel approach to malaria control: livestock treated with insecticidal compounds (‘endectocides’) that kill biting mosquitoes.ResultsSimulations of a malaria control programme showed marked differences across biting ecologies in the efficacy of both LLINs as a stand-alone tool and the combination of LLINs with endectocide-treated cattle. During the intervals between LLIN mass campaigns, concordant use of endectocides is projected to reduce the bounce-back in malaria prevalence that can occur as LLIN efficacy decays over time, especially if replacement campaigns are delayed. Integrating these approaches can also dramatically improve the attainability of local elimination; endectocidal treatment schedules required to achieve this aim are provided for malaria vectors with different biting ecologies.ConclusionsTargeting blood-feeding mosquitoes by treating livestock with endectocides offers a potentially useful complement to existing malaria control programmes centred on LLIN distribution. This approach is likely to be effective against vectors with a wide range of host-preferences and biting behaviours, with the exception of species that are so strictly anthropophilic that most blood meals are taken on humans even when humans are much less available than non-human hosts. Identifying this functional relationship in wild mosquito populations and ascertaining the extent to which it differs, within as well as between species, is a critical next step before targets can be set for employing this novel approach and combination.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-017-1748-5) contains supplementary material, which is available to authorized users.
“…We are still struggling to conquer malaria, but now have at our disposal some very sophisticated methods of attacking the mosquito vectors, such as with bacterial larvicides and entomopathogenic fungi; new drugs like artemisinin have replaced those to which the parasite has become resistant, and candidate malaria vaccines are reaching a new stage of maturity. An important question to pose at this stage is how some of these control strategies will combine in their impact and, in PNAS, Artzy-Randrup et al (2) warn that bednets and vaccines may interact in ways that either make the situation a whole lot better (synergistically) or actually much worse (antagonistically), depending on which stage of the malaria life cycle the vaccine targets.…”
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confidence: 99%
“…The vaccines and bednets may act in concert to diminish the availability of susceptibles as well as to reduce the per capita rate of infection, thereby tipping the system into negative growth. In contrast, vaccine-induced immunity against the blood stages may neither prevent infection nor impact on onward transmission, and Artzy-Randrup et al (2) emphasize that, under these circumstances, blood-stage vaccines will offer very little other than personal protection against clinical symptoms. This result is certainly possible, although many blood-stage antigens bear the signature of immune selection (3, 4), suggesting that antibodies against them have some impact on the success of the parasite.…”
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confidence: 99%
“…As ArtzyRandrup et al (2) are careful to point out, malaria is a complex clinical phenomenon that cannot be linked to parasite densities or past exposure in a simple way. Immunity Fig.…”
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