Negative spatial association between lymphatic filariasis and malaria in West Africa.

Objective To determine the relationship between human lymphatic filariasis, caused by Wuchereria bancrofti, and falciparum malaria, which are co-endemic throughout West Africa. Methods We used geographical information systems and spatial statistics to examine the prevalence of lymphatic filariasis in relation to malaria prevalence, mosquito species distributions, vegetation and climate. Results A negative spatial association between W. bancrofti and falciparum malaria prevalence exists. Interspecies competition between parasites, seasonality, differences in the distribution and vector competence of Anopheles vectors, agricultural practices and insecticide resistance may be factors driving current (and potentially future) spatial distributions. Conclusion Further investigating these factors will become crucial as large-scale lymphatic filariasis and malaria control programmes are implemented in West Africa that may influence the epidemiology of both diseases

Negative Spatial Association Between Lymphatic Filariasis and Malaria in Africa

Human lymphatic filariasis (LF), caused by Wuchereria bancrofti, is a disabling parasitic disease endemic throughout sub-Saharan Africa. A detailed inter-country study in West Africa using a grid sampling technique for the rapid assessment of LF distribution has demonstrated that W. bancrofti prevalence varies considerably throughout Benin, Burkina Faso, Ghana and Togo. Here we show, using geographic information systems (GIS) and spatial statistics that a robust negative association between LF and malaria prevalence exists. This is a surprising finding, given that in rural West Africa both diseases are transmitted by mosquitoes of the Anopheles gambiae complex. A key factor distinguishing the two disease epidemiologies may be the different distributions and vector competence of the An. gambiae cytoforms. Alternatively interspecies competition between the parasites, with W. bancrofti being more dominant where malaria transmission is more seasonal, may drive the spatial distributions. Differentiating between the various hypotheses may become crucial as large-scale LF and malaria control programmes are implemented in West Africa that may impact on the epidemiology of both diseases.

Search for excited neutrinos in Z decay

Excited neutrinos decaying into a neutrino and a photon are searched for in the ALEPH detector at LEP. No evidence is found for Z decay into v̄v∗ or v̄∗v∗ final states. Upper limits are derived on excited neutrino couplings up to excited neutrino masses close to the Z mass. Lower limits on the v∗ mass, independent of the v∗ decay modes, are deduced from the total Z width

Search for a very light Higgs boson in Z decays

A search has been made for a very light Higgs boson in the processes e+e- → e+e-H and e+e- →μ+μ-H using data collected by ALEPH at the LEP e+e- collider at centre of mass energies close to the Z peak. The mass range between 0 and 57 MeV is unambigously excluded at the 95% confidence level. If we combine this with our previously published analysis, the complete range from 0 to 24 GeV is excluded at 95% CL. The search is extended to light Higgs bosons of the minimal supersymmetric standard model, with the result that all possibilities of coupling are excluded for Higgs masses below 3 GeV

Determination of the leptonic branching ratios of the Z

The ratios of the numbers of Z bosons decaying to e+e−, μ+μ− and τ+τ− pairs to the number decaying to hadrons have been measured. The branching ratios and partial widths for each channel were determined and found to be equal, consistent with lepton universality. The mean leptonic branching ratio was found to be 0.0321 ± 0.0013 and the leptonic partial width to be 85.4 ± 5.3 MeV. The partial widths for hadronic decays and for invisible decays were deduced to be 1833 ± 116 MeV and 569 ± 92 MeV, respectively. The number of light neutrino types, assuming only the standard model value for the ratio , was found to be 3.35 ± 0.41

Search for neutralino production in Z decays

Limits on Z decay branching ratios into neutralinos are reported. They were obtained from searches for monojets, acoplanar jets, acoplanar lepton pairs, single photons and acoplanar photon pairs as signaturs for the reactions e+e- → χχ′ and e+e- → χχ′, where χ is the lightest neutralino and χ′ any heavier one. The data sample used for these searches corresponds to about 23 000 events of Z decay into multihadrons, collected at LEP by the ALEPH detector for centre of mass energies at and near the Z peak. The results obtained are used to restrict the parameter space of the minimal supersymmetric standard model

Search for a new weakly interacting particle

A search for events of the type e+e−→ℓ+ℓ−X0, where X0 can be any weakly interacting particle which couples to the Z, has been performed with the ALEPH detector at LEP, by searching for acollinear lepton pairs. Such particles can be excluded up to a mass of 7.0 GeV/c2 for a value of the ratio of branching fractions, Br(Z→X0l+l−)/Br(Z→l+l−), greater than 2.5 × 10−3 if the X0 has third component of isospin, I3 greater than and decays to a pair of virtual gauge bosons. When this analysis is combined with the previous results of the Higgs particle searches from ALEPH, this limit can be extended to an X0 mass of 60 GeV/c2