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At least 19 recordsLinked to original sources
PubMed1992

Mathematical modelling and theory for estimating the basic reproduction number of canine leishmaniasis.

The paper describes a mathematical model for canine leishmaniasis and presents formulae which can be used to estimate the basic reproduction number, R0. The primary concern has been to devise methods of estimation which make best use of those data most easily obtained by fieldwork, e.g. surveys of prevalence in dog (by age) and sandfly populations. A range of formulae are offered which are more or less demanding of data, and which consequently give more or less precise estimates of R0. They include methods for assessing the influence on R0 of heterogeneous biting rates of sandflies on dogs, in which the essence of heterogeneous transmission can be captured merely by measuring relative rather than absolute contact rates.

Animals↗
PubMed1992

Epidemiology of canine leishmaniasis: prevalence, incidence and basic reproduction number calculated from a cross-sectional serological survey on the island of Gozo, Malta.

Assessment of the resilience of canine leishmaniasis to control or, more ambitiously, the effort needed to eradicate infection, requires an estimate of the basic case reproduction number (R0). This paper applies the theoretical results of Hasibeder, Dye & Carpenter (1992) to data from a cross-sectional survey on the Maltese island of Gozo in which dogs of known age, sex and occupation (pet, guard etc) were subjected to three different serological tests for the presence of specific antibody (IFAT, DAT and ELISA). Difficulties in interpreting these test results, and hence of determining the proportion of dogs infected, present the main obstacle to estimating R0: estimates are critically dependent on the choice of threshold separating seropositives from seronegatives. The data do, however, allow a robust comparative analysis of risk which shows that the force of infection experienced by working dogs is about three times higher than that of pet dogs, a degree of non-homogeneous contact which actually has little effect on estimates of R0. We suggest a cautious point estimate of R0 congruent to 11, and comment briefly on its significance for leishmaniasis control.

Age Factors↗
PubMed1991

Reproduction numbers and thresholds in stochastic epidemic models. I. Homogeneous populations.

We compare threshold results for the deterministic and stochastic versions of the homogeneous SI model with recruitment, death due to the disease, a background death rate, and transmission rate beta cXY/N. If an infective is introduced into a population of susceptibles, the basic reproduction number, R0, plays a fundamental role for both, though the threshold results differ somewhat. For the deterministic model, no epidemic can occur if R0 less than or equal to 1 and an epidemic occurs if R0 greater than 1. For the stochastic model we find that on average, no epidemic will occur if R0 less than or equal to 1. If R0 greater than 1, there is a finite probability, but less than 1, that an epidemic will develop and eventuate in an endemic quasi-equilibrium. However, there is also a finite probability of extinction of the infection, and the probability of extinction decreases as R0 increases above 1.

Computer Simulation↗
PubMed2026

Nipah virus in the era of global connectivity: molecular evolution, transmission risk, and preparedness strategies.

Nipah virus (NiV) is a highly pathogenic zoonotic RNA virus belonging to the genus Henipavirus within the family Paramyxoviridae, representing a continuing global health concern due to its high case fatality rate and potential for epidemic expansion in the era of increasing international connectivity. The virus demonstrates strong evolutionary adaptability driven by the absence of proofreading mechanisms during RNA replication, enabling genetic diversification that may influence host range, virulence, and transmission dynamics. Molecular pathogenesis of NiV is primarily mediated through interaction of viral glycoproteins with ephrin-B2 and ephrin-B3 receptors, facilitating host cell entry, endothelial damage, and neuroinvasion. Immune evasion facilitated by the action of accessory proteins encoded by the P gene (P, V, W, and C) acts to suppress innate antiviral immunity through the inhibition of interferon induction and JAK/STAT signaling. Human-to-human transmission of Nipah virus remains limited, with epidemiological evidence indicating basic reproduction numbers generally below unity; however, respiratory involvement and healthcare-associated exposure may enhance cluster outbreaks. Global travel, ecological disruption, and fragmented surveillance systems contribute to spillover risk, particularly in South and Southeast Asia where fruit bats of the genus Pteropus serve as natural reservoirs. Despite advances in vaccine technology, including subunit, viral vector, mRNA-based platforms, and monoclonal antibody therapies, no licensed prophylactic or therapeutic agent is currently available for human use. Global preparedness remains challenged by the scarcity of high-containment biosafety facilities, limited research funding, and absence of integrated One Health surveillance networks. Ethical considerations surrounding wildlife population control further complicate disease mitigation strategies. Emerging genomic surveillance, artificial intelligence-assisted predictive modeling, and regional data-sharing frameworks are essential for early detection and response. Strengthening molecular research on viral-host interactions and transmission determinants will be critical for preventing future Nipah virus outbreaks in an increasingly interconnected world.

Genomic surveillance↗
PubMed1991

An epidemiological model for the dynamics of Chagas' disease.

A model for the transmission dynamics of Chagas' disease is presented. The structure of the model is similar to that of the Ross-Macdonald model for malaria but includes an extra infectious compartment (chronically ill individuals) which is characteristic of Chagas' disease. In Chagas' disease there are two-main forms of transmission, by blood transfusion and by vector biting. The former is more common in urban environments and the latter is characteristic of rural settings. The characteristic long chronic (frequently asymptomatic) stage of Chagas' disease is potentially a risk factor that could enhance disease transmission by blood transfusion. The model evaluates the relative importance of both transmission modes in populations of constant size. The main results indicate that there is a strong tendency of the disease to reach an asymptotically stable endemic equilibrium point. Also, the magnitude of the basic reproductive number is very sensitive to the length of the chronic stage of the disease and hence it follows that early detection of cases (reducing the length of this stage) is important for the eventual eradication of the disease.

Animals↗
PubMed1991

A general solution of the problem of mixing of subpopulations and its application to risk- and age-structured epidemic models for the spread of AIDS.

A central aspect in the study of the dynamics of sexually transmitted diseases is that of mixing. The study of the effects of social structure in disease dynamics has received considerable attention over the last few years as a result of the AIDS epidemic. In this paper, we formulate a generalization of the Blythe and Castillo-Chavez social/sexual framework for human interactions through the incorporation of age structure, and derive an explicit expression in terms of a preference function for the general solution to this formulation. We emphasize the role played by proportionate mixing, the only separable solution to this mixing framework, through the discussion of several specific cases, and we formulate an age-structured epidemic model for a single sexually active homosexual population, stratified by risk and age, with arbitrary risk- and age-dependent mixing as well as variable infectivity. In the special case of proportionate mixing in age and risk, an explicit expression for the basic reproductive number is computed.

Acquired Immunodeficiency Syndrome↗
PubMed2026

The Re-Emergence of Bundibugyo Ebolavirus in Uganda and the Democratic Republic of Congo: Epidemiological Drivers, Response Strategies, and Implications for Global Health Security.

Bundibugyo ebolavirus (BDBV) is one of the least studied species within the genus Orthoebolavirus (family Filoviridae), despite its capacity to cause severe Ebola virus disease (EVD) with substantial mortality. First identified during a 2007-2008 outbreak in Bundibugyo District, western Uganda (149 reported cases, 37 deaths; case-fatality rate [CFR] approximately 25-36%), BDBV re-emerged in 2012 in Orientale Province, Democratic Republic of the Congo (DRC) (57-59 cases, 29-34 deaths; CFR 34-58%), before resurfacing in Ituri Province, DRC, in April-May 2026. By 11 August 2026, this third outbreak had grown to 4566 laboratory-confirmed cases and 2128 deaths (CFR ≈ 47%) across five DRC provinces and Uganda, becoming the largest, fastest-growing BDBV epidemic on record and the second-largest Ebola-family outbreak overall. This narrative review, not a systematic review or meta-analysis, summarizes peer-reviewed literature, preprints, and official situation reports from WHO, Africa CDC, US CDC, ECDC, and national health ministries, identified through PubMed, Scopus, Web of Science, Google Scholar, and Embase from inception to 12 August 2026, to examine BDBV historical evolution, virology and pathogenesis, drivers of re-emergence, surveillance and response, therapeutic and vaccine gaps, and global health security implications. The 2026 outbreak, unfolding amid conflict and mass displacement in eastern DRC, has been marked by an estimated basic reproduction number of 1.4-2.1 (central estimate 1.71), disproportionate infection among healthcare workers (7.2% of confirmed cases in DRC, 20% in Uganda), and the continued absence of licensed BDBV-specific vaccines or therapeutics. Findings underscore the need for sustained genomic and ecological surveillance, decentralized rapid diagnostics, broadly protective pan-filovirus vaccines, conflict-sensitive response strategies, and strengthened Uganda-DRC collaboration. Because the evidence base for the ongoing outbreak remains preliminary, findings should be interpreted cautiously and revisited as further peer-reviewed data emerge.

Bundibugyo ebolavirus↗
PubMed2025

Estimating Re and overdispersion in secondary cases from the size of identical sequence clusters of SARS-CoV-2.

The wealth of genomic data that was generated during the COVID-19 pandemic provides an exceptional opportunity to obtain information on the transmission of SARS-CoV-2. Specifically, there is great interest to better understand how the effective reproduction number [Formula: see text] and the overdispersion of secondary cases, which can be quantified by the negative binomial dispersion parameter k, changed over time and across regions and viral variants. The aim of our study was to develop a Bayesian framework to infer [Formula: see text] and k from viral sequence data. First, we developed a mathematical model for the distribution of the size of identical sequence clusters, in which we integrated viral transmission, the mutation rate of the virus, and incomplete case-detection. Second, we implemented this model within a Bayesian inference framework, allowing the estimation of [Formula: see text] and k from genomic data only. We validated this model in a simulation study. Third, we identified clusters of identical sequences in all SARS-CoV-2 sequences in 2021 from Switzerland, Denmark, and Germany that were available on GISAID. We obtained monthly estimates of the posterior distribution of [Formula: see text] and k, with the resulting [Formula: see text] estimates slightly lower than estimates obtained by other methods, and k comparable with previous results. We found comparatively higher estimates of k in Denmark which suggests less opportunities for superspreading and more controlled transmission compared to the other countries in 2021. Our model included an estimation of the case detection and sampling probability, but the estimates obtained had large uncertainty, reflecting the difficulty of estimating these parameters simultaneously. Our study presents a novel method to infer information on the transmission of infectious diseases and its heterogeneity using genomic data. With increasing availability of sequences of pathogens in the future, we expect that our method has the potential to provide new insights into the transmission and the overdispersion in secondary cases of other pathogens.

COVID-19↗
PubMed1990

Population biology of pseudorabies in swine.

A deterministic mathematical model of the population biology of pseudorabies in swine was used to clarify some of the basic features of the host-virus relationship and to inquire into the circumstances that promote or impede virus persistence in a single herd. When the basic reproductive rate of the infection (ie, the number of secondary infections resulting from the introduction of a single infective animal into a wholly susceptible herd) is greater than unity, the model suggests that the number of infective individuals in the herd will undergo highly damped oscillations to a final equilibrium level. The most important determinants of virus persistence are herd size and the density at which sows are maintained. There is a threshold density of susceptible individuals below which the virus will eventually be eliminated from the herd, even when specific control measures are lacking. Test and removal strategies hasten virus elimination when herd density is already below threshold, but are otherwise likely to succeed only when the removal of latent infections reduces the basic reproductive rate of the infection below unity. Vaccination strategies may also result in virus elimination, but only in relatively small herds.

Animals↗
PubMed1992

Survival curves, reproductive life span and age-related pathology of Mus caroli.

Although Mus caroli is being used in a number of laboratories as an experimental animal, basic information concerning its life span, reproductive ability, and age-related pathologies has been unavailable. Here we present this basic information, and discuss the similarities to and differences from the laboratory mouse, Mus musculus domesticus [strains A/StTrWo and (A/StTrWo x C57BL/6NNia)F1] and, from published data, wild-type Mus musculus.

Aging↗
PubMed1990

On the definition and the computation of the basic reproduction ratio R0 in models for infectious diseases in heterogeneous populations.

The expected number of secondary cases produced by a typical infected individual during its entire period of infectiousness in a completely susceptible population is mathematically defined as the dominant eigenvalue of a positive linear operator. It is shown that in certain special cases one can easily compute or estimate this eigenvalue. Several examples involving various structuring variables like age, sexual disposition and activity are presented.

Age Factors↗
PubMed1990

Loglinear models, sexual behavior and HIV: epidemiological implications of heterosexual transmission.

An analysis is presented of sexual behaviour data from a "random" sample (n = 780) of the adult population of England and Wales. Sex stratified frequency distributions of the reported number of sex partners/time were analysed for heterosexuals, demographic characteristics associated with the number of sex partners/time were identified, and epidemiological parameters (the basic reproductive rate of HIV and the doubling time of the epidemic) were calculated. These analyses suggest that the size of the group at risk for acquiring the virus by heterosexual transmission may be large and that the age of first sexual intercourse (for males and females) is decreasing in younger cohorts. Members of the potential heterosexual at-risk group may be identified by demographic variables such as marital status (males and females) and age (females only), but not by socioeconomic class. The epidemiological implications of our results for the heterosexual transmission of HIV are discussed.

Adolescent↗
PubMed1991

The population dynamics of nematode infections of ruminants: periodic perturbations as a model for management.

We propose and analyse a model for the dynamics of directly transmitted nematode infections of ruminants which allows for the long-term effects of the annual removal of hosts. The model is a simple continuous-time formulation which captures the principal features of parasite transmission and the acquisition of immunity to infection by the host. Analysis of the simplest version of the model, which assumes a constant host population through time, indicates that its equilibrium is locally stable for feasible biological parameters. The regular removal of hosts involved in most management strategies is modelled in terms of periodic perturbations. The analysis indicates that the periodic removal of parasitized hosts corresponds effectively to a reduction in the basic reproductive rate of infection. We also demonstrate that the system exhibits a dramatic peak in parasite numbers during each grazing season at its dynamic equilibrium. This phenomenon (which is characteristically observed in real systems) is discussed in terms of the balance between acquired immunity and periodic perturbations of the parasite population.

Animals↗
PubMed1988

The population biology of parasite-induced changes in host behavior.

The ability of parasites to change the behavior of infected hosts has been documented and reviewed by a number of different authors (Holmes and Bethel, 1972; Moore, 1984a). This review attempts to quantify the population dynamic consequences of this behavior by developing simple mathematical models for the most frequently recorded of such parasite life cycles. Although changes in the behavior of infected hosts do occur for pathogens with direct life cycles, they are most commonly recorded in the intermediate hosts of parasites with complex life cycles. All the changes in host behavior serve to increase rates of transmission of the parasites between hosts. In the simplest case the changes in behavior increase rates of contact between infected and susceptible conspecific hosts, whereas in the more complex cases fairly sophisticated manipulations of the host's behavioral repertory are achieved. Three topics are dealt with in some detail: (1) the behavior of the insect vectors of such diseases as malaria and trypanosomiasis; (2) the intermediate hosts of helminths whose behavior is affected in such a way as to make them more susceptible to predation by the definitive host in the life cycle; and (3) the behavior and fecundity of molluscs infected with asexually reproducing parasitic flatworms. In each case an expression is derived for R0, the basic reproductive rate of the parasite when first introduced into the population. This is used to determine the threshold numbers of definitive and intermediate hosts needed to maintain a population of the pathogen. In all cases, parasite-induced changes in host behavior tend to increase R0 and reduce the threshold number of hosts required to sustain the infection. The population dynamics of the interaction between parasites and their hosts are then explored using phase plane analyses. This suggests that both the parasite and intermediate host populations may show oscillatory patterns of abundance. When the density of the latter is low, parasite-induced changes in host behavior increase this tendency to oscillate. When intermediate host population densities are high, parasite population density is determined principally by interactions between the parasites and their definitive hosts, and changes in the behavior of intermediate hosts are less important in determining parasite density. Analysis of these models also suggests that both asexual reproduction of the parasite within a host and parasite-induced reduction in host fecundity may be stabilizing mechanisms when they occur in the intermediate hosts of parasite species with indirect life cycles.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Controlling HIV in Africa: effectiveness and cost of an intervention in a high-frequency STD transmitter core group.

Since 1985, a population of over 1,000 predominantly HIV-positive female prostitutes residing in a low-income area of Nairobi, has been enrolled in a sexually transmitted disease (STD)/HIV control programme. The major elements of the programme include the diagnosis and treatment of conventional STD, and the promotion of condom use to prevent the transmission of HIV and other sexually transmitted infections. Using estimates of numbers of HIV-seropositive prostitutes, numbers of sexual contacts, susceptibility of clients to HIV, HIV transmission efficiency, rates of condom use and the basic reproductive rate of HIV infection in Kenya, we estimate that the programme is responsible for preventing between 6,000 and 10,000 new cases of HIV infection per year among clients and contacts of clients. The total annual operating cost of the programme is approximately US$77,000 or between US$8.00 and US$12.00 for each case of HIV infection prevented. Programmes to reduce the transmission of HIV and other sexually transmitted infections which are targeted at high-frequency STD transmitters, such as prostitutes, can be effective and relatively inexpensive to undertake. More such programmes should be developed and evaluated in different settings.

Acquired Immunodeficiency Syndrome↗
PubMed1986

[Is the postmenopausal-age-at-death variable a fitness-maximizing reproductive strategy?].

On the basis of the complete 18th century vital statistics available for 811 women from Ostfriesland (Germany), an attempt is made to examine the relationship between the postmenopausal age at death and the reproductive behaviour (reproductive effort and reproductive management). Although reproductive activities appeared to have a basically life-shortening effect in the population under study, this was independent of the amount of reproductive effort. The positive correlation reported in the literature to exist between the number of (surviving) children and the age at death was confirmed in our analysis; and it can partly be explained by the interference of another relationship, i.e. between the age at the last parturition and longevity. This correlation is interpreted as an expression of fitness-maximizing reproductive management. To this belongs the idea that the existence of unmarried children, i.e. the sub-optimal social position of one's descendants, had a life-lengthening effect on the women investigated. Whereas the effects found are largely statistically significant, they are on the whole very minor, so that we may surmise that only a small part of the total variance of the postmenopausal age at death can be interpreted as an expression of an adaptive reproductive strategy.

Female↗
PubMed1992

Cell lineages, developmental timing, and spatial pattern formation in embryos of free-living soil nematodes.

From soils of various origins we have isolated a number of nematode strains and cultured them on agar plates. We have analyzed their anatomy, reproduction, and particularly their pattern of embryogenesis. With respect to early cleavage we can define six different classes. The basic scheme of embryogenesis is similar in all strains but considerable differences were observed in detail. Embryogenesis is more than five times longer in the slowest strain than in the fastest. The following general correlation was found: The slower embryogenesis proceeds in a strain, the relatively earlier the cleavage of germline cells occurs. In the fastest strain the primordial germ cell P4 is present at the 24-cell stage, while in the slowest strain it is already generated in the 5-cell stage. We hypothesize that germline cleavages have to occur within a certain time limit to preserve germline quality. The typical reversal of cleavage polarity in the division of the germline cell P2 is absent in the slowest, on other grounds apparently more primitive strain. This results in an unusual spatial arrangement of cells transiently. However, prior to gastrulation as a consequence of compensatory cell migrations (which may indicate the necessity for cell interactions), the pattern becomes very similar to that in the other strains. We propose that a standard cellular configuration is required at the beginning of gastrulation to ensure normal further development. Early cell interactions might be necessary to achieve this standard pattern. In about half of the analyzed strains cellular structures can be marked with an antibody raised against germline-specific granules of Caenorhabditis elegans. Our results do not support the notion that the staining pattern for P granules is a useful indicator for phylogenetic relationship.

Animals↗