Heterogeneity in susceptibility to infection can explain high reinfection rates

Heterogeneity in susceptibility and infectivity is inherent to infectious disease transmission in nature. Here we are concerned with the formulation of mathematical models that capture the essence of heterogeneity while keeping a simple structure suitable of analytical treatment. We explore the consequences of host heterogeneity in the susceptibility to infection for epidemiological models for which immunity conferred by infection is partially protective, known as susceptible-infected-recovered-infected (SIRI) models. We analyze the impact of heterogeneity on disease prevalence and contrast the susceptibility profiles of the subpopulations at risk for primary infection and reinfection. We present a systematic study in the case of two frailty groups. We predict that the average rate of reinfection may be higher than the average rate of primary infection, which may seem paradoxical given that primary infection induces life-long partial protection. Infection generates a selection mechanism whereby fit individuals remain in S and frail individuals are transferred to R. If this effect is strong enough we have a scenario where, on average, the rate of reinfection is higher than the rate of primary infection even though each individual has a risk reduction following primary infection. This mechanism may explain high rates of tuberculosis reinfection recently reported. Finally, the enhanced benefits of vaccination strategies that target the high-risk groups are quantified.http://dx.doi.org/10.1016/j.jtbi.2009.03.01

The Importance of Heterogeneity to the Epidemiology of Tuberculosis

Although less well-recognised than for other infectious diseases, heterogeneity is a defining feature of TB epidemiology. To advance toward TB elimination, this heterogeneity must be better understood and addressed. Drivers of heterogeneity in TB epidemiology act at the level of the infectious host, organism, susceptible host, environment and distal determinants. These effects may be amplified by social mixing patterns, while the variable latent period between infection and disease may mask heterogeneity in transmission. Reliance on notified cases may lead to misidentification of the most affected groups, as case detection is often poorest where prevalence is highest. Assuming average rates apply across diverse groups and ignoring the effects of cohort selection may result in misunderstanding of the epidemic and the anticipated effects of control measures. Given this substantial heterogeneity, interventions targeting high-risk groups based on location, social determinants or comorbidities could improve efficiency, but raise ethical and equity considerations

Symmetries on bifurcation theory The appropriate context

SIGLEAvailable from British Library Document Supply Centre- DSC:D175503 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

On the final size of epidemics with seasonality

We first study an SIR system of differential equations with periodic coefficients describing an epidemic in a seasonal environment. Unlike in a constant environment, the final epidemic size may not be an increasing function of the basic reproduction number R-0 or of the initial fraction of infected people. Moreover, large epidemics can happen even if R-0 1, the final epidemic size is bigger than the fraction 1-1/R-0 of the initially nonimmune population. In summary, the basic reproduction number R-0 keeps its classical threshold property but many other properties are no longer true in a seasonal environment. These theoretical results should be kept in mind when analyzing data for emerging vector-borne diseases (West-Nile, dengue, chikungunya) or air-borne diseases (SARS, pandemic influenza); all these diseases being influenced by seasonality

Small-word networks decrease the speed of Muller's ratchet

Muller's ratchet is an evolutionary process that has been implicated in the extinction of asexual species, the evolution of non-recombining genomes, such as the mitochondria, the degeneration of the Y chromosome, and the evolution of sex and recombination. Here we study the speed of Muller's ratchet in a spatially structured population which is subdivided into many small populations (demes) connected by migration, and distributed on a graph. We studied different types of networks: regular networks (similar to the stepping-stone model), small-world networks and completely random graphs. We show that at the onset of the small-world network - which is characterized by high local connectivity among the demes but low average path length - the speed of the ratchet starts to decrease dramatically. This result is independent of the number of demes considered, but is more pronounced the larger the network and the stronger the deleterious effect of mutations. Furthermore, although the ratchet slows down with increasing migration between demes, the observed decrease in speed is smaller in the stepping-stone model than in small-world networks. As migration rate increases, the structured populations approach, but never reach, the result in the corresponding panmictic population with the same number of individuals. Since small-world networks have been shown to describe well the real contact networks among people, we discuss our results in the light of the evolution of microbes and disease epidemic

Small-word networks decrease the speed of Muller's ratchet

Muller's ratchet is an evolutionary process that has been implicated in the extinction of asexual species, the evolution of non-recombining genomes, such as the mitochondria, the degeneration of the Y chromosome, and the evolution of sex and recombination. Here we study the speed of Muller's ratchet in a spatially structured population which is subdivided into many small populations (demes) connected by migration, and distributed on a graph. We studied different types of networks: regular networks (similar to the stepping-stone model), small-world networks and completely random graphs. We show that at the onset of the small-world network - which is characterized by high local connectivity among the demes but low average path length - the speed of the ratchet starts to decrease dramatically. This result is independent of the number of demes considered, but is more pronounced the larger the network and the stronger the deleterious effect of mutations. Furthermore, although the ratchet slows down with increasing migration between demes, the observed decrease in speed is smaller in the stepping-stone model than in small-world networks. As migration rate increases, the structured populations approach, but never reach, the result in the corresponding panmictic population with the same number of individuals. Since small-world networks have been shown to describe well the real contact networks among people, we discuss our results in the light of the evolution of microbes and disease epidemic

Partial classification of heteroclinic behaviour associated with the perturbation of hexagonal planforms

Physical systems often exhibit pattern-forming instabilities. Equivariant bifurcation theory is often used to investigate the existence and stability of spatially doubly periodic solutions with respect to the hexagonal lattice. Previous studies have focused on the six- and twelve-dimensional representation of the hexagonal lattice where the symmetry of the model is perfect. Here, perturbation of group orbits of translation-free axial planforms in the six- and twelve-dimensional representations is considered. This problem is studied via the abstract action of the symmetry group of the perturbation on the group orbit of the planform. A partial classification for the behaviour of the group orbits is obtained, showing the existence of homoclinic and heteroclinic cycles between equilibria

Isolation And Characterization Of A Lectin From Annona Muricata Seeds

A lectin with a high affinity for glucose/mannose was isolated from Annona muricata seeds (Annonaceae) by gel filtration chromatography on Sephacryl S-200, ion exchange chromatography on a DEAE SP-5 PW column, and molecular exclusion on a Protein Pak Glass 300 SW column. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (PAGE) yielded two protein bands of approximately 14 kDa and 22 kDa. However, only one band was seen in native PAGE. The Mr of the lectin estimated by fast-performance liquid chromatography-gel filtration on Superdex 75 was 22 kDa. The lectin was a glycoprotein with 8% carbohydrate (neutral sugar) and required divalent metal cations (Ca2+, Mg 2+, and Mn2+) for full activity. Amino acid analysis revealed a large content of Glx, Gly, Phe, and Lys. The lectin agglutinated dog, chicken, horse, goose, and human erythrocytes and inhibited the growth of the fungi Fusarium oxysporum, Fusarium solani, and Colletotrichum musae. © 2003 Plenum Publishing Corporation.2207/08/15655661Allen, A.K., Neuberger, A., Sharon, N., (1973) Biochem. J., 131, pp. 155-162Bones, C., Loiseau, P., Cortes, D., Myint, S.H., Hocquemiller, R., Gayral, P., (1991) Plant Med., 57, pp. 434-436Bradford, M.M., (1976) Anal. Biochem., 72, pp. 248-254Branch, L.C., Silva, I.M.F., (1983) Acta Amazônica., 13, pp. 737-797Coelho, M.B., Freire, M.G.M., Toyama, M.H., Marangoni, S., Novello, J.C., Macedo, M.L.R., (2003) Protein and Peptide Letter, 10, pp. 1-9Datta, P.K., Figueroa, M.O.D.C.R., Lajolo, F.M., (1991) Plant Physiol., 97, pp. 856-862Dubois, M., Gilles, K.A., Hamilton, J.L., Rebers, P.A., Smith, F., (1956) Anal. Chem, 28, pp. 350-356Freire, M.G.M., Gomes, V.M., Corsini, R.E., Machado, O.L.T., De Simone, S.G., Novello, J.C., (2002) Plant Physiol. Biochem., 40, pp. 61-68Goldstein, I.J., Hughes, R.C., Monsigny, M., Osawa, T., Sharon, N., (1980) Nature, 285, pp. 66-73Gomes, V.M., Da Cunha, M., Miguens, F.C., Fernandes, K.V.S., Rose, T.L., Xavier-Filho, J., (1998) Plant Sci., 138, pp. 81-89Henrikson, R.L., Meredith, S.C., (1984) Anal. Biochem., 136, pp. 65-71Laemmli, U.K., (1970) Nature, 227, pp. 680-685Lis, H., Sharon, N., (1984) Biology of Carbohydrates, pp. 1-85. , Ginsburg, V., and Robbins, P. W. (eds), Wiley, New YorkLis, H., Sharon, N., (1986) Annu. Rev. Biochem., 55, pp. 35-67Moreira, R.A., Monteiro, A.C.O., Horta, A.C.G., Oliveira, J.T.A., Cavada, B.S., (1997) Phytochemistry, 2, pp. 139-144Moreira, R.A., Castelo-Branco, C.C., Monteiro, A.C.O., Tavares, R.O., Beltramini, L.M., (1998) Phytochemistry, 47, pp. 1183-1188Peumans, W.J., Verhaert, P., Pfüller, U., Van Damme, E.J.M., (1984) FEBS Lett., 177, pp. 261-265Sampietro, A.R., Isla, M.I., Quiroga, E.N., Vattuone, M.A., (2001) Plant Sci., 160, pp. 659-667Sharon, N., Lis, H., (1990) FASEB J., 4, pp. 3198-3208Shibuya, N., Goldstein, I.J., Shafer, J.A., Peumans, W.J., Broekaert, W.F., (1986) Arch. Biochem. Biophys., 249, pp. 215-224Singh, R.S., Tiwary, A.K., Kennedy, J.F., (1999) Crit. Rev. Biotechnol., 19, pp. 145-178Utarabhand, P., Akkayamont, P., (1995) Phytochemistry, 38, pp. 281-285Van Damme, E.J.M., Peumans, W.J., Barre, A., Rougé, P., (1998) Crit. Rev. Plant. Sci., 17, pp. 575-692Van Parijs, J., Broekaert, W.F., Goldstein, I.J., Peumans, W.J., (1991) Planta, 183, pp. 258-264Van Parijs, J., Broekaert, W.F., Peumans, W.J., Geuns, J.M., Van Laere, A.J., (1992) Arch. Microbiol., 158, pp. 19-25Wang, H.X., Ng, T.B., Ooi, V.E.C., (1999) Int. J. Biochem. Cell Biol., 31, pp. 595-599Xu, Q., Lu, Y., Wang, X., Gu, H., Chen, Z., (1998) Plant Physiol. Biochem., 36, pp. 899-90