Modelling the effect of treatment and behavioral change in HIV transmission dynamics

In this paper we analyze a model for the HIV-infection transmission in a male homosexual population. In the model we consider two types of infected individuals. Those that are infected but do not know their serological status and/or are not under any sort of clinical /therapeutical treatment, and those who are. The two groups of infectives differ in their incubation time, contact rate with susceptible individuals, and probability of disease transmission. The aim of this article is to study the roles played by detection and changes in sexual behavior in the incidence and prevalence of HIV. The analytical results show that there exists a unique endemic equilibrium which is globally asymptotically stable under a range of parameter values whenever a detection /treatment rate and an indirect measure of the level of infection risk are sufficiently large. However, any level of detection/ treatment rate coupled with a decrease of the transmission probability lowers the incidence rate and prevalence level in the population. In general, only significant reductions in the transmission probability (achieved through, for example, the adoption of safe sexual practices) can contain effectively the spread of the disease.     

Identification of a second distinct strain of beet mild yellowing luteovirus using monoclonal antibodies and transmission studies

The variation among isolates of beet mild yellowing luteovirus (BMYV), collected from commercial crops of sugar beet during 1990, 1992 and 1993, was studied using monoclonal antibodies and transmissions to indicator species. The common strain of BMYV, which occurs throughout the sugar-beet root growing area, reacts with monoclonal antibodies MAFF 24, BWYV-BC-510H and BYDV-PAV-IL-1, and infects Capsella bursa-pastoris. A second strain, which failed to react with monoclonal antibody BYDV-PAV-IL-1 and which did not infect C. bursa-pastoris, was identified in 11% of sampled infected plants. The implications of the properties of this strain for the epidemiology of BMYV are discussed.     

Genetic variation in North Africa and Eurasia: Neolithic demic diffusion vs. paleolithic colonisation

The hypothesis that both genetic and linguistic similarities among Eurasian and North African populations are due to demic diffusion of neolithic farmers is tested against a wide database of allele frequencies. Demic diffusion of farming and languages from the Near East should have determined clines in areas defined by linguistic criteria; the alternative hypothesis of cultural transmission does not predict clines. Spatial autocorrelation analysis shows significant gradients in three of the four linguistic families supposedly affected by neolithic demic diffusion; the Afroasiatic family is the exception. Many such gradients are not observed when populations are jointly analyzed, regardless of linguistic classification. This is incompatible with the hypothesis that major cultural transformations in Eurasia (diffusion of related languages and spread of agriculture) took place without major demographic changes. The model of demic diffusion seems therefore to provide a mechanism explaining coevolution of linguistic and biological traits in much of the Old World. Archaeological, linguistic, and genetic evidence agree in suggesting a multidirectional process of gene flow from the Near East in the neolithic. However, the possibility should be envisaged that some allele frequency patterns can predate the neolithic and depend on the initial spread of Homo sapiens sapiens from Africa into Eurasia. © 1994 Wiley-Liss, Inc.     

Interactions between a seed-borne strain of cucumber mosaic cucumovirus and its lupin host

The relationship between time of inoculation with cucumber mosaic cucumovirus (CMV) and the growth, seed production and rate of seed transmission of virus in lupin (Lupinus angustifolius cv. Illyarrie) was studied in field-grown plants. Plants inoculated at the seedling stage (2 days post-emergence) showed 45% mortality. Plants infected through the seed were more stunted than plants inoculated at the seedling stage. Plants inoculated up to the mid-vegetative growth stage (58 days post-emergence) yielded ≤ 27% of the dry matter and ≤ 9% of the seed of healthy plants. Late inoculation (114 days post-emergence) did not affect dry matter yield, but reduced seed yield to 75% of that of healthy plants. Rate of seed transmission depended on the time of inoculation of plants. The maximum rate was 24.5% for plants that were inoculated at the mid-vegetative growth stage (58 days post-emergence). However, early inoculation caused a large reduction in seed yield, and it was shown that plants inoculated at the beginning of flowering (94 days post-emergence) produced greater numbers of infected progeny than plants inoculated at earlier or later times. No relationship was observed between seed weight and transmission of CMV. Infectious CMV was recovered from the embryo, but not from the testa. A simple seed transmission model was used to evaluate several hypothetical epidemics and to determine the time of inoculation which results in greatest rates of seed transmission of CMV. For example, when fewer than 73% of plants in a crop become infected with CMV, then the rate of transmission of virus in crop seeds will be greatest when inoculations are at the beginning of flowering.     

POLLEN DISCOUNTING AND THE SPREAD OF A SELFING VARIANT IN TRISTYLOUS EICHHORNIA PANICULATA: EVIDENCE FROM EXPERIMENTAL POPULATIONS

Floral traits that increase self-fertilization are expected to spread unless countered by the effects of inbreeding depression, pollen discounting (reduced outcross pollen success by individuals with increased rates of self-fertilization), or both. Few studies have attempted to measure pollen discounting because to do so requires estimating the male outcrossing success of plants that differ in selfing rate. In natural populations of tristylous Eichhornia paniculata, selfing variants of the mid-styled morph are usually absent from populations containing all three style morphs but often predominate in nontrimorphic populations. We used experimental garden populations of genetically marked plants to investigate whether the effects of population morph structure on relative gamete transmission by unmodified (M) and selfing variants (M‘) of the mid-styled morph could explain their observed distribution. Transmission through ovules and self and outcross pollen by plants of the M and M’ morphs were compared under trimorphic, dimorphic (S morph absent), and monomorphic (L and S morphs absent) population structures. Neither population structure nor floral morphology affected female reproductive success, but both had strong effects on the relative transmission of male gametes. The frequency of self-fertilization in the M' morph was consistently higher than that of the M morph under all morph structures, and the frequency of self-fertilization by both morphs increased as morph diversity of experimental populations declined. In trimorphic populations, total transmission by the M and M' morphs did not differ. The small, nonsignificant increase in selfing by the M' relative to the M morph was balanced by decreased outcross siring success, particularly on the S morph. In populations lacking the S morph, male gamete transmission by the M' morph was approximately 1.5 times greater than that by the M morph because of both increased selfing and increased success through outcross pollen donation. Therefore, gamete transmission strongly favored the M' morph only in the absence of the S morph, a result consistent with the distribution of the M' morph in nature. This study indicates that floral traits that alter the selfing rate can have large and context-dependent influences on outcross pollen donation.     

On the evolution of protamines in bony Fish: Alternatives to the “Retroviral horizontal transmission” hypothesis

Fish protamines are highly specialized molecules which are responsible for chromatin condensation during the last stages of spermatogenesis (spermiogenesis). However, not all fish contain protamines in their sperm nuclei; rather, there seems to be a random distribution of protamines within this group. The origin of this sporadic presence of protamines in the sperm and its significance have not yet been precisely determined. In this paper we have conducted an exhaustive survey of the literature available on the different types of nuclear protein composition of the sperm of teleost fish in order to try to correlate these data with what is presently known about the taxonomy of this group. The results of this analysis have allowed us to make the following observations. The divergence between protamines and histones has occurred several times during the evolution of the bony fish. However, the relative frequency of this divergence is almost negligible during the differentiation of genera and species (intrafamily variation) and is very small during the differentiation of families (interfamily variation). Nevertheless, the divergence is very noticeable among the different orders. It is therefore possible to conclude from all this that the sporadic distribution of protamines in bony fish is not a random event as initially believed. Furthermore, such a heterogeneous distribution of protamines cannot be easily accounted for by a mechanism of horizontal retroviral transmission through repeated and independent acquisition of a prot amine gene as has been recently proposed (Jankowski, Stater, Dixon (1986) J Mol Evol 23:1–10). Rather, it could possibly be explained by a repeated and independent loss of the expression of the protamine gene (or loss of the gene itself) which mainly occurred during the diversification of the orders of this group.Correspondence to: J. Ausio     

Sex differentiation studies relating to releaser aggregation pheromones of the desert locust,Schistocerca gregaria

Behavioural responses of nymphs and adults in the gregarious phase of the desert locust,Schistocerca gregaria (Forskal) (Orthoptera: Acrididae) were investigated in a single-chamber bioassay system to a choice of two columns of air, one permeated with airborne volatiles emanating from either sex of nymphs or adults and the other untreated. There was no sexual differentiation in the production of or response to nymphal volatiles. Young adults of either sex did not produce a stimulus with significant activity. Of the older adults, only the males produced the aggregation stimulus to which both sexes were equally responsive. Charcoal-trapped volatiles from the two sexes of nymphs and adults evoked similar aggregation responses. Antennae of the older adults showed significantly higher EAG responses than those of fifth instar nymphs to all four volatile collections, of which volatiles from older adult males were the most stimulatory and evoked the highest EAG amplitudes.     

Aphid activities during sieve element punctures

Aphid salivation in sieve elements and phloem sap ingestion were linked to waveforms in the Electrical Penetration Graph (EPG). Non-viruliferousRhopalosiphum padi (L.) (Hemiptera, Aphididae) on barley yellow dwarf virus (BYDV) infected wheat could acquire the virus, which was used as an indication for phloem sap ingestion, whereas virus inoculation by viruliferous aphids on healthy plants was associated with salivation in sieve elements or other phloem cells. Probing was monitored and the waveforms recorded were related to ELISA results of test plants. The EPG patterns A, B, and C are indicative of the stylet pathway phase, whereas patterns E1 and E2 reflect the phloem (sieve element) phase with an unknown activity (E1) or with ingestion and concurrent salivation (E2). Aphids showing pathway and E1 rarely acquired virus, suggesting that little or no phloem sap ingestion can occur during these patterns, whereas those showing additionally pattern E2 did so substantially, indicating phloem sap ingestion. The main pattern related to virus inoculation was E1, although some aphids were able to inoculate plants during pathway. Pattern E1 clearly reflects the most important salivation into sieve elements. Pattern E2 had no clear contribution to virus inoculation, supporting the present hypothesis that during this pattern the saliva is mixed with the phloem sap in the single canal at the stylet tips and ingested immediately, without reaching the plant tissue. Sustained sap ingestion did not affect virus inoculation. So, BYDV inoculation mainly occurs during the first period of a sieve element puncture which is always formed by E1. Implications on persistent virus transmission are discussed.     

Pollen calendar for cracow (southern Poland), 1982–1991

Summary During 1982 – 1991 pollen deposition in the centre of Cracow (southern Poland) was investigated using the gravimetric method. 32 taxa of the 84 identified were taken into consideration, and nearly all of them can be allergenic. The beginning of mass pollen fall was observed in the second decade of March, and the third decade of September saw the completion of the yearly cycle of abundant appearance of pollen in the aeroplankton. Tree pollen dominates quantitatively.     

Pathogenesis of SIVmac251 after atraumatic inoculation of the rectal mucosa in rhesus monkeys

Intrarectal inoculation of rhesus monkeys with low doses of SIV_mac led to a prolonged clinical and virological latency that was not observed for high intrarectal doses or for intravenous inoculation. Animals infected intrarectally with low virus doses remained negative for serum antibody responses to SIV for at least one year even though they readily transferred SIV to naive recipients via transfusion of whole blood.