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At least 19 recordsLinked to original sources

PubMed1988

Modulation of human malaria transmission by anti-gamete transmission blocking immunity.

Natural Plasmodium vivax malaria infections in man evoke anti-gamete transmission blocking antibodies which influence the infectivity of malaria patients to the vector mosquito. In this study, entomological, immunological and parasitological data obtained through the monitoring of an epidemic of human vivax malaria in Sri Lanka were used in a mathematical simulation to assess the effect of naturally induced transmission blocking immunity on malaria transmission. A mathematical model to describe malaria transmission accounting for transmission blocking immunity was developed from the basic differential equations originally stated by R. Ross and the epidemic was simulated using the available data. An attempt was made to predict the monthly malaria incidence by means of the mathematical simulation, with and without accounting for transmission blocking immunity. A plausible mathematical solution of the epidemic could be obtained when transmission blocking immunity was accounted for, and it was not possible to obtain such a plausible solution in the absence of immunity. Thus, the postulated occurrence of transmission blocking immunity was essential to describe adequately this malaria epidemic, indicating that, at least in epidemic situations, naturally occurring transmission blocking immunity has a controlling influence on malaria incidence.

Animals↗

PubMed1985

Signal transmission in the catfish retina. I. Transmission in the outer retina.

Extrinsic current, either pulsatile or white-noise modulated, was injected into the (cone) horizontal-cell soma and axon, and resulting responses were recorded from nearby points. In the case of white-noise inputs, signal transmission between the two points was characterized by Wiener kernels. The signal transmission within the lamina, the S-space, formed by the (cone) horizontal-cell somas and axons is quasi-linear and very fast, indicating that the laminae are purely resistive networks within the frequency range of the light-evoked response. There exists signal transaction between the lamina formed by the somas and axons. The forward transmission is constant gain, low pass, but there is a filter for the reverse transmission to impede the backflow of high-frequency components. Signals in the horizontal-cell soma are transmitted to the bipolar cells. The transmission is sign noninverting for the on-center bipolar cells and sign inverting for the offcenter cells. The transmission is quasi-linear excluding complex mechanisms in the transmission. We believe that the forward and direct transmission of signals from the horizontal to bipolar cells is the most straightforward interpretation of the observation. The transfer functions between the horizontal and bipolar cells differ considerably from one bipolar cell to the next.

Animals↗

PubMed1992

Method to estimate relative transmission efficiencies of Anopheles species (Diptera: Culicidae) in human malaria transmission.

A mathematical expression was derived to estimate the relative malaria transmission efficiency of an anopheline species with respect to a standard well-characterized species for which all vector parameters can be sufficiently determined. The method is particularly useful in situations where multiple anopheline species contribute to human malaria transmission and requires the estimation of the man-biting rate, the sporozoite rate, and the human malaria incidence. Under stable conditions of vector abundance, the average sporozoite rate in a species during a transmission season would by itself reflect its relative transmission efficiency. This "efficiency" then was used to calculate the "effective human-biting rate"; i.e., the human-biting rate of that species if it were to have ecological properties identical to those of the standard species. The standard well-characterized species then could be used with the effective human-biting rate of all species to quantify transmission, thus overcoming the need to measure vector parameters for all anopheline species contributing to transmission. An expression also was derived to calculate the relative contribution made by each species to malaria transmission. The usefulness of this method was illustrated using entomological and epidemiological data from Kataragama, Sri Lanka.

Animals↗

PubMed1992

Comparison of female to male and male to female transmission of HIV in 563 stable couples. European Study Group on Heterosexual Transmission of HIV.

OBJECTIVE: To identify risk factors for heterosexual transmission of HIV and to compare the efficiency of male to female and female to male transmission. DESIGN: Cohort study of heterosexual couples. Regular partners of HIV infected subjects were tested and both members of the couples interviewed every six months. HIV prevalence in partners was analysed according to the characteristics of the couples. SETTING: Nine European countries. SUBJECTS: 563 couples comprising 156 female index patients with their 159 male partners and 400 male index patients with their 404 female partners. Partners reporting risk factors other than sexual contacts with the index patient were excluded. MAIN OUTCOME MEASURES: HIV infection in partners and high risk sexual behaviour. RESULTS: Overall, 19 (12%) male partners and 82 (20%) female partners were infected with HIV, suggesting that male to female transmission is 1.9 (95% confidence interval 1.1 to 3.3) times more effective than female to male transmission. An advanced stage of HIV infection in the index patient (odds ratio 17.6; 4.9 to 62.7) and sexual contacts during menses (3.4; 1.0 to 11.1) increased the risk of female to male transmission and stage of infection (2.7; 1.5 to 4.9), anal sex (5.1; 2.9 to 8.9), and age of the female partner (3.9; 1.2 to 13.0 for age > 45 years) increased the risk of male to female transmission. None of the 24 partners who had used condoms systematically since the first sexual contact was infected. CONCLUSIONS: Several factors which potentiate the risk of transmission through unprotected vaginal intercourse have been identified. Knowledge of these factors could be helpful for counselling patients infected with HIV and their sexual partners.

Adolescent↗

PubMed1991

A mathematical model for Plasmodium vivax malaria transmission: estimation of the impact of transmission-blocking immunity in an endemic area.

We have developed a multi-state mathematical model to describe the transmission of Plasmodium vivax malaria; the model accommodates variable transmission-blocking/enhancing immunity during the course of a blood infection, a short memory for boosting immunity, and relapses. Using the model, we simulated the incidence of human malaria, sporozoite rates in the vector population, and the level of transmission-blocking immunity for the infected population over a period of time. Field data from an epidemiological study conducted in Kataragama in the south of Sri Lanka were used to test the results obtained. The incidence of malaria during the study period was simulated satisfactorily. The impact of naturally-acquired transmission-blocking immunity on malaria transmission under different vectorial capacities was also simulated. The results show that at low vectorial capacities, e.g., just above the threshold for transmission, the effect of transmission-blocking immunity is very significant; however, the effect is lower at higher vectorial capacities.

Animals↗

PubMed1992

Nitrergic transmission: nitric oxide as a mediator of non-adrenergic, non-cholinergic neuro-effector transmission.

1. The possibility that transmission at some non-adrenergic, non-cholinergic (NANC) neuro-effector junctions is mediated by nitric oxide (NO) arose from the discoveries that NO mediated the effects of nitrovasodilator drugs and that endothelium-derived relaxing factor (EDRF) was NO or a NO-yielding substance. 2. NO donated by nitrovasodilator drugs or formed by endothelial cells activates soluble guanylate cyclase in smooth muscle and the consequent increase in cyclic guanosine monophosphate (cGMP) results in relaxation. The relaxations produced by stimulation of some NANC nerves are also due to a rise in cGMP. 3. The biosynthesis of NO by oxidation of a terminal guanidino nitrogen of L-arginine is inhibited by some NG-substituted analogues of L-arginine. These substances block EDRF formation by NO synthase and endothelium-dependent vasodilatation, and the blockade is overcome by L-arginine 4. NANC relaxations in some tissues are blocked by NG-substituted analogues of L-arginine and restored by L-arginine. Other agents that affect endothelium-dependent vasodilator responses produce corresponding changes in responses to stimulation of these NANC nerves. Such observations indicate that transmission is mediated by NO: we have termed this mode of transmission nitrergic. 5. There is evidence for nitrergic innervation of smooth muscle in the gastrointestinal tract, genito-urinary system, trachea and some blood vessels (penile and cerebral arteries). 6. The recognition of a mediator role for NO in neurotransmission calls for reconsideration of previously accepted generalizations about mechanisms of transmission. 7. Studies on nitrergic transmission will provide new insights into physiological control mechanisms and pathophysiological processes and may lead to new therapeutic developments.

Animals↗

PubMed1991

On the application of mathematical models of schistosome transmission dynamics. I. Natural transmission.

The many mathematical models of the transmission dynamics of schistosomes that have been published since 1965 have had little impact on field studies or on the design of schistosome control programmes. At least in part, this is due to limited interaction between theoretician and field worker, resulting in unrealistic models that are not easily applied to field data. This review aims to make explicit the assumptions and limitations of existing models and their relationships with field data. A basic model is described which considers the mean number of schistosomes per person and the prevalence of patent infections of snails. Various modifications to this model are introduced. These include: prepatent infections of snails; loss of infection of snails; the effects of snail population dynamics; the effects of miracidia and cercariae population dynamics; miracidia searching efficiency; reservoir hosts; heterogeneous patterns of transmission; seasonality; and predisposition to infection. Variation in levels of infection with age and the effects of acquired immunity to infection are also considered. Published models of schistosome transmission dynamics are reviewed within this framework. Approaches to the modelling of schistosome control measures are considered in a companion paper. It is suggested that future theoretical studies give greater attention to the details of snail population dynamics, heterogeneous patterns of transmission and the effects of acquired immunity. There is a need for field studies explicitly designed to provide estimates of transmission parameters and for studies of the epidemiological effects of acquired immunity.

Age Factors↗

PubMed1988

Transmission of hepatitis B virus infection in Ethiopia with emphasis on the importance of vertical transmission.

This two-year controlled study was conducted to define the mode of transmission of hepatitis B infection in Ethiopia. Twenty-five of 500 (5%) expectant mothers were identified as HbsAg positive (Group A). A control group of 29 mothers negative for HBsAg (Group B) was randomly selected. These 54 mothers and their families (husbands, infants and the infants' older siblings) were followed for two years with determinations of serological markers of ongoing or past hepatitis B virus infection at 6, 12 and 24 months. Social and clinical data as well as possible factors contributing to the spread of HBV (ie tattoos, circumcision, etc.) were compiled from questionnaires. Twenty-one of the 25 (84%) HBsAg positive mothers had anti-HBe and none had HBeAg. One case of vertical hepatitis B virus transmission was seen while horizontal transmission during the study period occurred in two infants and in two older siblings. Potential risk factors for non-perinatal transmission were highly prevalent in both groups and may represent the main route of transmitting the infection, while, as shown in the present study, the vertical transmission of HBV infection only plays a minor role in the maintenance of the high infection rate in Ethiopia. Vaccinating all babies soon after birth would, therefore, be an effective means of eradicating or reducing the hepatitis B virus infection and its sequelae.

Adult↗

PubMed1991

Lack of correlation between maternal antibodies to V3 loop peptides of gp120 and perinatal HIV-1 transmission. The NYC Perinatal HIV Transmission Collaborative Study.

Recent reports have suggested that maternal antibodies to specific epitopes of the variable region 3 (V3 loop) of gp120 of HIV-1 might protect against perinatal transmission. In an attempt to confirm these findings, sera from 34 HIV-1-seropositive mothers, representing 13 episodes of mother-to-infant transmission and 23 episodes of non-transmission (two mothers had two pregnancies each during the study period), were tested for the presence of antibodies to various regions of the gp120 V3 loop. Synthetic peptides were generated from HIV-1MN. Of the four peptides tested by enzyme-linked immunosorbent assay (ELISA), only antibody to the C53 peptide (Env310-322, principal neutralizing determinant) was present in maternal sera. Antibody to the C53 sequence was present in 11 specimens from transmitting mothers and 21 from non-transmitting mothers (84.6 and 91.3%, respectively, P = 0.6). No reactivity was detected against the C51, C57, or C58 peptide sequences, located on the sides of the V3 loop. In an antigen-limited ELISA, only two specimens from transmitting mothers and two specimens from non-transmitting mothers had detectable 'high-affinity' antibodies to C53 at low antigen concentrations (15.4 and 8.7%, respectively; P = 0.6). Our results do not support previous reports that epitope-specific antibodies to the V3 loop peptides protect against perinatal transmission. Further research is required to determine whether any specific maternal humoral response might influence HIV-1 perinatal transmission.

Acquired Immunodeficiency Syndrome↗

PubMed1989

Genital mucosal transmission of simian immunodeficiency virus: animal model for heterosexual transmission of human immunodeficiency virus.

An animal model for the heterosexual transmission of human immunodeficiency virus (HIV) was developed by the application of simian immunodeficiency virus (SIV) onto the genital mucosas of both mature and immature, male and female rhesus macaques. Virus preparations were infused into the vaginal vaults or the urethras (males) of the animals through a soft plastic pediatric nasogastric feeding tube. The macaques that were infected by this route (six males and nine females) developed SIV-specific antibodies, and SIV was isolated from peripheral mononuclear cells of all seropositive animals. One male and one female infected by this route developed severe acquired immunodeficiency syndrome-like disease with retroviral giant-cell pneumonia. As few as two inoculations of cell-free SIV containing 50 50% tissue culture infective doses induced persistent viremia. Cell-free virus preparations were capable of producing infection by the genital route. Much higher doses of virus were required to transmit SIV by this route than are required for transmission by intravenous inoculation. Thus, it appears that the mucous membranes of the genital tract act as a barrier to SIV infection. Spermatozoa and seminal plasma were not required for the genital transmission of SIV. Rarely, SIV was recovered from mononuclear cells in semen and vaginal secretions. The SIV-rhesus macaque model is suitable for assessing the role of cofactors in heterosexual transmission of HIV and will be useful for testing the effectiveness of spermicides, pharmacologic agents, and vaccines in preventing the heterosexual transmission of HIV.

Acquired Immunodeficiency Syndrome↗

PubMed1991

Oral transmission of transmissible gastroenteritis virus by muscle and lymph node from slaughtered pigs.

A study was conducted in the USA to determine whether transmissible gastroenteritis (TGE) virus could be transmitted from carcases of slaughtered pigs. Transmissible gastroenteritis virus was transmitted to 6-day-old piglets by dosing with homogenates of muscle and lymph node collected from 500 clinically normal pigs at the time of slaughter. All piglets in 2 separately housed litters showed clinical signs of TGE with 5 piglets dying within 10 d of oral dosing with homogenates. Transmissible gastroenteritis virus was isolated from 2 of these piglets and all piglets developed TGE antibody. Transmissible gastroenteritis virus was not isolated in tissue culture from muscle and lymph node homogenates, but was isolated from 4 (0.8%) of 500 tonsil samples collected from the same pigs. A survey of 250 serum samples provided an estimate of the prevalence of slaughtered pigs with TGE antibody of 34.8% in the sample population. The results indicate that carcases of some pigs from TGE endemic areas contain viable TGE virus, and that there would be a substantial risk of introducing TGE virus into Australia by the importation of uncooked pig meat from these areas.

Administration, Oral↗

PubMedDate not supplied

Age trends in transmissible and non-transmissible components of family resemblance for stature.

Yearly measurements of recumbent length and stature on participants in the Fels Longitudinal Study of Growth and their first-degree relatives were submitted to path analysis. Using a model consistent with simple polygenic inheritance, two parameters were estimated at each age: t2 or transmissibility, and s, or non-transmissible sibling resemblance. Transmissibility showed no long-term age trends, whereas non-transmissible sibling resemblance declined steadily from age four years to the late teens. The factors controlling family resemblance for stature (genes and common family environment) make different contributions at different points in the growth cycle of these family members. These differences are more discernable in the Fels data because all family members, including parents, are measured at the same age throughout childhood.

Adolescent↗

PubMed1992

Simultaneous acquisition of emission and transmission data for improved thallium-201 cardiac SPECT imaging using a technetium-99m transmission source.

Transmission computed tomography (TCT) data provides useful complementary information to single-photon emission computed tomography (SPECT) reconstructions, especially for cardiac studies. In particular, TCT data has been used to correct for nonuniform attenuation in the chest. Typically the transmission data are acquired in a separate acquisition, but simultaneous acquisition is preferable both to save time and to avoid difficulties involved with registration. In this work, we present a technique for simultaneously acquiring 201Tl SPECT and TCT data using a 99mTc sheet source that requires only minor equipment modifications. The use of these isotopes results in cross-contamination of the emission and transmission data. We present a practical technique to compensate for this contamination using post-acquisition image processing. This technique was evaluated by performing phantom and patient studies. The resulting images compare well with data obtained from separate emission and transmission studies.

Heart↗

PubMed1992

Mother-to-child transmission of human immunodeficiency virus type 1: risk of infection and correlates of transmission.

One thousand eight hundred eighty-seven children born to human immunodeficiency virus type 1 (HIV-1) seropositive mothers, including 1045 infants prospectively followed up from birth, were studied. Intravenous drug use was the most frequent maternal risk factor, although the percentage of women infected by sexual contact increased from 5.8% in 1985 to 28.5% in 1990. Of the 551 first children followed up from birth and older than 15 months of age, 101 (18.3%) acquired infection and seroconverted to HIV-1. Another 31 (5.6%) asymptomatic seronegative children showed the presence of viral markers, for an apparent mother-to-offspring transmission rate of 23.9%. Overlapping results were seen in 22 second-born children followed up from birth. Of 59 sibships with definite infection status, when the first child was infected, 14 (40%) of 35 second children were infected, whereas when the first child was not infected, only 2 of 24 (8.3%) second children were infected. Discordance in HIV-1 transmission was found in 1 of 18 pairs of twins. Univariate and multivariate analyses of possible risk factors for HIV-1 transmission performed on the entire population of children and in the cohort of those followed up from birth were basically in agreement in indicating that the development of symptoms in the mother before delivery and breast-feeding (indeed adopted in only 22 infants in whom HIV-1 infection was identified at birth) were significantly and independently associated with a higher transmission rate. In addition, girls were more frequently infected than boys.(ABSTRACT TRUNCATED AT 250 WORDS)

Breast Feeding↗

PubMed1992

Low risk of mother-to-child transmission of human T lymphotropic virus type II in non-breast-fed infants. The NYC Perinatal HIV Transmission Collaborative Study.

The transmissibility of human T lymphotropic virus (HTLV) type II from mother to child was investigated. Of 236 women enrolled during pregnancy in a study of mother-to-child transmission of human immunodeficiency virus in 1986-1988, 21 (8.9%) were seropositive for HTLV-I/II. All 21 mothers were infected with HTLV-II by synthetic peptide testing and polymerase chain reaction (PCR). HTLV-II-infected women were older (median age, 34 vs. 28 years), more likely to be black (70% vs. 38%), and more likely to report past or current intravenous drug use (85% vs. 56%) than HTLV-II-uninfected women. Of 20 non-breast-fed infants born to 19 of these HTLV-II-infected women, none had detectable HTLV-II by PCR done on peripheral blood mononuclear cells obtained at birth to 36 months of age. Serologic testing of these infants revealed gradual disappearance of HTLV-I/II antibody. While this study does not rule out the possibility of perinatal HTLV-II transmission, the data suggest that it occurs rarely in the absence of breast-feeding.

Adult↗

PubMed1991

Man-to-woman sexual transmission of the human immunodeficiency virus. Risk factors related to sexual behavior, man's infectiousness, and woman's susceptibility. Italian Study Group on HIV Heterosexual Transmission.

To investigate the risk factors for man-to-woman sexual transmission of the human immunodeficiency virus (HIV), we carried out a cross-sectional study of 368 women who were steady partners of HIV-infected men attending 16 Italian clinical centers. Information was collected from the medical records of the infected men and by direct interviews with the women. In a logistic regression analysis, the woman's awareness of her partner's seropositivity (odds ratio [OR], 0.2; 95% confidence interval [CI], 0.0 to 1.1), use of condoms (OR, 0.3; 95% CI, 0.1 to 1), and oral contraceptive use (OR, 0.5; 95% CI, 0.3 to 1.0) were negatively associated with transmission of the HIV infection. An increased risk was found in women having sexual intercourse more than twice a week (OR, 2.4; 95% CI, 1.2 to 4.9) and in women who had been sexually exposed to HIV for between 2 and 5 years (OR, 3.5; 95% CI, 1.8 to 6.7). The transmission rate was higher in couples who engaged in anal sex (OR, 2.8; 95% CI, 1.3 to 6.3); in women reporting vaginitis (OR, 4.9; 95% CI, 2.4 to 10.2) or genital warts (OR, 33.3; 95% CI, 4.5 to 244.1); and in those using intrauterine devices (OR, 3.1; 95% CI, 1.4 to 7.1). The risk for women was also associated with a CD4+ cell count lower than 400/mm3 in their partners. Knowledge of the HIV status of the partner led to increased condom use but did not induce a lower frequency of sexual intercourse or an avoidance of anal sex.

Adolescent↗

PubMed1979

Transmissible gastroenteritis in neonatal dogs: experimental intestinal infection with transmissible gastroenteritis virus.

Fourteen neonatal dogs (4 through 11 days of age) were exposed orally to the Purdue strain of transmissible gastroenteritis (TGE) virus, and six dogs of similar age were noninoculated controls. Clinical signs of enteric disease did not develop. Both exposed and control dogs had normal fecal passages and appetite throughout the experiment. Jejunal epithelium from dogs euthanatized at 12, 24, 48, and 96 hours and at 10 days after exposure did not exhibit morphologic alterations detectable by light microscopy. Electron microscopic examination indicated that jejunal epithelial cells contained TGE viral particles as early as 12 hours after dogs were exposed. There were no apparent morphologic alterations or signs of desquamation of virus-infected cells, however. Results of pig transmission studies indicated that viable TGE virus was in jejunal tissue of the dogs as early as 12 hours and as late as 10 days after exposure to the virus.

Animals↗

PubMed1990

The transmission of onchocerciasis at a forest village in Sierra Leone. II. Man-fly contact, human activity and exposure to transmission.

In the first of these papers we reported on the biting-densities of Simulium damnosum s.l., vector of onchocerciasis, at sites in and near to a village in the forest area of Sierra Leone that was well separated from any large Simulium breeding river. It was found that biting-densities and transmission levels were higher in open farmland than at riverside sites. In this paper we examine the relative time spent by the villagers at the same five sites in and near to the village of Baoma Lungibu, and compare the time spent and activity, with known Simulium biting-densities and transmission indices. It is concluded that, in this situation, the highest risk of infection with onchocerciasis was to persons of either sex in the 20-39 age group who were engaged in farming, or travelling through open farmland, during the months of June to August at the beginning of the wet season. Activities in and close to the village, even by the riverside, where shade cover was heavy, presented little risk of infection.

Adolescent↗