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1.
Trans R Soc Trop Med Hyg ; 87(1): 3-6, 1993.
Artículo en Inglés | MEDLINE | ID: mdl-8465388

RESUMEN

The assessment of malarial infectivity, for example in the evaluation of transmission blocking immunity, is generally based on counting oocysts in mosquitoes fed on infected blood. Ultimate transmission of the disease may, however, depend on the sporozoite load in the mosquito and its relationship to the size of the inoculum introduced to man. We conducted a laboratory study on Anopheles tessellatus infected with 108 different natural isolates of Plasmodium vivax from patients and 24 of P. falciparum to determine the relationship between oocyst numbers, sporozoite loads, and the effect of these on mosquito mortality. It was found that the P. vivax parasite density was positively correlated with the proportion of mosquitoes infected by a given feed at both the midgut and gland stages of parasite development (correlation coefficient [r] = 0.77, P < 0.001 and r = 0.6, P < 0.05 respectively). A significant positive linear correlation was observed between the number of oocysts and sporozoites in P. vivax (r = 0.5; P < 0.05); the proportions of mosquitoes infected with oocysts and sporozoites were also similarly related, although in general about 15% of mosquitoes infected with oocysts failed to develop salivary gland infections with sporozoites. The number of mosquitoes infected with P. falciparum parasites was too low for statistical analysis. Infection with either species of parasite did not appear to affect mosquito survival, nor was parasite density in the mosquito correlated with mosquito mortality.


Asunto(s)
Anopheles/parasitología , Plasmodium falciparum/crecimiento & desarrollo , Animales , Apicomplexa , Recuento de Huevos de Parásitos , Plasmodium vivax/crecimiento & desarrollo
2.
Parasite Immunol ; 14(4): 385-96, 1992 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-1437231

RESUMEN

Serum effects on gametocyte infectivity, that is, transmission blocking/enhancing immunity, were measured in the sera of 196 acute Plasmodium vivax patients who were residents of a malaria region in Kataragama, southern Sri Lanka. Direct mosquito feedings were also performed on 170 of these patients. Sera of about 48% of patients suppressed gametocyte infectivity significantly (by more than 75%) and of a smaller proportion (12%) had pronounced infectivity enhancing effects. Transmission immunity did not increase with age of patients, rather, immunity tended to be higher in younger patients. Data suggest that immunity levels are boosted by reinfections only if they occur within a period of 4 months from the previous infection, i.e., that immune memory for boosting does not last beyond 4 months. Enhancing effects in the sera of patients correlated with the absence of gametocytes at the time of investigation suggesting that enhancement occurs early during the course of a blood infection, and blocking later, when serum antibodies reach higher levels. The blocking and enhancing effects of serum appears to depend not only on the antibody concentration in serum, but also on the intrinsic infectivity of the parasite isolate against which it is tested: thus, infectivity enhancing effects were potentiated by low intrinsic infectivities of the parasite isolate. The direct infectivity of patients to mosquitoes correlated with transmission immunity indicating that transmission immunity is an influential factor determining infectivity of malaria patients.


Asunto(s)
Malaria Vivax/transmisión , Plasmodium vivax/inmunología , Adolescente , Adulto , Anciano , Animales , Anticuerpos Antiprotozoarios/inmunología , Niño , Preescolar , Técnica del Anticuerpo Fluorescente , Humanos , Inmunidad , Terapia de Inmunosupresión , Lactante , Malaria Vivax/epidemiología , Malaria Vivax/inmunología , Persona de Mediana Edad , Estudios Seroepidemiológicos , Sri Lanka/epidemiología
3.
J Med Entomol ; 29(2): 188-96, 1992 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-1495028

RESUMEN

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.


Asunto(s)
Anopheles/parasitología , Mordeduras y Picaduras de Insectos/epidemiología , Insectos Vectores/parasitología , Malaria/transmisión , Animales , Humanos , Incidencia , Malaria/epidemiología , Matemática
4.
Parasite Immunol ; 14(1): 75-86, 1992 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-1557232

RESUMEN

Antibodies to two peptides DDAAD and (NANP)40 representing the repetitive sequence of circumsporozoite antigens (CS protein) of P. vivax and P. falciparum respectively were measured in a cohort of 149 and 107 individuals respectively at four, 6 monthly blood surveys performed on residents of Kataragama, a P. vivax malaria endemic region in southern Sri Lanka. The prevalence of antibodies to the CS protein of both species was relatively low being less than 20% to either peptide in the population as a whole, this being consistent with the low entomological inoculation rates in the area. A marked age related prevalence pattern was evident, with the prevalence of antibodies increasing with age to reach between 25 to 30% in the 25-50 year age group in both P. vivax and P. falciparum. The population had had a life long exposure to P. vivax malaria but not to P. falciparum, an epidemic of which occurred in this region a few months prior to the beginning of this study. Nevertheless, the age-related prevalence of these antibodies was identical with respect to the two species. This suggests that the age-related prevalence pattern reflected differences in inoculation rates between the age groups due to differences in exposure to inoculation rather than an age acquired response resulting from a cumulative experience over several years. An analysis of antibody prevalence in individuals showed first, that sporozoite inoculations must have been clustered rather than homogeneously distributed in the population and secondly, that sero-conversion did not correlate with malaria infections in these individuals.


Asunto(s)
Envejecimiento/fisiología , Anticuerpos Antiprotozoarios/inmunología , Malaria Falciparum/inmunología , Malaria Vivax/inmunología , Plasmodium falciparum/inmunología , Plasmodium vivax/inmunología , Proteínas Protozoarias/inmunología , Adolescente , Adulto , Secuencia de Aminoácidos , Animales , Niño , Preescolar , Ensayo de Inmunoadsorción Enzimática , Humanos , Lactante , Recién Nacido , Malaria Falciparum/epidemiología , Malaria Vivax/epidemiología , Persona de Mediana Edad , Datos de Secuencia Molecular , Prevalencia , Sri Lanka/epidemiología
5.
Am J Trop Med Hyg ; 45(4): 479-87, 1991 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-1951856

RESUMEN

The infectious reservoir of Plasmodium vivax and P. falciparum in a malaria endemic region in Sri Lanka was defined in a population of 3,625 by directly feeding mosquitoes on a sample of infected individuals during a period of 17 months. The malaria case incidence in this population was concurrently monitored. P. vivax gametocyte densities were highest in the youngest age groups, and decreased steadily with increasing age. However, the infectivity per gametocyte appeared to be lower in the younger age groups than in the older ones. There was no significant correlation between the age of patients and their gametocyte densities for P. falciparum, to which this population was only recently exposed, nor was there a discernible trend in the infectivity per gametocyte in different age groups. The average infectivity of patients was lowest in the youngest (0-5 years) and the oldest (greater than 50) age groups. The contribution made by P. vivax patients in the different age groups to the reservoir of infection was estimated. Patients in the 6-25 year age groups made the largest contribution to the reservoir, followed by those in the 26-50 year age group. Patients in the youngest and the oldest age groups contributed least to the infectious reservoir. When population sizes in the different age groups were taken into consideration, the age groups between 6 and 50 years contributed almost equally to approximately 87% of the infectious reservoir. The reservoir of P. falciparum malaria was very small, being confined to 9% of the patients, and this appears to be a characteristic of epidemic malaria, as was the case with P. falciparum.


Asunto(s)
Anopheles/parasitología , Reservorios de Enfermedades , Insectos Vectores/parasitología , Malaria Falciparum/epidemiología , Malaria Vivax/epidemiología , Enfermedad Aguda , Adolescente , Factores de Edad , Animales , Niño , Preescolar , Humanos , Lactante , Malaria Falciparum/sangre , Malaria Falciparum/transmisión , Malaria Vivax/sangre , Malaria Vivax/transmisión , Persona de Mediana Edad , Plasmodium falciparum/crecimiento & desarrollo , Plasmodium vivax/crecimiento & desarrollo , Sri Lanka/epidemiología
6.
Am J Trop Med Hyg ; 45(1): 77-85, 1991 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-1867350

RESUMEN

The occurrence of malaria infections due to Plasmodium vivax and P. falciparum was monitored in a population of 3,023 people living in six contiguous villages in Kataragama, an area of endemic malaria in southern Sri Lanka, over a period of 17 months. The annual incidence of malaria in this population during the study period was 25.8%. Malaria attacks were clustered, occurring more frequently than expected in certain individuals and housing groups and less frequently than expected in others. In one of these villages, the distribution of cases was examined in relation to locality and to the type of house construction. There was a strong association between the malaria incidence and house construction, independent of location. The risk of getting malaria was greater for inhabitants of the poorest type of house construction (incomplete, mud, or cadjan (palm) walls, and cadjan thatched roofs) compared to houses with complete brick and plaster walls and tiled roofs. Houses that were better constructed had a significantly lower malaria incidence rate (10.5%) than those that were poorly constructed (21.2%; P less than 0.01, by Student's t-test). There was also a significantly higher number of indoor resting mosquitoes collected from the poorly constructed houses than from those better constructed; the average (geometric mean) of mosquito densities found in houses of better versus poor construction were 0.97 and 1.89 per collection in the dry season, and 1.95 and 3.42 per collection in the wet season, respectively (P less than 0.05 in both seasons). This indicated that the higher malaria risk associated with poorly constructed houses was at least partly due to higher human-mosquito contact among their inhabitants.


Asunto(s)
Vivienda , Malaria/epidemiología , Animales , Anopheles , Humanos , Malaria/etiología , Plasmodium falciparum , Plasmodium vivax , Factores de Riesgo , Sri Lanka
7.
Bull World Health Organ ; 69(6): 725-34, 1991.
Artículo en Inglés | MEDLINE | ID: mdl-1786621

RESUMEN

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.


Asunto(s)
Malaria Vivax/transmisión , Modelos Biológicos , Plasmodium vivax , Animales , Anopheles/inmunología , Anopheles/parasitología , Humanos , Inmunidad , Insectos Vectores/inmunología , Insectos Vectores/parasitología , Malaria Vivax/parasitología , Sri Lanka/epidemiología
10.
Am J Trop Med Hyg ; 42(4): 298-308, 1990 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-2184688

RESUMEN

Parasitological and entomological parameters of malaria transmission were monitored for 17 months in 3,625 residents in a Plasmodium vivax malaria endemic region in southern Sri Lanka; the study area consisted of 7 contiguous villages where routine national malaria control operations were being conducted. Malaria was monitored in every resident; fever patients were screened and 4 periodical mass blood surveys were conducted. An annual malaria incidence rate of 23.1% was reported during the period: 9.3% was due to P. vivax and 13.8% was due to P. falciparum; there had been a recent epidemic of the latter in this region, whereas the P. falciparum incidence rate in the previous 10 years had been negligible. There was a wide seasonal fluctuation in the malaria incidence, with the peak incidence closely following the monsoon rains. The prevalence of malaria due to both species detected at the 4 mass blood surveys ranged from 0.98% (at low transmission) to 2.35% (at peak transmission periods). Adults and children developed acute clinical manifestations of malaria. Entomological measurements confirmed a low degree of endemicity with estimated inoculation rates of 0.0029 and 0.0109 (infectious bites/man/night) for P. vivax and P. falciparum, respectively. Several anopheline species contributed to the transmission, and the overall man biting rates (MBR) showed a marked seasonal variation. Malaria at Kataragama, typical of endemic areas of Sri Lanka, thus presents characteristics of "unstable" transmission. Malaria was clustered in the population. There was a low clinical tolerance to P. falciparum malaria, to which most had only been at risk, compared to P. vivax, to which most had had a life-long exposure.


Asunto(s)
Anopheles/fisiología , Insectos Vectores/fisiología , Malaria/transmisión , Adolescente , Adulto , Factores de Edad , Animales , Niño , Preescolar , Femenino , Humanos , Incidencia , Lactante , Malaria/epidemiología , Malaria/inmunología , Masculino , Persona de Mediana Edad , Control de Mosquitos , Plasmodium falciparum/aislamiento & purificación , Plasmodium vivax/aislamiento & purificación , Lluvia , Estaciones del Año , Factores Sexuales , Sri Lanka/epidemiología
11.
Am J Trop Med Hyg ; 42(2): 104-10, 1990 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-1690521

RESUMEN

Monoclonal antibodies against variant epitopes of a highly polymorphic protein (PV200) in schizonts of Plasmodium vivax have been used to analyze the variety of genetically distinct populations of parasites present in the peripheral blood of individual P. vivax infections in Sri Lanka. In 9 out of 10 isolates of freshly drawn P. vivax infected blood from different individuals, parasites of only 1 PV200 serotype was found within each individual infection, even though parasites were serotypically distinct between individuals. In 1 isolate parasite population, 3 distinct PV200 serotypes were identified. Thus, most P. vivax infections appeared to consist of a single genetically homogeneous population of parasites within the detection limits of the technique. The prevalence of P. vivax infections in an area of malaria transmission in southern Sri Lanka and the densities of oocysts in mosquitoes fed on P. vivax infected individuals indicated that parasite populations would be transmitted many times before encountering parasites of other origins, and that individual populations would tend to reduce to genetic homogeneity during transmission. These expectations are consistent with the high proportion of genetically homogeneous P. vivax isolates observed.


Asunto(s)
Anticuerpos Monoclonales/inmunología , Variación Genética , Malaria/parasitología , Plasmodium vivax/genética , Proteínas Protozoarias/genética , Adulto , Animales , Anopheles/parasitología , Variación Antigénica , Antígenos de Protozoos/genética , Antígenos de Protozoos/inmunología , Cruzamientos Genéticos , Epítopos/genética , Epítopos/inmunología , Humanos , Malaria/epidemiología , Persona de Mediana Edad , Plasmodium vivax/inmunología , Prevalencia , Proteínas Protozoarias/inmunología , Sri Lanka/epidemiología , Sobreinfección/epidemiología
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