Allelic Diversity at the Merozoite Surface Protein-1 (MSP-1) Locus in Natural Plasmodium falciparum Populations: a Brief Overview

The merozoite surface protein-1 (MSP-1) locus of Plasmodium falciparum codes for a major asexual blood-stage antigen currently proposed as a major malaria vaccine candidate. The protein, however, shows extensive polymorphism, which may compromise its use in sub-unit vaccines. Here we compare the patterns of allelic diversity at the MSP-1 locus in wild isolates from three epidemiologically distinct malaria-endemic areas: the hypoendemic southwestern Brazilian Amazon (n = 54), the mesoendemic southern Vietnam (n = 238) and the holoendemic northern Tanzania (n = 79). Fragments of the variable blocks 2, 4a, 4b and 6 or 10 of this single-copy gene were amplified by the polymerase chain reaction, and 24 MSP-1 gene types were defined as unique combinations of allelic types in each variable block. Ten different MSP-1 types were identified in Brazil, 23 in Vietnam and 13 in Tanzania. The proportion of genetically mixed infections (isolates with parasites carrying more than one MSP-1 version) ranged from 39% in Brazil to 44% in Vietnam and 60% in Tanzania. The vast majority (90%) of the typed parasite populations from Brazil and Tanzania belonged to the same seven most frequent MSP-1 gene types. In contrast, these seven gene types corresponded to only 61% of the typed parasite populations from Vietnam. Non-random associations were found between allelic types in blocks 4a and 6 among Vietnamese isolates, the same pattern being observed in independent studies performed in 1994, 1995 and 1996. These results suggest that MSP-1 is under selective pressure in the local parasite population. Nevertheless, the finding that similar MSP-1 type frequencies were found in 1994 and 1996 argues against the prominence of short-term frequency-dependent immune selection of MSP-1 polymorphisms. Non-random associations between MSP-1 allelic types, however, were not detected among isolates from Brazil and Tanzania. A preliminary analysis of the distribution of MSP-1 gene types per host among isolates from Tanzania, but not among those from Brazil and Vietnam, shows significant deviation from that expected under the null hypothesis of independent distribution of parasites carrying different gene types in the human hosts. Some epidemiological consequences of these findings are discussed

A comparative study on IgG-ELISA, IgM-IFT and Kato-Katz methods for epidemiological purposes in a low endemic area for schistosomiasis

The high sensitivity and the possibility of automation of the enzyme-linked-immunosorbent-assay (ELISA) has indicated this technique as one of the most useful serological test for epidemiological studies. In the present study, an ELISA for detection of IgG antibodies against adult worm antigens (IgG-ELISA) was investigated for epidemiological purposes, in a rural area of the municipality of Itariri (São Paulo, Brazil). Blood on filter paper (1,180 samples) from about 650 schoolchildren were submitted to ELISA and the data compared to the results of the parasitological method of Kato-Katz and also to the IgM-IFT (immunofluorescence test for IgM antibodies to gut associated antigens). The prevalence rates respectively of 8.5%, 43.0%, and 56.2% by the Kato-Katz, IgG-ELISA, and IgM-IFT methods suggest the poor sensitivity of the parasitological method for detection of Schistosoma mansoni eggs in individuals with low worm burden, situation commonly observed in low endemic areas. These results can partially explain the poor degree of agreement between the IgG-ELISA and the Kato-Katz, as suggested by the Kappa index of 0.170. Otherwise, the Kappa index of 0.675 showed substantial agreement between the two serological tests. Some discrepancy of results between the two serological techniques must be better investigated.

The Epidemiological Impact of Antimeningococcal B Vaccination in Cuba

The incidence of invasive meningococcal disease (IMD) before (1984-1988) and after (1989-1994), a nationwide intervention with VA-MENGOC-BC vaccination started in 1989, was compared. The prevaccination period incidence density (ID> 8.8/ 105 year-person) was higher than the postvaccination ID (ID< 6.5/ 105 year-person). The percentage proportional differences from the start to the end of each period of ID in the vaccinal period was higher (87%) than the prevaccinal (37%) with significant differences among vaccinated groups (< 25 years old). A break-point (Chow test) was confirmed by the decrease in the ID between 1989 and 1990 in children under 1 year old, 5-9, 10-14, 15-19 and 50-54 years. Comparison of ID using maps showed a decrease in IMD in all municipalities during the postvaccination period. These findings support the epidemiological impact of VA-MENGOC-BC vaccination in the reduction of IMD morbidity.

Evolution of the clinical and epidemiological knowledge about Chagas disease 90 years after its discovery

Three different periods may be considered in the evolution of knowledge about the clinical and epidemiological aspects of Chagas disease since its discovery: (a) early period concerning the studies carried out by Carlos Chagas in Lassance with the collaboration of other investigators of the Manguinhos School. At that time the disease was described and the parasite, transmitters and reservoirs were studied. The coexistence of endemic goiter in the same region generated some confusion about the clinical forms of the disease; (b) second period involving uncertainty and the description of isolated cases, which lasted until the 1940 decade. Many acute cases were described during this period and the disease was recognized in many Latin American countries. Particularly important were the studies of the Argentine Mission of Regional Pathology Studies, which culminated with the description of the Romaña sign in the 1930 decade, facilitating the diagnosis of the early phase of the disease. However, the chronic phase, which was the most important, continued to be difficult to recognize; (c) period of consolidation of knowledge and recognition of the importance of Chagas disease. Studies conducted by Laranja, Dias and Nóbrega in Bambuí updated the description of Chagas heart disease made by Carlos Chagas and Eurico Villela. From then on, the disease was more easily recognized, especially with the emphasis on the use of a serologic diagnosis; (d) period of enlargement of knowledges on the disease. The studies on denervation conducted in Ribeirão Preto by Fritz Köberle starting in the 1950 decade led to a better understanding of the relations between Chagas disease and megaesophagus and other visceral megas detected in endemic areas.

Mepraia spinolai in the Southeastern Pacific Ocean Coast (Chile) - First insular record and feeding pattern on the Pan de Azúcar Island

In a field collection performed at Pan de Azúcar Island in Northern Chile, 95 specimens representing all instars of Mepraia spinolai were collected. The intestinal contents of 55 specimens were examined for Trypanosoma cruzi infection and were found to be negative. This is the first record of an insular habitat for M. spinolai, where the insects had fed mainly on seabirds (78%), some on marine mammals (5%), and some on reptiles (7%).

Domestic and peridomestic transmission of American cutaneous leishmaniasis: changing epidemiological patterns present new control opportunities

Predictions that deforestation would reduce American cutaneous leishmaniasis incidence have proved incorrect. Presentations at a recent international workshop, instead, demonstrated frequent domestication of transmission throughout Latin America. While posing new threats, this process also increases the effectiveness of vector control in and around houses. New approaches for sand fly control and effective targeting of resources are reviewed.

Transmission of tuberculosis in Havana, Cuba: a molecular epidemiological study by IS6110 restriction fragment length polymorphism typing

The combination of molecular and conventional epidemiological methods has improved the knowledge about the transmission of tuberculosis in urban populations. To examine transmission of tuberculosis in Havana, Cuba, with DNA fingerprinting, we studied 51 out of 92 Mycobacterium tuberculosis strains isolated from tuberculosis patients who resided in Havana and whose infection was culture-confirmed in the period from September 1997 to March 1998. Isolates from 28 patients (55%) had unique IS6110 restriction fragment length polymorphism (RFLP) patterns, while isolates from 23 others (45%) had identical patterns and belonged to 7 clusters. Three clusters consisting of six, five and two cases were each related to small outbreaks that occurred in a closed setting. Three other clustered cases were linked to a large outbreak that occurred in another institution. Younger patients were more correlated to clustering than older ones. The finding that 45% of the isolates had clustered RFLP patterns suggests that recent transmission is a key factor in the tuberculosis cases in Havana. The IS6110 RFLP typing made it possible to define the occurrence of outbreaks in two closed institutions.

Replacing oxamniquine by praziquantel against Schistosoma mansoni infection in a rural community from the sugar-cane zone of Northeast Brazil: an epidemiological follow-up

A group of 52 villagers was followed-up for three years regarding Schistosoma mansoni infection. All villagers were periodically surveyed by the Kato-Katz method. In March 1997 and March 1998 the positives were treated with oxamniquine (15-20 mg/kg), and in March 1999, with praziquantel (60 mg/kg). All infection indices decreased substantially between March 1999 and March 2000: prevalence of infection (from 32.7% to 21.2%), prevalence of moderate/heavy infection (from 7.7% to 1.9%), intensity of infection (from 23.1 epg to 7.4 epg) and reinfection (from 35.7% to 14.3%). Negativation increased from 53.8 to 82.4. An optimistic prognostic is assumed in the short term for the introduction of praziquantel in the study area.

Epidemiological and Serological Aspects in Canine Toxoplasmosis in Animals with Nervous Symptoms

The presence of anti-Toxoplasma gondii IgM and IgG antibodies was studied in samples of blood serum taken from eighty dogs with nervous symptoms at the Serviço de Enfermidades Infecciosas dos Animais, Faculdade de Medicina Veterinária e Zootecnia, Unesp, Botucatu, São Paulo, Brazil. The frequency of IgG titers were 16 (13.7%), 64 (13.7%), and 256 (5%), and for IgM titers were 16 (7.5%), 64 (15%), and 256 (8.7%). Positive reactions were more frequent in the older animals, males, from a rural environment, in constant contact with small animals, principally birds and rodents. There was a higher frequency of a positive reaction in dogs fed with kitchen food, especially in those fed with raw ingredients. The most common neurological pictures were alterations in consciousness, in movement, and in the hand-cart test. The percentage of reagents with specific IgM antibodies was high, indicating active infections, but the possibility of co-infection with the distemper virus can not be discarded, and this may be a predisposing factor for toxoplasmosis infection, once the distemper virus has a potent immunosupressive action.

Epidemiological Aspects of Head Lice in Children Attending Day Care Centres, Urban and Rural Schools in Uberlândia, Central Brazil

From November 1996 to March 2000, a total of 884 children between 0 and 15 years, from 11 institutions including day care centres, public urban and public rural schools in Uberlândia, State of Minas Gerais, central Brazil, were examined for head louse infestation. Children's sex, race, age and some hairs characteristics were shown to be associated to parasite infestation. A prevalence rate of 35% was found and the highest rates were observed in black, female children, with long, dark, wavy hairs. Hairs density and thickness did not seem to influence significantly the distribution of this pediculosis in Uberlândia's schoolchildren. Differences observed between the prevalence rates of head lice in children from the urban institutions suggest there is a greater epidemiological heterogeneity in this group when compared to the rural schoolchildren.

A Rural Community in a Brazilian Western Amazonian Region: Some Demographic and Epidemiological Patterns

Some demographic and epidemiological patterns of the rural population of Monte Negro, locality situated in the State of Rondônia (Brazil), Western Amazonia, are described based on a sample of 924 randomly selected individuals, approximately 10% of the whole population. The main features of this sample are (1) the illiteracy rates in the parental generation were 23% for fathers and 20% for mothers. Among children, this figure dropped to 6%; (2) housing in Monte Negro is characterized by being constructed with wood (92%), and also a floor (75%). Nevertheless, only 32% of these houses had electric energy; (3) the mean ages for the parental generation were 41.9 for males and 36.3 for females. These values for the offspring generation were 12.2 and 10.5, respectively; (4) the sex-ratio of the offspring generation was 1.32;(5) the bioassay of kinship was estimated as .033 for this long range migrant population; (6) the prevalence of some macrophage dependent infectious disease was conspicuously high; (7) the reported number of malarial episodes among males and females was statistically different, suggesting that malaria may be, in part, a "professional" disease; (8) the prevalence of serum-positive reactions against B-hepatitis is distressing. It has a strong age dependence and reaches 74% among adult males. Conversely, signs of active infection (AgHbs) rises to 16% among children.

Epidemiological and immunological aspects of human visceral leishmaniasis on Margarita Island, Venezuela

Sixty-five patients were diagnosed with visceral leishmaniasis (VL) on Margarita Island in the decade from 1990 to1999; 86.2% were <= 3 years old. All were leishmanin-negative at diagnosis. Evaluation of 23 cured patients in 1999 revealed that 22/23 had converted to leishmanin-positive; five had persisting antibodies to rK39 antigen, with no clinical evidence of disease. Leishmanin tests were positive in 20.2% of 1,643 healthy individuals from 417 households in endemic areas. Of the positive reactors, 39.8% were identified in 35 (8.4%) of the households, 15 of which had an antecedent case of VL, a serologically positive dog or both. Weak serological activity to rK39 antigen was detected in 3 of 488 human sera from the endemic areas. The presence of micro-foci of intense peri-urban transmission and the apparent absence of other Trypanosomatidae causing human disease offer a unique opportunity for the study of reservoirs, alternative vectors and evaluation of control measures on the Island.

Relationship between antennal sensilla pattern and habitat in six species of Triatominae

In order to determine if habitat similarity is correlated with a similarity of sensilla pattern, we analyzed six species of Triatominae present in two biogeographic regions of Brazil: the "caatinga" and the "cerrado". In broad terms Triatoma infestans (cerrado) and T. brasiliensis (caatinga) are found in human domiciles, T. sordida (cerrado) and T. pseudomaculata (caatinga) colonize peridomestic habitats, and Rhodnius neglectus (cerrado) and R. nasutus (caatinga) inhabit palm tree crowns. The number and distribution of four sensilla types (bristles, thin and thick walled trichoidea, and basiconica) were compared in these species. Sexual dimorphism of sensilla patterns was noted in T. sordida, T. brasiliensis and T. pseudomaculata. A principal component analysis showed three main groups: (i) species that live in the palms, (ii) domiciliated species and (iii) those living in the peridomestic habitat. T. infestans almost exclusively domestic, was placed at the centre of the canonical map and some individuals of other species overlapped there. These results support the idea that the patterns of antennal sensilla are sensitive indicators of adaptive process in Triatominae. We propose that those species that inhabit less stable habitats possess more types of sensilla on the pedicel, and higher number of antennal sensilla.