Infectivity of Leishmania promastigotes is associated with surface antigenic expression.

Differentiation between a non-infective and an infective Leishmania promastigote population was demonstrated. Promastigotes in the stationary phase (day 5) were found to be highly infective in vitro to BALB/c mouse peritoneal macrophages, compared with those of the logarithmic phase (day 3). The infective promastigotes showed surface antigenic determinants different from non-infective ones. Polyclonal anti-3 day and anti-5 day antibodies were bound specifically to the surface of corresponding promastigotes in both SRIA and IFAT; no strong cross-reactions were observed otherwise. Also, polyclonal anti-5 day but not anti-3 day antibodies recognized efficiently the antigenic molecules on the surface of late stage (day 7) sandfly promastigotes. This clearly indicates the appearance of new antigenic molecules on the surface of infective promastigote forms. Intracellular multiplication of Leishmania was significantly inhibited by anti-5 day antibodies compared with anti-3 day antibodies. The presence of new surface molecules on late stage promastigotes may contribute to Leishmania infectivity.

Host availability limits population density of Panstrongylus megistus.

In order to determine whether host availability limits triatomine population growth, 5th-stage Panstrongylus megistus were maintained in feeding chambers containing 0, 1, 2, or 3 mice. During the 5-day feeding period, triatomines exposed to two or three mice gained significantly more weight than did bugs exposed to one mouse. In addition, half of the bugs exposed to two or three mice molted, as compared to one-fifth of the P. megistus exposed to one mouse. Thus, weight gain and molting were related to host density. In contrast, bug mortality was related to the triatomine-mouse ratio, being greatest among bugs exposed to one mouse. Twenty-nine nonplastered mud-stick houses in a Chagas' disease endemic area were censused and examined for triatomines. About 70% of houses with greater than or equal to 4 persons contained dense bug populations, while only 20% of houses with 1-3 persons were densely infested. Moreover, blood-meal identifications demonstrated that two-thirds of the P. megistus collected from these houses fed on man. The density of triatomines present in infested houses is related to the number of persons available as hosts.

Destruction of Leishmania mexicana amazonensis promastigotes by normal human serum.

Fresh normal human serum was observed to have a lethal effect on Leishmania mexicana amazonensis promastigotes obtained from laboratory-bred Lutzomyia longipalpis or on promastigotes grown in liquid culture medium, inoculated with the same isolates. Heat inactivation abolished the Leishmania lytic activity from the sera. Resistance of culture promastigotes to lysis by normal human serum was investigated in three isolates of L. m. amazonensis. Development of resistance (up to 7%) was found in only one isolate, obtained from the bone marrow in a human case of visceral leishmaniasis.

A nine year prospective study of Chagas' disease in a defined rural population in northeast Brazil.

The association between infection with Trypanosoma cruzi and the development of electrocardiographic alterations and mortality was studied longitudinally for 9 years in a population residing in an endemic area in Castro Alves, Bahia, Brazil. Annual censuses were begun in 1973. At 3 year intervals from 1974 to 1983, the population was examined serologically and subjected to electrocardiography using standardized techniques. Of 1,751 individuals registered during the 10 censuses, 1,541 (88%) were examined serologically at least once. Of 747 individuals in constant residence and originally seronegative, 24 were seropositive upon subsequent evaluation, giving a seroconversion rate of 4.92/1,000 person-years (PY). The overall rate of development of an abnormal ECG was 25.7/1,000 PY for seropositive individuals and 12.5/1,000 PY for seronegative individuals, a relative risk of 2. The 10-14-year-old seropositive group had the highest risk of developing ECG abnormalities (24.1/1,000 PY, relative risk = 3.5). The age-adjusted mortality rate of seropositive individuals was slightly higher than for seronegative individuals (8.9 vs. 7.8/1,000 PY). In sero-positive individuals, mortality was strongly associated with the presence of ventricular conduction defects and arrhythmias. Ventricular conduction defects appeared most frequently in younger individuals. Older individuals presented the highest risk of development of frequent and multifocal extrasystoles.

Association between household triatomine density and incidence of Trypanosoma cruzi infection during a nine-year study in Castro Alves, Bahia, Brazil.

We studied the association between human incidence of Trypanosoma cruzi infection and household infestation density of Panstrongylus megistus in Castro Alves, Bahia, Brazil. During a 9-year period, 19 persons seroconverted; 17 were children, 17 lived in nonplastered houses, and 13 lived in houses infested with triatomines. Although 6 seroconverting persons lived in houses where triatomines could not be found, the risk of seroconversion was significantly greater in infested houses and 16 times greater in densely infested houses (greater than 15 bugs/person-hour of search). The highest rate of seroconversion (6/100 person-years exposure) occurred in houses containing the greatest number of bugs infected with T. cruzi (greater than 6 infected bugs/person-hour). These observations suggest that vector control measures could have a dramatic impact on transmission of T. cruzi by P. megistus.

An outbreak of Chagas' disease in southwestern Bahia, Brazil.

An outbreak of 20 cases of acute Chagas' disease followed the movement of Triatoma infestans into the county of Riacho de Santana, Bahia, Brazil. The outbreak was unusual in that the majority of cases occurred in adults. Vector control measures were implemented. Three years after the outbreak, a rural community was examined to determine the extent of human infection and disease due to Trypanosoma cruzi. Ninety of 440 residents (20.5%) had serologic evidence of infection, but rates of electrocardiographic (EKG) abnormalities were low. Comparison of age-specific rates of seropositivity and EKG abnormalities with rates from areas with endemic Chagas' disease supported the hypothesis of a recent epidemic. Control measures appear to have interrupted transmission in the region.

Megaesophagus and seroreactivity to Trypanosoma cruzi in a rural community in northeast Brazil.

The relationship of symptoms and radiographic abnormalities suggestive of esophageal motility disorders with electrocardiographic (ECG) alterations and seroreactivity to Trypanosoma cruzi was studied in a defined population in a rural area endemic for Chagas' disease in Bahia, Brazil. Between January and June 1981, 680 individuals 5 years of age or older were examined with serologic tests, ECGs and questionnaires for esophageal motility disorder. Of these, 39.9% were seropositive for Chagas' disease. Symptoms of dysphagia occurred 2.5 times more frequently among seropositive individuals than among seronegative individuals. Radiographic esophageal abnormalities were 3.6 times more frequent among seropositive individuals than among seronegative individuals in the symptomatic group. Symptoms and radiographic abnormalities were more common in men than in women although this was not statistically significant. Among seropositive individuals the percentage with symptoms of dysphagia increased with age, with a peak prevalence rate of 23.9% in the 45- to 64-year-old age group. Also, in the seropositive group, 41.7% with X-ray abnormalities of the esophagus and 26.3% with symptoms of dysphagia presented an abnormal ECG.

The epidemiology and household distribution of seroreactivity to Trypanosoma cruzi in a rural community in northeast Brazil.

The prevalence rates and household distribution of seroreactivity to Trypanosoma cruzi by complement fixation (CF) and indirect immunofluorescent antibody methods were determined in a population of 1,087 persons living in a rural area endemic for Chagas' disease in northeast Brazil. There was a gradual rise in the rate of seropositivity to 60% by age 20. Between ages 20 and 55 the prevalence rate remained at about 60%, but declined thereafter. The decline in the older age groups was not accompanied by a fall in geometric mean titer, suggesting that the decline might better be explained by an increased mortality among those seropositive than by a decrease in CF reactivity associated with age. There was variation in the rates of seropositivity in children among the geographic subunits, but the rates among adults were fairly uniform. Household clustering of seropositivity was demonstrated when both household size and age distribution were taken into account. The presence of a seropositive child less than 5 years of age was a good indicator of a household with a high rate of seropositivity; screening for young seropositive children might be a useful tool to locate high risk households. Seropositive children in households where the mother was seropositive but the father seronegative were significantly younger than seropositive children in households where the father was seropositive but the mother seronegative even though the age distribution and the overall rate of seropositivity in both groups of children were similar; thus, conversion to seropositivity earlier in life in children of seropositive mothers may not be due solely to increased exposure, but may indicate that the immunologic response in such children differed from that of children from seronegative mothers.

Prevalence of parasitemia and seroreactivity to Trypanosoma cruzi in a rural population of Northeast Brazil.

Age-specific prevalence rates of parasitemia and seroreactivity to Trypanosoma cruzi were determined in a rural area endemic for Chagas' disease in Northeast Brazil. Parasitemia was detected by blood cultures and xenodiagnosis, and serum antibodies to the parasite were measured by the complement fixation (CF) and indirect immunofluorescence (IFA) tests. Of the 116 persons examined, 39 (33.7%) had antibodies and 23 (19.8%) had parasitemia. Ninety-six percent of parasitemic individuals were seropositive and 56% of seropositive individuals were parasitemic. The percentage of seropositive individuals with detectable parasitemia declined with age; all seropositive children in the 1- to 4-year age group and two-thirds of seropositive persons 5-19 years old had parasitemia while only one-third of seropositive adults above 19 years had parasitemia. CF and IFA tests were equally sensitive in detecting persons with parasitemia. Xenodiagnosis was more sensitive than culture for detecting parasitemia, but the two methods together were more sensitive than either method alone. Using the age-dependent relationship of parasitemia to seropositivity determined in this study, the prevalence rate of T. cruzi parasitemia was estimated in a much larger adjacent population in which seropositivity rates and the demographic structure were already known.

Comparison of the polymerase chain reaction and serology for the detection of canine visceral leishmaniasis.

The polymerase chain reaction (PCR) and serology was evaluated for the diagnosis of canine visceral leishmaniasis in Bahia, Brazil in a study of 125 dogs. The PCR was 100% sensitive in 25 dogs that had Leishmania demonstrated by either culture or hamster inoculation. It was 100% specific for 35 dogs from the northeastern United States, all were PCR negative. However, 22 of 54 Brazilian dogs that were culture-hamster inoculation-negative were positive by PCR. The nature of the PCR product was identified by hybridization with specific Leishmania probes. Whereas the sensitivity of serology in relationship to infection, as determined by hamster or culture assay was more than 80%, sensitivity of serology was only 63% when compared with PCR. These results raise questions about the use of serology to detect Leishmania infection in dogs, and suggest that the PCR might serve as a better gold standard to define Leishmania infection than culture or hamster inoculation.

Studies on control of visceral leishmaniasis: impact of dog control on canine and human visceral leishmaniasis in Jacobina, Bahia, Brazil.

To assess the effect of removing leishmania-infected dogs on the incidence of visceral leishmaniasis, a controlled intervention study was performed in northeast Brazil. The attempted elimination of seropositive dogs resulted in an initial significant decrease in the annual incidence of seroconversion among dogs from 36% to 6% over the first two years. In the following two years, the incidence increased to 11% and 14%, respectively. In a control area in which dogs were surveyed but seropositive dogs were not removed, the cumulative incidence did not vary significantly from year to year, ranging from 16% to 27%. In the intervention area, the prevalence of dog seropositivity decreased from 36% before the intervention to 10% and remained stable. These findings suggest that attempting to remove seropositive dogs is insufficient as a measure for eradicating visceral leishmaniasis in dogs. However, the force of transmission of infection among dogs can be reduced by such programs. Also, when the number of human cases before and after the start of the intervention was calculated, a significant decrease in incidence of disease in the intervention area was observed among children less than 15 years of age (P < 0.01). The results of this intervention study suggest that the elimination of the majority of seropositive dogs may affect the cumulative incidence of seroconversion in dogs temporarily and may also diminish the incidence of human cases of visceral leishmaniasis.

House construction, triatomine distribution, and household distribution of seroreactivity to Trypanosoma cruzi in a rural community in northeast Brazil.

Household distribution of seroreactivity to Trypanosoma cruzi in inhabitants was analyzed in relation to house construction and the distribution of Panstrongylus megistus, the principal domestic vector of Chagas' disease in a rural area in northeast Brazil. No children residing in mud-brick houses were seroreactive to T. cruzi. The highest rates of seroreactivity occurred in residents of unplastered mud-stick houses, and were twice as high as those found in persons living in mud-brick houses or plastered mud-stick houses. Two-thirds of seroreactive children in this area resided in unplastered mud-stick houses. Over 90% of the P. megistus infestations were found in mud-stick houses. Mud-brick houses had the lowest infestation rates of P. megistus and the lowest household rates of seroreactivity to T. cruzi.

Trypanosoma cruzi infection in dogs and cats and household seroreactivity to T. cruzi in a rural community in northeast Brazil.

The prevalence of Trypanosoma cruzi parasitemia as determined by xenodiagnosis on domestic dogs and cats was correlated with household rates of seroreactivity to T. cruzi and household Panstrongylus megistus infestation in a rural area in northeast Brazil where P. megistus was the only domiciliary triatomine vector. T. cruzi infection was present in about 18% of domestic dogs and cats. Two-thirds of seroreactive children below age 10 resided in houses with T. cruzi-infected animals. In houses with a T. cruzi-infected dog or cat, as well as at least one infected P. megistus, the household rate of seroreactivity to T. cruzi was five times greater than in houses with non-infected domestic animals and no infected triatomine vectors. Domestic dogs and cats are important reservoirs of T. cruzi in an endemic area where P. megistus is the only domiciliary triatomine vector.

A three-year follow-up study of infection with Trypanosoma cruzi and electrocardiographic abnormalities in a rural community in northeast Brazil.

The relationship between parasitemia, seroreactivity to Trypanosoma cruzi, and electrocardiographic abnormalities was studied in 115 individuals from a rural community in northeast Brazil where Chagas' disease is endemic. Vector control measures were introduced, and after 3 years 106 of the original participants were located and re-examined. Serum antibodies to T. cruzi were measured by complement fixation and indirect fluorescent antibody tests and parasitemia by xenodiagnosis and blood cultures. On both examinations more seropositive children than seropositive adults showed parasitemia, and parasitemia was more likely to persist over the 3-year period in younger individuals. Electrocardiographic (ECG) abnormalities were seen more frequently in seropositive individuals without parasitemia. However, ECG abnormalities, as expected, were more prevalent in older individuals and therefore no specific inverse relationship between ECG findings and parasitemia could be shown. The decreased prevalence of infection noted in younger individuals following the introduction of vector control measures indicates that this approach limited transmission.

Breeding structure of the sand fly Lutzomyia longipalpis (Lutz & Neiva) in Brazil.

Eleven populations of Lutzomyia longipalpis (Lutz & Neiva), the sand fly vector of Leishmania chagasi, from different areas of Brazil were analyzed for genetic variation at 16 enzyme loci. In this region, the prevalence of visceral leishmaniasis (VL) caused by L. chagasi is spotty and reproductive isolation among populations of Lu. longipalpis has been reported. It is thought that morphologically similar cryptic species with varying vectorial capacity may be responsible for the discontinuous distribution of VL. The aim was to study the genetic structure of populations within this region and to identify demes that may represent sibling species. Genotypic frequencies within populations were in close compliance to Hardy-Weinberg expectations, suggesting there are no sympatric species among these 11 populations. Levels of genetic distance between pairs of populations were very low (< 0.03), consistent with local populations within a single sand fly species. When genotypic frequency data for all populations were pooled, 9 of the 13 polymorphic loci deviated from Hardy-Weinberg expectations, indicating some degree of genetic substructuring. Estimates of effective migration rates (N(e)m) among all populations were low, 2.73, suggesting that gene flow is restricted among populations, which is probably the reason for the observed genetic substructuring.

An outbreak of acute Chagas's disease in the São Francisco Valley region of Bahia, Brazil: triatomine vectors and animal reservoirs of Trypanosoma cruzi.

Following reports of an unusually high incidence of acute Chagas's disease and the appearance of large numbers of Triatoma infestans in the southwestern region of the State of Bahia, triatomine bugs (Hemiptera: Reduviidae) and domestic animals in one of the affected communities were surveyed and examined for infection with Trypanosoma cruzi. Triatoma infestans was prevalent in houses and was also found in peridomestic habitats. T. sordida and T. pseudomaculata occupied peridomestic and sylvatic habitats and T. brasiliensis was found only among rocks far from houses. Panstrongylus megistus, formerly present in the region, was not found. Trypanosoma cruzi was detected in 19.5% of Triatoma infestans, 11.5% of T. sordida, 19% of dogs, 29% of cats and 100% of rats examined. A disproportionate number of early instar bugs were infected with Trypanosoma cruzi, suggesting that a rapid increase in the rate of transmission had recently occurred. The history of the domestic triatomine fauna of the region since 1912 is reviewed, and it is proposed that the relatively recent arrival of Triatoma infestans initiated a domestic cycle linked to peridomestic and sylvatic cycles of Trypanosoma cruzi transmission. Increased human mobility, the use of DDT for malaria control, and drought conditions are considered as factors which might have contributed to the outbreak of human infection.

Epidemiological aspects of three Trypanosoma cruzi zymodemes in Bahia State, Brazil.

Culture forms of 104 stocks of Trypanosoma cruzi isolated in different regions of the State of Bahia were compared by electrophoresis of six enzymes. The three distinct combinations of isoenzyme patterns seen were designated ZI, Z2 and Z3. In an area of endemic Chagas's disease in eastern Bahia, T. cruzi Z1 was associated with sylvatic mammals and sylvatic triatomines, whereas T. cruzi Z2 was associated with a separate domestic cycleof transmission. T. cruzi Z1 was also found in sylvatic triatomines from other parts of the State. In contrast, in an area of the São Francisco Valley region of western Bahia, both T. cruzi Z1 and Z2 were isolated from man, domestic animals, and peridomestic rats. T. cruzi Z3 was isolated from an armadillo and from Panstrongylus geniculatus, a triatomine commonly found in armadillo burrows. Both T. cruzi Z1 and Z2 appeared to be pathogenic in man: T. cruzi Z1 was isolated from patients with acute Chagas's disease and from a single patient with chronic cardiac manifestations. T. cruzi Z2 was isolated from some asymptomatic individuals but was also associated with acute disease and chronic cardiac and digestive syndromes.

Comparison of filtration staining (Bell) and thick smear (Kato) for the detection of quantitation of Schistosoma mansoni eggs in faeces.

We compare results of one Bell and one Kato-Katz examination performed on each of 315 stool specimens from residents in an area in north-eastern Brazil endemic for schistosomiasis mansoni. The prevalence of Schistosome infection detected by the Bell technique was 76% and by the Kato-Katz technique was 63%. 81% (44/54) of the infections missed by a Kato-Katz smear were light infections (one of 50 epg range by Bell examination). Over, all, 55% (44/80) of stools in this egg count range by the Bell technique were negative on a single Kato-Katz smear. This implies that five Kato-Katz smears per stool would ensure a 95% probability (0.55(5) X 100) of detecting such light infections. However, a single Kato-Katz smear detected eggs in 97% (124/128) of stools with a Bell count greater than 100 epg. For stools positive by both methods the egg counts per gram of stool were higher (p less than 0.001) by Kato-Katz examination. Geometric mean egg counts for the infected population were 199 epg by the Kato-Katz and 92 epg by the Bell methods. 64% (59 v. 36) more persons were classified as heavily infected (greater than 400 epg) by the Kato-Katz method than by the Bell method. The differing measurements of schistosome infection obtained with the Bell and Kato-Katz methods must be considered when comparing data on morbidity-infection relationships.

A three year follow-up of chemotherapy with oxamniquine in a Brazilian community with endemic schistosomiasis mansoni.

Oral oxamniquine was tested as a control strategy for endemic schistosomiasis in a rural area of Bahia, Brazil. Adults were treated with a single dose (12.5 to 15 mg per kg) and children (less than 12 years old) with a total of 20 mg per kg in two doses. The 191 (infected) persons treated represented 69% of the infected population in the study area. Follow-up stool examinations (Kato-Katz method) at one, 3, 6, 13, 25 and 33 months showed the cure rate declining from 80% at three months to 46% at 33 months. Over one half of those not cured showed a decrease in egg counts throughout the follow-up which, after 33 months, remained 66% below the pre-treatment levels. Stool examinations conducted on all study area residents during three years before chemotherapy showed the prevalence and intensity of Schistosoma mansoni infection to be high and stable. 33 months after the chemotherapy the prevalence was 41% and for infected individuals the geometric mean egg count was 121 epg, a decline of respectively 35% and 40% from pre-treatment levels for each index. Chemotherapy of infected persons with oxamniquine protected the community as a whole from high worm burdens for almost three years, although at this point the prevalence began to rise towards pretreatment levels.

Factors controlling the volume of feces produced by triatomine vectors of Chagas' disease.

Triatomine species influenced volume of feces produced; Triatoma dimidiata produced the largest volume of feces followed by Panstrongylus megistus, Rhodnius prolixus, and Triatoma infestans. Moreover, stage and sex affected fecal production; 5th-stage female nymphs excreted the largest volume of feces. The amount of blood ingested was significantly correlated with the volume of feces produced in 10 out of 11 experimental groups. Triatome size and volume of feces produced were less closely correlated. Indeed, a "threshold" minimum amount of blood must be ingested before bugs are stimulated to defecate. The defecation habits of triatomines probably influence the vectorial capacity of a triatomine species to a lesser degree than do the density of domestic infestations, host affinity, and the degree of adaptation to the domestic habitat.