The influence of marital status on HIV infection in an HIV hyperendemic area of rural South Africa, 2000–2017

Marital status is one of the factors whose impact on HIV infection has always been studied but contradictory findings have been reported. The drastic changes in marriage patterns in South Africa influences the role of marital status on HIV infection. This study aims to give evidence-based information on the association between marital status and HIV infection in a hyperendemic HIV area in rural South Africa. This study was conducted on longitudinal data collected from the African Health Research Institute (AHRI) based in northern rural KwaZulu-Natal from 2000 to 2017 using multivariable Cox regression. The multivariable Cox regression results found marital status to be a significant factor of HIV infection. Compared to those who were married, the risk of HIV infection was approximately two times in those who were never married while those who were widowed presented as much as twice the risk of HIV infection. In addition, less educated participants were at more risk of HIV infection than those with tertiary education. Furthermore, as expected, the risk of HIV infection increased with age (20–24 HR: 3.05 (2.32–4.02); 25–34 HR: 3.98 (3.12–5.07) and 35–49 HR: 4.36 (3.36–5.67). Women were more susceptible to HIV infection than men were. This study found marital status to be an influential factor of HIV infection together with other socio-economic and demographic factors. This finding will help guide policy makers on empowerment programmes and policies targeting HIV and other health related issues in rural South Africa.     

Behçet's disease in Israel: the influence of ethnic origin on disease expression and severity

OBJECTIVE: To evaluate the relationship between ethnic origin and manifestations of Beh?et's disease (BD) in Israel. METHODS: We studied 100 Israeli patients with BD, 66 Jews and 34 Arabs. The 3 largest ethnic groups of Jewish patients originated from Iran/Iraq (n = 21), Turkey (n = 12), and North African countries (n = 21). Patients were evaluated with respect to the entire spectrum of disease manifestations, and a systemic severity score for BD was calculated for each patient. Disease expression was compared between Jewish and Arab patients and among Jewish ethnic groups. RESULTS: There were no statistically significant differences between Jewish and Arab patients with respect to male:female ratio, prevalence of HLA-B5, age of disease onset, or disease duration. Disease expression and severity score were also similar in the 2 groups, but Arab patients had a higher rate of posterior uveitis (20.6 vs 4.6%; p < 0.03). Among the 3 largest Jewish ethnic groups, patients of North African origin had a significantly higher rate of ocular disease (p < 0.01), mainly in the form of anterior uveitis (p < 0.01). These patients also had higher rates of arthritis, overall vascular disease, deep vein thrombosis, and neuro-Beh?et without reaching statistical significance. The disease severity score in this group was significantly higher compared to the other Jewish ethnic groups (p < 0.02). CONCLUSION: The expression of BD is similar in Israeli Jewish and Arab patients but the latter have more severe eye disease. The disease in Israeli Jewish patients is most severe in those originating from North African countries.     

Prevalence and features of asthma–chronic obstructive pulmonary disease overlap in Northern Italy general population

Objective: There is controversy about the diagnostic criteria, prevalence, symptoms, and spirometry characteristics of asthma–chronic obstructive pulmonary disease (COPD) overlap (ACO). Recent data indicate that the fixed method for diagnosing airway obstruction (AO) may overestimate ACO prevalence in the elderly, and a variable method may be more accurate. We aimed at estimating ACO prevalence in a general population sample and comparing patient and clinical features in subjects with ACO, COPD, and asthma. Methods: We analyzed data from a cross-sectional study estimating COPD prevalence in randomly selected adults aged 20–79 years in Verona, Italy, and estimated prevalence and analyzed characteristics of asthma, COPD, and ACO. ACO was defined as AO (Forced Expiratory Volume in one second–FEV₁/ Forced Vital Capacity–FVC < Lower Limit of Normal–LLN), highly positive bronchodilator test (≥15% increase in FEV₁ and FVC ≥400 mL), and personal self-reported history of physician diagnosed asthma and atopy. Results: One thousand two hundred and thirty-six patients were included; 207 (16.7%) had asthma, COPD, or ACO (mean ages: 61.2, 59.7, and 57.2 years, respectively). The 3 groups had similar clinical and demographic variables; however, spirometry revealed differences between ACO and COPD patients, particularly post-bronchodilator FEV₁ reversibility, which was detected in ACO and asthma patients but not in those with COPD. Conclusion: ACO prevalence in Northern Italy was estimated at 2.1%, in the range of values reported by previous studies. Marked differences between ACO and COPD revealed by spirometry may have important clinical implications in terms of treatment for patients with ACO.     

Inland valley rice production systems and malaria infection and disease in the savannah of Côte d'Ivoire

In sub-Saharan Africa, lowlands developed for rice cultivation favour the development of Anopheles gambiae s. l. populations. However, the epidemiological impact is not clearly determined. The importance of malaria was compared in terms of prevalence and parasite density of infections as well as in terms of disease incidence between three agroecosystems: (i) uncultivated lowlands, 'R0', (ii) lowlands with one annual rice cultivation in the rainy season, 'R1' and (iii) developed lowlands with two annual rice cultivation cycles, 'R2'. We clinically monitored 2000 people of all age groups, selected randomly in each agroecosystem, for 40 days (in eight periods of five consecutive days scheduled every 6 weeks for 1 year). During each survey, a systematic blood sample was taken from every sick and asymptomatic person. The three agroecosystems presented a high endemic situation with a malaria transmission rate of 139-158 infective bites per person per year. The age-standardized annual malaria incidence reached 0.9 malaria episodes per person in R0, 0.6 in R1 and 0.8 in R2. Children from 0 to 9-year-old in R0 and R2 had two malarial attacks annually, but this was less in R1 (1.4 malaria episodes per child per year). Malaria incidence varied with season and agroecosystem. In parallel with transmission, a high malaria risk occurs temporarily at the beginning of the dry season in R2, but not in R0 and R1. Development of areas for rice cultivation does not modify the annual incidence of malarial attacks despite their seasonal influence on malaria risk. However, the lower malaria morbidity rate in R1 could be explained by socio-economic and cultural factors.     

Prevalence of metabolic alterations predictive of cardiovascular disease risk in the Québec population

BACKGROUND: It is well established that cardiovascular diseases (CVD) are the most important cause of morbidity and mortality in North America and in industrialized countries. Furthermore, the presence of CVD risk factors is widespread in Canada, and two-thirds of adult Canadians present at least one traditional risk factor for CVD. Objective: To quantify the prevalence of metabolic alterations predictive of an increased risk of CVD in a representative sample of the Québec population. METHODS: A representative sample of the Québec population was obtained through the Québec Health Survey 1990. The cohort of 1844 subjects (907 men and 937 women), aged from 18 to 74 years, completed the evaluation, which consisted of interviews, validated questionnaires for personal and family history of CVD risk factors, and a physical examination. Anthropometric measurements, blood pressure, fasting plasma lipoprotein-lipid levels as well as fasting glucose and insulin concentrations were obtained. RESULTS: Thirty one per cent of the Québec population had a normal body weight defined by body mass index (BMI) less than 25 kg/m2 with a healthy metabolic profile (glycemia less than 6.1 mmol/L, total cholesterol less than 5.2 mmol/L, low density lipoprotein-cholesterol less than 3.4 mmol/L, triglycerides less than 2.3 mmol/L and high density lipoprotein-cholesterol greater than 0.90 mmol/L). On the other hand, 28% of the population was treated for known metabolic chronic diseases (CVD, diabetes, dyslipidemias and hypertension), whereas the remaining 33% of the Québec population (BMI greater than 25 kg/m2) were characterized by an altered metabolic profile predictive of an increased CVD risk. Furthermore, 75% of men and 70% of women with an altered metabolic profile presented at least two CVD risk factors. Overall, women tended to display a significantly healthier metabolic risk profile than men (P<0.05). CONCLUSIONS: According to our results, only 31% of the Québec population is nonobese without major alterations in their metabolic risk profile. Indeed, 61% of Quebecers are either characterized by chronic diseases or by an altered metabolic profile increasing their risk for the development of CVD and type 2 diabetes. Such a high prevalence should be a source of concern justifying the development of simple screening tools for early identification of the asymptomatic carriers of this cluster of metabolic abnormalities.     

Prevalence of hepatitis B and C in the sera of patients with HIV infection in São Paulo, Brazil

The objective of this study was to evaluate the prevalence of hepatitis B and C viruses in a group of HIV infected patients, followed at a single institution since 1996. 1,693 HIV positive patients (1,162 male, 531 female) were tested for HBV infection. Virological markers for HBV included HBsAg and total anti-HBc by ELISA. 1,457 patients (1,009 male, 448 female) were tested for HCV infection. Detection of HCV antibodies was carried out by ELISA. A sample of HCV antibody positive patients was tested for HCV by PCR to confirm infection. Of 1,693 patients tested for HBV, 654 (38.6%) and 96 (5.7%) were anti-HBc and HBsAg positive, respectively. Of 1, 457 patients tested for HCV, 258 (17.7%) were anti-HCV positive. 82 of these patients were also tested by PCR and 81 were positive (98%). Of 1,411 patients tested for HBV and HCV 26 (1.8%) were positive for both viruses.     

Prevalence and clinical aspects of Behcet’s disease in the north of Israel

Behcet’s disease (BD) has a higher prevalence in countries along the ancient silk route, but the actual prevalence in Israel is unknown. We evaluated the occurrence and clinical expression of BD in the northern region of Israel: in the whole population and by ethnic groups. The sample included all adult patients with BD (International Study Group criteria) treated at three medical centers in northern Israel. Patient data were collected by file review and physician survey. Relevant demographic data for the population served by the medical centers were obtained from the official Israeli authorities. A total of 112 patients were identified. The overall prevalence of BD was 15.2/100,000 and was similar in men and women. The prevalence rates among the Jewish, Arab, and Druze populations were 8.6, 26.2, and 146.4 per 100,000, respectively. Age at disease onset was similar in all ethnic groups and significantly lower in males (28.6±9.7 vs 32.9±11.3, p=0.03). There were no differences in disease manifestations by sex or ethnicity. All Druze patients were HLA-B5 positive, compared to 80.8% of the Arab patients and 72.0% of the Jewish patients. Recurrent oral ulcers in family members were more common in Arab patients (p=0.004). The BD severity index was significantly lower in Druze patients (p=0.05), mainly in males (p=0.03). This study confirms the high prevalence of BD in Israel and the variability in disease rates and expression by ethnic origin. Our findings, particularly regarding the Druze population, call for further field surveys and genetic studies.     

Are haemochromatosis mutations related to the severity of liver disease in hepatitis C virus infection?

It has been proposed that iron overload may adversely affect liver disease outcome. The recent identification of 2 mutations in the HFE gene related to hereditary haemochromatosis (Cys282Tyr and His63Asp) provided an opportunity to test whether they are associated with hepatic iron accumulation and the activity and severity of liver disease in hepatitis C virus (HCV) infection. We investigated the prevalence of HFE mutations in 135 male patients with chronic HCV hepatitis, and correlated genotype distribution with different parameters of iron status and the activity and severity of liver disease. Of these 135 patients, 6 (4.4%) carried Cys282Tyr and 32 (23.7%) carried His63Asp, frequencies which were similar to those observed in healthy controls. Serum iron levels and transferrin saturation (but not ferritin levels or liver iron content) were significantly higher in carriers than in non-carriers of HFE mutations. No difference was observed in serum ALT, AST and GGT levels between carriers and non-carriers. Finally, scores for necroinflammatory activity and fibrosis in the liver were significantly higher in HFE carriers than in non-carriers. Patients with chronic HCV infection carrying HFE mutations tend to present more evident body iron accumulation and a higher degree of necroinflammatory activity and fibrosis in the liver. HFE gene mutations might be an additional factor to be considered among those implicated in the determination of a worse prognosis of the liver disease in chronic HCV infection.     

Scaling laws describe memories of host–pathogen riposte in the HIV population

The enormous genetic diversity and mutability of HIV has prevented effective control of this virus by natural immune responses or vaccination. Evolution of the circulating HIV population has thus occurred in response to diverse, ultimately ineffective, immune selection pressures that randomly change from host to host. We show that the interplay between the diversity of human immune responses and the ways that HIV mutates to evade them results in distinct sets of sequences defined by similar collectively coupled mutations. Scaling laws that relate these sets of sequences resemble those observed in linguistics and other branches of inquiry, and dynamics reminiscent of neural networks are observed. Like neural networks that store memories of past stimulation, the circulating HIV population stores memories of host–pathogen combat won by the virus. We describe an exactly solvable model that captures the main qualitative features of the sets of sequences and a simple mechanistic model for the origin of the observed scaling laws. Our results define collective mutational pathways used by HIV to evade human immune responses, which could guide vaccine design.Viruses can infect humans to cause infectious diseases, which, on occasion, lead to outbreaks that reach pandemic proportions resulting in millions of deaths. One prominent example of such a virus is HIV. Vaccination, a procedure that aims to protect humans from infectious pathogens, is one of the greatest triumphs of modern medicine. Vaccines induce human immune responses that are specific for a pathogen, which then lie ready and waiting to abort infection. However, no effective vaccine for HIV exists, and there is no known example of HIV being cleared by natural human immune responses. This is because of the extraordinarily high mutability of the virus and its ability to rapidly down-regulate the human immune system (1, 2). The high mutability enables HIV to evade natural or vaccine-induced immune responses (2, 3), while down-regulation of the host immune system hinders the development of potent responses (2). This is in contrast to many other viruses that can often be cleared by effective natural responses and vaccinated against successfully (4). These viruses accumulate mutations in a directed fashion, guided by selective pressure due to successful vaccine-induced or natural immune responses (1, 5). The lack of effective natural immune responses or successful vaccines, and the enormous diversity of human immune pressures [e.g., T-cell responses (6)], implies that HIV has evolved in the human population in response to myriad, usually ineffective, immune responses. We set out to study the properties of such a virus population.In past and current work (7–9), we have tried to define the functional constraints on HIV evolution with the practical goal of identifying its mutational vulnerabilities, and then harnessing this knowledge to inform vaccine design. Toward this end, we analyzed sequences of HIV proteins derived from virus samples extracted from diverse patients. Following a statistical approach pioneered in the study of neuronal networks (10, 11), we inferred a model for the probability of occurrence of mutant strains (a “prevalence landscape”) by maximizing the entropy of this inferred probability distribution subject to the constraints of reproducing the observed frequency of single and double mutations in the sequence data (8, 9). This model also accurately reproduces higher-order statistics characterizing the sequence data, such as the probability of observing sequences with a certain number of mutations, even though these quantities are not directly constrained in the inference procedure (Fig. S1 and SI Text). Theoretical studies suggest that, for HIV strains that are phylogenetically relatively close, the rank order of the prevalence of strains is the same as the rank order of their intrinsic replicative fitness (12). This may seem surprising because the viral sequences used to infer our model are samples obtained from patients during the course of nonequilibrium host–pathogen combat, and so the effective in-host fitness of a viral strain can be different from its intrinsic fitness. Although immune responses drive sequence evolution in each patient, they are a perturbative effect at the population level, making the rank order of prevalence and fitness statistically similar (12). This is because of the great diversity of human immune responses directed toward different regions of the viral proteome, and deleterious mutations made to evade the immune response in one host tend to revert upon transmission to another host (13). In vitro and in vivo studies testing our predictions for fitness support this conclusion (8, 9).The maximum entropy model for the prevalence/fitness is described by the following:P(z)=exp(−H(z))Q, H(z)=−∑i=1Nhizi−∑i=1N−1∑j=i+1NJijzizj,[1]where P(z) is the probability of observing a sequence of amino acids z = {z₁, z₂, …, z_N}, with N the total length of the protein sequence. Amino acids at each site i are identified as either consensus (z_i = 0) or mutant (z_i = 1). Here, the partition function Q ensures that the probabilities of all sequences sum to 1. The fields, h_i, and couplings, J_ij, in the Hamiltonian are obtained by fitting the observed probabilities of single and double mutations in sequences of HIV proteins (Methods). A positive coupling between a pair of sites implies that sequences with both sites mutated are observed more often than would be expected if mutations at these sites were independent. Thus, positive couplings indicate potentially synergistic or compensatory interactions between mutations. Mutations of both sites in a negatively coupled pair are observed less often than would be expected if the sites were independent, indicating a potential antagonistic or deleterious interaction between mutations at these sites. Similarly, point mutations are observed more often at sites with positive fields than at those with negative fields, when interactions with other sites in the sequence background are neglected. (Although related to epistasis, we emphasize that the overall effect of a particular mutation on fitness must be considered in the context of a particular sequence background: for example, mutation at a site i where the field h_i is positive may nonetheless lead to a decrease in viral fitness if there exist significant negative couplings between site i and other mutated sites in the sequence background.) For clarity and consistency, we use the language of fitness to describe the results presented below.     

Time Trends of the Prevalence of Asthma,Rhinitis and Eczema in Thai Children–ISAAC (International Study of Asthma and Allergies in Childhood) Phase Three

Using the same questionnaire as in ISAAC Phase One study conducted in 1995, the ISAAC Phase Three was carried out in Bangkok and Chiang Mai, Thailand, in 2001, among children aged 6–7 and 13–14 years. There was an increase in the prevalence of the three diseases in the younger age group, i.e., current asthma, rhinitis, rhinoconjunctivitis, and flexural eczema. In the older age group, the prevalence of rhinitis and rhinoconjunctivitis increased. There was no change of prevalence of asthma in Bangkok, but prevalence decreased in Chiang Mai. Prevalence of eczema in older children increased in Bangkok, but remained the same in Chiang Mai.     

CCR△532 mutation does not influence the susceptibility to HCV infection, severity of liver disease and response to therapy in patients with chronic hepatitis C

AIM: To study whether CCR5Delta32 mutation was associated with viral infection and severity of liver disease. METHODS: Two hundred and fifty two histologically proven, chronic HCV patients (mean age: 41 +/- 14 years; M/F: 164/88) were genotyped. PCR based genotyping of 32 bp deletion at the CCR5 locus was done. Four-hundred and eight matched healthy controls were studied to assess susceptibility to HCV infection. To assess correlation of immune gene polymorphism with severity of HCV related liver disease, patients with chronic HCV infection were divided into those with a fibrosis score of <= 2 (mild) or > 2 (severe) and histological activity index (HAI) of <= 5 or > 5. For correlation between CCR5Delta32 mutations and response to therapy, 129 patients who completed therapy were evaluated. RESULTS: The majority (89.4%) of the patients were infected with genotype 3. The frequency of homozygous CCR5Delta32 mutants was comparable to HCV patients as compared to the healthy controls (0.7% vs 0%, P = 0.1). Further more, the frequency of CCR5Delta32 mutation was comparable in patients with mild or severe liver disease. (P = NS). There was also no association observed with response to therapy and CCR5Delta32 mutation. CONCLUSION: CCR5Delta32 mutation does not have a role in disease susceptibility, severity or response to therapy in patients with chronic hepatitis C infection.     

Prevalence of autoantibodies and the risk of autoimmune thyroid disease in children with chronic hepatitis C virus infection treated with interferon-α

AIM: To evaluate the prevalence of autoantibodies in chronic hepatitis C virus (HCV)-infected children focusing on thyroid autoimmunity. METHODS: We investigated the prevalence of auto-antibodies in 123 chronic HCV-infected children before, during and after monotherapy with interferon-alpha (IFN-alpha) or combined treatment with interferon-alpha or peginterferon-alpha and ribavirin. Besides antibodies against smooth muscle (SMA), nuclei (ANA), and liver/kidney microsomes (LKM), the incidence of anti-thyroid peroxidase antibodies as well as thyroid function parameters (TSH, FT3 and FT4) were determined. RESULTS: We found that 8% of children had autoantibodies before treatment. During treatment, 18% of children were found positive for at least one autoantibody; 15.5% of children developed pathologic thyroid values during IFN-alpha treatment compared to only one child before therapy. Six children had to be substituted while developing laboratory signs of hypothyroidism. CONCLUSION: Our data indicate a strong correlation between interferon-alpha treatment and autoimmune phenomena, notably the emergence of thyroid antibodies. The fact that some children required hormone replacement underlines the need of close monitoring in particularly those who respond to therapy and have to be treated for more than 6 mo.     

Prevalence of autoantibodies and the risk of autoimmune thyroid disease in children with chronic hepatitis C virus infection treated with interferon-α

INTRODUCTION Since the discovery of the hepatitis C virus (HCV) in 1989[1], an increasing number of studies report an association of chronic HCV infection with autoimmune phenomena. In studies among adult patients, the prevalence of autoantibodies in chro…     

Prevalence of autoantibodies and the risk of autoimmune thyroid disease in children with chronic hepatitis C virus infection treated with interferon-α

AIM: To evaluate the prevalence of autoantibodies in chronic hepatitis C virus (HCV)-infected children focusing on thyroid autoimmunity.METHODS: We investigated the prevalence of autoantibodies in 123 chronic HCV-infected children before,during and after monotherapy with interferon-alpha (TFN-α) or combined treatment with interferon-α or peginterferon-α and ribavirin. Besides antibodies against smooth muscle (SMA), nuclei (ANA), and liver/kidney microsomes (LKM), the incidence of antithyroid peroxidase antibodies as well as thyroid function parameters (TSH, FT3 and FT4) were determined.RESULTS: We found that 8% of children had autoantibodies before treatment. During treatment,18% of children were found positive for at least one autoantibody; 15.5% of children developed pathologic thyroid values during IFN-α treatment compared to only one child before therapy. Six children had to be substituted while developing laboratory signs of hypothyroidism.CONCLUSION: Our data indicate a strong correlation between interferon-α treatment and autoimmune phenomena, notably the emergence of thyroid antibodies. The fact that some children required hormone replacement underlines the need of close monitoring in particularly those who respond to therapy and have to be treated for more than 6 mo.     

Plasmodium falciparum malaria in south-west Nigerian children: is the polymorphism of ICAM-1 and E-selectin genes contributing to the clinical severity of malaria?

Plasmodium falciparum malaria remains a major public health hazard in sub-Saharan African children. While the factors that determine the variations in clinical outcome of a malaria have not been completely defined, both host and parasite factors, as well as the complex molecular interactions between them have been implicated. The cyto-adherent properties of the P. falciparum-infected red blood cells are considered as key properties in the pathogenesis of malaria and the polymorphisms of the host adhesion molecules could contribute to the severity of malaria. Clinical information and blood samples were collected from 223 children from Ibadan (south-west Nigeria), median age of 34.5 months, presenting with different clinical manifestations of malaria--clinically asymptomatic parasitism (ACP), acute uncomplicated malaria (UM) and severe malaria (SM)--as defined by WHO criteria. The polymorphisms of genes coding for four human adhesion molecules at six different loci (ICAM-1 exons 2, 4 and 6, E-selectin exon 2, CD36 exon 10, and PECAM exon 3) were studied. DNA samples were prepared for further genotyping of the six exons mentioned above by PCR-RFLPs using the appropriate restriction digests for each loci. The ICAM-1 exon 4 locus was monomorphic. All the other loci were at Hardy-Weinberg equilibrium (HWE).The E-selectin locus had very low heterozygosity (approximately 0.06) in contrast to the other loci under study (0.23-0.44). Once the data was further processed for covariates (age and parasite density) and taking as the reference category the ACP group, results show that in the presence of the G allele at the ICAM-1 exon 6 there is an increased risk (3.6 times) of severe malaria. As far as the T allele in the E-selectin exon is concerned, the number of sampled DNAs with the T allele within both the UM and SM categories is too low for drawing any relevant conclusion at this stage. In conclusion, these results suggest that genetic polymorphisms at host adhesion molecules loci are an important variable in the susceptibility to severe malaria. Further studies of host loci are needed to further delineate which polymorphisms are associated with severe malaria and increase our knowledge of the biology of host-parasite interactions.     

Epidemiological and ecological aspects related to malaria in the area of influence of the lake at Porto Primavera dam, in western São Paulo State, Brazil

A study was carried out in the area of influence of the Porto Primavera Hydroelectric Power Station, in western S?o Paulo State, to investigate ecological and epidemiological aspects of malaria in the area and monitor the profile of the anopheline populations following the environmental changes brought about by the construction of the lake. Mosquitoes captured were analyzed by standardized indicator species analysis (ISA) before and during different flooding phases (253 m and 257 m elevations). The local human population was studied by means of parasitological (thin/thick blood smears), molecular (PCR) and serological tests. Serological tests consisted of Enzyme Linked Immunosorbent Assay (ELISA) with synthetic peptides of the circumsporozoite protein (CSP) from classic Plasmodium vivax, P. vivax variants (VK247 and "vivax-like"), P. malariae and P. falciparum and Indirect Immunofluorescence Assay (IFA) with asexual forms of P. vivax, P. malariae and P. falciparum. The results of the entomological survey indicated that, although the Anopheles darlingi population increased after the flooding, the population density remained very low. No malaria, parasite infection or DNA was detected in the inhabitants of the study area. However, there was a low frequency of antibodies against asexual forms and a significant prevalence of antibodies against P. vivax, P. vivax variants, P. falciparum and P. malariae; the presence of these antibodies may result from recent or less recent contact with human or simian Plasmodium (a parallel study in the same area revealed the existence of a sylvatic cycle). Nevertheless, these results suggest that, as in other places where malaria is present and potential vectors circulate, the local epidemiological conditions observed could potentially support the transmission of malaria in Porto Primavera Lake if infected individuals are introduced in sufficient numbers. Further studies are required to elucidate the phenomena described in this paper.