Effect of Beef Silver Skin (Epimysium) Levels on Meat Emulsion Stability, Quality Attributes, and Texture Parameters.

The epimysium, also known as silver skin, is a fascia of connective tissue that surrounds each muscle. During fabrication, epimysium is removed from intact cuts, and it can be used as a source of collagen in processed meats to reduce production costs. However, little is known about the emulsifying properties of this collagen source. Thus, this study aimed to evaluate the effect of three levels of beef epimysium (silver skin, 0, 5, and 10%) on meat emulsion stability and on its cooked characteristics. Beef silver skin partially replaced ground beef, pork, and fat trimming, while all the other ingredients remained constant across formulations. The inclusion of silver skin did not affect (p > 0.05) chemical composition, total cooking loss, water loss, and raw emulsion color. Cooking fat loss linearly increased (p = 0.02) while cooked emulsion L* linearly decreased (p = 0.04) as silver skin level increased. Hardness, gumminess, and chewiness decreased linearly as silver skin levels increased (p < 0.01). Overall, incorporating silver skin into meat emulsions reduced stability, increased fat loss, and led to a weaker cooked emulsion matrix.

Effects of cutting time and maceration on preference and nitrogen balance in beef steers fed mixed birdsfoot trefoil-timothy grass hay cut at sunrise or sundown.

Forages cut at sundown usually contain a greater concentration of nonstructural carbohydrates (NSC) than those cut at sunrise. Maceration can speed up the rate of moisture loss of cut forage during field drying and reduce NSC utilization by plant cells. We aimed to evaluate the effects of cutting time and forage maceration on feed preference, apparent total tract digestibility of nutrients, and N balance in growing steers. A mixed sward of birdsfoot trefoil and timothy grass was divided into two halves, with the first half cut at sundown (1800 h) after a sunny day and the second half at sunrise (0600 h) the next day. Approximately 50% of the sundown- and sunrise-cut herbage were macerated. Forages were harvested as hay resulting in four treatments: 1) sunrise-cut hay (AM); 2) AM plus maceration (AM-M); 3) sundown-cut hay (PM); and 4) PM plus maceration (PM-M). Hays were offered as the sole feed source to four crossbred steers (296.1 ± 7.25 kg) according to a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Each period lasted 21 d with 14 d for diet adaptation and 7 d for collection. Hays cut at sundown had 15% greater NSC than those cut at sunrise. A cutting time by maceration interaction was found (P < 0.05) for intake and apparent digestibility of crude protein (CP), indicating that these two variables decreased more when maceration was applied to sundown- versus sunrise-cut hays. Similarly, interaction effects were observed (P < 0.05) for total digestible nutrients and digestible energy, showing that maceration decreased the energetic value of sundown-cut hays but did not change that of sunrise-cut hays. Steers fed hays cut at sundown had decreased urinary N excretion and improved retained N (P < 0.05), whereas N retention was reduced by maceration (P < 0.05). In addition, six crossbred steers were used to assess feed preference, 2 wk before (period 1) and 1 wk after (period 2) the digestibility trial. Animals were randomly assigned to receive a sequence of the four hays combined in pairs. The intake rate was greater for sundown- than sunrise-cut hays, and it was decreased by maceration. Steers showed the greatest preference for PM hay, while AM-M was the most rejected. In conclusion, shifting forage cutting from sunrise to sundown increased hay NSC concentration, which resulted in improved N utilization and preference. Forage maceration during field drying decreased CP concentration and N retention in beef steers under the conditions of our study.

Plasmodium falciparum purine nucleoside phosphorylase as a model in the search for new inhibitors by high throughput screening.

Studies have shown that inhibition of Plasmodium falciparum Purine Nucleoside Phosphorylase (PfPNP) blocks the purine salvage pathway in vitro and in vivo. In this study, PfPNP was evaluated as a model in the search for new inhibitors using surface plasmon resonance (SPR). Its expression, purification, oligomeric state, kinetic constants, calorimetric parameters and kinetic mechanisms were obtained. PfPNP was immobilized on a CM5 sensor chip and sensorgrams were produced through binding the enzyme to the substrate MESG and interactions between molecules contained in 10 fractions of natural extracts. The oligomeric state showed that recombinant PfPNP is a hexamer. The true steady-state kinetic parameters for the substrate inosine were: KM 17 µM, kcat 1.2 s-1, VMax 2.2 U/mg and kcat/KM 7 × 10-4; for MESG they were: KM 131 µM, kcat 2.4 s-1, VMax 4.4 U/mg and kcat/KM 1.8 × 10-4. The thermodynamic parameters for the substrate Phosphate were: ΔG - 5.8 cal mol-1, ΔH - 6.5 cal mol-1 and ΔS - 2.25 cal mol-1/degree. The ITC results demonstrated that the binding of phosphate to free PfPNP led to a significant change in heat and association constants and thermodynamic parameters. A sequential ordered mechanism was proposed as the kinetic mechanism. Three plant extracts contained molecules capable of interacting with PfPNP, showing different levels of affinity. The identification of plant extract fractions containing molecules that interact with recombinant PfPNP using SRP validates this target as a model in the search for new inhibitors. In this study, we showed for the first time the true steady-state kinetic parameters for reactions catalyzed by PfPNP and a model using PfPNP as a target for High-throughput Screening for new inhibitors through SPR. This knowledge will allow for the development of more efficient research methods in the search for new drugs against malaria.

Warifteine and methylwarifteine inhibited the type 2 immune response on combined allergic rhinitis and asthma syndrome (CARAS) experimental model through NF-кB pathway.

CARAS is an airway inflammation of allergic individuals, with a type 2 immune response. The pharmacotherapy is based on drugs with relevant side effects. Thus, the goal of this study evaluated the alkaloids warifteine (War) and methylwarifteine (Mwar) from Cissampelos sympodialis in CARAS experimental model. Therefore, BALB/c mice were ovalbumin (OVA) sensitized and challenged and treated with both alkaloids. Treated animals showed a decrease (p < 0.05) of allergic signs as sneezing and nasal rubbings, histamine nasal hyperreactivity, and inflammatory cell migration into the nasal (NALF) and the bronchoalveolar (BALF) fluids, main eosinophils. In the systemic context, only Mwar reduced eosinophilia, however, both alkaloids reduced the serum levels of OVA-specific IgE. Histological analysis revealed that the alkaloids decreased the inflammatory cells into the subepithelial and perivascular regions of nasal tissue and the peribronchiolar and perivascular regions of lung tissue. Hyperplasia/hypertrophy of nasal and lung goblet cells were reduced in alkaloid treated animals; however, the treatment did not change the number of mast cells. The lung hyperactivity was attenuated by reducing hyperplasia of fibroblast and collagen fiber deposition and hypertrophy of the lung smooth muscle layer. The immunomodulatory effect was by decreasing of type 2 and 3 cytokines (IL-4/IL-13/IL-5 and IL-17A) dependent by the increasing of type 1 cytokine (IFN-γ) into the BALF of treated sick animals. Indeed, both alkaloids reduced the NF-кB (p65) activation on granulocytes and lymphocytes, indicating that the alkaloids shut down the intracellular transduction signals underlie the transcription of TH2 cytokine gens.

Explaining meat quality of bulls and steers by differential proteome and phosphoproteome analysis of skeletal muscle.

The objective of this study was to evaluate the differential proteome and phosphoproteome between bulls and steers during conversion of muscle to meat, as well as after 14 days of aging. Twelve male Nellore (Bos taurus indicus) calves were used, and six calves were randomly selected for surgical castration. Calves were fed the same diet and were harvested after 230 days on feed. Longissimus muscle was sampled just after stunning (0d postmortem), at deboning (1d postmortem) and after aging (14d postmortem) for differential proteome analysis. Castration upregulated (P < 0.05) the abundance of glycolytic enzymes, while the oxidative phosphorylation protein ATP5B was downregulated (P < 0.05). In addition, abundance of troponin T fast isoform (TNNT3) was upregulated by castration (P < 0.05), while the slow isoform (TNNT1) tended to be decreased (P < 0.10). The creatine kinase M-type was markedly fragmented postmortem. Abundance of phosphorylated PGM1 increased during the first 24 h postmortem and was highly correlated with carcass pH. Further, abundance of the phosphorylated myofibrillar proteins ACTA1 and MYLPF were positively correlated with sarcomere shortening. Overall, our finds demonstrated that abundance and phosphorylation of glycolytic enzymes are associated with changes in beef tenderness and intramuscular fat. SIGNIFICANCE: The design of the present study allowed to clarify the key proteins related to changes during conversion of muscle to meat such as pH decline and sarcomere shortening. In addition, the correlation between some biomarker and meat quality traits were confirmed.

Corrigendum: Much More than a Cardiotonic Steroid: Modulation of Inflammation by Ouabain.

[This corrects the article on p. 895 in vol. 8, PMID: 29176951.].

Much More than a Cardiotonic Steroid: Modulation of Inflammation by Ouabain.

Since the discovery of ouabain as a cardiotonic steroid hormone present in higher mammals, research about it has progressed rapidly and several of its physiological and pharmacological effects have been described. Ouabain can behave as a stress hormone and adrenal cortex is its main source. Direct effects of ouabain are originated due to the binding to its receptor, the Na+/K+-ATPase, on target cells. This interaction can promote Na+ transport blockade or even activation of signaling transduction pathways (e.g., EGFR/Src-Ras-ERK pathway activation), independent of ion transport. Besides the well-known effect of ouabain on the cardiovascular system and blood pressure control, compelling evidence indicates that ouabain regulates a number of immune functions. Inflammation is a tightly coordinated immunological function that is also affected by ouabain. Indeed, this hormone can modulate many inflammatory events such as cell migration, vascular permeability, and cytokine production. Moreover, ouabain also interferes on neuroinflammation. However, it is not clear how ouabain controls these events. In this brief review, we summarize the updates of ouabain effect on several aspects of peripheral and central inflammation, bringing new insights into ouabain functions on the immune system.

Effect of post-weaning growth rate on carcass traits and meat quality of Nellore cattle.

This study evaluated the effects of growth rate during post-weaning growing phase on carcass traits and beef quality. Thirty-four Nellore young bulls were randomly assigned to one of three treatments: LOW, MEDIUM or HIGH growth rate during post-weaning growing phase followed by high growth rate in the finishing phase. The growth rate affected (P<0.05) all carcass traits evaluated at the end of post-weaning growing phase, except ultimate pH. Carcass dressing was greatest (P<0.05) for the HIGH growth rate group in both phases. Beef from the HIGH group exhibited the greatest (P<0.05) sarcomere length and a* and b* colour values at the end of post-weaning growing phase. However, post-weaning growth rate did not affected (P>0.05) collagen content and solubility, myofibrillar fragmentation index and Warner-Bratzler shear force. Our data suggest that a low post-weaning growth rate produces lighter and leaner carcasses, but it does not affect meat quality traits in Nellore young bulls.

Inhibition of the Myotoxicity Induced by Bothrops jararacussu Venom and Isolated Phospholipases A2 by Specific Camelid Single-Domain Antibody Fragments.

Antivenoms, produced using animal hyperimmune plasma, remains the standard therapy for snakebites. Although effective against systemic damages, conventional antivenoms have limited efficacy against local tissue damage. Additionally, the hypersensitivity reactions, often elicited by antivenoms, the high costs for animal maintenance, the difficulty of producing homogeneous lots, and the instability of biological products instigate the search for innovative products for antivenom therapy. In this study, camelid antibody fragments (VHH) with specificity to Bothropstoxin I and II (BthTX-I and BthTX-II), two myotoxic phospholipases from Bothrops jararacussu venom, were selected from an immune VHH phage display library. After biopanning, 28 and 6 clones recognized BthTX-I and BthTX-II by ELISA, respectively. Complementarity determining regions (CDRs) and immunoglobulin frameworks (FRs) of 13 VHH-deduced amino acid sequences were identified, as well as the camelid hallmark amino acid substitutions in FR2. Three VHH clones (KF498607, KF498608, and KC329718) were capable of recognizing BthTX-I by Western blot and showed affinity constants in the nanomolar range against both toxins. VHHs inhibited the BthTX-II phospholipase A2 activity, and when tested for cross-reactivity, presented specificity to the Bothrops genus in ELISA. Furthermore, two clones (KC329718 and KF498607) neutralized the myotoxic effects induced by B. jararacussu venom, BthTX-I, BthTX-II, and by a myotoxin from Bothrops brazili venom (MTX-I) in mice. Molecular docking revealed that VHH CDRs are expected to bind the C-terminal of both toxins, essential for myotoxic activity, and to epitopes in the BthTX-II enzymatic cleft. Identified VHHs could be a biotechnological tool to improve the treatment for snake envenomation, an important and neglected world public health problem.

Obesity-Driven Gut Microbiota Inflammatory Pathways to Metabolic Syndrome.

The intimate interplay between immune system, metabolism, and gut microbiota plays an important role in controlling metabolic homeostasis and possible obesity development. Obesity involves impairment of immune response affecting both innate and adaptive immunity. The main factors involved in the relationship of obesity with inflammation have not been completely elucidated. On the other hand, gut microbiota, via innate immune receptors, has emerged as one of the key factors regulating events triggering acute inflammation associated with obesity and metabolic syndrome. Inflammatory disorders lead to several signaling transduction pathways activation, inflammatory cytokine, chemokine production and cell migration, which in turn cause metabolic dysfunction. Inflamed adipose tissue, with increased macrophages infiltration, is associated with impaired preadipocyte development and differentiation to mature adipose cells, leading to ectopic lipid accumulation and insulin resistance. This review focuses on the relationship between obesity and inflammation, which is essential to understand the pathological mechanisms governing metabolic syndrome.

Novel camelid antibody fragments targeting recombinant nucleoprotein of Araucaria hantavirus: a prototype for an early diagnosis of Hantavirus Pulmonary Syndrome.

In addition to conventional antibodies, camelids produce immunoglobulins G composed exclusively of heavy chains in which the antigen binding site is formed only by single domains called VHH. Their particular characteristics make VHHs interesting tools for drug-delivery, passive immunotherapy and high-throughput diagnosis. Hantaviruses are rodent-borne viruses of the Bunyaviridae family. Two clinical forms of the infection are known. Hemorrhagic Fever with Renal Syndrome (HFRS) is present in the Old World, while Hantavirus Pulmonary Syndrome (HPS) is found on the American continent. There is no specific treatment for HPS and its diagnosis is carried out by molecular or serological techniques, using mainly monoclonal antibodies or hantavirus nucleoprotein (N) to detect IgM and IgG in patient serum. This study proposes the use of camelid VHHs to develop alternative methods for diagnosing and confirming HPS. Phage display technology was employed to obtain VHHs. After immunizing one Lama glama against the recombinant N protein (prNΔ85) of a Brazilian hantavirus strain, VHH regions were isolated to construct an immune library. VHHs were displayed fused to the M13KO7 phage coat protein III and the selection steps were performed on immobilized prNΔ85. After selection, eighty clones recognized specifically the N protein. These were sequenced, grouped based mainly on the CDRs, and five clones were analyzed by western blot (WB), surface plasmon resonance (SPR) device, and ELISA. Besides the ability to recognize prNΔ85 by WB, all selected clones showed affinity constants in the nanomolar range. Additionaly, the clone KC329705 is able to detect prNΔ85 in solution, as well as the native viral antigen. Findings support the hypothesis that selected VHHs could be a powerful tool in the development of rapid and accurate HPS diagnostic assays, which are essential to provide supportive care to patients and reduce the high mortality rate associated with hantavirus infections.

Ultrasonography of the distal limbs in Nellore and Girolando calves 8 to 12 months of age.

BACKGROUND: Ultrasonography can be used anywhere and allows rapid, noninvasive differentiation of soft tissue structures of the musculoskeletal system. The objectives of this study were to describe the ultrasonographic appearance of the structures of the metacarpo-/metatarsophalangeal and the interphalangeal joints, the appearance of the growth plates of the distal metacarpus/metatarsus and of the proximal phalanx and to measure the cross-sectional dimensions of the DDFT and SDFT in Nellore and Girolando calves eight to 12 months of age. RESULTS: In the longitudinal dorsal view the common digital extensor tendon and the digital extensor tendon were depicted as echogenic parallel fiber bundles located directly under the skin. The joint spaces appeared as anechoic interruptions of the hyperechogenic bone surfaces. The normal amount of synovial fluid could not be depicted. The growth plates were seen as anechoic interruptions of the bone surface proximal and distal to the fetlock joint space. In transverse sonograms of the distal palmar/plantar regions, the flexor tendons and branchs of the suspensory ligament were imaged as echogenic structures. The lumen of the digital flexor tendon sheath could not be imaged in these normal cattle. The thin digital distal annular ligament and the reversal of positions of the DDFT and SDFT could be appreciated. No significant differences were found between the cross-sectional measurements of the DDFT and the SDFT from Nellore and Girolando in any age, thoracic/pelvic limbs, right/left sides and lateral/medial digits. CONCLUSIONS: The results of this study establish important ultrasonographic reference data of the normal structures of the distal limbs and the normal dimensions of the flexor tendons in Nellore and Girolando calves for use in clinical practice.

Natural Plasmodium infection in monkeys in the state of Rondônia (Brazilian Western Amazon).

BACKGROUND: Simian malaria is still an open question concerning the species of Plasmodium parasites and species of New World monkeys susceptible to the parasites. In addition, the lingering question as to whether these animals are reservoirs for human malaria might become important especially in a scenario of eradication of the disease. To aid in the answers to these questions, monkeys were surveyed for malaria parasite natural infection in the Amazonian state of Rondônia, Brazil, a state with intense environmental alterations due to human activities, which facilitated sampling of the animals. METHODS: Parasites were detected and identified in DNA from blood of monkeys, by PCR with primers for the 18S rRNA, CSP and MSP1 genes and sequencing of the amplified fragments. Multiplex PCR primers for the 18S rRNA genes were designed for the parasite species Plasmodium falciparum and Plasmodium vivax, Plasmodium malariae/Plasmodium brasilianum and Plasmodium simium. RESULTS: An overall infection rate of 10.9% was observed or 20 out 184 monkey specimens surveyed, mostly by P. brasilianum. However, four specimens of monkeys were found infected with P. falciparum, two of them doubly infected with P. brasilianum and P. falciparum. In addition, a species of monkey of the family Aotidae, Aotus nigriceps, is firstly reported here naturally infected with P. brasilianum. None of the monkeys surveyed was found infected with P. simium/P. vivax. CONCLUSION: The rate of natural Plasmodium infection in monkeys in the Brazilian state of Rondônia is in line with previous surveys of simian malaria in the Amazon region. The fact that a monkey species was found that had not previously been described to harbour malaria parasites indicates that the list of monkey species susceptible to Plasmodium infection is yet to be completed. Furthermore, finding monkeys in the region infected with P. falciparum clearly indicates parasite transfer from humans to the animals. Whether this parasite can be transferred back to humans and how persistent the parasite is in monkeys in the wild so to be efficient reservoirs of the disease, is yet to be evaluated. Finding different species of monkeys infected with this parasite species suggests indeed that these animals can act as reservoirs of human malaria.

Design and heterologous expression of dengue virus envelope protein (E) peptides and their use for serological diagnosis.

Viruses belonging to the Flaviviridae family are found and distributed in most of the tropical and sub-tropical regions of the world. The genus has more than 56 members, most of which cause clinical symptoms in humans. The clinical diagnosis of dengue requires laboratory confirmation because of the similarity of symptoms with a series of other acute fevers and the primary use antibodies or antigens for detection. In this work, peptides E(1) and E(2) of the envelope protein (E) of the dengue virus were mapped using bioinformatics methods. These peptides were then expressed in a prokaryotic system and purified. An indirect ELISA for antibodies IgG and IgM from laboratory samples previously characterised was then used with the peptides to detect anti-dengue antibodies. For IgG using the peptide E(1), the sensitivity of the indirect ELISA was 88.3% and the specificity was 56%; using the peptide E(2), the sensitivity was 90% and the specificity was 59%; and using a combination of both peptides, the sensitivity was 93.3% and the specificity was 78%. For IgM using the peptide E(1), the sensitivity was 88% and the specificity was 66%; using the peptide E(2), the sensitivity was 88% and the specificity was 69%; and when used in combination, the peptides E(1)/E(2) demonstrated a sensitivity of 90% and a specificity of 86%. These results indicate that the use of the E(1) and E(2) peptides of the E protein are an alternative for serological diagnosis of dengue fever.

Rapid turnover of Plasmodium falciparum var gene transcripts and genotypes during natural non-symptomatic infections.

The var genes of Plasmodium falciparum code for the antigenically variant erythrocyte membrane proteins 1 (PfEMP1), a major factor for cytoadherence and immune escape of the parasite. Herein, we analyzed the var gene transcript turnover in two ongoing, non-symptomatic infections at sequential time points during two weeks. The number of different circulating genomes was estimated by microsatellite analyses. In both infections, we observed a rapid turnover of plasmodial genotypes and var transcripts. The rapidly changing repertoire of var transcripts could have been caused either by swift elimination of circulating var-transcribing parasites stemming from different or identical genetic backgrounds, or by accelerated switching of var gene transcription itself.

Rapid turnover of Plasmodium falciparum var gene transcripts and genotypes during natural non-symptomatic infections

Os genes var de Plasmodium falciparum codificam as proteínas variantes da superfície do eritrócito infectado (PfEMP1). Neste estudo examinamos a mudança de transcritos destes genes var em duas infecções assintomáticas durante um curto prazo e estimamos simultaneamente o número de genomas circulantes nas mesmas amostras por análise de microssatélites. Nas duas infecções observamos uma rápida mudança de genótipos e transcritos de genes var. A mudança acelerada do repertório de transcritos possivelmente foi causada pela rápida eliminação de parasitas circulantes transcrevendo genes var a partir de genomas iguais ou diferentes, ou pela mudança acelerada da própria transcrição (switching) de genes var.

Plasmodium falciparum rhoptry protein RSP2 triggers destruction of the erythroid lineage.

The destruction of erythrocytes and defects in erythropoiesis are among the most frequently observed causes of morbidity in severe Plasmodium falciparum malaria. The molecular mechanisms involved remain unclear, despite extensive investigation. We show here, for the first time, that tagging with the parasite rhoptry protein ring surface protein 2 (RSP2) is not restricted to the surfaces of normal erythrocytes, as previously reported, but that it extends to erythroid precursor cells in the bone marrow of anemic malaria patients. Monoclonal mouse antibodies and human sera from patients with severe anemia, reacting with RSP2-tagged erythrocytes, induced cell destruction by phagocytosis and complement activation in vitro. Our observations reveal a new parasite mechanism implicated in the destruction of normal erythrocytes and probably dyserythropoiesis in malaria patients. These data suggest that the tagging of host cells with RSP2 may trigger anemia in falciparum malaria.

Seasonal malaria transmission and variation of anopheline density in two distinct endemic areas in Brazilian Amazonia.

Studies on seasonal anopheline fauna variation were performed in two distinct settlements in the State of Rondônia, Brazil: one at the Madeira River banks (Portuchuelo) with stable native Amazonian population; the other at an inland lumber-extracting farm (Urupá) in dry land, in which adults are mostly migrants. During a 6-yr period (1994-2000), 8,638 adult anophelines were collected: 2,684 in Urupá and 5,954 in Portuchuelo. Anopheles darlingi represented >95% of total mosquitoes caught. Dissection of 4,424 A. darlingi females yielded a very low sporozoite infection index below 0.1%. Oocysts were found in both localities in approximately 0.1% of dissected mosquitoes. Determination of the hour biting rates disclosed seasonal variations in both localities. However, in Portuchuelo, mosquito density peaked at the acme of the rainy season, whereas at Urupá it peaked in the dry season. The increase in mosquito density and incidence of malaria cases were coincident. The high mosquito densities observed in the riverine settlement of Portochuelo sector B, which permits evaluation in > 10,000 mosquitoes' bites/person/year, could explain, in spite of the low mosquito's infection index, the previously described development of natural immunity in the local population that is not observed in the dry land agroindustrial settlement of Urupá.

High prevalence of asymptomatic Plasmodium vivax and Plasmodium falciparum infections in native Amazonian populations.

The epidemiology of malaria in 2 riverine localities in Rondjnia, Brazilian western Amazjnia, was assessed by a 1-year study at Portuchuelo, and a cross-sectional survey at riverine communities at Rio Machado (= Ji-Parana). Plasmodium spp. infections were diagnosed by light microscopy and by polymerase chain reaction (PCR) amplification of ribosomal DNA. PCR was 6-7 times more efficient than microscopy for detecting plasmodial infections. Both Plasmodium vivax and Plasmodium falciparum infections occurred as asymptomatic and symptomatic forms of the disease. The relation between symptomatic and asymptomatic clinical forms was roughly similar for both species of Plasmodium. Symptomless patients were monitored for 2 months. The prevalence of symptomless infections was 4-5 times higher than the symptomatic ones--respectively, 20% and 4.6% for Portuchuelo and 49.5% and 10% for Ji-Parana. Symptomatic malaria occurred mostly in patients in younger age groups. In contrast, there was a significant association of symptomless malaria with older age groups (medians of 26.5 and 21 years, respectively, for Portuchuelo and Ji-Parana), whereas the age medians for symptomatic malaria were 14 and 8 years, respectively, in the 2 regions. Symptomatic malaria also was more prevalent in groups living for shorter times in Amazjnia (13 and 4 years, respectively, for Portuchuelo and Ji-ParanA) as compared with symptomless malaria, which was more prevalent in groups living for longer periods in the region (medians of 25.5 and 18 years, respectively, for Portuchuelo and Ji-Paraná). The high prevalence of symptomless malaria may pose new problems for the currently adopted strategy for the control of malaria in the Amazonian region, which is essentially based on the treatment of symptomatic patients.