Anti-PfGARP activates programmed cell death of parasites and reduces severe malaria.

Malaria caused by Plasmodium falciparum remains the leading single-agent cause of mortality in children1, yet the promise of an effective vaccine has not been fulfilled. Here, using our previously described differential screening method to analyse the proteome of blood-stage P. falciparum parasites2, we identify P. falciparum glutamic-acid-rich protein (PfGARP) as a parasite antigen that is recognized by antibodies in the plasma of children who are relatively resistant-but not those who are susceptible-to malaria caused by P. falciparum. PfGARP is a parasite antigen of 80 kDa that is expressed on the exofacial surface of erythrocytes infected by early-to-late-trophozoite-stage parasites. We demonstrate that antibodies against PfGARP kill trophozoite-infected erythrocytes in culture by inducing programmed cell death in the parasites, and that vaccinating non-human primates with PfGARP partially protects against a challenge with P. falciparum. Furthermore, our longitudinal cohort studies showed that, compared to individuals who had naturally occurring anti-PfGARP antibodies, Tanzanian children without anti-PfGARP antibodies had a 2.5-fold-higher risk of severe malaria and Kenyan adolescents and adults without these antibodies had a twofold-higher parasite density. By killing trophozoite-infected erythrocytes, PfGARP could synergize with other vaccines that target parasite invasion of hepatocytes or the invasion of and egress from erythrocytes.

The human malaria-Aotus monkey model: a historical perspective in antimalarial chemotherapy research at the Gorgas Memorial Laboratory-Panama.

The human malaria-Aotus monkey model has served the malaria research community since its inception in 1966 at the Gorgas Memorial Laboratory (GML) in Panama. Spanning over five decades, this model has been instrumental in evaluating the in vivo efficacy and pharmacokinetics of a wide array of candidate antimalarial drugs, whether used singly or in combination. The animal model could be infected with drug-resistant and susceptible Plasmodium falciparum and Plasmodium vivax strains that follow a characteristic and reproducible course of infection, remarkably like human untreated and treated infections. Over the years, the model has enabled the evaluation of several synthetic and semisynthetic endoperoxides, for instance, artelinic acid, artesunate, artemether, arteether, and artemisone. These compounds have been evaluated alone and in combination with long-acting partner drugs, commonly referred to as artemisinin-based combination therapies, which are recommended as first-line treatment against uncomplicated malaria. Further, the model has also supported the evaluation of the primaquine analog tafenoquine against blood stages of P. vivax, contributing to its progression to clinical trials and eventual approval. Besides, the P. falciparum/Aotus model at GML has also played a pivotal role in exploring the biology, immunology, and pathogenesis of malaria and in the characterization of drug-resistant P. falciparum and P. vivax strains. This minireview offers a historical overview of the most significant contributions made by the Panamanian owl monkey (Aotus lemurinus lemurinus) to malaria chemotherapy research.

Gastrointestinal tract pathology of the owl monkey (Aotus spp.).

Owl monkeys are small nocturnal new world primates in the genus Aotus that are most used in biomedical research for malaria. Cardiomyopathy and nephropathy are well-described common diseases contributing to their morbidity and mortality; less is known about lesions affecting the gastrointestinal tract. Records from a 14-year period (2008-2022) at the Keeling Center for Comparative Medicine and Research were queried to identify instances of spontaneous gastrointestinal disease that directly contributed to the cause of death from the 235 adult owl monkeys submitted for necropsy. Of the 235, 10.6% (25/235) had gastrointestinal disease listed as a significant factor that contributed to morbidity and mortality. Diagnoses included candidiasis (3/25), gastric bloat (4/25), and intestinal incarceration and ischemia secondary (11/25), which included intussusception (4/25), mesenteric rent (3/25), strangulating lipoma (2/25), intestinal torsion (1/25), and an inguinal hernia (1/25). Intestinal adenocarcinomas affecting the jejunum (4/25) were the most common neoplasia diagnosis. Oral squamous cell carcinoma (1/25) and intestinal lymphoma (2/25) were also diagnosed. This report provides evidence of spontaneous lesions in the species that contribute to morbidity and mortality.

A call-to-action to assist in efforts to protect owl monkeys (Aotus spp.).

The majority of the 11 species of owl monkeys (Aotus spp.) have declining populations or are listed as data deficient. Deforestation due to agriculture, development, or logging poses threats to owl monkeys throughout their range. In some areas, Aotus are hunted for bushmeat or trapped for the wildlife trade. In Colombia, the country with the greatest number of Aotus species, owl monkeys are also threatened by civil unrest. To help combat these challenges, nonprofit organizations and field researchers in habitat countries have successfully implemented a variety of conservation projects such as censusing and monitoring owl monkey populations, establishing protected areas, reforesting degraded areas, filing lawsuits to protect wild populations, helping law enforcement with environmental regulation, and promoting environmental education. We highlight some of the conservation successes and suggest actions people around the world can take to contribute to these important efforts.

Intergroup encounters in pair-living primates: Comparative analysis and a case study of pair-living and monogamous owl monkeys (Aotus azarae) of Argentina.

The function of intergroup encounters (IGEs) may differ substantially among species of different group sizes and social organizations. Research in group-living primates has shown that the behavioral responses during IGEs can vary widely from affiliative to neutral or aggressive interactions; still, little is known about IGEs in pair-living taxa. We conducted a systematic literature review to find relevant studies on the functions of IGEs in pair-living nonhuman primates that could inform analyses of IGE data (n = 242 IGEs, 21 groups and 10 solitary individuals, 1997-2020) from wild owl monkeys, a pair-living, monogamous primate with extensive biparental care. We identified 1315 studies published between 1965 and 2021; only 13 of them (n = 10 species) contained raw data on the number of IGEs. Our review of those studies showed that IGEs are common, but highly variable in their nature and characteristics in pair-living primates. To examine the non-mutually exclusive hypotheses of resource-, and mate defense, and infanticide avoidance we analyzed data from the Owl Monkey Project 27-year long database to build first an a priori model set. To incorporate prior knowledge from the literature review, we conducted our analyses as a consecutive series of binomial logistic regressions. All IGEs including all biologically relevant parameters (N = 156) were codified into three different behavioral categories (Reaction, Agonism, and Physical Aggression). The analysis showed that owl monkeys regularly engaged in IGEs, most of which were agonistic. They showed more reaction when infants were present, but reactions were less physically aggressive when infants and pregnant females were involved. Overall, our results lend more support for the infant and mate defense hypotheses than they do for the resource defense one.

Single-cell transcription analysis of Plasmodium vivax blood-stage parasites identifies stage- and species-specific profiles of expression.

Plasmodium vivax and P. falciparum, the parasites responsible for most human malaria worldwide, exhibit striking biological differences, which have important clinical consequences. Unfortunately, P. vivax, unlike P. falciparum, cannot be cultivated continuously in vitro, which limits our understanding of its biology and, consequently, our ability to effectively control vivax malaria. Here, we describe single-cell gene expression profiles of 9,215 P. vivax parasites from bloodstream infections of Aotus and Saimiri monkeys. Our results show that transcription of most P. vivax genes occurs during short periods of the intraerythrocytic cycle and that this pattern of gene expression is conserved in other Plasmodium species. However, we also identify a strikingly high proportion of species-specific transcripts in late schizonts, possibly associated with the specificity of erythrocyte invasion. Our findings provide new and robust markers of blood-stage parasites, including some that are specific to the elusive P. vivax male gametocytes, and will be useful for analyzing gene expression data from laboratory and field samples.

Asymmetric dimethyl arginine in captive owl monkeys (Aotus sp).

Only four of 40 animals had measurable asymmetric dimethyl arginine (ADMA) levels. The young primate had the lowest value (53.4 ng/ml) when compared with the two adults (218.8 ± 9.3 ng/ml) and the elderly one (320.5 ng/ml). The ADMA levels in this study may relate to the echocardiographic abnormalities found, and possible hypertensive individuals.

Adiponectin levels in captive Owl Monkeys (Aotus sp.).

The mean serum value of adiponectin in captive Aotus sp. is 541.99 ng/mL ± 73.05. There is no influence of sex or age, but there is a moderate positive correlation between body weight and adiponectin levels in males.

The importance of auditory, olfactory, and visual cues for insect foraging in owl monkeys (Aotus nancymaae).

Nocturnal mammals have unique sensory adaptations to facilitate foraging at night. Owl monkeys (Aotus spp.) are pair-living nocturnal platyrrhines adept at capturing insect prey under low-light conditions. Owl monkeys use acoustic and chemical cues in intraspecific communication and use olfaction to detect fruit as they forage. We conducted an experiment to determine which cues (auditory, olfactory, and visual) Aotus nancymaae rely upon when foraging for insects. We scored the behavior of 23 captive owl monkeys during a series of trials in which monkeys were provided sensory boxes with insect cues either present (experimental box) or absent (control box). Each cue was tested alone and in combination with all other cues (multimodal cues). We used generalized linear mixed models to determine which cues elicited the greatest behavioral response. Owl monkeys approached and spent more time near experimental boxes than control boxes. Male owl monkeys were quicker than their female partners to approach the sensory boxes, suggesting that males may be less neophobic than females. The owl monkeys exhibited behaviors associated with olfaction and foraging (e.g., sneezing, trilling) during trials with multimodal cues and when only olfactory cues were present. When only visual or auditory cues were present, owl monkeys exhibited fewer foraging-related behaviors. After approaching a sensory box, however, they often touched boxes containing visual cues. A. nancymaae may rely on olfactory cues at night to detect a food source from several meters away and then rely more on visual cues once they are closer to the food source. Their use of sensory cues during insect foraging differs from nocturnal strepsirrhines, possibly reflecting physiological constraints associated with phylogeny, given that owl monkeys evolved nocturnality secondarily from a more recent diurnal ancestor.

Plasmodium vivax spleen-dependent genes encode antigens associated with cytoadhesion and clinical protection.

Plasmodium vivax, the most widely distributed human malaria parasite, causes severe clinical syndromes despite low peripheral blood parasitemia. This conundrum is further complicated as cytoadherence in the microvasculature is still a matter of investigations. Previous reports in Plasmodium knowlesi, another parasite species shown to infect humans, demonstrated that variant genes involved in cytoadherence were dependent on the spleen for their expression. Hence, using a global transcriptional analysis of parasites obtained from spleen-intact and splenectomized monkeys, we identified 67 P. vivax genes whose expression was spleen dependent. To determine their role in cytoadherence, two Plasmodium falciparum transgenic lines expressing two variant proteins pertaining to VIR and Pv-FAM-D multigene families were used. Cytoadherence assays demonstrated specific binding to human spleen but not lung fibroblasts of the transgenic line expressing the VIR14 protein. To gain more insights, we expressed five P. vivax spleen-dependent genes as recombinant proteins, including members of three different multigene families (VIR, Pv-FAM-A, Pv-FAM-D), one membrane transporter (SECY), and one hypothetical protein (HYP1), and determined their immunogenicity and association with clinical protection in a prospective study of 383 children in Papua New Guinea. Results demonstrated that spleen-dependent antigens are immunogenic in natural infections and that antibodies to HYP1 are associated with clinical protection. These results suggest that the spleen plays a major role in expression of parasite proteins involved in cytoadherence and can reveal antigens associated with clinical protection, thus prompting a paradigm shift in P. vivax biology toward deeper studies of the spleen during infections.

Molecular data aids pinworm diagnosis in night monkeys (Aotus spp., Primates: Aotidae) with the resurrection of a Trypanoxyuris species (Nematoda: Oxyuridae).

Neotropical primates (Platyrrhines) are commonly parasitized by pinworm nematodes of the genus Trypanoxyuris Vevers, 1923. The taxonomic identity of Trypanoxyuris sampled in night monkeys (Aotus Iliger) has been rather controversial. Two species have been described, namely T. microon (Linstow, 1907) and T. interlabiata (Sandosham, 1950). The latter was synonymized with T. microon considering that the observed morphological differences corresponded to different developmental stages of the nematode rather than to differences between both species. Here, we used an integrative taxonomy approach, based on morphological and molecular data along with host identity, in order to assess the validity of both species. Our results evidenced that these different morphotypes correspond to different and reciprocally monophyletic groups; thus, we propose the resurrection of T. interlabiata. We redescribe both pinworm species using specimens sampled in Aotus monkeys from Colombia and discuss the advantages of combining molecular and morphological data to uncover pinworm diversity, and to understand the potential forces determining the diversification process in pinworms from platyrrhine primates.

SELECTED OPHTHALMIC TESTS AND OCULAR DIMENSIONS IN RELATION TO ACTIVITY PATTERN IN THREE NEOTROPICAL NONHUMAN PRIMATES: BLACK-TUFTED MARMOSET (CALLITHRIX PENICILLATA), GUIANAN SQUIRREL MONKEY (SAIMIRI SCIUREUS), AND AZARA'S NIGHT MONKEY (AOTUS AZARAE INFULATUS).

The goals of this study were to compare ocular morphology, determine the reference intervals of selected ophthalmic tests, ocular measurements, intraocular pressure, and tear production, and to establish possible relationships in the visual ecology of three different Neotropical nonhuman primates (NHP). Nineteen black-tufted marmosets (Callithrix penicillate), 24 Guianan squirrel monkeys (Saimiri sciureus), and 24 night monkeys (Aotus azarae infulatus) were included in the study. Schirmer tear test, ocular dimensions, ocular ultrasonography, intraocular pressure, central corneal thickness, and corneal touch threshold were determined. The ratio of the average corneal diameters and axial diameters (CD/AGL) were established. No significant difference was noted between males and females, nor left and right eyes, for all three species for all measurements (P > 0.05). CD/AGL ratio was significantly higher (P < 0.0001) in night monkeys (a nocturnal species) as compared to black-tufted marmoset and Guianan squirrel monkeys (two diurnal species). The reference intervals will aid veterinary ophthalmologists to more accurately diagnose pathological changes in the eyes of these species. In addition, ocular dimension comparison will allow other NHP species to be evaluated and examined in relationship to behavioral traits (nocturnal versus diurnal).

Plasmodium falciparum in Aotus nancymaae: A New Model for Placental Malaria.

Plasmodium falciparum-infected erythrocytes that display the variant surface antigen VAR2CSA bind chondroitin sulfate A (CSA) to sequester in placental intervillous spaces, causing severe sequelae for mother and offspring. Here, we establish a placental malaria (PM) monkey model. Pregnant Aotus infected with CSA-binding P. falciparum CS2 parasites during the third trimester developed pronounced sequestration of late-stage parasites in placental intervillous spaces that express VAR2CSA and bind specifically to CSA. Similar to immune multigravid women, a monkey infected with P. falciparum CS2 parasites over successive pregnancies acquired antibodies against VAR2CSA, with potent functional activity that was boosted upon subsequent pregnancy infections. Aotus also developed functional antibodies after multiple acute PM episodes and subsequent VAR2CSA immunization. In summary, P. falciparum infections in pregnant Aotus monkeys recapitulate all the prominent features of human PM infection and immunity, and this model can be useful for basic mechanistic studies and preclinical studies to qualify candidate PM vaccines. Clinical Trials Registration: NCT02471378.

Replacement of owl monkey centromere satellite by a newly evolved variant was a recent and rapid process.

Alpha satellite DNA is a major DNA component of primate centromeres. We previously reported that Azara's owl monkey has two types of alpha satellite DNA, OwlAlp1 and OwlAlp2. OwlAlp2 (344 bp) exhibits a sequence similarity throughout its entire length with alpha satellite DNA of closely related species. OwlAlp1 (185 bp) corresponds to the part of OwlAlp2. Based on the observation that the CENP-A protein binds to OwlAlp1, we proposed that OwlAlp1 is a relatively new repetitive DNA that replaced OwlAlp2 as the centromeric satellite DNA. However, a detailed picture of the evolutionary process of this centromere DNA replacement remains largely unknown. Here, we performed a phylogenetic analysis of OwlAlp1 and OwlAlp2 sequences, and also compared our results to alpha satellite DNA sequences of other primate species. We found that: (i) OwlAlp1 exhibits a higher similarity to OwlAlp2 than to alpha satellite DNA of other species, (ii) OwlAlp1 has a single origin, and (iii) sequence variation is lower in OwlAlp1 than in OwlAlp2. We conclude that OwlAlp1 underwent a recent and rapid expansion in the owl monkey lineage. This centromere DNA replacement could have been facilitated by the heterochromatin reorganization that is associated with the adaptation of owl monkeys to a nocturnal lifestyle.

Out of the shadows: Multilocus systematics and biogeography of night monkeys suggest a Central Amazonian origin and a very recent widespread southeastward expansion in South America.

Night monkeys (Aotus, Cebidae) are a widely distributed genus of Neotropical primates with a poorly understood taxonomy and biogeography. The number of species in the genus varies from one to nine, depending on the author, and there are at least 18 known karyotypes, varying from 2n = 46 to 2n = 58. Historically, night monkeys are divided into two species groups: red- and grey-necked groups from south and north of the Amazon-Solimões River, respectively. Here, we used 10 nuclear and 10 mitochondrial molecular markers from a wide taxonomic and geographic sample to infer phylogeny, divergence times, and biogeography of the genus. For phylogenetic reconstruction we used Maximum Likelihood (ML) and Bayesian Inferences (BI). Biogeographic models were generated using the 'BioGeoBEARS' software. We found support for nine taxa of Aotus and rejected the existence of monophyletic "red necked" and "grey necked" species groups. We suggest a taxonomic reclassification of the genus, which is better represented by two clades named northern group, which contains Aotus miconax, A. nancymae, A. trivirgatus, A. vociferans, A. lemurinus, A. griseimembra, A. zonalis, and A. brumbacki, and southern group, which contains A. nigriceps, A. boliviensis, A. infulatus, and A. azarae. The results suggest that the most recent common ancestor of all species of Aotus arose in the central Amazon basin in the Early Pliocene. The evolutionary history of night monkeys was guided by dispersal, vicariance and founder events. The end of the Andean uplift and the subsequent changes in the Amazon landscape, as well as the Amazon-Solimões and Tapajós rivers may have played an important role in the origin and diversification of Aotus, respectively. However, most of the Amazonian rivers seem not to have been geographical barriers to dispersal of night monkeys. The herein named southern group is fruit of a very recent diversification guided by dispersal, crossing the Tapajós, Xingú, Tocantins, and Guapore rivers and reaching the Cerrado in the last 1.6 My.

Selective use of primate CD4 receptors by HIV-1.

Individuals chronically infected with HIV-1 harbor complex viral populations within their bloodstreams. Recently, it has come to light that when these people infect others, the new infection is typically established by only one or a small number of virions from within this complex viral swarm. An important goal is to characterize the biological properties of HIV-1 virions that seed and exist early in new human infections because these are potentially the only viruses against which a prophylactic HIV-1 vaccine would need to elicit protection. This includes understanding how the Envelope (Env) protein of these virions interacts with the T-cell receptor CD4, which supports attachment and entry of HIV-1 into target cells. We examined early HIV-1 isolates for their ability to infect cells via the CD4 receptor of 15 different primate species. Primates were the original source of HIV-1 and now serve as valuable animal models for studying HIV-1. We find that most primary isolates of HIV-1 from the blood, including early isolates, are highly selective and enter cells through some primate CD4 receptor orthologs but not others. This phenotype is remarkably consistent, regardless of route of transmission, viral subtype, or time of isolation post infection. We show that the weak CD4 binding affinity of blood-derived HIV-1 isolates is what makes them sensitive to the small sequence differences in CD4 from one primate species to the next. To substantiate this, we engineered an early HIV-1 Env to have high, medium, or low binding affinity to CD4, and we show that it loses the ability to enter cells via the CD4 receptor of many primate species as the binding affinity gets weaker. Based on the phenotype of selective use of primate CD4, we find that weak CD4 binding appears to be a nearly universal property of HIV-1 circulating in the bloodstream. Therefore, weak binding to CD4 must be a selected and important property in the biology of HIV-1 in the body. We identify six primate species that encode CD4 receptors that fully support the entry of early HIV-1 isolates despite their low binding affinity for CD4. These findings will help inform long-standing efforts to model HIV-1 transmission and early disease in primates.

Lipid profile, apolipoproteins A-1 and B in owl monkeys (Aotus infulatus) in captivity.

BACKGROUND: Owl monkeys (Aotus infulatus) are frequently affected by heart diseases and, as in humans, dyslipidemia is one of the predisposing factors for adverse cardiovascular events. In view of this, the study of the lipid profile and plasma apolipoproteins can contribute to the clinical management of this neotropical primate species. METHODS: Lipid profile as well as A-1 and B apolipoprotein values were analyzed in 60 owl monkeys, studying their relationship with body biometry and the presence of cardiac alterations. RESULTS: Animals suspected of having heart disease did not show significant differences (p < .05) in terms of biometry or in relation to lipid profile and apolipoproteins A-1 and B values; however, higher values of LDL and ApoB and ApoB/ApoA-1 were observed in this group. CONCLUSIONS: This study is the first to describe the lipid profile and apolipoprotein values in owl monkeys, and further work will be needed to better elucidate the worthiness of LDL, ApoB, and the ApoB/ApoA-1 ratio in this primate species.

Detection of early myocardial cell death in owl monkeys (Aotus nancymai) using complement component C9 immunohistochemistry in formalin-fixed paraffin-embedded heart tissues: A retrospective study.

BACKGROUND: Owl monkeys are commonly used in biomedical research which is affected by the high incidence of cardiomyopathy in this species. Occasionally, owl monkeys with no clinical signs of heart disease are found dead and at necropsy show no, or very mild, cardiomyopathy. A possible explanation for sudden death is acute myocardial infarction; however, early myocardial changes may be difficult to assess by conventional stains and light microscopy. METHODS: Complement component C9 immunohistochemistry was performed in paraffin-embedded heart tissue samples from owl monkeys who died suddenly, or were euthanized due to sickness, to determine whether these animals suffered from acute myocardial infarcts. RESULTS AND CONCLUSION: C9 deposits were found in the myocardium of 19 out of 20 (95%) animals. The findings in this study suggest owl monkeys suffer from acute myocardial infarcts, and complement component C9 immunohistochemistry may be a useful diagnostic tool.

Occurrence and clinical significance of abnormal liver findings by ultrasound in captive owl monkeys.

BACKGROUND: Imaging diagnostic methods are essential for a complete understanding of the liver function and may aid in early detection of hepatic disorders. METHODS: Sixty-nine owl monkeys were grouped in three age groups (AG): AG1 (<2 years old, n = 14), 2 (2-6 years old, n = 21), and 3 (>7 years old, n = 34). The animals were evaluated by ultrasound, liver function tests, and hemogram. RESULTS: The ultrasound revealed abnormal findings in the parenchyma ("starry sky" and steatosis) and/or in the gallbladder (cholelithiasis, septum, and wall edema) in 17 individuals, with higher incidence in AG3 individuals. Seven hepatic individuals showed alterations in the blood tests. CONCLUSION: Our study reported the occurrence of abnormal liver findings by ultrasound in owl monkeys and their associated clinical analyses. We recommend the regular use of ultrasound to evaluate liver condition in owl monkeys, particularly in old individuals.

Pathways to paternal care in primates.

Natural selection will favor male care when males have limited alternative mating opportunities, can invest in their own offspring, and when care enhances males' fitness. These conditions are easiest to fulfill in pair-bonded species, but neither male care nor stable "breeding bonds" that facilitate it are limited to pair-bonded species. We review evidence of paternal care and extended breeding bonds in owl monkeys, baboons, Assamese macaques, mountain gorillas, and chimpanzees. The data, which span social/mating systems and ecologies, suggest that there are multiple pathways by which conditions conducive to male care can arise. This diversity highlights the difficulty of making inferences about the emergence of male care in early hominins based on single traits visible in the fossil record. We discuss what types of data are most needed and the questions yet to be answered about the evolution of male care and extended breeding bonds in the primate order.