Hematological and Serum Biochemical Reference Intervals for Alphaxalone Sedated Common Marmosets (Callithrix jacchus)

Marmosets are routinely used in biomedical research, therefore there is an increasing need for updated reference intervals calculated using a large sample size, correct statistics, and considering different variables. Hematological and biochemical values from 472 healthy common marmosets sedated with alphaxalone were collected over a ten-year period (2013-2023). The variables assumed to have influenced the blood-based parameters were compared, i.e., sex, age, housing condition, pregnancy, and contraceptive use. Reference intervals were calculated based on observed percentiles without parametric assumptions, and with parametric assumptions following Box-Cox transformation. Juvenile marmosets showed increased ALP, phosphate, WBC, lymphocyte count, and basophil count and decreased levels of GGT and Fe compared to adults. Marmosets housed strictly indoors showed increased ALT and GGT levels and decreased levels of total bilirubin and neutrophil count compared to marmosets housed with outdoor access. Pregnant marmosets showed increased ALP, total bilirubin, neutrophil count, monocyte count, and basophil count, and decreased levels of AST, ALT, cholesterol, Fe, and lymphocyte count compared to non-pregnant marmosets. Etonogestrel contracepted marmosets showed decreased P-LCR compared to females who were not contracepted. Updated reference intervals will aid researchers and veterinarians in identifying physiological and pathological changes, as well as improve the reproducibility of research in this species.

Long-acting reversible contraception with etonogestrel implants in female macaques (Macaca mulatta and Macaca fascicularis)

Introduction

Contraception is often required for management and population control purposes in group-housed and free-roaming non-human primates. Long-acting reversible contraceptives, including subdermal progestin-releasing implants, are preferred as they eliminate challenges associated with frequent administration. Etonogestrel (ENG)-releasing subdermal implants are reversible and long-acting for a minimum of 3 years, and are commercially available for human use as Implanon® or Nexplanon®.

Methods

A retrospective analysis was performed detailing the contraceptive effectiveness and reversibility of subdermal placement of one-fourth or one-third of an ENG implant (68 mg/implant) in 129 female rhesus macaques (Macaca mulatta) and 67 cynomolgus macaques (Macaca fascicularis) at the Biomedical Primate Research Centre (Rijswijk, Netherlands). Furthermore, single cross-sectional ENG serum concentrations were measured for 16 rhesus and 10 cynomolgus macaques, and hemoglobin and blood chemistry pre-ENG and at timepoints >0.5, >1.5, and > 2.5 years post-ENG insertion were evaluated for 24 rhesus macaques. Finally, data were obtained using trans-abdominal ultrasound regarding the influence of ENG on uterine volume and endometrial thickness in 14 rhesus and 11 cynomolgus macaques.

Results

As a contraceptive ENG was in 99.80% (CI 93.50-99.99) and 99.95% (CI 99.95-100) effective in rhesus and cynomolgus macaques, respectively. Prolonged ENG durations of implant use in 14 rhesus macaques (range 3.1-5.0 years) and eight cynomolgus macaques (range 3.2-4.0 years) resulted in no unintended pregnancies. A total of 17 female macaques were allowed to breed after ENG removal, and among them, 14 female macaques (82%) had an uneventful delivery. Serum ENG concentrations with a median ENG duration of 1.2 years (range 0.1-6.0 years) and 1.9 years (range 0.6-4.7 years) resulted in median concentrations of 112 pg./mL (range 0-305 pg./mL) and 310 pg./mL (range 183-382 pg./mL) for rhesus and cynomolgus macaques, respectively. ENG had no clinical effect on hemoglobin and blood chemistry parameters nor on the thickness of the endometrial lining or uterus volume.

Conclusion

This study indicates that both one-fourth and one-third of the ENG implants are effective, long-acting, reversible, and safe contraceptive to use in macaques.

Longitudinal positron emission tomography and postmortem analysis reveals widespread neuroinflammation in SARS-CoV-2 infected rhesus macaques

BACKGROUND

Coronavirus disease 2019 (COVID-19) patients initially develop respiratory symptoms, but they may also suffer from neurological symptoms. People with long-lasting effects after acute infections with severe respiratory syndrome coronavirus 2 (SARS-CoV-2), i.e., post-COVID syndrome or long COVID, may experience a variety of neurological manifestations. Although we do not fully understand how SARS-CoV-2 affects the brain, neuroinflammation likely plays a role.

METHODS

To investigate neuroinflammatory processes longitudinally after SARS-CoV-2 infection, four experimentally SARS-CoV-2 infected rhesus macaques were monitored for 7 weeks with 18-kDa translocator protein (TSPO) positron emission tomography (PET) using [¹⁸F]DPA714, together with computed tomography (CT). The baseline scan was compared to weekly PET-CTs obtained post-infection (pi). Brain tissue was collected following euthanasia (50 days pi) to correlate the PET signal with TSPO expression, and glial and endothelial cell markers. Expression of these markers was compared to brain tissue from uninfected animals of comparable age, allowing the examination of the contribution of these cells to the neuroinflammatory response following SARS-CoV-2 infection.

RESULTS

TSPO PET revealed an increased tracer uptake throughout the brain of all infected animals already from the first scan obtained post-infection (day 2), which increased to approximately twofold until day 30 pi. Postmortem immunohistochemical analysis of the hippocampus and pons showed TSPO expression in cells expressing ionized calcium-binding adaptor molecule 1 (IBA1), glial fibrillary acidic protein (GFAP), and collagen IV. In the hippocampus of SARS-CoV-2 infected animals the TSPO⁺ area and number of TSPO⁺ cells were significantly increased compared to control animals. This increase was not cell type specific, since both the number of IBA1⁺TSPO⁺ and GFAP⁺TSPO⁺ cells was increased, as well as the TSPO⁺ area within collagen IV⁺ blood vessels.

CONCLUSIONS

This study manifests [¹⁸F]DPA714 as a powerful radiotracer to visualize SARS-CoV-2 induced neuroinflammation. The increased uptake of [¹⁸F]DPA714 over time implies an active neuroinflammatory response following SARS-CoV-2 infection. This inflammatory signal coincides with an increased number of TSPO expressing cells, including glial and endothelial cells, suggesting neuroinflammation and vascular dysregulation. These results demonstrate the long-term neuroinflammatory response following a mild SARS-CoV-2 infection, which potentially precedes long-lasting neurological symptoms.

Reference Intervals and Percentiles for Hematologic and Serum Biochemical Values in Captive Bred Rhesus (Macaca mulatta) and Cynomolgus Macaques (Macaca fascicularis)

Several physiological characteristics and housing conditions are known to affect hematologic and serum biochemical values in macaques. However, the studies that have been conducted either report values calculated based on a small number of animals, were designed specifically to document the effect of a particular condition on the normal range of hematologic and serum biochemical values, or used parametric assumptions to calculate hematologic and serum biochemical reference intervals. We conducted a retrospective longitudinal cohort study to estimate reference intervals for hematologic and serum biochemical values in clinically healthy macaques based on observed percentiles without parametric assumptions. Data were obtained as part of the Biomedical Primate Research Centre (Rijswijk, The Netherlands) health monitoring program between 2018 and 2021. In total, 4009 blood samples from 1475 macaques were analyzed with a maximum of one repeat per year per animal. Data were established by species, gender, age, weight-for-height indices, pregnancy, sedation protocol, and housing conditions. Most of the parameters profoundly affected just some hematologic and serum biochemical values. A significant glucose difference was observed between the ketamine and ketamine-medetomidine sedation protocols. The results emphasize the importance of establishing uniform experimental groups with validated animal husbandry and housing conditions to improve the reproducibility of the experiments.

Multigenerational Social Housing and Group-Rearing Enhance Female Reproductive Success in Captive Rhesus Macaques (Macaca mulatta)

Simple Summary

It is currently common practice to house non-human primates at biomedical research facilities, e.g., rhesus macaques, in social groups. To enhance female reproductive success, peer groups are formed. In these breeding groups, infants are taken from their mother at an age of ten months and housed with animals of approximately the same age. Yet for welfare, leaving offspring with their mother and allowing multigenerational groups including families is preferred. This argues that a trade-off between female reproductive success and welfare exists. In this retrospective study we investigated the differences in female rhesus macaque reproductive success between peer groups and multigenerational groups. Our results show that females in multigenerational groups have more births per year and have higher offspring survival compared with those in peer groups. Thus, housing rhesus macaques in multigenerational groups provides a win−win situation, rather than a trade-off, in which female reproductive success and animal welfare can simultaneously be optimized.

Abstract

To optimize costs and reproductive success, rhesus macaques in biomedical primate research facilities are often peer-reared. Older, dependent infants are typically removed from their natal group to enhance female reproduction. The minimal husbandry age-norm of infant removal is ten months. These practices deviate from species-specific behavior and may reduce welfare, suggesting a trade-off between female reproduction and welfare. However, the effect of breeding group type and rearing history on female reproductive success (i.e., birth rate; inter-birth interval (IBI); offspring survival) is unclear. This retrospective study investigated whether group type (i.e., peer groups versus multigenerational groups) and rearing history (i.e., peer- or hand-reared; group-reared with peer- or hand-reared mother; group-reared) affected female reproductive success in captive rhesus macaques. Data on female reproduction between 1996 and 2019 were collected at the Biomedical Primate Research Centre, Rijswijk. Birth rates were higher in multigenerational breeding groups than in peer groups. Moreover, group-reared females had higher offspring survival than peer- or hand-reared females. IBI was not affected by breeding group type or female rearing history. However, females in both peer and multigenerational breeding groups typically conceived earlier after giving birth than the husbandry infant removal age-norm of ten months. Thus, infant removal at an age of ten months does not enhance a female’s reproduction. Altogether, female reproduction and non-human primate welfare can simultaneously be optimized through multigenerational breeding groups and group-rearing.

Overweight Management through Mild Caloric Restriction in Multigenerational Long-Tailed Macaque Breeding Groups

Caloric restriction (CR) is an effective method to reduce overweight in captive non-human primates (NHPs). CR has been applied to individually- and pair-housed NHPs, but whether applying CR can be effective and safe in group-housed NHPs has not yet been assessed. This study investigates the effect of mild (20%) CR on adult overweight and biochemical parameters, immature growth, veterinary consultations, and reproductive success in multigenerational long-tailed macaque (Macaca fascicularis) breeding groups. Data were derived from anthropometric measurements and blood samples during yearly health checks, complemented with retrospective data on veterinary consultations and reproductive success. Adult body measures decreased after CR, with heavier individuals and females losing more weight compared to leaner individuals and males. CR lowered cholesterol levels in adults but had no overall effect on other biochemical parameters. Yet, biochemical parameters of individuals with high baseline values were reduced more compared to individuals with low baseline values. Immature growth, veterinary consultations and reproductive success were not influenced by CR. Thus, CR targeted the right individuals, i.e., overweight adults, and had no adverse effects on the variables examined in this study. This implies that mild CR can be a valuable overweight management strategy in group-housed NHPs.

Novel application of [18F]DPA714 for visualizing the pulmonary inflammation process of SARS-CoV-2-infection in rhesus monkeys (Macaca mulatta)

Rationale

The aim of this study was to investigate the application of [¹⁸F]DPA714 to visualize the inflammation process in the lungs of SARS-CoV-2-infected rhesus monkeys, focusing on the presence of pulmonary lesions, activation of mediastinal lymph nodes and surrounded lung tissue.

Methods

Four experimentally SARS-CoV-2 infected rhesus monkeys were followed for seven weeks post infection (pi) with a weekly PET-CT using [¹⁸F]DPA714. Two PET images, 10 min each, of a single field-of-view covering the chest area, were obtained 10 and 30 min after injection. To determine the infection process swabs, blood and bronchoalveolar lavages (BALs) were obtained.

Results

All animals were positive for SARS-CoV-2 in both the swabs and BALs on multiple timepoints pi. The initial development of pulmonary lesions was already detected at the first scan, performed 2-days pi. PET revealed an increased tracer uptake in the pulmonary lesions and mediastinal lymph nodes of all animals from the first scan obtained after infection and onwards. However, also an increased uptake was detected in the lung tissue surrounding the lesions, which persisted until day 30 and then subsided by day 37–44 pi. In parallel, a similar pattern of increased expression of activation markers was observed on dendritic cells in blood.

Principal conclusions

This study illustrates that [¹⁸F]DPA714 is a valuable radiotracer to visualize SARS-CoV-2-associated pulmonary inflammation, which coincided with activation of dendritic cells in blood. [¹⁸F]DPA714 thus has the potential to be of added value as diagnostic tracer for other viral respiratory infections.

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[¹⁸F]DPA714 PET can visualize alterations in the lungs after a SARS-CoV-2 infection.

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The PET signal increases in unaffected lung tissue till day 30 post infection.

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Dendritic cell activation in blood is increased till day 30/37 post infection

Brain Inflammation and Intracellular α-Synuclein Aggregates in Macaques after SARS-CoV-2 Infection

SARS-CoV-2 causes acute respiratory disease, but many patients also experience neurological complications. Neuropathological changes with pronounced neuroinflammation have been described in individuals after lethal COVID-19, as well as in the CSF of hospitalized patients with neurological complications. To assess whether neuropathological changes can occur after a SARS-CoV-2 infection, leading to mild-to-moderate disease, we investigated the brains of four rhesus and four cynomolgus macaques after pulmonary disease and without overt clinical symptoms. Postmortem analysis demonstrated the infiltration of T-cells and activated microglia in the parenchyma of all infected animals, even in the absence of viral antigen or RNA. Moreover, intracellular α-synuclein aggregates were found in the brains of both macaque species. The heterogeneity of these manifestations in the brains indicates the virus’ neuropathological potential and should be considered a warning for long-term health risks, following SARS-CoV-2 infection.

Medical imaging of pulmonary disease in SARS-CoV-2-exposed non-human primates

Chest X-ray (CXR), computed tomography (CT), and positron emission tomography-computed tomography (PET-CT) are noninvasive imaging techniques widely used in human and veterinary pulmonary research and medicine. These techniques have recently been applied in studies of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-exposed non-human primates (NHPs) to complement virological assessments with meaningful translational readouts of lung disease. Our review of the literature indicates that medical imaging of SARS-CoV-2-exposed NHPs enables high-resolution qualitative and quantitative characterization of disease otherwise clinically invisible and potentially provides user-independent and unbiased evaluation of medical countermeasures (MCMs). However, we also found high variability in image acquisition and analysis protocols among studies. These findings uncover an urgent need to improve standardization and ensure direct comparability across studies.

Light-Induced Smooth Endoplasmic Reticulum Rearrangement in a Unique Interlaced Compartmental Pattern in Macaca mulatta RPE

Purpose

To investigate light-induced modifications of the smooth endoplasmic reticulum of the RPE in primates.

Methods

Eyes of three terminally anesthetized Rhesus monkeys were exposed to 5000 lux for 10 minutes or kept in the dark. Transmission electron microscopy and electron tomography were conducted on small fragments of retina sampled from different regions of the retina.

Results

RPE cells smooth endoplasmic reticulum shows a previously unknown arrangement characterized by an interlaced compartmental pattern (ICP). Electron tomograms and 3D-modelling demonstrated that the smooth endoplasmic reticulum with an ICP (ICPSER) consisted of four parallel, independent and interwoven networks of tubules arranged as interconnected coiled coils. Its architecture realized a compact labyrinthine structure of tightly packed tubules stabilized by intertubular filamentous tethers. On average, the ICPSER is present in about 14.6% of RPE cells. Although ICPSER was preferentially found in cells located in the peripheral and in the para/perifoveal retina, ICPSER cells significantly increased in number upon light exposure in the para/perifovea and in the fovea.

Conclusions

An ICPSER is apparently a unique feature to primate RPE. Its rapid appearance in the area centralis of the retina upon light exposure suggests a function related to the foveate structure of primate retina or to the diurnal habits of animals that may require additional protection from photo-oxidation or enhanced requests of visual pigments regeneration.

A Comparative Study of Chest CT With Lung Ultrasound After SARS-CoV-2 Infection in the Assessment of Pulmonary Lesions in Rhesus Monkeys (Macaca Mulatta)

Lung ultrasound (LUS) is a fast and non-invasive modality for the diagnosis of several diseases. In humans, LUS is nowadays of additional value for bedside screening of hospitalized SARS-CoV-2 infected patients. However, the diagnostic value of LUS in SARS-CoV-2 infected rhesus monkeys, with mild-to-moderate disease, is unknown. The aim of this observational study was to explore correlations of the LUS appearance of abnormalities with COVID-19-related lesions detected on computed tomography (CT). There were 28 adult female rhesus monkeys infected with SARS-CoV-2 included in this study. Chest CT and LUS were obtained pre-infection and 2-, 7-, and 14-days post infection. Twenty-five animals were sub-genomic PCR positive in their nose/throat swab for at least 1 day. CT images were scored based on the degree of involvement for lung lobe. LUS was scored based on the aeration and abnormalities for each part of the lungs, blinded to CT findings. Most common lesions observed on CT were ground glass opacities (GGOs) and crazy paving patterns. With LUS, confluent or multiple B-lines with or without pleural abnormalities were observed which is corresponding with GGOs on CT. The agreement between the two modalities was similar over the examination days. Pleural line abnormalities were clearly observed with LUS, but could be easily missed on CT. Nevertheless, due to the air interface LUS was not able to examine the complete volume of the lung. The sensitivity of LUS was high though the diagnostic efficacy for mild-to-moderate disease, as seen in macaques, was relatively low. This leaves CT the imaging modality of choice for diagnosis, monitoring, and longitudinal assessment of a SARS-CoV-2 infection in macaques.

Retrospective Evaluation of a Minor Dietary Change in Non-Diabetic Group-Housed Long-Tailed Macaques (Macaca fascicularis)

Macaques in captivity are prone to becoming overweight and obese, which may cause several health problems. A diet that mimics the natural diet of macaques may prevent these problems and improve animal welfare. Adjusting captive diets towards a more natural composition may include increasing fiber content and lowering the glycemic index, i.e., reducing the impact on blood glucose levels. Such a dietary change was implemented in our long-tailed macaque (Macaca fascicularis) breeding colony. The basic diet of monkey chow pellets remained the same, while the supplementary provisioning of bread was replaced by grains and vegetables. This study is a retrospective evaluation, based on electronic health records, that investigated whether this minor dietary change had a beneficial effect on relative adiposity and overweight-related health parameters in 44 non-diabetic, group-housed, female long-tailed macaques. Relative adiposity was measured with a weight-for-height index and blood samples were collected during yearly health checks. Glycemic response and lipid metabolism were evaluated using several biochemical parameters. Relative adiposity and overweight status did not differ after dietary change. Yet, relatively heavy individuals generally lost body weight, while relatively lean individuals gained body weight, leading to a more balanced body weight dynamic. Dietary change did not affect HbA1c and triglyceride levels, while fructosamine and cholesterol levels were significantly reduced. Thus, the minor dietary change had no significant effect on overweight status, but some biochemical parameters related to the risk of diabetes and cardiovascular disease were positively affected. This study emphasizes the importance of evaluating husbandry changes and that critically reviewing husbandry practices can provide valuable insights to improve animal health and welfare.

The utility of voluntary weighing in captive group-living rhesus macaques (Macaca mulatta)

Bodyweight is an important health and welfare indicator for captive non-human primates (NHPs). Bodyweight can be measured during routine handling procedures, which cause stress. Alternatively, animals can be trained to step onto a scale, but training success varies greatly between individuals. Being able to weigh animals regularly without having to handle or train them is thus desirable for monitoring animal health and welfare. This study investigates the utility, ie the participation, reliability and time investment, of voluntary weighing in captive NHPs living in large social groups. Subjects of the study were 92 rhesus macaques (Macaca mulatta) housed in four social groups at the Biomedical Primate Research Centre in Rijswijk, The Netherlands. A scale was placed in their home enclosure during several sessions. Individuals were unwilling to step onto an unbaited scale. When likeable food items were used to attract individuals to the scale, 68% of them stepped onto the scale. Age and dominance rank did not affect stepping onto the scale, whereas exploratory tendency and social group did. The level of agreement between bodyweight by voluntary weighing and bodyweight measured during sedation was very high. These results show that the majority of rhesus macaques in social groups can be weighed voluntarily and that voluntary weighing is reliable. When optimising and further developing the method, voluntary weighing can form a valuable tool in the captive management of NHPs.

Effect of Housing Conditions on Cortisol and Body Fat Levels in Female Rhesus Macaques

Macaques are among the most commonly used non-human primates in biomedical research. They are highly social animals, yet biomedical studies often require group-living animals to be pair-housed in a controlled environment. A change in environment causes only short-term stress in adapting individuals, while non-adapting animals may experience long-term stress that can adversely affect study results. Individuals likely differ in their ability to adapt depending on individual characteristics. Changes in cortisol and body fat levels may reflect these different individual responses. Here, we investigate the long-term effect of a change from group- to pair-housing on cortisol and body fat levels in 32 female rhesus macaques, exploring whether age, dominance rank, original cortisol, and body fat levels are related to long-term stress in pair-housing. Hair samples were analyzed for cortisol levels, while anthropometric measurements and computed tomography were performed to quantify body fat. Monkeys served as their own control with a 7.5-month period between the measurements. Cortisol levels increased, while average body fat levels did not differ when individuals were moved from group- to pair-housing. Cortisol and body fat levels were not significantly correlated. Changes in cortisol were independent of age and dominance rank, whereas individual variation in body fat alterations was related to the group-housed body fat level and dominance rank. Although this study did not identify individual characteristics related to long-term stress in pair-housing, the individual variation confirms that some individuals are more resilient to change than others and provides possibilities for future refinement studies.

Bronchoalveolar lavage affects thorax computed tomography of healthy and SARS-CoV-2 infected rhesus macaques (Macaca mulatta)

Medical imaging as method to assess the longitudinal process of a SARS-CoV-2 infection in non-human primates is commonly used in research settings. Bronchoalveolar lavage (BAL) is regularly used to determine the local virus production and immune effects of SARS-CoV-2 in the lower respiratory tract. However, the potential interference of those two diagnostic modalities is unknown in non-human primates. The current study investigated the effect and duration of BAL on computed tomography (CT) in both healthy and experimentally SARS-CoV-2-infected female rhesus macaques (Macaca mulatta). In addition, the effect of subsequent BALs was reviewed. Thorax CTs and BALs were obtained from four healthy animals and 11 experimentally SARS-CoV-2-infected animals. From all animals, CTs were obtained just before BAL, and 24 hours post-BAL. Additionally, from the healthy animals, CTs immediately after, and four hours post-BAL were obtained. Thorax CTs were evaluated for alterations in lung density, measured in Hounsfield units, and a visual semi-quantitative scoring system. An increase in the lung density was observed on the immediately post-BAL CT but resolved within 24 hours in the healthy animals. In the infected animals, a significant difference in both the lung density and CT score was still found 24 hours after BAL. Furthermore, the differences between time points in CT score were increased for the second BAL. These results indicate that the effect of BAL on infected lungs is not resolved within the first 24 hours. Therefore, it is important to acknowledge the interference between BAL and CT in rhesus macaques.

A Stepwise Male Introduction Procedure to Prevent Inbreeding in Naturalistic Macaque Breeding Groups

Male introductions into captive primate breeding groups can be risky and unsuccessful. However, they are necessary to prevent inbreeding in naturalistic breeding groups. The procedure used to introduce new individuals may affect the success and influence the risks associated with group introductions. At the Biomedical Primate Research Centre (BPRC) in Rijswijk, the Netherlands, male rhesus macaque (Macaca mulatta) introductions into naturalistic social groups with a matrilineal structure and without a breeding male achieve relatively high success rates. This paper describes the male introduction procedure used at the BPRC. Males are stepwise familiarized with and introduced to their new group, while all interactions between the new male and the resident females are closely monitored. Monitoring the behaviour of the resident females and their new male during all stages of the introduction provides crucial information as to whether or not it is safe to proceed. The BPRC introduction procedure is widely applicable and may improve the management of captive primate groups in any housing facility worldwide. Thus, the careful introduction management can minimize the risk associated with male introductions and enhance the welfare of captive primates.

How the COVID-19 pandemic highlights the necessity of animal research

Recently, a petition was offered to the European Commission calling for an immediate ban on animal testing. Although a Europe-wide moratorium on the use of animals in science is not yet possible, there has been a push by the non-scientific community and politicians for a rapid transition to animal-free innovations. Although there are benefits for both animal welfare and researchers, advances on alternative methods have not progressed enough to be able to replace animal research in the foreseeable future. This trend has led first and foremost to a substantial increase in the administrative burden and hurdles required to make timely advances in research and treatments for human and animal diseases. The current COVID-19 pandemic clearly highlights how much we actually rely on animal research. COVID-19 affects several organs and systems, and the various animal-free alternatives currently available do not come close to this complexity. In this Essay, we therefore argue that the use of animals is essential for the advancement of human and veterinary health.

Tolerant and intolerant macaques show different levels of structural complexity in their vocal communication

We tested the social complexity hypothesis which posits that animals living in complex social environments should use complex communication systems. We focused on two components of vocal complexity: diversity (number of categories of calls) and flexibility (degree of gradation between categories of calls). We compared the acoustic structure of vocal signals in groups of macaques belonging to four species with varying levels of uncertainty (i.e. complexity) in social tolerance (the higher the degree of tolerance, the higher the degree of uncertainty): two intolerant species, Japanese and rhesus macaques, and two tolerant species, Tonkean and crested macaques. We recorded the vocalizations emitted by adult females in affiliative, agonistic and neutral contexts. We analysed several acoustic variables: call duration, entropy, time and frequency energy quantiles. The results showed that tolerant macaques displayed higher levels of vocal diversity and flexibility than intolerant macaques in situations with a greater number of options and consequences, i.e. in agonistic and affiliative contexts. We found no significant differences between tolerant and intolerant macaques in the neutral context where individuals are not directly involved in social interaction. This shows that species experiencing more uncertain social interactions displayed greater vocal diversity and flexibility, which supports the social complexity hypothesis.

Evaluation of the Novel PET Tracer [11C]HACH242 for Imaging the GluN2B NMDA Receptor in Non-Human Primates

PURPOSE

There are currently no positron emission tomography (PET) radiotracers for the GluN2B (NR2B) binding sites of brain N-methyl-D-aspartate (NMDA) receptors. In rats, the GluN2B antagonist Ro25-6981 reduced the binding of N-((5-(4-fluoro-2-[¹¹C]methoxyphenyl)pyridin-3-yl)methyl)cyclopentanamin ([¹¹C]HACH242). This paper reports the evaluation of [¹¹C]HACH242 PET in non-human primates at baseline and following administration of the GluN2B negative allosteric modulator radiprodil.

PROCEDURES

Eight 90-min dynamic [¹¹C]HACH242 PET scans were acquired in three male anaesthetised rhesus monkeys, including a retest session of subject 1, at baseline and 10 min after intravenous 10 mg/kg radiprodil. Standardised uptake values (SUV) were calculated for 9 brain regions. Arterial blood samples were taken at six timepoints to characterise pharmacokinetics in blood and plasma. Reliable input functions for kinetic modelling could not be generated due to variability in the whole-blood radioactivity measurements.

RESULTS

[¹¹C]HACH242 entered the brain and displayed fairly uniform uptake. The mean (± standard deviation, SD) T_max was 17 ± 7 min in baseline scans and 24 ± 15 min in radiprodil scans. The rate of radioligand metabolism in plasma (primarily to polar metabolites) was high, with mean parent fractions of 26 ± 10 % at 20 min and 8 ± 5 % at 85 min. Radiprodil increased [¹¹C]HACH242 whole-brain SUV in the last PET frame by 25 %, 1 %, 3 and 17 % for subjects 1, 2, 3 and retest of subject 1, respectively. The mean brain to plasma ratio was 5.4 ± 2.6, and increased by 39 to 110 % in the radiprodil condition, partly due to lower parent plasma radioactivity of -11 to -56 %.

CONCLUSIONS

The present results show that [¹¹C]HACH242 has a suitable kinetic profile in the brain and low accumulation of lipophilic radiometabolites. Radiprodil did not consistently change [¹¹C]HACH242 brain uptake. These findings may be explained by variations in cerebral blood flow, a low fraction of specifically bound tracer, or interactions with endogenous NMDA receptor ligands at the binding site. Further experiments of ligand interactions are necessary to facilitate the development of radiotracers for in vivo imaging of the ionotropic NMDA receptor.

Factors determining male introduction success and long-term stability in captive rhesus macaques

The entrance of new males into non-human primate groups bears high social risk, yet migration is necessary to prevent inbreeding. Males are not always accepted in their new group. In the wild, males may increase the likelihood of successful group entry by choosing a new group based on their own and the group's characteristics. Understanding whether these characteristics also determine a male's ability to enter captive groups is crucial to improve introduction management. This study aims to identify which factors determine male introduction success (i.e. male stays in the group for at least 4 weeks) and long-term stability (i.e. the male does not cause considerable behavioural problems after success) after male introductions in captive groups of rhesus macaques (Macaca mulatta), creating one-male groups. We studied 64 male introductions at the breeding colony of the Biomedical Primate Research Centre in Rijswijk, The Netherlands. 49 (77%) introductions were successful, with the male obtaining a long-term stable social position in the group in 38 (59%) introductions. Introductions of males that reached at least prime age, into groups with more adult females, but without pregnant females were most successful. Moreover, long-term stability was highest when males were heavier, were at least 3.5 years old when they were first removed from their natal group, and groups had few matrilines and no pregnant females were present. Males should be introduced at the time they would naturally immigrate, when they are strongest. Moreover, groups should consist of few large matrilines, as observed in the wild, with philoatric females and males that are removed at natural age. Our study highlights the importance of composing naturalistic groups and mimicking natural migration patterns to maintain long-term stable breeding groups in captivity.

Determining overweight and underweight with a new weight-for-height index in captive group-housed macaques

Housing primates in naturalistic groups provides social benefits relative to solitary housing. However, food intake may vary across individuals, possibly resulting in overweight and underweight individuals. Information on relative adiposity (the amount of fat tissue relative to body weight) is needed to monitor overweight and underweight of group-housed individuals. However, the upper and lower relative adiposity boundaries are currently only known for macaques living solitarily in small cages. We determined the best measure of relative adiposity and explored the boundaries of overweight and underweight to investigate their incidence in group-housed adult male and female rhesus macaques and long-tailed macaques living in spacious enclosures at the Biomedical Primate Research Centre (BPRC), the Netherlands. During yearly health checks different relative adiposity measures were obtained. For long-tailed macaques, comparable data on founder and wild animals were also available. Weight-for-height indices (WHI) with height to the power of 3.0 (WHI3.0) for rhesus macaques and 2.7 (WHI2.7) for long-tailed macaques were optimally independent of height and were highly correlated with other relative adiposity measures. The boundary for overweight was similar in group-housed and solitary-housed macaques. A lower boundary for underweight, based on 2% body fat similar to wild primates, gave a better estimate for underweight in group-housed macaques. We propose that for captive group-housed rhesus macaques relative adiposity should range between 42 and 67 (WHI3.0) and for long-tailed macaques between 39 and 62 (WHI2.7). The majority of group-housed macaques in this facility have a normal relative adiposity, a considerable proportion (17-23%) is overweight, and a few (0-3%) are underweight.

Involvement of the Red Nucleus in the Compensation of Parkinsonism may Explain why Primates can develop Stable Parkinson's Disease

Neurological compensatory mechanisms help our brain to adjust to neurodegeneration as in Parkinson's disease. It is suggested that the compensation of the damaged striato-thalamo-cortical circuit is focused on the intact thalamo-rubro-cerebellar pathway as seen during presymptomatic Parkinson, paradoxical movement and sensorimotor rhythm (SMR). Indeed, the size of the red nucleus, connecting the cerebellum with the cerebral cortex, is larger in Parkinson's disease patients suggesting an increased activation of this brain area. Therefore, the red nucleus was examined in MPTP-induced parkinsonian marmoset monkeys during the presymptomatic stage and after SMR activation by neurofeedback training. We found a reverse significant correlation between the early expression of parkinsonian signs and the size of the parvocellular part of the red nucleus, which is predominantly present in human and non-human primates. In quadrupedal animals it consists mainly of the magnocellular part. Furthermore, SMR activation, that mitigated parkinsonian signs, further increased the size of the red nucleus in the marmoset monkey. This plasticity of the brain helps to compensate for dysfunctional movement control and can be a promising target for compensatory treatment with neurofeedback technology, vibrotactile stimulation or DBS in order to improve the quality of life for Parkinson's disease patients.

Defining predictive factors for reproductive output in captive common marmosets (Callithrix jacchus)

Common marmosets (Callithrix jacchus) demonstrate variations in reproductive output, not only in terms of total reproductive output during a lifetime but also in litter size per parturition. The present study explores factors, such as parents’ litter size, parturition number, maternal body weight at conception and maternal age, which may account for this variation. A retrospective analysis of clinical records of a captive breeding colony was conducted over a 9‐year period yielding reproductive summaries of 26 dams and 22 sires producing a total of 115 litters. Dams born from litters of  ≤2 (N = 20) more often produced litters of ≤2, whereas dams born from litters of >2 (N = 6) more often produced litters of >2 (p < 0.05). The dams’ maternal body weight at the time of conception had also a significant effect on subsequent litter size. In addition, the chance of triplets was higher after the second parturition. Maternal age, interbirth interval, and season of birth had no effect on litter size. Factors relating to the sire had a negligible effect on the size of the litter. Multivariate statistical modeling revealed that the dams’ original litter size, maternal bodyweight at conception and parturition number are determining factors for the number of babies per litter. This study identified factors determining marmoset litter size, some of which (maternal litter size) are novel to this study and were not reported previously. Further exploration of the potential role of maternal litter size as a determinant of the litter sizes produced by marmoset breeders is warranted.

An experimental Staphylococcus aureus carriage and decolonization model in rhesus macaques (Macaca mulatta)

Our human model of nasal colonization and eradication of S. aureus is limited by safety issues. As rhesus macaques are closely related to humans and natural hosts for S. aureus, we developed an experimental decolonization and inoculation protocol in these animals. Animals were screened for nasal carriage of S. aureus and 20 carriers were selected. Decolonization was attempted using nasal mupirocin (10 animals) or mupirocin plus trimethoprim/sulfadiazine intramuscularly (10 animals) both once daily for 5 days, and checked by follow-up cultures for 10 weeks. Intranasal inoculation was performed with S. aureus strain 8325–4 in culture-negative animals. 11/20 animals, of which 5 received mupirocin and 6 the combination treatment, became culture-negative for S. aureus for 10 weeks and these 11 animals were subsequently inoculated. Swabs were taken once a week for 5 weeks to test for the presence of the inoculated strain. In 3 animals, strain 8325–4 was cultured from the nose 1 week after inoculation, indicating short-term survival of this strain only, a finding similar to that previously found in our human model. These data demonstrate that rhesus macaques may constitute a relevant animal model to perform S. aureus eradication and inoculation studies with relatively limited invasive handling of the animals.

25-OH-vitamin D, parathyroid hormone, and calcium serum levels in captive common marmosets (Callithrix jacchus): Reference values and effect of age, sex, season, and closure of long bone epiphyses

BACKGROUND

To date, reference values for 25-OH-vitamin D, parathyroid hormone (PTH), and calcium in serum of common marmosets (Callithrix jacchus) based on a large sample size are not available.

METHODS

Serum reference values for these parameters were determined and correlated with sex, age, season of sampling, and time of long bone epiphyseal closure in captive-housed marmosets.

RESULTS AND CONCLUSIONS

The 90% reference range for serum 25-OH-vitamin D is 47.40-370.4 nmol/L, for PTH 2.10-30.51 pmol/L, and for calcium 2.08-2.63 mmol/L. Lower levels of vitamin D were measured in fall compared with the other seasons. Levels of PTH were higher in males than in females, and calcium levels were lower in younger animals compared with older marmosets. No other effects of age, sex, season, or timing of growth plate closure were found.

Comparative virulence of in vitro-cultured primate- and pig-associated Helicobacter suis strains in a BALB/c mouse and a Mongolian gerbil model

BACKGROUND

Helicobacter suis (H. suis) is the most prevalent gastric non-H. pylori Helicobacter species in humans. This bacterium mainly colonizes the stomach of pigs, but it has also been detected in the stomach of nonhuman primates. The aim of this study was to obtain better insights into potential differences between pig- and primate-associated H. suis strains in virulence and pathogenesis.

MATERIALS AND METHODS

In vitro-isolated H. suis strains obtained from pigs, cynomolgus monkeys (Macaca fascicularis), and rhesus monkeys (Macaca mulatta) were used for intragastric inoculation of BALB/c mice and Mongolian gerbils. Nine weeks and six months later, samples of the stomach of inoculated and control animals were taken for PCR analysis and histopathological examination.

RESULTS

The cynomolgus monkey-associated H. suis strain only colonized the stomach of mice, but not of Mongolian gerbils. All other H. suis strains colonized the stomach in both rodent models. In all colonized animals, severe gastric inflammation was induced. Gastric lymphoid follicles and destruction of the antral epithelium were observed in infected gerbils, but not in mice. Infection with both pig- and primate-associated H. suis strains evoked a similar marked Th17 response in mice and gerbils, accompanied by increased CXCL-13 expression levels.

CONCLUSIONS

Apart from the cynomolgus monkey-associated strain which was unable of colonizing the stomach of Mongolian gerbils, no substantial differences in virulence were found in rodent models between in vitro-cultured pig-associated, cynomolgus monkey-associated and rhesus monkey-associated H. suis strains. The experimental host determines the outcome of the immune response against H. suis infection, rather than the original host.

Variable BCG efficacy in rhesus populations: Pulmonary BCG provides protection where standard intra-dermal vaccination fails

M.bovis BCG vaccination against tuberculosis (TB) notoriously displays variable protective efficacy in different human populations. In non-human primate studies using rhesus macaques, despite efforts to standardise the model, we have also observed variable efficacy of BCG upon subsequent experimental M. tuberculosis challenge. In the present head-to-head study, we establish that the protective efficacy of standard parenteral BCG immunisation varies among different rhesus cohorts. This provides different dynamic ranges for evaluation of investigational vaccines, opportunities for identifying possible correlates of protective immunity and for determining why parenteral BCG immunisation sometimes fails. We also show that pulmonary mucosal BCG vaccination confers reduced local pathology and improves haematological and immunological parameters post-infection in animals that are not responsive to induction of protection by standard intra-dermal BCG. These results have important implications for pulmonary TB vaccination strategies in the future.

Peptococcus simiae sp. nov., isolated from rhesus macaque faeces and emended description of the genus Peptococcus

A study of the faecal microbiome in three healthy female rhesus macaques revealed the presence of a novel obligately anaerobic, chemoorganoheterotrophic, non-sporing, coccoid, non-motile, Gram-stain-positive bacterial species. Three strains of this species, designated as M108T, M916-1/1, and M919-2/1, were non-haemolytic, H2S-positive, catalase-positive, bile- and NaCl-sensitive and required peptone for growth. Strains also were asaccharolytic, able to utilize sulfite, thiosulfate and elemental sulfur as electron acceptors, and produced acetic and butyric acids as metabolic end-products. Strain M108T is characterized by the prevalence of C14 : 0, C16 : 0 and C18 : 1ω9cis dimethyl acetal among the cellular fatty acids, and the presence of MK-10 menaquinone. The DNA G+C content was found to be 51 mol%. Phylogenetic analysis of partial 16S rRNA gene sequences of strains M108T, M916-1/1 and M919-2/1 placed these strains into the genus Peptococcus (family Peptococcaceae). On the basis of phenotypic and genotypic properties we conclude that these strains represent a novel bacterial species for which the name Peptococcus simiae sp. nov. is proposed. The type strain is M108T (=DSM 100347T=VKM B-2932T).

Advantages and Risks of Husbandry and Housing Changes to Improve Animal Wellbeing in a Breeding Colony of Common Marmosets (Callithrix jacchus)

Between 1975 and 2014, housing conditions for laboratory-housed marmosets changed dramatically after the introduction of new guidelines designed to improve their care and wellbeing. According to these guidelines, our facility provided marmosets with outside enclosures, switched to deep litter as bedding material, and discontinued the use of disinfectant agents in animal enclosures. However, both deep litter and access to outside enclosures hypothetically increase the risk of potential exposure to pathogenic microorganisms. We evaluated whether these housing and husbandry modifications constituted an increased veterinary risk for laboratory-housed common marmosets (Callithrix jacchus). After the animals had been exposed to these new housing conditions for 2.5 y, we examined their intestinal bacterial flora and feces, the deep litter, and insects present in the housing. In addition, we assessed the marmosets' general health and the effect of outdoor housing on, for example, vitamin D levels. Although numerous bacterial strains--from nonpathogenic to potentially pathogenic--were cultured, we noted no increase in illness, mortality, or breeding problems related to this environmental microflora. Housing laboratory marmosets in large enriched cages, with both indoor and outdoor enclosures, providing them with deep litter, and eliminating the use of disinfectants present an increased veterinary risk. However, after evaluating all of the collected data, we estimate that the veterinary risk of the new housing conditions is minimal to none in terms of clinical disease, disease outbreaks, abnormal behavior, and negative effects on reproduction.

Preclinical Evaluation of a Chimeric Malaria Vaccine Candidate in Montanide ISA 720®: Immunogenecity and Safety in Rhesus Macaques

Several malarial antigens are in development as potential vaccine candidates as part of a concerted effort to control the disease, which kills more than one million people per year. Although some antigens have demonstrated an impact against the malaria parasite, Plasmodium falciparum, many researchers hypothesize that a combination of antigens will be required to generate high levels of efficacy against clinical disease. PfCP2.9 is a chimeric protein that includes MSP119 and domain III of AMA1 [AMA1 (111)] of Plasmodium falciparum in a single recombinant molecule. The antigen, formulated in Seppic's ISA 720 adjuvant, is approaching Phase I clinical testing in humans. The purpose of this study was to assess the safety of this vaccine and to explore possible dosage levels for clinical evaluation. Groups of five monkeys each were immunized i.m. with 25 microg, 50 microg, 100 microg and 200 microg of PfCP2.9/ISA 720 in 0.5 mL on days 0 and 112. The mean anti-PfCP2.9 titres to the 50 microg dose group were higher than the other dose groups; however, there was no statistically significant difference between the anti-CP2.9 titres of any of the groups, suggesting that the immune response to PfCP2.9 was saturated at 25 microg. One animal in the 100 microg dose group elicited a higher antibody and IFN-gamma response to PfCP2.9 than the rest of the cohort; this animal developed a small sterile abscess following the second vaccination, which spontaneously resolved within one week.

IN CONCLUSION

(a) 50 microg is highly immunogenic, appears safe, and is likely to be an appropriate dose for clinical evaluation; and (b) a conservative trial design is warranted to avoid any unexpected reactogenicity with the PfCP2.9/ISA 720 formulation.

Micromelic dysplasia-like syndrome in a captive colony of common marmosets (Callithrix jacchus)

Over several years, 0% to 5% of adolescent animals in a captive colony of common marmosets (Callithrix jacchus) showed severely bended arms and legs over several years. The animals showed no pain, discomfort, or altered behavior but were unable to stretch their distal limbs to their full extent. To characterize the lesion morphologically, the bones of 4 affected marmosets were compared macroscopically and radiographically with those of 6 unaffected animals. The deformities were characterized by mid- to distal diaphyseal bending and pronounced shortening of long bones. The morphology and density of other bones including the skull and vertebrae were unaffected. Although vitamin D values were low in a fifth affected marmoset during 10 to 16 mo of age, lesions associated with rickets were not observed. To our knowledge, this report is the first to describe a micromelic dysplasia-like syndrome comprising severe, idiopathic bending and shortening of long bones in a colony of marmosets.

Preclinical evaluation of [(18)F]PK-209, a new PET ligand for imaging the ion-channel site of NMDA receptors

INTRODUCTION

The present study was designed to assess whether [(18)F]PK-209 (3-(2-chloro-5-(methylthio)phenyl)-1-(3-([(18)F]fluoromethoxy)phenyl)-1-methylguanidine) is a suitable ligand for imaging the ion-channel site of N-methyl-D-aspartate receptors (NMDArs) using positron emission tomography (PET).

METHODS

Dynamic PET scans were acquired from male rhesus monkeys over 120min, at baseline and after the acute administration of dizocilpine (MK-801, 0.3mg/kg; n=3/condition). Continuous and discrete arterial blood samples were manually obtained, to generate metabolite-corrected input functions. Parametric volume-of-distribution (VT) images were obtained using Logan analysis. The selectivity profile of PK-209 was assessed in vitro, on a broad screen of 79 targets.

RESULTS

PK-209 was at least 50-fold more selective for NMDArs over all other targets examined. At baseline, prolonged retention of radioactivity was observed in NMDAr-rich cortical regions relative to the cerebellum. Pretreatment with MK-801 reduced the VT of [(18)F]PK-209 compared with baseline in two of three subjects. The rate of radioligand metabolism was high, both at baseline and after MK-801 administration.

CONCLUSIONS

PK-209 targets the intrachannel site with high selectivity. Imaging of the NMDAr is feasible with [(18)F]PK-209, despite its fast metabolism. Further in vivo evaluation in humans is warranted.

Challenges in oral administration of metronidazole dissolved in drinking water to rhesus monkeys (Macaca mulatta)

Intestinal pathogens such as Entamoeba spp. and Giardia spp. protozoans are not uncommon among rhesus macaques (Macaca mulatta) in research facilities. These infections affect the health of the macaques, potentially causing severe diarrhea, and also pose a risk of zoonotic transmission to human caretakers. Infections must therefore be treated, but no standard treatment for intestinal protozoans in macaques has been developed. Metronidazole is commonly used to treat infections with Giardia spp. and Entamoeba spp. in veterinary medicine, but evidence-based information on effectiveness and dosages for nonhuman primates is lacking, and administration of drugs to nonhuman primates is challenging. The authors designed a study to determine whether oral administration of metronidazole dissolved in drinking water would be successful in rhesus macaques. They monitored daily fluid intake of macaques given water with or without metronidazole and with or without flavored syrup. Metronidazole addition, with or without flavored syrup, resulted in a decrease in fluid intake. Although it was possible to administer metronidazole in drinking water to some macaques, the authors conclude that this strategy is not a practical clinical method because of variation in the amount of water and metronidazole ingested by the macaques.

Anatomical description and morphometry of the skeleton of the common marmoset (Callithrix jacchus)

Callithrix jacchus (common marmoset) is regularly used in biomedical research, including for studies involving the skeleton. To support these studies, skeletons of healthy animals that had been euthanized for reasons not interfering with skeletal anatomy were prepared. The marmoset dental formula 2I-1C-3P-2M of each oral quadrant is atypical for New World monkeys which commonly possess a third molar. Seven cervical, 12–13 thoracic, 7–6 lumbar, 2–3 sacral and 26–29 caudal vertebrae are present, the thoracolumbar region always comprising 19 vertebrae. A sigmoid clavicle connects the scapula with the manubrium of the sternum. Depending on the number of thoracic vertebrae, 4–5 sternebrae are located between the manubrium and xiphoid process. Wide interosseous spaces separate the radius from the ulna, and the tibia from the fibula. A small sesamoid bone is inserted in the m. abductor digiti primi longus at the medial border of the carpus, a pair of ovoid sesamoid bones is located at the palmar/plantar sides of the trochleae of each metapodial bone, and round fabellae articulate with the proximal surfaces of the femoral condyles. Male marmosets possess a small penile bone. Both the front and hind feet have five digits. The hallux possesses a flat nail, whereas all other digits present curved claws. Interestingly, a central bone is present in both the carpus and tarsus. This study provides a description and detailed illustrations of the skeleton of the common marmoset as an anatomical guide for further biomedical research.

Elimination of Schistosoma mansoni Adult Worms by Rhesus Macaques: Basis for a Therapeutic Vaccine?

Background

Among animal models of schistosomiasis, the rhesus macaque is unique in that an infection establishes but egg excretion rapidly diminishes, potentially due to loss of adult worms from the portal system via shunts or death by immune attack.

Principal Findings

To investigate this, six rhesus macaques were exposed to Schistosoma mansoni cercariae and the infection monitored until portal perfusion at 18 weeks. Despite a wide variation in worm numbers recovered, fecal egg output and circulating antigen levels indicated that a substantial population had established in all animals. Half the macaques had portal hypertension but only one had portacaval shunts, ruling out translocation to the lungs as the reason for loss of adult burden. Many worms had a shrunken and pallid appearance, with degenerative changes in intestines and reproductive organs. Tegument, gut epithelia and muscles appeared cytologically intact but the parenchyma was virtually devoid of content. An early and intense IgG production correlated with low worm burden at perfusion, and blood-feeding worms cultured in the presence of serum from these animals had stunted growth. Using immunoproteomics, gut digestive enzymes, tegument surface hydrolases and antioxidant enzymes were identified as targets of IgG in the high responder animals.

Significance

It appears that worms starve to death after cessation of blood feeding, as a result of antibody-mediated processes. We suggest that proteins in the three categories above, formulated to trigger the appropriate mechanisms operating in rhesus macaques, would have both prophylactic and therapeutic potential as a human vaccine.

Infection with blood-dwelling schistosome worms is a major cause of human disease in many tropical countries. Despite intensive efforts a vaccine has proved elusive, not least because the chronic nature of the infection provides few pointers for vaccine development. The rhesus macaque appears unique among animal models in that adult worms establish but are eventually lost. We investigated whether this was due to pathological or immunological causes by monitoring the fate of a schistosome infection, and were able to rule out escape of worms from the portal system as a result of egg-induced vascular shunts. A substantial worm population established in all animals but there was a wide variation in the numbers recovered at 18 weeks. We observed a strong inverse association between the rapidity and intensity of the IgG response and worm burden. Rather than an acute lethal attack, immune-mediated elimination of worms appeared to be a prolonged process directed against vital components of exposed surfaces, causing worms to starve to death. We suggest that if the mechanisms deployed by the rhesus macaque could be replicated in humans by administration of key recombinant antigens, they would form the basis for a vaccine with both prophylactic and therapeutic properties.

Immunogenicity in rhesus of the Plasmodium vivax mosquito stage antigen Pvs25H with Alhydrogel and Montanide ISA 720

Pvs25 is an ookinete surface protein from Plasmodium vivax that is the target of transmission-blocking antibodies. Two immunogenicity trials in rhesus monkeys with a recombinant form of the protein, Pvs25H, were undertaken. Monkeys were vaccinated with Pvs25H adsorbed to Alhydrogel or emulsified in Montanide ISA 720 at 0, 4 and 27 weeks (study 1) or in Montanide ISA 720 at 0 and 18 weeks (study 2) with 1.5 or 15 microg Pvs25H in 0.1 or 0.5 mL of emulsion (four combinations). Immunogenicity was assessed by ELISA and by membrane-feeding experiments using P. vivax-infected blood from human volunteers (studies 1 and 2) or from chimpanzees (study 1). Both vaccine trials generated antibodies that blocked transmission of P. vivax to mosquitoes. Antibody titres and transmission blocking were higher with Montanide ISA 720 than with Alhydrogel in the first trial and with the 15 microg Pvs25H/0.5 mL ISA 720 combination in the second trial.

PrimaTB STAT-PAK assay, a novel, rapid lateral-flow test for tuberculosis in nonhuman primates

Tuberculosis (TB) is the most important zoonotic bacterial disease in nonhuman primates (NHP). The current diagnostic method, the intradermal palpebral tuberculin test, has serious shortcomings. We characterized antibody responses in NHP against Mycobacterium tuberculosis to identify immunodominant antigens and develop a rapid serodiagnostic test for TB. A total of 422 NHP were evaluated, including 243 rhesus (Macaca mulatta), 46 cynomolgus (Macaca fascicularis), and 133 African green (Cercopithecus aethiops sabaeus) monkeys at five collaborative centers. Of those, 50 monkeys of the three species were experimentally inoculated with M. tuberculosis. Antibody responses were monitored every 2 to 4 weeks for up to 8 months postinfection by MultiAntigen Print ImmunoAssay with a panel of 12 recombinant antigens. All of the infected monkeys produced antibodies at various levels and with different antigen recognition patterns. ESAT-6 and MPB83 were the most frequently recognized proteins during infection. A combination of selected antigens which detected antibodies in all of the infected monkeys was designed to develop the PrimaTB STAT-PAK assay by lateral-flow technology. Serological evaluation demonstrated high diagnostic sensitivity (90%) and specificity (99%). The highest rate of TB detection was achieved when the skin test was combined with the PrimaTB STAT-PAK kit. This novel immunoassay provides a simple, rapid, and accurate test for TB in NHP.

Effect of adjuvant on reactogenicity and long-term immunogenicity of the malaria Vaccine ICC-1132 in macaques

ICC-1132 is a malaria vaccine candidate based on a modified hepatitis B virus core particle (HBc) bearing putative protective epitopes from the circumsporozoite protein (CS) of Plasmodium falciparum. While the epitope carrier itself is immunogenic, its potency can be increased by formulation with adjuvants. As a prelude to Phase I clinical trials, rhesus macaques were immunised twice with GMP grade ICC--1132 in saline or formulated with the adjuvants Alhydrogel (Alhydrogel) or Montanide((R)) ISA 720 (Montanide). Both adjuvant formulations gave significant humoral responses after the first injection, with titres increasing further after the second dose. The Montanide formulation was the most immunogenic, but undesirable reactogenicity in the form of sterile abscesses was associated with higher dosage levels of ICC--1132. These side effects could be avoided with lower antigen load, or by formulation of the second dose in Alhydrogel. Such measures also reduced peak titres and longevity of antibodies against CS, demonstrating the delicate balance between immunogenicity and reactogenicity of new vaccine formulations.

Protection of macaques against Mycobacterium tuberculosis infection by a subunit vaccine based on a fusion protein of antigen 85B and ESAT-6

Various new tuberculosis (TB) vaccine candidates in combination with new delivery systems, including subunit vaccines, are currently being evaluated by a number of laboratories. One vaccine candidate that has shown promising protective capacity in mice and guinea pigs is a fusion of Ag85B and ESAT-6. In this study, we have investigated the efficacy of this Ag85B-ESAT-6 fusion protein vaccine in a non-human primate model for TB. Vaccination of cynomolgus monkeys with the Ag85B-ESAT-6 fusion protein in two different adjuvant (DDA/MPL, AS02A) resulted in a reduction in bacterial number and/or lung pathology in animals challenged with Mycobacterium tuberculosis. Vaccination prevented an increase in C-reactive protein serum levels, general activation of CD4 and CD8 subsets and boosted development of humoral and cellular immune responses to a spectrum of mycobacterial antigens on exposure to M. tuberculosis infection. We show, in two independent experiments, that vaccination of primates with Ag85B-ESAT-6 induces protective immune responses, suggesting that Ag85B-ESAT-6 is a strong candidate for further clinical evaluation. As far as we are aware this is the first report of protection in primates with a subunit vaccine.

Juvenile rhesus monkeys have more colonic granulomas than adults after primary infection with Schistosoma mansoni

Adults and children have differences in their susceptibility to schistosomiasis. Whether this age-dependent innate susceptibility influences parasite-caused granulomogenesis is difficult to assess in humans. Therefore, we exposed juvenile and adult female rhesus monkeys to primary infection with Schistosoma mansoni. Hepatic and intestinal granuloma formation was observed in both pre-pubescent and adult monkeys. Two distinct stages of granulomas were discerned, the exudative and the productive stage. In the intestine, more granulomas were generated in the colon than in the ileum. In contrast to the adult animals, the juvenile rhesus monkeys had higher numbers of colonic granulomas, these higher numbers being predominantly of the more advanced productive stage. Juvenile animals had a statistically non-significant increased worm burden. These results suggest that juvenile rhesus monkeys have a significantly more intense and advanced colonic response towards entrapped S. mansoni eggs after primary schistosome infections and, thereby, are more susceptible to parasite infection.

TB diagnosis in non-human primates: comparison of two interferon-γ assays and the skin test for identification of Mycobacterium tuberculosis infection

In general non-human primates are highly susceptible to infections with Mycobacterium tuberculosis which therefore presents an explosive health threat to colonies. To screen for M. tuberculosis infections in non-human primates, the skin test is routinely used. However, the reliability of this test in primates is debatable. The aim of this study was to compare relatively easy in vitro diagnostic tests for TB with the skin test for detection of a tuberculosis (TB) infection. Two in vitro assays, a whole blood interferon-gamma (WB IFN-gamma) assay and in vitro stimulation of isolated lymphocytes (PBMC IFN-gamma) were evaluated during both experimental TB infections in macaques as well as during an outbreak of TB in a macaque quarantine facility. The WB IFN-gamma assay was also evaluated on healthy old and new world monkeys. Our results show that both in vitro assays detected TB infection in macaques. All experimentally infected animals showed TB-specific responses in both assays. In contrast, several TB animals were not diagnosed TB positive using the skin test. In addition, during the outbreak in the quarantine facility one animal was not detected using the routinely used skin test, but it showed strong positive responses in the WB assay. In conclusion, the in vitro assays are a valuable tool for screening non-human primates for TB infection, especially because the assays cause relatively less stress for the animals compared to the skin test and give reproducible and reliable results.

Transfected Plasmodium knowlesi produces bioactive host gamma interferon: a new perspective for modulating immune responses to malaria parasites

Transgenic pathogenic microorganisms expressing host cytokines such as gamma interferon (IFN-gamma) have been shown to manipulate host-pathogen interaction, leading to immunomodulation and enhanced protection. Expression of host cytokines in malaria parasites offers the opportunity to investigate the potential of an immunomodulatory approach by generating immunopotentiated parasites. Using the primate malaria parasite Plasmodium knowlesi, we explored the conditions for expressing host cytokines in malaria parasites. P. knowlesi parasites transfected with DNA constructs for expressing rhesus monkey (Macaca mulatta) IFN-gamma under the control of the heterologous P. berghei apical membrane antigen 1 promoter, produced bioactive IFN-gamma in a developmentally regulated manner. IFN-gamma expression had no marked effect on in vitro parasite development. Bioactivity of the parasite-produced IFN-gamma was shown through inhibition of virus cytopathic effect and confirmed by using M. mulatta peripheral blood cells in vitro. These data indicate for the first time that it is feasible to generate malaria parasites expressing bioactive host immunomodulatory cytokines. Furthermore, cytokine-expressing malaria parasites offer the opportunity to analyze cytokine-mediated modulation of malaria during the blood and liver stages of the infection.

Experimental infection of the olive baboon (Paplio anubis) with Plasmodium knowlesi: severe disease accompanied by cerebral involvement

Experimental systems that model some of the complex interactions between parasite and host can be extremely valuable in identifying and developing new prophylactics and therapeutics against human diseases. Because primates have similar immune systems to humans, we have characterized a baboon model for understanding host response to Plasmodium knowlesi. Ten intact olive baboons (Papio anubis) of either sex were experimentally infected with P. knowlesi H strain erythrocytic parasites. The infection in these baboons was either acute or chronic. Animals with acute infection developed multiple system organ dysfunction and cerebral involvement. In chronically infected animals, only the spleen was moderately enlarged. The P. knowlesi parasitemia profile in baboons and rhesus monkeys was comparable. However, some clinical symptoms of the baboons and P. falciparum-infected humans were similar. These studies demonstrate for the first time that P. anubis is a suitable host for P. knowlesi for studying clinical symptoms and pathology.

Juvenile rhesus monkeys have lower type 2 cytokine responses than adults after primary infection with Schistosoma mansoni

Adults and children have differences in their susceptibility to schistosomiasis. The relative influences of age-dependent innate resistance and acquired immunity in the differences between susceptibility to schistosomiasis are difficult to assess in humans. Therefore, we exposed juvenile and adult female rhesus monkeys to primary infection with Schistosoma mansoni. In contrast to the adult animals, the juvenile rhesus monkeys had low levels of interleukin (IL)-4 and IL-5 production by peripheral blood mononuclear cells after schistosome infection, as well as lower levels of parasite-antigen-specific antibody (IgG, IgM, and IgA) responses, and produced limited antigen-specific or total IgE. Juvenile animals had statistically nonsignificant increased worm burdens and tissue or fecal egg counts, compared with that of adults, whereas circulating schistosome antigens were significantly higher in infected juvenile monkeys. These results suggest that juvenile rhesus monkeys have reduced type 2 cytokine responses after primary schistosome infections and perhaps are more susceptible to parasite infection.