Laboratory diagnosis of malaria in nonhuman primates

Pseudoreticulocytosis by the ADVIA 2120 Hematology Analyzer and Other Hematologic Changes in a Cynomolgus Macaque (Macaca fascicularis) With Malaria

Important hematologic changes can be observed in nonhuman primates with malaria, including inaccurate reticulocyte counts by the ADVIA 2120 hematology analyzer. A 5-year-old male purpose-bred cynomolgus macaque ( Macaca fascicularis) imported from a commercial source in Cambodia was enrolled in a nonclinical toxicity study investigating the effects of an immunomodulatory pharmaceutical agent. On study day 22, an increase in large unstained cells (LUCs), due to increased monocytes (2.20 × 103/µl, reference interval: 0.17-0.76 × 103/µl), was reported by the analyzer during a scheduled hematologic evaluation, which prompted blood smear review and revealed that the macaque had a high burden of Plasmodium spp.. The macaque did not have clinical signs for the infection at this time point. Progressively higher parasite burdens and persistently increased monocytes (markedly increased by study day 56, 10.38 × 103/µl) were observed at subsequent hematologic evaluations. New Methylene Blue stain manual reticulocyte counts were performed on study day 43 and at later time points, and showed that the analyzer reported erroneous higher reticulocyte counts (study day 43: +6.7%, +266.2 × 109/L; study day 50: +18.9%, +409.8 × 109/L) compared with the manual reticulocyte counts (pseudoreticulocytosis). The magnitude of regenerative response was considered inadequate for the severity of anemia at these time points. Atypical reticulocyte scatter plot distributions from the analyzer were also observed at time points with high parasite burdens, and combined with increased LUCs, may suggest high burden parasitemia. Verification of automated reticulocyte counts is important in cases with high malarial parasite burdens and the recognition of pseudoreticulocytosis is prudent in assessing appropriateness of the regenerative response. Increases in monocytes correlated with higher parasite burdens and marked increases may be an indicator of advanced disease.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Non-proliferative and Proliferative Lesions of the Non-human Primate (M. fascicularis)

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in most tissues and organs from the nonhuman primate used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Variability of Spleen and Mesenteric Lymph Node in Control Cynomolgus Monkeys ( Macaca fascicularis) from Nonclinical Safety Studies: A Retrospective Assessment

We assessed the variability of spleen and mesenteric lymph node (MLN) microscopic observations and the correlations of these observations with other study data from 478 control cynomolgus monkeys from 53 routine nonclinical safety studies. Spleen weight parameters (absolute and relative to body or brain weights) were highly variable both within a control group on an individual study (up to 5.11-fold) and among animals with the same light microscopic observation. Grades for microscopic observations were also highly variable. The most frequent microscopic observations for spleen were changes in the size and number of germinal centers (58%), acidophilic (hyaline) material in lymphoid follicles (52%), and compound lymphoid follicles (20%). The most frequent microscopic observations in the MLN were eosinophil infiltrates (90%), changes in size and number of germinal centers (42%), and brown pigment (21%). The only meaningful relationships ( r² > 0.3) were positive correlations between reticuloendothelial hyperplasia and malarial pigment in the spleen and between each of these observations and spleen weight parameters. We conclude that determination of test article-related effects on the immune system in routine monkey toxicology studies requires careful consideration and a weight-of-evidence approach due to the low numbers of animals/group, the inherent variability in spleen and MLN parameters, and the infrequent correlation among immune system-related end points.

Serological and molecular techniques applied for identification of Plasmodium spp. in blood samples from nonhuman primates

The aim of this study was to identify Plasmodium spp. in blood samples from nonhuman primates (NHPs) in the state of Maranhão, using classical and alternative techniques for examination of human malaria. A total of 161 blood samples from NHPs were analyzed: 141 from captive animals at a Wildlife Screening Center (CETAS) and 20 from free-living animals in a private reserve. The techniques used were microscopy, rapid diagnostic test (RDT), Indirect fluorescent antibody test (IFAT) and molecular techniques (semi-nested PCR, quantitative real-time PCR and LAMP). Two serological methods (dot-ELISA and indirect ELISA) were also standardized with rhoptry protein-soluble antigen of P. falciparum and P. berghei. Trophozoite forms of Plasmodium sp. were identified on slides from five different animals. No samples were positive through RDT and LAMP. Four samples were seropositive for P. malariae through IFAT. The samples showed low reactivity to ELISA. Plasmodium sp. was detected in 34.16% (55/161) of the samples using qPCR based on the 18S rRNA gene. After sequencing, two samples showed 100% identityl to P. malariae, one showed 97% identity to Plasmodium sp. ZOOBH and one showed 99% identity to P. falciparum . PCR was shown to be the most sensitive technique for diagnosing Plasmodium in NHP samples.

Malaria in cynomolgus monkeys used in toxicity studies in Japan

Plasmodium spp. protozoa cause malaria and are known to infect humans and a variety of animal species including macaque monkeys. Here we report both our experience with malaria recrudescence in cynomolgus monkeys (Macaca fascicularis) in a toxicity study and the results of a survey on Plasmodium infection in cynomolgus monkeys imported to Japan for laboratory use. A cynomolgus monkey from the toxicity study presented with severe anemia and Plasmodium protozoa in erythrocytes on a thin blood smear and was subsequently diagnosed with symptomatic malaria. In this animal, congestion and accumulation of hemozoin (malaria pigment) in macrophages were noted in the enlarged and darkly discolored spleen. As a follow-up for the experience, spleen sections from 800 cynomolgus monkeys in toxicity studies conducted between 2003 and 2013 were retrospectively examined for hemozoin deposition as a marker of Plasmodium infection. The origin of the animals included Cambodia, China, Indonesia, and Vietnam. Hemozoin deposition was confirmed in 44% of all examined monkeys. Monkeys from Indonesia showed the highest incidence of hemozoin deposition (approx. 80%). A high prevalence of Plasmodium infection in laboratory monkeys was also confirmed with polymerase chain reaction (PCR) by using Plasmodium genus-specific primers. Although Japan is not a country with endemic malaria, it is important to be aware of the prevalence and potential impact of background infection with Plasmodium spp. and recrudescence of symptomatic malaria in imported laboratory monkeys on pharmaceutical toxicity studies.

Experimental transfusion-induced Babesia microti infection: dynamics of parasitemia and immune responses in a rhesus macaque model

BACKGROUND

Babesiosis is an emerging tick-borne infection in humans. The increasing numbers of reported cases of transfusion-associated babesiosis (TAB), primarily caused by Babesia microti, represents a concern for the safety of the US blood supply.

STUDY DESIGN AND METHODS

This study investigated kinetics of parasitemia and innate immune responses and dynamics of antibody responses during B. microti infection in rhesus macaques (RMs) using blood smears, quantitative polymerase chain reaction (qPCR), flow cytometry, and indirect fluorescent antibody testing. A total of six monkeys were transfused with either hamster or monkey-passaged B. microti-infected red blood cells (two and four monkeys, respectively) simulating TAB.

RESULTS

The prepatent period in monkeys inoculated with hamster-passaged B. microti was 35 days compared with 4 days in monkeys transfused with monkey-passaged B. microti; the latter monkeys also had markedly higher parasitemia levels. The duration of the window period from the first detected parasitemia by qPCR analysis to the first detected antibody response ranged from 10 to 17 days. Antibody responses fluctuated during the course of the infection. Innate responses assessed by the frequencies of monocytes and activated B cells correlated with the kinetics and magnitude of parasitemia. On Day 14, additional activation peaks were noted for CD14+CD16+ and CD14-CD16+ monocytes and for CD11c+ myeloid dendritic cells, but only in animals transfused with monkey-passaged B. microti. Parasitemia persisted in these immunocompetent animals, similar to human infection.

CONCLUSION

The results suggest that transfusion-associated transmission of B. microti leads to rapid onset of parasitemia (Day 4) in RMs, detectable antibody response 14 days later, and persistent parasitemia.