Saffold virus is able to productively infect primate and rodent cell lines and induces apoptosis in these cells

10.1038/emi.2014.15Emerging Microbes and Infections3

Strict tropism for CD71+/ CD234+ human reticulocytes limits Plasmodium cynomolgi's zoonotic potential

Two malaria parasites of Southeast Asian macaques, Plasmodium knowlesi and P. cynomolgi, can infect humans experimentally. In Malaysia, where both species are common, zoonotic knowlesi malaria has recently become dominant, and cases are recorded throughout the region. By contrast, to date only a single case of naturally acquired P. cynomolgi has been found in humans. In this study we show that whereas P. cynomolgi merozoites invade monkey red blood cells (RBCs) indiscriminately in vitro, for humans they are restricted to reticulocytes expressing both transferrin receptor 1 (Trf1 or CD71) and the Duffy antigen/chemokine receptor (DARC or CD234). This likely contributes to the paucity of detectable zoonotic cynomolgi malaria. We further describe post-invasion morphological and rheological alterations in P. cynomolgi-infected human reticulocytes that are strikingly similar to those observed for P. vivax These observations stress the value of P. cynomolgi as a model in the development of blood stage vaccines against vivax malaria

Strict tropism for CD71+/ CD234+ human reticulocytes limits Plasmodium cynomolgi's zoonotic potential

Two malaria parasites of Southeast Asian macaques, Plasmodium knowlesi and P. cynomolgi, can infect humans experimentally. In Malaysia, where both species are common, zoonotic knowlesi malaria has recently become dominant, and cases are recorded throughout the region. By contrast, to date only a single case of naturally acquired P. cynomolgi has been found in humans. In this study we show that whereas P. cynomolgi merozoites invade monkey red blood cells (RBCs) indiscriminately in vitro, for humans they are restricted to reticulocytes expressing both transferrin receptor 1 (Trf1 or CD71) and the Duffy antigen/chemokine receptor (DARC or CD234). This likely contributes to the paucity of detectable zoonotic cynomolgi malaria. We further describe post-invasion morphological and rheological alterations in P. cynomolgi-infected human reticulocytes that are strikingly similar to those observed for P. vivax These observations stress the value of P. cynomolgi as a model in the development of blood stage vaccines against vivax malaria

Hepatic spheroids used as an in vitro model to study malaria relapse

Hypnozoites are the liver stage non-dividing form of the malaria parasite that are responsible for relapse and acts as a natural reservoir for human malaria Plasmodium vivax and P. ovale as well as a phylogenetically related simian malaria P. cynomolgi. Our understanding of hypnozoite biology remains limited due to the technical challenge of requiring the use of primary hepatocytes and the lack of robust and predictive in vitro models. In this study, we developed a malaria liver stage model using 3D spheroid-cultured primary hepatocytes. The infection of primary hepatocytes in suspension led to increased infectivity of both P. cynomolgi and P. vivax infections. We demonstrated that this hepatic spheroid model was capable of maintaining long term viability, hepatocyte specific functions and cell polarity which enhanced permissiveness and thus, permitting for the complete development of both P. cynomolgi and P. vivax liver stage parasites in the infected spheroids. The model described here was able to capture the full liver stage cycle starting with sporozoites and ending in the release of hepatic merozoites capable of invading simian erythrocytes in vitro. Finally, we showed that this system can be used for compound screening to discriminate between causal prophylactic and cidal antimalarials activity in vitro for relapsing malaria

Probing the distinct chemosensitivity of Plasmodium vivax liver stage parasites and demonstration of 8-aminoquinoline radical cure activity in vitro

Improved control of Plasmodium vivax malaria can be achieved with the discovery of new antimalarials with radical cure efficacy, including prevention of relapse caused by hypnozoites residing in the liver of patients. We screened several compound libraries against P. vivax liver stages, including 1565 compounds against mature hypnozoites, resulting in one drug-like and several probe-like hits useful for investigating hypnozoite biology. Primaquine and tafenoquine, administered in combination with chloroquine, are currently the only FDA-approved antimalarials for radical cure, yet their activity against mature P. vivax hypnozoites has not yet been demonstrated in vitro. By developing an extended assay, we show both drugs are individually hypnozonticidal and made more potent when partnered with chloroquine, similar to clinically relevant combinations. Post-hoc analyses of screening data revealed excellent performance of ionophore controls and the high quality of single point assays, demonstrating a platform able to support screening of greater compound numbers. A comparison of P. vivax liver stage activity data with that of the P. cynomolgi blood, P. falciparum blood, and P. berghei liver stages reveals overlap in schizonticidal but not hypnozonticidal activity, indicating that the delivery of new radical curative agents killing P. vivax hypnozoites requires an independent and focused drug development test cascade

Robust continuous in vitro culture of the Plasmodium cynomolgi erythrocytic stages

The ability to culture pathogenic organisms substantially enhances the quest for fundamental knowledge and the development of vaccines and drugs. Thus, the elaboration of a protocol for the in vitro cultivation of the erythrocytic stages of Plasmodium falciparum revolutionized research on this important parasite. However, for P. vivax, the most widely distributed and difficult to treat malaria parasite, a strict preference for reticulocytes thwarts efforts to maintain it in vitro. Cultivation of P. cynomolgi, a macaque-infecting species phylogenetically close to P. vivax, was briefly reported in the early 1980s, but not pursued further. Here, we define the conditions under which P. cynomolgi can be adapted to long term in vitro culture to yield parasites that share many of the morphological and phenotypic features of P. vivax. We further validate the potential of this culture system for high-throughput screening to prime and accelerate anti-P. vivax drug discovery efforts