Reversal of Chloroquine Resistance of Plasmodium vivax in Aotus Monkeys.

Chloroquine-resistant (CQR) vivax malaria has emerged as a threat to the malaria elimination agenda. The objective of this study was to assess if a combination of chloroquine (CQ) and prochlorperazine was able to reverse CQ resistance of the Plasmodium vivax AMRU-1 strain from Papua New Guinea in infected Aotus monkeys. For this purpose, in two independent experimental drug efficacy trials, a total of 18 Aotus monkeys infected with blood obtained from donor animals were randomly assigned to treatment and control groups and orally administered CQ at 10 mg/kg or prochlorperazine at 20 mg/kg, alone or in combination, for five consecutive days. Reversal of CQR was achieved in animals that received the drug combination, whereas neither drug alone produced cures. This same drug combination reverses CQR in P. falciparum and could be an alternative for treatment in humans with chloroquine-resistant P. vivax infections.

Characterization of P. vivax blood stage transcriptomes from field isolates reveals similarities among infections and complex gene isoforms.

Our understanding of the structure and regulation of Plasmodium vivax genes is limited by our inability to grow the parasites in long-term in vitro cultures. Most P. vivax studies must therefore rely on patient samples, which typically display a low proportion of parasites and asynchronous parasites. Here, we present stranded RNA-seq data generated directly from a small volume of blood from three Cambodian vivax malaria patients collected before treatment. Our analyses show surprising similarities of the parasite gene expression patterns across infections, despite extensive variations in parasite stage proportion. These similarities contrast with the unique gene expression patterns observed in sporozoites isolated from salivary glands of infected Colombian mosquitoes. Our analyses also indicate that more than 10% of P. vivax genes encode multiple, often undescribed, protein-coding sequences, potentially increasing the diversity of proteins synthesized by blood stage parasites. These data also greatly improve the annotations of P. vivax gene untranslated regions, providing an important resource for future studies of specific genes.

Tafenoquine and its potential in the treatment and relapse prevention of Plasmodium vivax malaria: the evidence to date.

Despite declining global malaria incidence, the disease continues to be a threat to people living in endemic regions. In 2015, an estimated 214 million new malaria cases and 438,000 deaths due to malaria were recorded. Plasmodium vivax is the second most common cause of malaria next to Plasmodium falciparum. Vivax malaria is prevalent especially in Southeast Asia and the Horn of Africa, with enormous challenges in controlling the disease. Some of the challenges faced by vivax malaria-endemic countries include limited access to effective drugs treating liver stages of the parasite (schizonts and hypnozoites), emergence/spread of drug resistance, and misperception of vivax malaria as nonlethal. Primaquine, the only 8-aminoquinoline derivative approved by the US Food and Drug Administration, is intended to clear intrahepatic hypnozoites of P. vivax (radical cure). However, poor adherence to a prolonged treatment course, drug-induced hemolysis in patients with glucose-6-phosphate dehydrogenase deficiency, and the emergence of resistance make it imperative to look for alternative drugs. Therefore, this review focuses on data accrued to date on tafenoquine and gives insight on the potential role of the drug in preventing relapse and radical cure of patients with vivax malaria.

Plasmodium vivax infection causes acute respiratory distress syndrome: a case report.

Plasmodium falciparum (Pf) is associated with numerous complications and high mortality, whereas Plasmodium vivax (Pv) infection is generally considered to be benign. However, severe complications, such as acute respiratory distress syndrome (ARDS) in Pv infection, are emerging. This case report highlights the complication of ARDS during the course of Pv infection in a 60-year-old woman. The diagnosis of the patient was made using microscopy, immunochromatography, and polymerase chain reaction assays for Pf and Pv species. The data indicated the presence of mono-Pv infection in the patient's blood, and Pf infection was specifically ruled out. The patient was discharged after intensive supportive care and antimalarial treatment. Pv infection is associated with ARDS and other complications such as sepsis and multi-organ dysfunction syndrome; this enhanced severity of Pv infection, if unrecognized, can lead to more deaths in malaria-endemic areas.

HEMATOLOGICAL CHANGES IN COMPLETE BLOOD PICTURE IN PAEDRIATRIC PATIENTS OF MALARIA CAUSED BY PLASMODIUM VIVAX AND FALCIPARUM.

BACKGROUND: Malaria is a major health problem and one of the major killers in paediatric population particularly in the developing world. High mortality is usually compounded by various haematological complications if left untreated. Their identification as risk factors for progression to severe disease may make the basis for optimal management of malaria. This study was conducted to determine various changes in the complete blood picture caused by malaria and to compare the severity of these changes among the prevalent species of plasmodia. METHODS: It was cross sectional study conducted in paediatric ward of Civil Hospital, Dow University of Health Sciences, Karachi over a period of six months. Children aged >2 months to 15 years, of either sex, with fever above 101 degrees F in the preceding 72 hours with positive malaria parasite on peripheral blood smear were included in the study. Children already on anti-malarial. treatment and long standing antibiotics, having co-morbidities like immune-compromised states, haemolytic disease or with any other haematological disorder were excluded from the study. Blood was tested for anaemia, leukopenia, leukocytosis, and thrombocytopenia. Data analysis was done via SPSS-15.0. RESULTS: Out of 374 children half were under 5 years of age with mean age of 66.7 +/- 46.8 months, 50.8% were female with male to female ratio of 1:1.03. Overall 364 (97.3%) children had anaemia with mean haemoglobin level of 11.7 +/- 6 g/dl. Overall mean WBC count was 10443 +/- 154 per cubic millimetre. Leukopenia was found in 39% cases. Mean platelets count of enrolled children was 69451 +/- 648 cubic millimetre and 51.3% cases had mild thrombocytopenia. Anaemia (p=0.012), leukopenia (p=0.001) and thrombocytopenia (p=0.004) were significantly more common in falciparum as compared to vivax malaria. CONCLUSION: We concluded that malaria frequently causes severe anaemia, leukopenia and thrombocytopenia in children. P. falciparum is the species more responsible for these changes.

Reduced polymorphism in the Kelch propeller domain in Plasmodium vivax isolates from Cambodia.

Polymorphism in the ortholog gene of the Plasmodium falciparum K13 gene was investigated in Plasmodium vivax isolates collected in Cambodia. All of them were Sal-1 wild-type alleles except two (2/284, 0.7%), and P. vivax K12 polymorphism was reduced compared to that of the P. falciparum K13 gene. Both mutant allele isolates had the same nonsynonymous mutation at codon 552 (V552I) and were from Ratanak Kiri province. These preliminary data should encourage additional studies for associating artemisinin or chloroquine resistance and K12 polymorphism.

Splenic abscess: Plasmodium vivax with secondary Escherichia coli infection.

Splenic abscess is a rare clinical entity as described in literature. The incidence is in the range of 0.14-0.7% and it has a high mortality rate. Hence, it is important to know its clinical presentation and complications, so that it can be treated early. We report a 40-year-old diabetic man who presented with fever with chills and rigor for the last 9 days and heaviness in the left hypochondrium for the last 6 days. He was initially diagnosed as having splenomegaly due to Plasmodium vivax (P. vivax), but was later found to have a splenic abscess due to Escherichia coli (E. coli). This was successfully managed by catheter drainage (CD) and antibiotic treatment.

Malaria-induced NLRP12/NLRP3-dependent caspase-1 activation mediates inflammation and hypersensitivity to bacterial superinfection.

Cyclic paroxysm and high fever are hallmarks of malaria and are associated with high levels of pyrogenic cytokines, including IL-1ß. In this report, we describe a signature for the expression of inflammasome-related genes and caspase-1 activation in malaria. Indeed, when we infected mice, Plasmodium infection was sufficient to promote MyD88-mediated caspase-1 activation, dependent on IFN-γ-priming and the expression of inflammasome components ASC, P2X7R, NLRP3 and/or NLRP12. Pro-IL-1ß expression required a second stimulation with LPS and was also dependent on IFN-γ-priming and functional TNFR1. As a consequence of Plasmodium-induced caspase-1 activation, mice produced extremely high levels of IL-1ß upon a second microbial stimulus, and became hypersensitive to septic shock. Therapeutic intervention with IL-1 receptor antagonist prevented bacterial-induced lethality in rodents. Similar to mice, we observed a significantly increased frequency of circulating CD14(+)CD16(-)Caspase-1(+) and CD14(dim)CD16(+)Caspase-1(+) monocytes in peripheral blood mononuclear cells from febrile malaria patients. These cells readily produced large amounts of IL-1ß after stimulation with LPS. Furthermore, we observed the presence of inflammasome complexes in monocytes from malaria patients containing either NLRP3 or NLRP12 pyroptosomes. We conclude that NLRP12/NLRP3-dependent activation of caspase-1 is likely to be a key event in mediating systemic production of IL-1ß and hypersensitivity to secondary bacterial infection during malaria.

Malariotherapy--insanity at the service of malariology.

From the early 1920s until the advent of penicillin in the mid 1940s, a clinical course of malaria was the only effective treatment of general paresis, a common manifestation of tertiary syphilis that was nearly always fatal. For a number of reasons, Plasmodium vivax became the parasite species most often employed for what became known as malariotherapy. This provided an opportunity, probably unique in the annals of medicine, to observe and investigate the biology, immunology and clinical evolution of a dangerous human pathogen in its natural host. There is little doubt that the lessons learned from these studies influenced the malaria research and control agendas. It is equally true that over the last 40 years, the insights afforded by malariotherapy have remained largely undisturbed on the dusty shelves of institutional libraries. In this chapter, we broadly review the published data derived from malariotherapy, and discuss its relevance to current challenges of P. vivax epidemiology, immunology and pathology.

Identification of a highly antigenic linear B cell epitope within Plasmodium vivax apical membrane antigen 1 (AMA-1).

Apical membrane antigen 1 (AMA-1) is considered to be a major candidate antigen for a malaria vaccine. Previous immunoepidemiological studies of naturally acquired immunity to Plasmodium vivax AMA-1 (PvAMA-1) have shown a higher prevalence of specific antibodies to domain II (DII) of AMA-1. In the present study, we confirmed that specific antibody responses from naturally infected individuals were highly reactive to both full-length AMA-1 and DII. Also, we demonstrated a strong association between AMA-1 and DII IgG and IgG subclass responses. We analyzed the primary sequence of PvAMA-1 for B cell linear epitopes co-occurring with intrinsically unstructured/disordered regions (IURs). The B cell epitope comprising the amino acid sequence 290-307 of PvAMA-1 (SASDQPTQYEEEMTDYQK), with the highest prediction scores, was identified in domain II and further selected for chemical synthesis and immunological testing. The antigenicity of the synthetic peptide was identified by serological analysis using sera from P. vivax-infected individuals who were knowingly reactive to the PvAMA-1 ectodomain only, domain II only, or reactive to both antigens. Although the synthetic peptide was recognized by all serum samples specific to domain II, serum with reactivity only to the full-length protein presented 58.3% positivity. Moreover, IgG reactivity against PvAMA-1 and domain II after depletion of specific synthetic peptide antibodies was reduced by 18% and 33% (P = 0.0001 for both), respectively. These results suggest that the linear epitope SASDQPTQYEEEMTDYQK is highly antigenic during natural human infections and is an important antigenic region of the domain II of PvAMA-1, suggesting its possible future use in pre-clinical studies.

Plasmodium vivax susceptibility to ferroquine.

The novel organometallic chloroquine analog ferroquine (SSR 97193) is effective against chloroquine-resistant Plasmodium falciparum. The ex vivo efficacy of ferroquine against Plasmodium vivax isolates was tested. Ferroquine has a potent ex vivo effect on P. vivax schizont maturation (median 50% inhibitory concentration, 15 nM; n = 42). No significant cross-sensitivity between ferroquine and other antimalarials was detected. This drug may be a suitable replacement for chloroquine in the treatment of drug-resistant P. vivax malaria.

A monkey's tale: the origin of Plasmodium vivax as a human malaria parasite.

The high prevalence of Duffy negativity (lack of the Duffy blood group antigen) among human populations in sub-Saharan Africa has been used to argue that Plasmodium vivax originated on that continent. Here, we investigate the phylogenetic relationships among 10 species of Plasmodium that infect primates by using three genes, two nuclear (beta-tubulin and cell division cycle 2) and a gene from the plastid genome (the elongation factor Tu). We find compelling evidence that P. vivax is derived from a species that inhabited macaques in Southeast Asia. Specifically, those phylogenies that include P. vivax as an ancient lineage from which all of the macaque parasites could originate are significantly less likely to explain the data. We estimate the time to the most recent common ancestor at four neutral gene loci from Asian and South American isolates (a minimum sample of seven isolates per locus). Our analysis estimates that the extant populations of P. vivax originated between 45,680 and 81,607 years ago. The phylogeny and the estimated time frame for the origination of current P. vivax populations are consistent with an "out of Asia" origin for P. vivax as hominoid parasite. The current debate regarding how the Duffy negative trait became fixed in Africa needs to be revisited, taking into account not only human genetic data but also the genetic diversity observed in the extant P. vivax populations and the phylogeny of the genus Plasmodium.

Acute renal failure in Plasmodium vivax malaria.

OBJECTIVES: To analyze incidence, clinical feature and outcome of acute renal failure due to Plasmodium vivax malaria. MATERIAL & METHOD: This is retrospective analysis of smear positive Plasmodium vivax patients with acute renal failure between Jan 1995 to Dec 2000. RESULT: Out of 577 cases of ARF, 93 [falciparum 74 (79.61%); vivax 19 (20.4%)] were related to complicated malaria. 3.2% (19/577) patients, 16 males and three females with age range 17-72, mean 43.3 +/- 13.4 years were due to vivax malaria. Thirteen had only vivax and six had mixed falciparum and vivax infection. The presenting features were fever (100%), jaundice (36.8%), hypotension--eight (42%), encephalopathy--11 (57.9%), sepsis--five (26.3%) and DIC--four (21%). The probable contributory factors for ARF were heavy parasitemia--11 (57.9%), hypotension--six (31.5%), hyperbilirubinemia--seven (36.8%), hemolysis--eight (42%) and DIC--four (21%). Oliguria was present in 47.3%, 13 (68.4%) patients required dialysis. Mortality was noted in 15.7% (3/19) patients. CONCLUSIONS: P. vivax malaria can cause ARF, which occurs more commonly in P. falciparum malaria. Renal ischemia is the dominant pathogenic mechanism that results in acute tubular necrosis. The prognosis of ARF in P. vivax malaria is favorable.

Diversity in the thrombospondin-related adhesive protein gene (TRAP) of Plasmodium vivax.

We analyzed 22 clinical isolates of Plasmodium vivax from Thailand and 17 from Brazil to investigate the extent of sequence variation in the thrombospondin-related adhesive protein of Plasmodium vivax (PvTRAP), a homologue of P. falciparum TRAP (PfTRAP) which has been considered to be a promising vaccine candidate. In total 54 haplotypes were identified from 73 distinct gene clones. Coexistence of different PvTRAP in circulation occurred in 10 and 13 isolates from Thailand and Brazil, respectively. Forty out of 48 substituted nucleotides are non-synonymous changes. Most of the substituted residues reside in the von Willebrand factor type A-domain (region II), a sulfated glycosaminoglycan-binding domain (region III) and a proline-rich region (region IV). All nucleotide substitutions are dimorphic. Two haplotypes from Thailand contain an inserted sequence encoding aspartic acid-serine-proline in the proline-rich region. Sequence analysis has revealed that nucleotide diversity in PvTRAP is low although Brazilian isolates display a higher degree of variation than those from Thailand. Phylogenetic construction using the neighbor joining method has shown that most of the Thai and the Brazilian isolates appear to be mainly clustered into distinct groups. Significantly greater than expected values of the mean number of non-synonymous (d(n)) than synonymous (d(s)) nucleotide substitutions per site were observed in regions II and III of PvTRAP. Analysis of the published PfTRAP sequences has shown a similar finding in regions II and IV suggesting that positive selection operates on the regions. Hence, different regions in PvTRAP and PfTRAP could be under different pressures in terms of immune selection, structural and/or functional constraints.