Parasite Susceptibility Research Articles

Poor resource quality lowers transmission potential by changing foraging behaviour

Summary Resource quality can have conflicting effects on the spread of disease. High‐quality resources could hinder disease spread by promoting host immune function. Alternatively, high‐quality food might enhance the spread of disease through other traits of hosts or parasites. Thus, to assess how resource quality shapes epidemics, we need to delineate mechanisms by which food quality affects key epidemiological traits. Here, we disentangle effects of food quality on ‘transmission potential’ – a key component of parasite fitness that combines transmission rate and parasite production – using a zooplankton host and fungal parasite. We estimated the components of transmission potential (i.e. parasite encounter rate, susceptibility and yield of parasite propagules) for hosts fed a high‐quality green alga and a low‐quality cyanobacterium. A focal experiment was designed to disentangle food quality effects on various components of transmission potential. The low‐quality resource decreased transmission potential by stunting host growth and altering foraging behaviour. Hosts reared on low‐quality food were smaller and had lower size‐corrected feeding rates. Due to their slower grazing, they encountered fewer parasite spores in the water. Smaller hosts also had lower risk of an ingested spore causing infection (i.e. lower susceptibility) and yielded fewer parasite propagules. Hosts switched from high‐ to low‐quality food during spore exposure also had low transmission potential – despite their large size – because the poor quality resource strongly depressed foraging. A follow‐up experiment investigated traits of the low‐quality resource that might have driven those results. Cyanobacterial compounds that can inhibit digestive proteases of a related grazer likely did not cause the observed reductions in transmission potential. Our study highlights the value of using mechanistic models to pinpoint how resource quality can change transmission potential. Overall, our results show that low‐quality resources could inhibit the spread of disease through effects on multiple components of transmission potential. They also provide insight into how disease outbreaks in wildlife may respond to shifts in resource quality caused by eutrophication or climate change.

Characterization of Isolates of Acanthamoeba from the Nasal Mucosa and Cutaneous Lesions of Dogs

Acanthamoeba spp. are free-living amoebae that are ubiquitously distributed in the environment and can cause encephalomyelitis in animals and humans. The factors that contribute to Acanthamoeba infections include parasite biology, genetic diversity, environmental spread, and host susceptibility. The aim of the present study was to characterize isolates of Acanthamoeba from the nasal mucosa and cutaneous lesions of dogs in order to access the occurence and pathogenicity of these organisms in this animal group. We studied 13 isolates of Acanthamoeba confirmed by polymerase chain reaction. They were sequenced, the genotype was determined, and their potential of pathogenicity was evaluated.

Association of Schistosoma mansoni-Specific IgG and IgE Antibody Production and Clinical Schistosomiasis Status in a Rural Area of Minas Gerais, Brazil

BackgroundStudies in murine models and human populations have indicated that the collagen-rich granulomatous response against parasite eggs trapped in the liver is associated with the development of severe hepatosplenic schistosomiasis, characterized by periportal fibrosis and portal hypertension. The role of the humoral response in parasite susceptibility has been well established, but its participation in disease severity remains poorly understood. In this work, we evaluated the relationship between parasite-reactive IgE and IgG levels and schistosomiasis morbidity in infected patients with similar parasite burdens.Methodology/Principal FindingsNinety-seven Schistosoma mansoni-infected individuals were subjected to clinical examination and abdominal ultrasound analysis. IgG reactivity and IgE concentration against Schistosoma mansoni soluble egg antigens (SEA) and adult worm antigen preparation (SWAP) were evaluated by ELISA assay. Multivariable linear regression models were used to evaluate the relationship between parasite-reactive antibodies and the co-variables investigated. The study population showed low parasite burden (median 30 eggs/g feces), constant re-infection, and signs of fibrosis was detected in more than 30% of individuals. Most infected individuals showed IgG reactivity, and the median concentrations of IgE anti-SEA and anti-SWAP antibodies were 1,870 and 1,375 ng/mL, respectively. There was no association between parasite burden and antibody response or any parameter of disease severity. However, IgG anti-SWAP level was positively associated with morbidity parameters, such as spleen size and thickness of portal vein at the entrance and secondary branch. In contrast, the data also revealed independent inverse correlations between concentration of parasite-reactive IgE and gallbladder wall thickness, a marker of fibrosis in schistosomiasis.Conclusions/SignificanceThe data indicate that IgG anti-SWAP is positively associated with severe schistosomiasis, independently of parasite burden, while high production of parasite-specific IgE is associated with mild disease in the human population. Antibody profiles are good correlates for schistosomiasis severity and could be tested as biomarkers of disease severity.

Quinine Dimers Are Potent Inhibitors of thePlasmodium falciparumChloroquine Resistance Transporter and Are Active against Quinoline-ResistantP. falciparum

Chloroquine (CQ) resistance in the human malaria parasite Plasmodium falciparum is primarily conferred by mutations in the "chloroquine resistance transporter" (PfCRT). The resistance-conferring form of PfCRT (PfCRT(CQR)) mediates CQ resistance by effluxing the drug from the parasite's digestive vacuole, the acidic compartment in which CQ exerts its antiplasmodial effect. PfCRT(CQR) can also decrease the parasite's susceptibility to other quinoline drugs, including the current antimalarials quinine and amodiaquine. Here we describe interactions between PfCRT(CQR) and a series of dimeric quinine molecules using a Xenopus laevis oocyte system for the heterologous expression of PfCRT and using an assay that detects the drug-associated efflux of H(+) ions from the digestive vacuole in parasites that harbor different forms of PfCRT. The antiplasmodial activities of dimers 1 and 6 were also examined in vitro (against drug-sensitive and drug-resistant strains of P. falciparum) and in vivo (against drug-sensitive P. berghei). Our data reveal that the quinine dimers are the most potent inhibitors of PfCRT(CQR) reported to date. Furthermore, the lead compounds (1 and 6) were not effluxed by PfCRT(CQR) from the digestive vacuole but instead accumulated to very high levels within this organelle. Both 1 and 6 exhibited in vitro antiplasmodial activities that were inversely correlated with CQ. Moreover, the additional parasiticidal effect exerted by 1 and 6 in the drug-resistant parasites was attributable, at least in part, to their ability to inhibit PfCRT(CQR). This highlights the potential for devising new antimalarial therapies that exploit inherent weaknesses in a key resistance mechanism of P. falciparum.

Increased pfmdr1 gene copy number and the decline in pfcrt and pfmdr1 resistance alleles in Ghanaian Plasmodium falciparum isolates after the change of anti-malarial drug treatment policy

BackgroundWith the introduction of artemisinin-based combination therapy (ACT) in 2005, monitoring of anti-malarial drug efficacy, which includes the use of molecular tools to detect known genetic markers of parasite resistance, is important for first-hand information on the changes in parasite susceptibility to drugs in Ghana. This study investigated the Plasmodium falciparum multidrug resistance gene (pfmdr1) copy number, mutations and the chloroquine resistance transporter gene (pfcrt) mutations in Ghanaian isolates collected in seven years to detect the trends in prevalence of mutations.MethodsArchived filter paper blood blots collected from children aged below five years with uncomplicated malaria in 2003–2010 at sentinel sites were used. Using quantitative real-time polymerase chain reaction (qRT-PCR), 756 samples were assessed for pfmdr1 gene copy number. PCR and restriction fragment length polymorphism (RFLP) were used to detect alleles of pfmdr1 86 in 1,102 samples, pfmdr1 184, 1034, 1042 and 1246 in 832 samples and pfcrt 76 in 1,063 samples. Merozoite surface protein 2 (msp2) genotyping was done to select monoclonal infections for copy number analysis.ResultsThe percentage of isolates with increased pfmdr1 copy number were 4, 27, 9, and 18% for 2003–04, 2005–06, 2007–08 and 2010, respectively. Significant increasing trends for prevalence of pfmdr1 N86 (×2 = 96.31, p <0.001) and pfcrt K76 (×2 = 64.50, p <0.001) and decreasing trends in pfmdr1 Y86 (×2 = 38.52, p <0.001) and pfcrt T76 (×2 = 43.49, p <0.001) were observed from 2003–2010. The pfmdr1 F184 and Y184 prevalence showed an increasing and decreasing trends respectively but were not significant (×2 = 7.39,p=0.060; ×2 = 7.49, p = 0.057 respectively). The pfmdr1 N86-F184-D1246 haplotype, which is alleged to be selected by artemether-lumefantrine showed a significant increasing trend (×2 = 20.75, p < 0.001).ConclusionIncreased pfmdr1 gene copy number was observed in the isolates analysed and this finding has implications for the use of ACT in the country although no resistance has been reported. The decreasing trend in the prevalence of chloroquine resistance markers after change of treatment policy presents the possibility for future introduction of chloroquine as prophylaxis for malaria risk groups such as children and pregnant women in Ghana.

Novel phenotypic assays for the detection of artemisinin-resistant Plasmodium falciparum malaria in Cambodia: in-vitro and ex-vivo drug-response studies

Artemisinin resistance in Plasmodium falciparum lengthens parasite clearance half-life during artemisinin monotherapy or artemisinin-based combination therapy. Absence of in-vitro and ex-vivo correlates of artemisinin resistance hinders study of this phenotype. We aimed to assess whether an in-vitro ring-stage survival assay (RSA) can identify culture-adapted P falciparum isolates from patients with slow-clearing or fast-clearing infections, to investigate the stage-dependent susceptibility of parasites to dihydroartemisinin in the in-vitro RSA, and to assess whether an ex-vivo RSA can identify artemisinin-resistant P falciparum infections. We culture-adapted parasites from patients with long and short parasite clearance half-lives from a study done in Pursat, Cambodia, in 2010 (registered with ClinicalTrials.gov, number NCT00341003) and used novel in-vitro survival assays to explore the stage-dependent susceptibility of slow-clearing and fast-clearing parasites to dihydroartemisinin. In 2012, we implemented the RSA in prospective parasite clearance studies in Pursat, Preah Vihear, and Ratanakiri, Cambodia (NCT01736319), to measure the ex-vivo responses of parasites from patients with malaria. Continuous variables were compared with the Mann-Whitney U test. Correlations were analysed with the Spearman correlation test. In-vitro survival rates of culture-adapted parasites from 13 slow-clearing and 13 fast-clearing infections differed significantly when assays were done on 0-3 h ring-stage parasites (10·88% vs 0·23%; p=0·007). Ex-vivo survival rates significantly correlated with in-vivo parasite clearance half-lives (n=30, r=0·74, 95% CI 0·50-0·87; p<0·0001). The in-vitro RSA of 0-3 h ring-stage parasites provides a platform for the molecular characterisation of artemisinin resistance. The ex-vivo RSA can be easily implemented where surveillance for artemisinin resistance is needed. Institut Pasteur du Cambodge and the Intramural Research Program, NIAID, NIH.

New, Combined, and Reduced Dosing Treatment Protocols Cure Trypanosoma cruzi Infection in Mice

The development of treatment protocols with reduced toxicity and equivalent or improved efficacy for Trypanosoma cruzi infection is a priority. We tested the effectiveness of benznidazole (BZ), nifurtimox (NFX), other prospective drugs in intermittent and combined treatment protocols to cure T. cruzi infection initiated with susceptible and drug-resistant parasite strains. A 40-day course of BZ, NFX, or the oxaborale AN4169 cured 100% of mice, whereas posaconazole (POS), and NTLA-1 (a nitro-triazole) cured approximately 90% and 20% of mice, respectively. Reducing the overall dosage of BZ or NFX by using an intermittent (once every 5 days) schedule or combining 5 daily doses of POS with 7 intermittent doses of BZ also provided approximately 100% cure. T. cruzi strains resistant to BZ were also found to be resistant to other drugs (POS), and extending the time of treatment or combining drugs did not increase cure rates with these isolates. Thus, dosing schedules for anti-T. cruzi compounds should be determined empirically, and compounds targeting different pathways may be combined to yield effective therapies with reduced toxicity. This work also suggests that standard treatment protocols using BZ and NFX may be significantly overdosing patients, perhaps contributing to the adverse events.

Molecular basis for benzimidazole resistance from a novel β-tubulin binding site model

Benzimidazole-2-carbamate derivatives (BzCs) are the most commonly used antiparasitic drugs for the treatment of protozoan and helminthic infections. BzCs inhibit the microtubule polymerization mechanism through binding selectively to the β-tubulin subunit in which mutations have been identified that lead to drug resistance. Currently, the lack of crystallographic structures of β-tubulin in parasites has limited the study of the binding site and the analysis of the resistance to BzCs. Recently, our research group has proposed a model to explain the interaction between the BzCs and a binding site in the β-tubulin. Herein, we report the homology models of two susceptible (Haemonchus contortus and Giardia intestinalis) parasites and one unsusceptible (Entamoeba histolytica) generated using the structure of the mammal Ovis aries, considered as a low susceptible organism, as a template. Additionally, the mechanism by which the principal single point mutations Phe167Tyr, Glu198Ala and Phe200Tyr could lead to resistance to BzCs is analyzed. Molecular docking and molecular dynamics studies were carried out in order to evaluate the models and the ligand–protein complexes’ behaviors. This study represents a first attempt towards understanding, at the molecular level, the structural composition of β-tubulin in all organisms, also suggesting possible resistance mechanisms. Furthermore, these results support the importance of benzimidazole derivative optimization in order to design more potent and selective (less toxic) molecules for the treatment of parasitic diseases.

Overexpression of Ubiquitin and Amino Acid Permease Genes in Association with Antimony Resistance in Leishmania tropica Field Isolates

The mainstay therapy against leishmaniasis is still pentavalent antimonial drugs; however, the rate of antimony resistance is increasing in endemic regions such as Iran. Understanding the molecular basis of resistance to antimonials could be helpful to improve treatment strategies. This study aimed to recognize genes involved in antimony resistance of Leishmania tropica field isolates. Sensitive and resistant L. tropica parasites were isolated from anthroponotic cutaneous leishmaniasis patients and drug susceptibility of parasites to meglumine antimoniate (Glucantime®) was confirmed using in vitro assay. Then, complementary DNA-amplified fragment length polymorphism (cDNA-AFLP) and real-time reverse transcriptase-PCR (RT-PCR) approaches were utilized on mRNAs from resistant and sensitive L. tropica isolates. We identified 2 known genes, ubiquitin implicated in protein degradation and amino acid permease (AAP3) involved in arginine uptake. Also, we identified 1 gene encoding hypothetical protein. Real-time RT-PCR revealed a significant upregulation of ubiquitin (2.54-fold), and AAP3 (2.86-fold) (P<0.05) in a resistant isolate compared to a sensitive one. Our results suggest that overexpression of ubiquitin and AAP3 could potentially implicated in natural antimony resistance.

Identification and characterisation of functional expressed sequence tags-derived simple sequence repeat (eSSR) markers for genetic linkage mapping of Schistosoma mansoni juvenile resistance and susceptibility loci in Biomphalaria glabrata

Biomphalaria glabrata susceptibility to Schistosoma mansoni has a strong genetic component, offering the possibility for investigating host–parasite interactions at the molecular level, perhaps leading to novel control approaches. The identification, mapping and molecular characterisation of genes that influence the outcome of parasitic infection in the intermediate snail host is, therefore, seen as fundamental to the control of schistosomiasis. To better understand the evolutionary processes driving disease resistance/susceptibility phenotypes, we previously identified polymorphic random amplification of polymorphic DNA and genomic simple sequence repeats from B. glabrata. In the present study we identified and characterised polymorphic expressed simple sequence repeats markers (Bg-eSSR) from existing B. glabrata expressed sequence tags. Using these markers, and with previously identified genomic simple sequence repeats, genetic linkage mapping for parasite refractory and susceptibility phenotypes, the first known for B. glabrata, was initiated. Data mining of 54,309 expressed sequence tag, produced 660 expressed simple sequence repeats of which dinucleotide motifs (TA)n were the most common (37.88%), followed by trinucleotide (29.55%), mononucleotide (18.64%) and tetranucleotide (10.15%). Penta- and hexanucleotide motifs represented <3% of the Bg-eSSRs identified. While the majority (71%) of Bg-eSSRs were monomorphic between resistant and susceptible snails, several were, however, useful for the construction of a genetic linkage map based on their inheritance in segregating F2 progeny snails derived from crossing juvenile BS-90 and NMRI snails. Polymorphic Bg-eSSRs assorted into six linkage groups at a logarithm of odds score of 3. Interestingly, the heritability of four markers (Prim1_910, Prim1_771, Prim6_1024 and Prim7_823) with juvenile snail resistance were, by t-test, significant (P<0.05) while an allelic marker, Prim24_524, showed linkage with the juvenile snail susceptibility phenotype. On the basis of our results it is possible that the gene(s) controlling juvenile resistance and susceptibility to S. mansoni infection in B. glabrata are not only on the same linkage group but lie within a short distance (42cM) of each other.

Toxoplasma gondii rhoptry 16 kinase promotes host resistance to oral infection and intestinal inflammation only in the context of the dense granule protein GRA15.

Toxoplasma gondii transmission between intermediate hosts is dependent on the ingestion of walled cysts formed during the chronic phase of infection. Immediately following consumption, the parasite must ensure survival of the host by preventing adverse inflammatory responses and/or by limiting its own replication. Since the Toxoplasma secreted effectors rhoptry 16 kinase (ROP16) and dense granule 15 (GRA15) activate the JAK-STAT3/6 and NF-κB signaling pathways, respectively, we explored whether a particular combination of these effectors impacted intestinal inflammation and parasite survival in vivo. Here we report that expression of the STAT-activating version of ROP16 in the type II strain (strain II+ROP16I) promotes host resistance to oral infection only in the context of endogenous GRA15 expression. Protection was characterized by a lower intestinal parasite burden and dampened inflammation. Host resistance to the II+ROP16I strain occurred independently of STAT6 and the T cell coinhibitory receptors B7-DC and B7-H1, two receptors that are upregulated by ROP16. In addition, coexpression of ROP16 and GRA15 enhanced parasite susceptibility within tumor necrosis factor alpha/gamma interferon-stimulated macrophages in a STAT3/6-independent manner. Transcriptional profiling of infected STAT3- and STAT6-deficient macrophages and parasitized Peyer's patches from mice orally challenged with strain II+ROP16I suggested that ROP16 activated STAT5 to modulate host gene expression. Consistent with this supposition, the ROP16 kinase induced the sustained phosphorylation and nuclear localization of STAT5 in Toxoplasma-infected cells. In summary, only the combined expression of both GRA15 and ROP16 promoted host resistance to acute oral infection, and Toxoplasma may possibly target the STAT5 signaling pathway to generate protective immunity in the gut.

Plasmodium falciparum susceptibility to anti-malarial drugs in Dakar, Senegal, in 2010: an ex vivo and drug resistance molecular markers study

BackgroundIn 2006, the Senegalese National Malaria Control Programme recommended artemisinin-based combination therapy (ACT) as the first-line treatment for uncomplicated malaria. Since the introduction of ACT, there have been very few reports on the level of resistance of P. falciparum to anti-malarial drugs. To determine whether parasite susceptibility has been affected by the new anti-malarial policies, an ex vivo susceptibility and drug resistance molecular marker study was conducted on local isolates obtained from the Centre de santé Elizabeth Diouf (Médina, Dakar, Senegal).MethodsThe prevalence of genetic polymorphisms in genes associated with anti-malarial drug resistance, i.e., pfcrt, pfdhfr, pfdhps and pfmdr1, were evaluated for a panel of 165 isolates collected from patients recruited from 17 August 2010 to 6 January 2011. The malaria isolates were assessed for susceptibility to chloroquine (CQ); quinine (QN); monodesethylamodiaquine (MDAQ), the active metabolite of amodiaquine; mefloquine (MQ); lumefantrine (LMF); dihydroartemisinin (DHA), the active metabolite of artemisinin derivatives; and doxycycline (DOX) using the Plasmodium lactate dehydrogenase (pLDH) ELISA.ResultsThe prevalence of the in vitro resistant isolates, or isolates with reduced susceptibility, was 62.1% for MQ, 24.2% for CQ, 10.3% for DOX, 11.8% MDAQ, 9.7% for QN, 2.9% for LMF and 0% for DHA. The Pfcrt 76T mutation was identified in 43.6% of the samples. The pfmdr1 86Y, 184F and 1246Y mutations were found in 16.2%, 50.0% and 1.6% of the samples, respectively. The pfdhfr 108N, 51I and 59R mutations were identified in 81.9%, 77.4% and 79.4% of the samples, respectively. The double mutant (108N and 51I) was detected in 75.5% of the isolates, and the triple mutant (108N, 51I and 59R) was detected in 73.6% of the isolates. The pfdhps 437G, 436A and 613S mutations were found in 54.4%, 38.6% and 1.2% of the samples, respectively. There was only one double mutant, 437G and 540E, and one quintuple mutant, pfdhfr 108N, 51I and 59R and pfdhps 437G and 540E. The prevalence of the quadruple mutant (pfdhfr 108N, 51I and 59R and pfdhps 437G) was 36.7%.ConclusionsThe results of this study indicate that an intensive surveillance of the in vitro P. falciparum susceptibility to anti-malarial drugs must be conducted in Senegal.

Use of artemether–lumefantrine to treat malaria during pregnancy: what do we know and need to know?

Artemether–lumefantrine is a fixed-dose combination containing 20 mg artemether/120 mg lumefantrine per tablet, used for treating uncomplicated malaria in patients weighing ≥5 kg. It is the first artemisinin-based combination registered in some European countries and in the USA. It is marketed in Europe as Riamet® (Novartis, Basel, Switzerland) and in malaria-endemic countries as Coartem® (Novartis). Safety concerns prevent early pregnancy usage, while limited postmarketing surveillance has delayed safety assessment and policy development. Large clinical studies, postmarketing surveillance and pharmacovigillance ongoing in some countries may soon bridge safety issues. Fatty diet requirements for optimal absorption, pregnancy-induced changes in pharmacokinetics, pregnancy-related anorexia and food taboos, and emerging reduced parasite sensitivity to artemisinin, challenges optimal artemether–lumefantrine dosing and efficacy during pregnancy. This evaluation addresses drug usage, safety concerns following early exposure, implications for changed pharmacokinetics and reduced parasite susceptibility. Clinical-use updates and strategies to address some knowledge gaps including key operational research are discussed.

Artemisinin resistance or artemisinin-based combination therapy resistance?

In his recent Comment in The Lancet Infectious Diseases, Joel Breman discussed parasite resistance to artemisinin-based combination therapy (ACT) and the heritability of this resistance.1Breman JG Resistance to artemisinin-based combination therapy.Lancet Infect Dis. 2012; 12: 820-822Summary Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 2Amaratunga C Sreng S Suon S et al.Artemisinin-resistant Plasmodium falciparum malaria in Pursat province, western Cambodia: a parasite-clearance-rate study.Lancet Infect Dis. 2012; 12: 851-858Summary Full Text Full Text PDF PubMed Scopus (253) Google Scholar The differences between artemisinin resistance and resistance to ACT (also termed ACT resistance) merit further clarification. Researchers have used many methods to try to prove the existence of artemisinin resistance. Lengthening of the parasite clearance time suggests artemisinin resistance. Amaratunga and colleagues2Amaratunga C Sreng S Suon S et al.Artemisinin-resistant Plasmodium falciparum malaria in Pursat province, western Cambodia: a parasite-clearance-rate study.Lancet Infect Dis. 2012; 12: 851-858Summary Full Text Full Text PDF PubMed Scopus (253) Google Scholar delayed mefloquine administration to exclude the contribution of mefloquine in parasite clearance during the first 72 h—the period most relevant to artemisinin action. This approach deviates from the standard treatment schedule for the purpose of their study—ie, to investigate the genetic basis of artemisinin resistance. This study design does not have a primary aim to show ACT resistance, which leads to ACT failures. The term “ACT resistance” is used loosely and often interchangeably with “artemisinin resistance”, although it should not be. Artemisinin resistance could contribute to ACT failure, but the combination of artemisinin with an efficacious partner drug can improve cure rates to an adequate level.3World Health Organization Global Malaria ProgrammeUpdate on artemisinin resistance.http://www.who.int/malaria/publications/atoz/arupdate042012.pdfDate: April 2012Google Scholar Evidence of artemisinin resistance has been scarce so far, and only a working definition of such resistance exists. The longer parasite clearance times reported in the Mekong subregion could be due to a non-progressive weakening of artemisinin activity. ACTs are still highly efficacious in most of this subregion, especially in Laos, Burma, and Vietnam.4World Health Organization Global Malaria ProgrammeThe status of drug-resistant malaria along the ThailandûMyanmar border. Revised 9 May 2012.http://www.who.int/malaria/publications/atoz/drug_resistance_myanmar_thailand_border_may_2012.pdfGoogle Scholar One exception is the decreasing efficacy of artesunate–mefloquine at the Cambodian–Thai border. Two locations in western Cambodia are good examples of ACT resistance, where, despite the policy switch from failing artesunate–mefloquine to dihydroartemisinin–piperaquine treatment, the 42 day treatment efficacies are only 73–89%, and more than 40% of patients have positive parasitaemia on day 3.3World Health Organization Global Malaria ProgrammeUpdate on artemisinin resistance.http://www.who.int/malaria/publications/atoz/arupdate042012.pdfDate: April 2012Google Scholar Existing mefloquine resistance and the unregulated availability of dihydroartemisinin–piperaquine in the private sector for the past 10 years could explain its failure. Scientists are trying to elucidate the basis of artemisinin resistance, whereas malaria control programmes focus on ACT resistance, especially the morbidity and mortality associated with inefficacy of the combined drugs. WHO, senior health authorities, and donor agencies have correctly emphasised artemisinin resistance as a public health warning, support for which is essential for maintenance of parasite susceptibility to artemisinins at the highest possible level or for elimination of those parasites. In view of the scarce choices of appropriate partner drugs, if artemisinin resistance becomes established, it will negatively affect global achievements in malaria control. I agree with Breman's concern about Africa, where great care should be taken in deployment of ACTs.5Wongsrichanalai C Thimasarn K Sirichaisinthop J Antimalarial drug combination policy: a caveat.Lancet. 2000; 355: 2245-2247Summary Full Text Full Text PDF PubMed Scopus (26) Google Scholar The availability of ACTs in Africa from drug vendors without parasitological diagnosis is a dangerous problem. For the online parasite clearance estimator see http://www.wwarn.org/toolkit/data-management/parasite-clearance-estimator For the online parasite clearance estimator see http://www.wwarn.org/toolkit/data-management/parasite-clearance-estimator I declare that I have no conflicts of interest. Artemisinin-resistant Plasmodium falciparum in Pursat province, western Cambodia: a parasite clearance rate studyHeritable artemisinin resistance is established in a second Cambodian province. To accurately identify parasites that are intrinsically susceptible or resistant to artemisinins, future studies should explore the effect of erythrocyte polymorphisms and specific immune responses on half-life variation. Full-Text PDF

Nestling sex predicts susceptibility to parasitism and influences parasite population size within avian broods

Vertebrate hosts differ in their level of parasite susceptibility and infestation. In avian broods, variation in susceptibility of nestlings to ectoparasites may be associated with non‐uniform distributions of parasites among brood mates, with parasites concentrating feeding on the most vulnerable hosts. The presence of a highly susceptible nestling in a brood can benefit the remaining young by reducing the parasite pressure they experience; however, from a parasite’s perspective, broods with fewer susceptible hosts may provide effectively fewer resources than broods of the same size containing a greater abundance of susceptible hosts, and this could limit the number of parasites that a host brood can sustain. To test whether variation in number of susceptible hosts affects the number of parasites in bird nests, we first examined the role of host sex and induced immunity (via methionine supplementation) on susceptibility of mountain bluebirds Sialia currucoides to parasitism by blow flies Protocalliphora spp. We then assessed the effect of variation in number of susceptible hosts on the number of parasites inhabiting the nest. Only females showed a benefit of methionine supplementation, gaining mass more rapidly following supplementation compared to males. This suggests that females are more susceptible to parasites in this system; this was further supported by parasite feeding trials, in which parasites extracted larger blood meals from female than male hosts. Finally, the abundance of parasites in nests was predicted by brood sex ratio: broods containing more female young harboured more parasites. Hence, within‐brood variation in host susceptibility to parasites can not only influence the costs of parasitism for individual nestlings, but may also have consequences for the size of parasite populations within nests. If patterns of maternal investment affect the abundance of nest‐dwelling parasites, these interactions may be important for understanding fitness consequences of maternal resource allocation in many vertebrate hosts.

Antagonistic, overlapping and distinct responses to biotic stress in rice (Oryza sativa) and interactions with abiotic stress

BackgroundEvery year, substantial crop loss occurs globally, as a result of bacterial, fungal, parasite and viral infections in rice. Here, we present an in-depth investigation of the transcriptomic response to infection with the destructive bacterial pathogen Xanthomonas oryzae pv. oryzae(Xoo) in both resistant and susceptible varieties of Oryza sativa. A comparative analysis to fungal, parasite and viral infection in rice is also presented.ResultsWithin 24 h of Xoo inoculation, significant reduction of cell wall components and induction of several signalling components, membrane bound receptor kinases and specific WRKY and NAC transcription factors was prominent, providing a framework for how the presence of this pathogen was signalled and response mounted. Extensive comparative analyses of various other pathogen responses, including in response to infection with another bacterium (Xoc), resistant and susceptible parasite infection, fungal, and viral infections, led to a proposed model for the rice biotic stress response. In this way, a conserved induction of calcium signalling functions, and specific WRKY and NAC transcription factors, was identified in response to all biotic stresses. Comparison of these responses to abiotic stress (cold, drought, salt, heat), enabled the identification of unique genes responsive only to bacterial infection, 240 genes responsive to both abiotic and biotic stress, and 135 genes responsive to biotic, but not abiotic stresses. Functional significance of a number of these genes, using genetic inactivation or over-expression, has revealed significant stress-associated phenotypes. While only a few antagonistic responses were observed between biotic and abiotic stresses, e.g. for a number of endochitinases and kinase encoding genes, some of these may be crucial in explaining greater pathogen infection and damage under abiotic stresses.ConclusionsThe analyses presented here provides a global view of the responses to multiple stresses, further validates known resistance-associated genes, and highlights new potential target genes, some lineage specific to rice, that play important roles in response to stress, providing a roadmap to develop varieties of rice that are more resistant to multiple biotic and abiotic stresses, as encountered in nature.

Validation of a simple resazurin-based promastigote assay for the routine monitoring of miltefosine susceptibility in clinical isolates of Leishmania donovani

Simple, cost-effective approach for routine surveillance of parasite susceptibility to antileishmanial drug miltefosine (MIL) is highly desirable for controlling emergence of drug resistance in visceral leishmaniasis (VL). We validated a simple resazurin-based fluorimetric assay using promastigotes to track natural MIL tolerance in Leishmania donovani parasites from VL cases (n = 17) against standard amastigote assay, in two different labs in India. The inter-stage MIL susceptibility correlated strongly (r = 0.70, p = 0.0018) using J774.A.1 macrophage cell line-based amastigote assay and fluorescence-based resazurin assay for promastigotes. Investigation of inter-stage MIL susceptibility for the same set of clinical isolates in another lab also showed a strong correlation (r = 0.72, p = 0.0012) using mouse peritoneal macrophages for amastigote assay and resazurin-based alamar blue assay for promastigotes. Additionally, parasites from post-kala-azar dermal leishmaniasis (PKDL) lesions (n = 7, r = 0.78, p = 0.046) and MIL-induced parasites (r = 0.92, p = 0.0001; n = 3) also exhibited a strongly correlated inter-stage miltefosine susceptibility. Thus, our results support the utility of resazurin assay as a simplified biological tool for MIL susceptibility monitoring in clinical isolates from MIL-treated VL/PKDL patients.

Estado actual y futuro de la terapia anti-leishmaniásica en Colombia

Pentavalent antimonials are the first choice to treat leishmaniasis in Colombia. However, a 600% increase in the total dose has been necessary in order to maintain their efficacy. Cure rates varying between 93 and 25% can reflect differences in parasite susceptibility, but are more likely secondary to deficiencies in compliance with treatment guidelines. We review the current situation of efficacy and use of pentavalent antimony compounds, amphotericin B, pentamidine and miltefosine and attempt a projection for the next following years. To determine the real situation of response to antileishmanial drugs and to extend their useful life, the establishment of surveillance mechanisms to cover all factors involved is necessary. A sentinel site surveillance strategy to allow punctual observations in time, in specific geographical areas and in particular local situations, is proposed.

LongRange™ (eprinomectin 5%) extended-release injection parasiticide and the utility of extended-activity antiparasitics in cattle

An extended-release injection, which is administered at a rate of 1mg eprinomectin/kg body weight, has been developed to provide up to 150 days control of parasites of cattle. The product can facilitate the achievement of two of the fundamental aims of parasite control. The first is protection of the host against the negative impact of susceptible parasites in order to ensure control of disease and to enhance performance. The second is to reduce parasite transmission and hence the challenge to animals when grazing. In addition, farmers and veterinarians can benefit from high levels of convenience and hence compliance from a single administration, which also limits handling stress in the cattle. This introductory paper provides some perspective on the practical applications for this extended-release product under various husbandry systems and in different classes of cattle and discusses its role in sustainable parasite control.

Caracterização do controle de Haematobia irritans e Rhipicephalus (Boophilus) microplus no Triângulo Mineiro e Alto Paranaíba, Minas Gerais

O controle eficaz de Haematobia irritans (mosca-dos-chifres) e Rhipicephalus (Boophilus) microplus (carrapato-do-boi) é um fator crucial à maior rentabilidade da pecuária brasileira, porém ainda constitui-se um desafio. Um maior conhecimento das práticas adotadas no combate destes parasitos faz-se necessário para que se possam estruturar estratégias de controle mais próximas da realidade do produtor rural e mais fáceis de serem executadas. Este estudo caracterizou, através de entrevistas, as práticas adotadas no controle desses ectoparasitos em 23 propriedades da mesorregião do Triângulo Mineiro e Alto Paranaíba, Minas Gerais. A maioria dos entrevistados reconheceu a importância desses parasitos para a atividade pecuária, entretanto, diversos problemas relativos ao controle parasitário foram observados. O controle da mosca-dos-chifres e do carrapato-do-boi era uma prática rotineira em, respectivamente, 17,4% e 95,7% das propriedades, geralmente realizado em função de elevado grau de infestação dos animais. Mais de seis aplicações de ectoparasiticidas eram realizadas por ano em todas as propriedades que empregavam tratamentos para o controle da mosca e em 76,5% daquelas que combatiam o carrapato. Os produtos eram aplicados principalmente com bombas costais manuais (63,6%) e sem a contenção dos animais em 45,5% das propriedades. A diluição dos produtos segundo recomendações dos fabricantes era realizada por 45,4% dos entrevistados, porém, 63,6% aplicavam um volume de solução por animal menor do que o tecnicamente recomendado. Utilizava-se principalmente a associação de piretróides e organofosforados para o controle de ambos os parasitos. Apesar de utilizar rotineiramente ectoparasiticidas, o uso de equipamento de proteção individual (EPI) não era comum entre os entrevistados. A maioria dos entrevistados conhecia algumas características epidemiológicas dos parasitos, entretanto, o controle parasitário adotado na maior parte das propriedades tende a comprometer não apenas a eficácia dos tratamentos, mas a suscetibilidade dos parasitos e a sustentabilidade do controle.