Asymptomatic infections in blood donors harbouring Plasmodium: an invisible risk detected by molecular and serological tools

Transfusion-Transmitted Malaria and Mitigation Strategies in Nonendemic Regions

Background

Malaria is a mosquito-borne infectious disease caused by protozoan parasites of the genus Plasmodium. These parasites can be transmitted by blood transfusion especially through Red Cell Blood Concentrates collected from asymptomatic and parasitemic donors. As migration of populations from endemic areas to Europe and overseas recreational travel to endemic regions increase, there is growing risk of transfusion-transmitted malaria (TTM) in nonendemic regions of the world. The present work provides an overview of the mitigation strategies in nonendemic countries and their effectiveness and discusses possible approaches to evolve the strategies in order to maintain both a safe and adequate blood supply.

Summary

The historical and current situation of malaria and TTM in Europe and on the North American continent are described. The infectivity of Plasmodium in blood components and the consequences of TTM are presented, along with the regulations and guidelines for TTM mitigation in Europe, USA, and Canada. The regulations/guidelines currently in place in Europe allow a certain amount of leeway for local policies. A questionnaire was used to survey European countries regarding their current strategies and recent TTM cases. From the questionnaire and published cases, approximately 20 cases of TTM were identified in the past 20 years in the USA and Europe. The vast majority of implicated donors have been former residents of malaria-endemic areas, particularly former residents of hyperendemic areas in Africa. The most recent TTM cases are discussed in detail to provide insight into the gaps in current strategies. The utility and uncertainties of pathogen reduction and serological and molecular testing methods are discussed.

Key Messages

Overall, the risk of transfusion-associated malaria in nonendemic countries is considered to be low and very few TTM cases occurred in these regions in the last 20 years. The questionnaire-based strategy with questions about risk in relation to malaria exposure with or without selective testing based on questioning seems to be relatively effective, although rare and sometimes fatal transmissions still occur. An outstanding question is whether in the future molecular methods may further improve the safety of blood products and help constrain the loss of donors.

The hidden Plasmodium malariae in blood donors: a risk coming from areas of low transmission of malaria

Malaria is an infectious vector-borne disease with other important routes of transmission, such as blood transfusion and organ/tissue transplantation, due to asymptomatic reservoirs of Plasmodium presenting with low parasitemia. Reports of transfusion-transmitted malaria have shown that in immunosuppressed recipients, infections can be fatal if they are not diagnosed and timely treated. All Plasmodium species can survive on blood components at temperatures from 2 to 6 °C for some days or even weeks. This report describes two candidates for blood donation harboring Plasmodium, infected in an area considered non-endemic. Blood samples were collected from donors who attended a blood bank in Sao Paulo and tested by microscopy, qPCR for Plasmodium genus-specific amplification, targeting the parasite 18S ribosomal subunit gene and a multiplex qPCR based on mtDNA of the five species. Under microscopy, only structures resembling Plasmodium were observed. The qPCR whose standard curve tested parasites varying from 2 to 0.1 parasites/ µL, showed the presence of Plasmodium DNA in the two blood donors, as did the multiplex qPCR that revealed the presence of P. malariae. The prevalence of positive donors varies according to the level of transmission, ranging from 0.7 to 55% in endemic areas. In non-endemic regions, prevalences are lower, however, transfusion malaria can evolve to severe cases, due to the lack of suspicion of this transmission route. Asymptomatic donors from low transmission regions pose a risk to blood banks, with particular emphasis on those located in areas with malaria elimination goals.

Howler monkeys are the reservoir of malarial parasites causing zoonotic infections in the Atlantic forest of Rio de Janeiro

BACKGROUND

Although malaria cases have substantially decreased in Southeast Brazil, a significant increase in the number of Plasmodium vivax-like autochthonous human cases has been reported in remote areas of the Atlantic Forest in the past few decades in Rio de Janeiro (RJ) state, including an outbreak during 2015-2016. The singular clinical and epidemiological aspects in several human cases, and collectively with molecular and genetic data, revealed that they were due to the non-human primate (NHP) parasite Plasmodium simium; however, the understanding of the autochthonous malarial epidemiology in Southeast Brazil can only be acquired by assessing the circulation of NHP Plasmodium in the foci and determining its hosts.

METHODOLOGY

A large sampling effort was carried out in the Atlantic forest of RJ and its bordering states (Minas Gerais, São Paulo, Espírito Santo) for collecting and examining free-living NHPs. Blood and/or viscera were analyzed for Plasmodium infections via molecular and microscopic techniques.

PRINCIPAL FINDINGS

In total, 146 NHPs of six species, from 30 counties in four states, were tested, of which majority were collected from RJ. Howler monkeys (Alouatta clamitans) were the only species found infected. In RJ, 26% of these monkeys tested positive, of which 17% were found to be infected with P. simium. Importantly, specific single nucleotide polymorphisms-the only available genetic markers that differentiate P. simium from P. vivax-were detected in all P. simium infected A. clamitans despite their geographical origin of malarial foci. Interestingly, 71% of P. simium infected NHPs were from the coastal slope of a mountain chain (Serra do Mar), where majority of the human cases were found. Plasmodium brasilianum/malariae was initially detected in 14% and 25% free-living howler monkeys in RJ and in the Espírito Santo (ES) state, respectively. Moreover, the malarial pigment was detected in the spleen fragments of 50% of a subsample comprising dead howler monkeys in both RJ and ES. All NHPs were negative for Plasmodium falciparum.

CONCLUSIONS/SIGNIFICANCE

Our data indicate that howler monkeys act as the main reservoir for the Atlantic forest human malarial parasites in RJ and other sites in Southeast Brazil and reinforce its zoonotic characteristics.

Recombinant proteins of Plasmodium malariae merozoite surface protein 1 (PmMSP1): Testing immunogenicity in the BALB/c model and potential use as diagnostic tool

Background

Plasmodium malariae is the third most prevalent human malaria-causing species and has a patchy, but ample distribution in the world. Humans can host the parasite for years without presenting significant symptoms, turning its diagnosis and control into a difficult task. Here, we investigated the immunogenicity of recombinant proteins of P. malariae MSP1.

Methods

Five regions of PmMSP1 were expressed in Escherichia coli as GST-fusion proteins and immunized in BALB/c mice. The specificity, subtyping, and affinity of raised antibodies were evaluated by enzyme-linked immunosorbent assays. Cellular immune responses were analyzed by lymphoproliferation assays and cytokine levels produced by splenocytes were detected by cytometry.

Results

We found that N-terminal, central regions, and PmMSP1₁₉ are strongly immunogenic in mice. After three doses, the induced immune responses remained high for 70 days. While antibodies induced after immunization with N-terminal and central regions showed similar affinities to the target antigens, affinities of IgG against PmMSP1₁₉ were higher. All proteins induced similar antibody subclass patterns (predominantly IgG1, IgG2a, and IgG2b), characterizing a mixed Th1/Th2 response. Further, autologous stimulation of splenocytes from immunized mice led to the secretion of IL2 and IL4, independently of the antigen used. Importantly, IgG from P. malariae-exposed individuals reacted against PmMSP1 recombinant proteins with a high specificity. On the other hand, sera from P. vivax or P. falciparum-infected individuals did not react at all against recombinant PmMSP1 proteins.

Conclusion

Recombinant PmMSP1 proteins are very useful diagnostic markers of P. malariae in epidemiological studies or in the differential diagnosis of malaria caused by this species. Immunization with recombinant PmMSP1 proteins resulted in a significant humoral immune response, which may turn them potential component candidates for a vaccine against P. malariae.

Transfusional Malaria and Associated Factors at the National Blood Transfusion Center of Niamey-Niger

SUMMARY

Problem. Transfusional malaria is an accidental transmission of Plasmodium via a blood transfusion. Its magnitude is underestimated and very little data on the assessment of this risk are available in Niger.

OBJECTIVE

This study aimed to determine the prevalence of plasmodial infection of blood bags at the National Blood Transfusion Center of Niamey (NBTC).

METHODOLOGY

A cross-sectional study to diagnose Plasmodium infection by microscopy and Rapid Diagnostic Test (RDT) was carried out during the rainy season (September to November 2015). Blood grouping was performed by the BETH-VINCENT technique.

RESULTS

One thousand three hundred and fifty-seven (1357) blood bags were collected. One hundred and fifty-seven (11.6%) of the donors were infected with Plasmodium by microscopy and 2.4% (9/369) by rapid diagnostic test. All infections were with P. falciparum (100%). The mean parasite density was 197 parasites/μL (SD=281; [80: 2000]). There were no significant differences in infection prevalence between the ABO blood groups (p = 0.3) or the rhesus positivity (p=08). There is also no significant difference in temporal (p = 0.1) and spatial (p = 0.6) distribution.

CONCLUSION

The transmission of transfusional malaria during the rainy season is a fact in Niger. Such risks were independent of the ABO blood type and positivity for the rhesus antigen. Pretransfusion diagnosis or posttransfusion therapy should be instituted to prevent it.

Risk of transfusion-transmitted malaria: evaluation of commercial ELISA kits for the detection of anti-Plasmodium antibodies in candidate blood donors

Background

Transfusion with Plasmodium-infected blood represents a risk for malaria transmission, a rare but severe event. Several non-endemic countries implement a strategy for the screening of candidate blood donors including questionnaire for the identification of at-risk subjects and laboratory testing of blood samples, often serology-based, with temporary deferral from donation for individuals with a positive result. In Italy, the most recent legislation, issued in November 2015, introduced the use of serological tests for the detection of anti-Plasmodium antibodies.

Methods

In the absence of a gold standard for malaria serology, the aim of this work was to evaluate five commercial ELISA kits, and to determine their accuracy (sensitivity and specificity) in comparison to immuno-fluorescence antibody test (IFAT), and their agreement (concordance of results). Serum samples from malaria patients or from subjects with malaria history (N = 64), malaria naïve patients with other parasitic infections (N = 15), malaria naïve blood donors (N = 8) and malaria exposed candidate blood donors (N = 36) were tested.

Results

The specificity of all ELISA kits was 100%, while sensitivity ranged between 53 and 64% when compared to IFAT on malaria patients samples. When tested on candidate blood donors’ samples, ELISA kits showed highly variable agreement (42–94%) raising the possibility that the same individual could be included or excluded from donation depending on the test in use by the transfusion centre.

Conclusions

These preliminary results indicate how the lack of a gold standard for malaria serology must be taken into account in the application and future revision of current legislation. There is need of developing more sensitive serological assays. Moreover, the adoption of a unique serological test at national level is recommended, as well as the development of screening algorithms based on multiple laboratory tests, including molecular assays.

Electronic supplementary material

The online version of this article (10.1186/s12936-019-2650-0) contains supplementary material, which is available to authorized users.

Chronic Plasmodium brasilianum infections in wild Peruvian tamarins

There is an increased interest in potential zoonotic malarias. To date, Plasmodium malariae that infects humans remains indistinguishable from Plasmodium brasilianum, which is widespread among New World primates. Distributed throughout tropical Central and South America, the Callitrichidae are small arboreal primates in which detection of natural Plasmodium infection has been extremely rare. Most prior screening efforts have been limited to small samples, the use of low-probability detection methods, or both. Rarely have screening efforts implemented a longitudinal sampling design. Through an annual mark-recapture program of two sympatric callitrichids, the emperor (Saguinus imperator) and saddleback (Saguinus fuscicollis) tamarins, whole blood samples were screened for Plasmodium by microscopy and nested PCR of the cytochrome b gene across four consecutive years (2012-2015). Following the first field season, approximately 50% of the samples collected each subsequent year were from recaptured individuals. In particular, out of 245 samples from 129 individuals, 11 samples from 6 individuals were positive for Plasmodium, and all but one of these infections was found in S. imperator. Importantly, the cytochrome b sequences were 100% identical to former isolates of P. malariae from humans and P. brasilianum from Saimiri sp. Chronic infections were detected as evidenced by repeated infections (7) from two individuals across the 4-year study period. Furthermore, 4 of the 5 infected emperor tamarins were part of a single group spanning the entire study period. Overall, the low prevalence reported here is consistent with previous findings. This study identifies two new natural hosts for P. brasilianum and provides evidence in support of chronic infections in wildlife populations. Given that callitrichids are often found in mixed-species associations with other primates and can be resilient to human-disturbed environments, they could contribute to the maintenance of P. malariae populations if future work provides entomological and epidemiological evidence indicating human zoonotic infections.