Transfusion-transmitted arboviruses: Update and systematic review

Background The detection of the first cases of transfusion-transmitted West Nile virus in 2002 posed a new challenge for transfusion safety. Institutions like the World Health Organization have stated that blood transfusion centers need to know the epidemiology of the different emerging infectious agents and their impact on blood transfusion. The aim of the study is to review the published cases of arbovirus transmission through transfusion of blood or blood components and to analyze their main clinical and epidemiological characteristics. Material and methods Systematic literature searches were conducted in MEDLINE, Embase and Scopus. Pairs of review authors selected a variety of scientific publications reporting cases of transfusion-transmitted arboviruses. Main clinical and epidemiological characteristics were reviewed of the cases described. The study protocol was registered in PROSPERO CRD42021270355. Results A total of 74 cases of transfusion-transmitted infections were identified from 10 arboviruses: West Nile virus (n = 42), dengue virus (n = 18), Zika virus (n = 3), yellow fever vaccine virus (n = 3), tick-borne encephalitis virus (n = 2), Japanese encephalitis virus (n = 2), Powassan virus (n = 1), St. Louis encephalitis virus (n = 1), Ross River virus (n = 1) and Colorado tick fever virus (n = 1). The blood component most commonly involved was red blood cells (N = 35, 47.3%; 95% confidence interval [CI] 35.9% to 58.7%). In 54.1% (N = 40; 95% CI: 42.7%-65.47%) of the cases, the recipient was immunosuppressed. Transmission resulted in death in 18.9% (N = 14; 95% CI: 10.0%-27.8%) of the recipients. In addition, 18 additional arboviruses were identified with a potential threat to transfusion safety. Discussion In the last 20 years, the number of published cases of transfusion-transmitted arboviruses increased notably, implicating new arboviruses. In addition, a significant number of arboviruses that may pose a threat to transfusion safety were detected. In the coming years, it is expected that transmission of arboviruses will continue to expand globally. It is therefore essential that all responsible agencies prepare for this potential threat to transfusion safety.


Discussion
In the last 20 years, the number of published cases of transfusion-transmitted arboviruses increased notably, implicating new arboviruses. In addition, a significant number of arboviruses that may pose a threat to transfusion safety were detected. In the coming years, it is expected that transmission of arboviruses will continue to expand globally. It is therefore essential that all responsible agencies prepare for this potential threat to transfusion safety.

Author summary
The transfusion of blood and blood components entails some risks and potential complications, chief among them the transmission of infectious agents. Organizations like the American Association of Blood Banks have warned of the risks posed by emerging and reemerging viruses for transfusion safety and have classified transmission of several arboviruses as a high or very high risk to the transfusion of blood and blood components. Following recommendations by the World Health Organization (WHO), this study aims to enable safe blood transfusion services, by making available the latest updated information of transfusion-transmitted arboviruses and comprehensive knowledge of the current epidemiology of reported cases.
Research revealed case reports of transfusion transmission of 10 arboviruses, with West Nile virus and dengue virus as the most prevalent. Main clinical characteristics of reported cases were collected, including the type of blood component transfused and the state of immunosuppression of the recipient. Research also revealed 18 additional arboviruses with potential risk of transmission through other direct transmission routes. This systematic review provides an updated overview of the clinical characteristics of reported cases of transfusion-transmitted arboviruses. It is the most complete record published to date that assesses the risk posed by arboviruses to blood transfusion.

Background
Throughout history, transfusion safety has been threatened by the emergence of various infectious agents [1]. Currently, health service consumers expect a total absence of transfusionrelated transmission of infectious diseases. However, the 2002 notification of the first cases of West Nile virus transmission through transfusion of blood components, highlighted the threat posed to transfusion safety by emerging and re-emerging infectious agents [2,3].
Among the emerging viruses, arboviruses are especially relevant due to their known or theoretical potential for transmission through blood transfusion. These viruses are transmitted by arthropods, mainly mosquitoes (genera Culex spp. and Aedes spp.) and ticks (particularly the genus Ixodes) but also flies, dragonflies, and lice. In humans, they can cause clinical presentations ranging from asymptomatic infections or mild flu-like symptoms, to severe, potentially fatal hemorrhagic and neurological syndromes. Their epidemiology is highly variable and unpredictable and may manifest as isolated and localized cases; seasonal waves; or widespread, epidemic outbreaks. Originally from tropical regions, arboviruses have now spread widely, producing numerous epidemic outbreaks over the past 20 years and constituting a major public health problem all over the planet. Arboviruses are classified into different taxonomic families: Flaviviridae, Bunyaviridae, Togaviridae, Rhabdoviridae, Reoviridae, and Asfarviridae. The most important arboviruses that cause disease in humans belong to the families Flaviviridae, Togaviridae and Bunyaviridae [4].
Threats to transfusion safety arising from new infectious agents have traditionally been addressed through the development of methods to screen blood donors, and this also holds true for arboviruses. Screening methods used include serological and non-serological antigen rapid testing techniques as well as nucleic acid (PCR) tests. These tests may be used routinely or according to the epidemiological profile of the areas or countries in question. However, they may not be sufficient to fully guarantee transfusion safety in the case of donors with a very low viral load and/or who are in the window period after infection [5].
In recent years, various international organizations have created tools to assess the transfusion risk posed by these newly emerging and re-emerging infectious agents. In 2009, the AABB Transfusion-Transmitted Diseases Committee, in collaboration with members of the Food and Drug Administration (FDA), the Centers for Disease Control and Prevention (CDC), and other agencies, developed guidance to identify infectious agents that could pose a real or potential risk to transfusion safety. In this process, 68 infectious agents, including arboviruses, were classified according to their epidemiological profile and the public's awareness and perception of them. Of  With the development of these risk assessment tools, major global public health entities have expressed the need for comprehensive knowledge of the epidemiological characteristics of the various emerging transfusion-transmitted infections and to evaluate their potential impact on donor selection criteria and the supply of blood and blood products [10].
The main objective of this study is, therefore, to review the published cases of arbovirus transmission through the transfusion of blood or blood components throughout the history of transfusion and to study their main clinical and epidemiological characteristics. For the research question in PICOT format, please see (S1 Table). The secondary objective is to, additionally, identify arboviruses that can be a threat to transfusion safety through other non-vector, non blood transfusion related direct routes of transmission such as: organ and/or hematopoietic stem cell transplantation, mother-to-child transmission, direct blood contact or by their prevalence in blood donors.

Design
This systematic literature review was designed and conducted in accordance with the Cochrane Handbook of Systematic Reviews of Interventions and reported in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement [11]. For the PRISMA checklist, please see the (S1 PRISMA Checklist). The protocol for this systematic review was published and registered in PROSPERO (www.crd.york.ac.uk/prospero, CRD42021270355).
First, a global descriptive analysis was completed including all cases of transfusion-transmitted arboviruses. Consequently, a brief study was conducted of the main clinical and epidemiological characteristics of reported cases of arboviral transfusion transmission. After a general analysis that included all cases, we specifically analyzed the arboviruses with the most reported cases of transmission through blood transfusion or blood components: West Nile virus and dengue virus. Finally, a descriptive analysis was performed of arboviruses that can be considered a potential threat to transfusion safety, based on published reports of any non-vector, non-blood related direct route of transmission or because of their prevalence in blood donors, regardless of reported evidence of transfusion transmission.

Source of data collection
Systematic literature searches were conducted in MEDLINE, Embase, Scopus using the server of University Miguel Hernández server.

Search strategy
The complete search strategy is described in more detail in the study protocol and (S1 Text). Initially, the authors have performed searches with free text terms in all three bibliographic databases using the term "transfusion" in combination with the name of the arboviruses being reviewed. In MEDLINE, Medical Subject Headings (MeSH) such as "Blood Transfusion"[-Mesh] OR "Transfusion Reaction"[Mesh] also served as search terms. In Embase the Entree thesaurus was used to search articles based on the following terms: "blood transfusion"/exp.
As a second search strategy, free text searches were performed in MEDLINE using the terms: "transplantation", "vertical transmission", "blood donors", while in Embase a free text search was conducted by entering the following terms in the Entree Thesaurus: "transplantation"/exp OR transplantation, "vertical transmission"/exp OR "vertical transmission" AND "blood donor"/exp OR "blood donor". In Scopus, we ran searches only using free text terms in the fields for title, abstract, and key words. Bibliographies of all included records to identify other potentially relevant publications were also hand-searched.
The authors included records published from the year of inception of each bibliographic database (start date-we did not apply any specific limits to the start date) to 10 November 2021 (end date). The records were entered into the Mendeley Desktop reference manager (Elsevier).

Study selection
In answer to the primary objective, selected publications were those in any language describing cases of transfusion-transmitted arboviruses transmitted through transfusion of blood or blood components. A wide variety of scientific studies (original articles, reviews, brief reports, case reports, letters to the editor, conference papers and others) were included reporting cases of arboviruses transmitted through transfusion of blood or blood components. Publications that collected cases of transmission in non-humans were excluded, as were publications that did not detail the specific type of arbovirus transmitted through the transfusion of blood or blood components.
Search records were independently evaluated by two review authors for inclusion in the publication overview. Any discrepancies were resolved by consensus. Inter-observer agreement was measured by determining the kappa index.
The bibliographic reference manager Mendeley Desktop was used to create folders containing records for each virus, eliminating duplicates. Titles and abstracts were screened to preselect records in any language that included general information on the possible transmission of arboviruses through the transfusion of blood or blood components. Consequently, full texts of all potentially relevant records were reviewed independently by two researchers. Records included, were those that reported cases of transfusion transmission of blood or blood components in humans over the entire period under study.
To answer to the secondary objective, publications in any language were first selected, describing cases stemming from direct non-vector or transfusion related routes of arbovirus transmission (e.g.: organ and/or hematopoietic stem cell transplantation, mother-to-child transmission, direct blood contact) or reports of prevalence of these arboviruses in blood donors. Consequently, a wide variety of records (original articles, reviews, brief reports, case reports, letters to the editor, conference papers and others) were included to accommodate this review. Lastly, for each encountered route of transmission and each arbovirus found prevalent in blood donors, one publication was selected for the produced publication overview, representing the routes of transmission or evidence of prevalence in screened blood donors. Representative publications were selected based on the following criteria: most recent date of publication, most cited publication, or publication in a journal with the highest impact factor. This evaluation was independently done by two review authors. Final selection for inclusion in the publication overview was determined by consensus. Inter-observer agreement was measured by determining the kappa index.

Data extraction and analysis
All data of cases of transfusion-transmitted arboviruses were extracted from the selected publications and directly entered into a Microsoft Excel database by a single review author. Data quality control was consequently done by a second review author. If a publication included more than one case of transfusion transmission, each case was recorded and entered separately in the database. Basic epidemiological and clinical data of the reported cases of transfusion transmission were then analyzed: type of blood component implicated, immunosuppression and clinical presentation in the recipient, fatality of the outcome following transmission as well as the plausibility of the respective transmission route. From the selected publications, study authors conclusions on transfusion transmission and mortality, attributable to the arboviral infection, were recorded. Determinants of potential alternative routes of transmission were additionally collected such as: exposure to the vector, prolonged hospital stay, additional patients infected by the same contaminated donated product or whether the authors themselves ruled out other potential explanations for the patient's infection.
Results were expressed as proportion with a 95% confidence interval (95% CI). The proportion was calculated as the number of the reported parameter under study divided by the total number of reported cases of transfusion transmission (Example: number of cases of transfusion-transmitted arboviruses related with the transfusion of red blood cells / total number of cases of transfusion-transmitted arboviruses x 100). The 95% CIs were for proportions (p±Z α/2 p (p(1-p)/n)).

Quality assessment
Due to the mainly descriptive objective of this study and the type of publications included (case reports, letters to the editor), no standard quality control tool, such as ROBINS-I or STROBE checklist, was applied for assessing risk of bias in non-randomized studies.

Results
The search strategy yielded a total of 5158 records. After eliminating duplicates, the authors screened the title and abstract of 2918 records and retrieved the full text of 199. The authors selected any records that suggest human transmission of arboviruses through blood transfusion or studies that display information that could facilitate the identification of other publications that report cases of transfusional transmission of arboviruses. Finally, 29 studies reporting cases of human transmission of arboviruses through transfusion of blood or blood components were included. Fig 1 presents the PRISMA flow chart, describing the selection process for including published studies of transfusion-transmitted arboviruses.
For the PRISMA flow chart with the process of selecting records describing non-vector and non-transfusion related direct routes of transmission of arboviruses and publications reporting the prevalence of arboviruses in blood donors, please see (S2 Flow Chart). A total of 32 records were selected for the publication overview with an interobserver K value of 0.84.   (Fig 2).

Arboviruses with a potential threat to transfusion safety
In addition to the 10 arboviruses involved in reported cases of transfusion-transmitted infections, 18 additional arboviruses were identified with a potential threat to transfusion safety by means of organ and/or hematopoietic stem cell transplantation, mother-to-child transmission, direct blood contact and/or prevalence in blood donors. The characteristics of published cases on these arboviruses are listed in Table 4. Reference studies on these other arboviruses describing the risk of direct transmission, are depicted in Table 5.

Discussion
Until the year 2000, transfusion transmission of arboviruses was almost anecdotal, with only one isolated case of transmission of Colorado tick fever virus and two cases of tick-borne  This study confirms the possibility that arboviruses can be transmitted through transfusion of blood and blood components. A total of 74 reported cases of suspected transfusion-transmitted infections from 10 arboviruses were identified. Infections were reported to be symptomatic in 63.5% and fatal in 18.9% of the reported cases. This transmission route therefore poses a considerable threat to transfusion safety, reportedly causing significant morbidity and mortality and an increased health spending. As more than 50% of affected patients were classified as immunocompromised, transmission of arboviruses through blood or blood components can additionally be considered a threat to a particularly vulnerable section of the population. Analysis of reported cases revealed that transfusion transmission occurred through various blood products. It is observed that transmission through platelet transfusion was found to be higher in cases of dengue virus transmission, compared to other arboviral transmission cases, including the West Nile virus cases. This finding could be related to signs of tropism of the dengue virus against platelets or at least some of their components, such as glycoprotein Ib (CD42b) [82].
In addition to the published cases of transfusion transmission of arboviruses, our review identified 18 additional arboviruses with potential threat to transfusion safety through solid       organ transplantation, mother-to-child transmission, blood contact or prevalence in blood donors. The results of this review further confirm identification of arboviruses with a high-risk of future transfusion transmission, as they were reported to be involved in direct non-vector related transmission and prevalent among blood donors. These are: Chikungunya virus, Crimean-Congo haemorrhagic virus, Eastern equine encephalitis virus, Heartland virus and Jamestown Canyong virus. Based on the results of this review, the reported rapid growth of arboviral cases in recent years can also be confirmed and seems to correspond to the expanding endemicity of arboviruses globally. According to literature, the increased frequency of outbreaks can be explained by multiple environmental and anthropogenic factors, including increased travel and trade, population growth, changing land use patterns, and the urbanization of rural areas [83].
These facts come on top of a growing list of emerging infectious diseases. It is estimated that from 1940 to 2004, 5.3 new viruses were discovered each year, of which at least two-thirds were zoonoses [84]. In consonance with their emerging nature, there is very little knowledge on some of these new arboviruses, such as the SFTS virus, which has already caused multiple deaths in South Korea [85].
To improve transfusion safety, blood banks have taken a number of measures. One common measure is the exclusion of donors presenting symptoms. This is a measure with limited effectiveness given the high rate of asymptomatic infections. Another measure taken is the cancellation of blood donations in affected regions, which is at times difficult to apply, if the epidemic outbreak is extensive and no contingency plans are in place to guarantee the supply of blood and blood components from other geographical regions. So far, the most useful measure is the application of nucleic acid testing (NAT) in donor screening. One example illustrating this success comes from the significant reduction in transmission of West Nile virus in the USA, after the implementation of NAT screening in 2003. However, NAT tests are not infallible: for instance, one case of West Nile virus transmission was reported in a donor with very low viremia who had undergone NAT screening, using a simple sample [56]. Another Table 4. Arboviruses that could pose a threat to transfusion safety due to direct non-vector related transmission mechanisms.
Pouch 2019 [67] Original article Solid organ transplantation: In 2017, 3 solid organ (heart, liver and lung) transplant recipients from a common donor developed encephalitis by Eastern equine encephalitis virus (EEEV).

Heartland virus Hevey 2019 [68]
Case report Solid organ transplantation: Heartland virus infection in a heart transplant recipient from the Heartland (U.S.A.).

Lindsey 2019 [69] Orginal article Screening in blood donors:
Of the 487 blood donors tested, 12 were positives, and 7 of those were confirmed for Heartland virus neutralizing antibodies by PRNT.

Jamestown Canyong virus Askar 2019 [70]
Case report Solid organ transplantation: Jamestown Canyon virus encephalitis in a heart transplant patient.

Mayo 2001 [71]
Letter to the Editor Screening in blood donors: Of the 1,086 sera collected from blood donors in 1990, 164 (15%) were positive by IFA.

La Crosse virus
R. Bowen 2013 [72] Conference abstract Blood contact: During the 2011 outbreak in China it was discovered that the virus was able to be transmitted person to person through blood contact, indicating the possibility this virus could be transmitted through a tainted blood product.
Charlier 2017 [12] Original article Vertical transmission: Transmission documented: 1 asymptomatic mother-to-child transmission documented serologically in cord serum, after a maternal infection.

Mayaro virus
Romeiro 2020 [73] Original article Screening in blood donors: 5608 blood donor samples were tested. IgM and IgG antibodies to MAYV were detected in 36 and 11 samples, respectively.

SFTS Virus
Zeng 2015 [77] Original article Screening in blood donors: 14,764 donor samples were tested for anti-SFTSV IgG antibodies, 86 of which were repeat-reactive and defined as seropositive.

Sindbis virus
Jöst 2011 [78] Letter to the Editor Screening in blood donors: 389 investigated blood donor samples were tested for SINVspecific-IgG antibodies, 4 were positive.
(Continued ) compromising aspect is the expense: the implementation of NAT testing for West Nile virus in the USA, had an estimated cost of USD 483,000-1,300,000 per quality-adjusted life year (QALY), clearly exceeding the widely accepted threshold of USD 50,000-100,000 per QALY [3,86]. Furthermore, implementing NAT tests requires human and logistical resources that are not available in all settings. As an alternative, techniques for the inactivation of pathogens such as methylene blue and visible light, could also be applied where available, as these methods were proven effective against several arboviruses [87,88]. In general, and despite limitations, the best probable strategy is probably to screen using NAT techniques and apply pathogen inactivation techniques to as many blood components as resources allow. In addition, blood transfusion centers should develop robust hemovigilance systems with the ability to trace blood products from infected donors, so that these can be destroyed prior to use or, in case these have already been transfused, the physician responsible for clinical management of the recipient, can be informed in a timely fashion.
The risk of transfusion-transmitted arbovirus infections is of particular concern in lowincome countries, usually in endemic areas or areas where extensive epidemic outbreaks occur. Particularly since blood bank systems are usually not based on voluntary donations, but rather on replacement donations. In addition, testing for infectious agents is not optimal, due to technical and resource constraints or a lack of qualified personnel, often relying on rapid diagnostic tests, known to have a poor sensitivity [89,90].
One limitation of this systematic review is the inherent difficulty of confirming the transmission of the arbovirus through the transfusion of blood components. Unequivocally concluding that an infection was transmitted through transfusion would require demonstrating that the infectious agent was found in samples from the donor or in residual blood components from the donation, that the recipient was not infected before receiving the transfusion, and that the virus was not transmitted through the bite of a vector. This is especially complicated in endemic areas, where the population is exposed to vector bites (mainly mosquitoes), with the possible exception of patients admitted to specific units such as: units specialized in transplantation and intensive care units. However, even in these "mosquito free" units, patients could have been infected before hospital admission. Phylogenetic analysis may be relevant to exclude the transfusion hypothesis, but if the donor and recipient reside in the same geographic area, the same genetic sequence may not be enough to confirm this exclusion [91]. Therefore, definitively classifying a case as transfusion transmission is often unfeasible.

Venezuelan equine encephalitis virus
Charlier 2017 [12] Original article Vertical transmission: virus documented in the brains of ten aborted fetuses; developmental brain lesions in infants borne by infected mothers.

PLOS NEGLECTED TROPICAL DISEASES
Similarly, a significant number of transfusion-transmitted arbovirus infections are likely to go undetected. If, despite the transmission, the recipient does not present symptoms, or if the transmission occurs in a geographical region during an epidemic outbreak, where transmission through the vector cannot be ruled out, transfusion transmission may go unnoticed.
Another limitation of the study is that conclusions of authors of the reviewed records on the plausibility of transfusion transmission and mortality as a consequence of the arboviral

PLOS NEGLECTED TROPICAL DISEASES
infection, were copied with limited information available to confirm these independently. In addition, each author may have applied different criteria in establishing the plausibility of arboviral transmission through the transfusion of blood or blood components and mortality as a possible outcome.
In conclusion, this review updated, characterized and classified cases of arbovirus transmission through transfusion. In addition, a significant number of arboviruses were identified with a potential threat to future transfusion safety. In recent years a global increase was seen in the number of epidemic outbreaks of various arboviruses. In the coming years, it is expected that this number will continue to increase. For this reason, it is important that each system or organization responsible for transfusion safety has adequate surveillance systems, contingency plans, and protocols in place to guarantee transfusion safety. The different regulatory agencies, public health bodies, medical communities, and the medical industry should collaborate closely and coordinate efforts to provide a rapid and effective response to any threat to transfusion safety.
Supporting information S1 Table. PICOT research question.