Climate change, emerging infections and blood donations

The article by Flaherty et al.1 provides interesting insights into issues relating to blood transfusions and emerging infectious diseases from those who travel to various locations in the world and return home. Much of the heightened concern related to these diseases can be traced to globalization and climate change. In many ways, both of these impacts are related in that changing environmental conditions are affecting movement and shifting trends in the world population.2,3 Changes in the global climate can be considered the greatest impact man will face over the next 100 years.4 This impact will not only cause variation in the geographic characteristics of the planet, but also modification of infectious diseases' distribution.5 One of the key factors influencing this change is weather and its impact on the distribution of vectors. Impacts from global change can shift the endemic areas traditionally associated with various diseases historically categorized as rare, at least in the developed nations.6 A variation in climatic conditions will also cause population shifts along with a new pattern of travelling.7 Migrations and travels (between and within countries) could constitute an unchecked source of emerging infections that could spread into non-affected areas, resulting in public health threats that may not be well understood by the local health communities. Another big challenge is migration due to global events and wars, where whole populations are being moved, in many cases with little or minimal health screening. As a result of globalization and travel the risk of new and emerging infections is likely to increase in the years to come.8 An enhanced spread of infectious diseases associated with travel and migrations will include impacts related to blood transfusion, hence the traditional assumption of minimal risk associated with blood safety is being challenged by climate change and travel activities.1 Blood transfusions are an important aspect of medicine and safety of this product is paramount. Infections transmitted by transfusions can result in complications and represent a major public health concern.8 Developed regions have managed to minimize this risk through various approaches including donor screening and deferral; however, as pointed out by Flaherty further risk reduction can be achieved by improving strategies of blood screening and pathogen inactivation.8 An approach based upon a (self-reported) questionnaire as a standard procedure to screen potentially contaminated blood donors may not be enough in the case of diseases without an effective blood screening test. Furthermore, a deferral strategy due to previous travel may inappropriately exclude a large number of potential blood donations.1 Flaherty examined the feasibility of relaxing the blood donation restrictions for some infectious diseases on the basis of available evidence, suggesting little risk of transfusion-transmitted infections when travelling to certain locations. As mentioned earlier,one of the major factors influecing the changing geographic distribution of many infectious diseases is climate change favorable to vectors.9 A varied distribution of infectious diseases due to climate change favourable to vectors is also becoming a major issue in the evaluation of blood donors.10 Some communicable diseases, such as the Zika virus, are of particular concern, since a large number of infected people may be asymptomatic and present themselves as a health donor. This becomes even more critical when sensitivity and specificity of screening has not been well established.9 Even greater concern exists for diseases that do not have an effective and efficient testing protocol. This can eliminate a large number of suitable blood donors solely on the basis of travel history.1 Most questionnaires evaluate donors based on foreign travel, but with the spread of infectious diseases this concept may also be changing. As seen with many emerging infections (e.g. Zika virus, Babesiosis, Chagas disease) transmission can also result in issues of travel even within a geographical region (e.g. the USA); thus, extending concerns for the blood supply to those travelling within a country.10 These occurrences will require a new strategy in selecting blood donors. Flaherty provided an interesting conclusion that for some major parasitic infections such as Malaria and Chagas disease a relaxation of selective criteria could be recommended in light of the new screening methods. With a high demand for blood donations this could dramatically increase the number of participants. In fact for malaria, the most common transfusion-transmitted infection, a direct DNA testing has been in use for over 10 years in the UK for non-immune travelers returning from endemic countries. Furthermore there have only been three reported cases of malaria in the US through the transfusion route so far.1 Likewise for Chagas disease a blood donor serology test is available for those born in Latin America or who spent a considerable period of time in the region.1 For other viral diseases the available screening methods are either not routinely performed (as for Hepatitis E Virus) or the effectiveness needs improvement [as for West Nile virus (WNV)]. WNV is the most relevant mosquito-borne virus in northern latitude regions.11,12 Since the introduction of the current WNV screening test, several cases of WNV transmitted infections have been reported, posing the recommendation of longer deferral periods, which are currently 28 days for those returning home from an endemic area and extended up to 6 months following complete recovery.11 The latter deferral guidelines are applied to other infections transmitted by Aedes mosquitos, all endemic in the Americas, and which is the vector for Zika, Dengue and Chikungunya viruses.13 The latter two arboviruses, Dengue and Chikungunya, can cause acute disease characterized by fever and severe arthralgia.13,14 Chikungunya seems to confer life-long immunity after infection, with a substantial proportion of the population in endemic areas being protected.11,14 Although both viruses are potentially transmissible by blood, no cases of transfusion transmission of Chikungunya have been recorded so far. Since 10–25% of infected individuals are asymptomatic with high viremic titers, legitimate concerns about transmission of Chikungunya by blood exist.11,14 These high-titer asymptomatic infections can easily avert routine donor screening based upon a self-reported questionnaire.11 As noted by Flaherty, an important emerging issue for the US blood supply is the Zika virus.1 There are concerns about potential transmission of this mosquito-borne infection through blood transfusion because a large proportion (80%) of people infected with this flavivirus remain asymptomatic, and the risk of transmission from blood donors is high based on screening alone (without blood testing).15 This is further complicated by this disease’s transmission through sexual contact. Although Zika clinical disease is generally mild or asymptomatic, increasing evidence suggests that Zika virus infection during pregnancy may be associated with severe microcephaly in infants. The severity of these complications highlights the need to protect pregnant women and to ensure the safety of blood supplies, both in areas experiencing ongoing Zika virus transmission and in zones frequented by travelers returning from an infected area. A screening based upon clinical examination and an antibody-test would not be satisfactory to significantly reduce the risk of blood contamination in blood donors.16 As a result, some agencies, including the World Health Organization and the Food and Drug Administration (FDA), recommend deferring or halting blood donations from individuals within, or returning from, areas with active Zika virus transmission. Moreover, the FDA recommends universal nucleic acid testing for the Zika virus on blood donors returning from risky areas, as well as encouraging the employment of transfusion specialists to implement strategies of peri-surgical patient blood management to avoid transfusion of blood components at risk of contamination with emerging pathogens.15 For other relevant transmission-related parasitic infections, a deferral strategy is the only screening approach available, with significant limitations and drawbacks making the establishment of a blood screening test imperative. In particular, international travelers presenting Yersinia symptoms are deferred for 28 days following full recovery1, yet the transmission of the bacterium could still occur from asymptomatic donors. Furthermore donors with symptoms of Babesiosis and Leishmania (an infection rarely transmitted with blood component production due to leuko-reduction technology) are permanently excluded from blood donations. For Babesiosis, this is even a greater threat, with the disease becoming endemic in various locations of the USA (e.g. eastern New York) along with an expansion of its geographic range.17 Implementing new blood screening tests and expanding testing for emerging diseases will certainly increase the safety of blood donation and the availability of blood, although it may be subject to careful economic cost evaluation. It is important to remember that despite blood donation being an altruistic activity, organizations dealing with blood collection often profit from this product.18 This does not include that in several countries donors also receive an actual payment for the blood donation from profit-organizations.19 Conflict of interest: None declared.