A whole new set of ungovernable pathogens are being loosed on the world's blood supplies. A warming climate has allowed blood-borne tropical diseases to flourish where once they were unheard of, and they're getting around.
The state of blood supplies became worrisome after tennis star Arthur Ashe's death from AIDS 20 years ago in 1993 -- the result of an HIV-tainted transfusion administered during a routine heart bypass operation in the late 1980s.
Hospitals and blood banks now routinely screen potential donors for HIV and hepatitis in order to keep these diseases from accidentally finding their way into patients. But recent outbreaks of diseases such as West Nile fever, dengue fever and malaria -- all carried by mosquitoes -- have posed new problems for the health of European blood banks.
During the summer heat wave of 2010, when global average temperatures reached a 30-year high, an outbreak of West Nile fever erupted in southeastern Europe. The first cases were in Greece, where 261 cases and 32 deaths were reported. Although West Nile virus had been seen in animals, these were the first reported cases in humans.
Additional cases were reported in Romania, Hungary and parts of Russia. In total, there were 900 confirmed cases.
Europe also saw its first case of nonimported dengue fever in 2010, when a local case was reported in southern France. More than 1,000 cases of the disease are brought into Europe every year from areas where it's endemic, usually by migrants or visitors predominantly from urban areas in Asia and South America.
Disease vectors spread; some infections spread farther
But until 2010 there were no locally originating cases. The patient in question had not been traveling outside Europe and could have contracted the disease only by being bitten in France by a member of the vector species, the Asian tiger mosquito (Aedes albopictus).
Since then, the Asian tiger mosquito has been found over a substantial area in Europe. In 2012, colonies were found in 20 European countries, as far north as Germany, Belgium and the Netherlands, as far south as Sicily and as far east as Croatia.
Jan Semenza, researcher at the Unit of Scientific Advice at the European Centre for Disease Prevention and Control in Stockholm, said: "Climate change has introduced several public health issues. For one thing, now there are new pathogens in Europe which have never been seen here before."
Tropical and sub-Saharan vector-borne diseases are seeing an upsurge in Europe, largely because climate conditions have become favorable to carriers, which include mosquitoes, ticks, triatomine bugs, sand flies and black flies.
Many of the diseases carried by these insects, including West Nile fever, have latency periods sometimes lasting months, when an infected person has no symptoms and is unlikely to be a suspected carrier. For this reason, potential blood donors may unwittingly donate tainted blood.
Although transfusion-transmitted cases of diseases such as West Nile and dengue fever, both carried by mosquitoes, have not been documented in Europe, there have been several cases of transfusion-transmitted leishmaniasis. Leishmaniasis is normally transmitted to humans through the bite of infected female sand flies.
Endemic to South America, parts of Africa and Asia, the disease doesn't have any symptoms for a large proportion of the carriers. Several cases have been documented resulting from intravenous drug users in Spain sharing infected needles.
Difficulties of broad-scale blood screening
Blood banks have sets of standard procedures in place when it comes to protecting the blood supply. They can refuse donations from certain populations, to include those returning or migrating from areas where certain diseases are prevalent. But that decreases the available donor pool and can create blood shortages in areas where it's most needed.
These were the conditions in Greece in 2010, when in several areas the outbreak of West Nile fever coincided with local outbreaks of malaria. Deferral created a roadblock to testing, as well as imposing additional strains on the already strapped public health infrastructure. A blood shortage ensued.
Screening each sample for several pathogens is possible, but it can get expensive. "The problem with testing," Semenza said, "is really several questions, each with its own cost. For instance, when do we test and how long do we test for? A year after someone was exposed? Two years?
"And how many organisms do we need to test for? One? Two? There is a limit to the cost-effectiveness," he added. For some blood-borne diseases, it can take months if not years for blood to show a positive reaction for the disease in question.
Because it is hardly feasible to test each blood donor and each donation for every possible pathogen, pre-emptive treatment and new technology may hold some promise. One pre-emptive technique, pathogen reduction, involves treating donated blood to eliminate the possibility of infection from a range of microorganisms, rather than targeting each and every known disease individually.
Currently used in France, Poland, Spain, Switzerland and the United Kingdom, various compounds, among these riboflavin (vitamin B2) and methylene blue in combination with light, are used to inactivate known pathogens in platelets or blood plasma.
The development of artificial blood and blood components may further reduce risk of infection through tainted blood. Two types of synthetic coagulation factors -- the main therapeutic components of fresh frozen plasma -- have been in use for several years.
Artificial red blood cells with synthetic membranes are under development. In Russia and South Africa, a simple polyhemoglobin -- an oxygen-carrying blood substitute -- is already in limited clinical use.