2019 Aug 5. doi: 10.1111/trf.15470. [Epub ahead of print]

Prevalence of Babesia in Canadian blood donors: June-October 2018.



The erythrocytic protozoan parasite Babesia microti, the cause of human babesiosis, is transmitted not only by tick bites but also via blood transfusion. B. microti is endemic in the northeastern/upper midwestern United States, where partial screening of blood donations has been implemented. In Canada, a 2013 study of approximately 14,000 donors found no B. microti antibody-positive samples, suggesting low risk at that time.


Between June and October 2018, 50,752 Canadian donations collected from sites near the US border were tested for Babesia nucleic acid by transcription-mediated amplification (TMA). Reactive donations were tested for B. microti by IgG immunofluorescence assay and polymerase chain reaction. A subset of 14,758 TMA nonreactive samples was also screened for B. microti antibody. Donors who tested reactive/positive were deferred, asked about risk factors, and were requested to provide a follow-up sample for supplemental testing.


One sample from Winnipeg, Manitoba, was TMA and antibody reactive. Of the 14,758 TMA-nonreactive donations tested for antibody, four reactive donations were identified from southwestern Ontario near Lake Erie. None of the interviewed donors remembered any symptoms, likely tick exposure, or relevant travel within Canada or the United States.


This is the largest B. microti prevalence study performed in Canada. The results indicate very low prevalence, with only one TMA-confirmed-positive donation of 50,752 tested. This donor was from the only region in Canada where autochthonous infection has been reported. Seropositive donations in southwestern Ontario suggest low prevalence; travel should not be ruled out given the proximity to the US border.


For more: I would caution authorities in believing there is a low prevalence of Babesa. I’ve heard it takes a trained eye to see it and is rarely detected using only 1 diagnostic test. I think the word is out on the seriousness of tick-borne disease. Let’s not go back in time by adopting a carefree approach. We should be looking hard and using accurate testing methods.  This clearly shows there were more than 200 Babesia transfusion-transmissions reported. It also shows you don’t have to reside in an endemic area or travel to an endemic area to get it. The article also clearly points out that the geographic range of ticks is expanding, which means the pathogens they carry will as well.

According to Dr. Ken Singleton, Babesia is rarely detected using one diagnostic test alone.


Lyme-aware physicians generally screen for 2 strains—Babesia microti and WA-1 (Babesia duncani)—by testing for antibodies (by IFA or ELISA testing) made by the body against those organisms.

Another very useful test for Babesia is known as the FISH (fluorescent in situ hybridization) test. The FISH test is performed on thin blood smears (tests used to detect germs in white blood cells) and is able to detect the RNA (genetic material) of Babesia. If this test is positive, it is very strong evidence of the presence of active Babesia. The advantage of the FISH test is that it will detect other subspecies of Babesia in addition to B. microti and B. duncani. (A direct thick and thin blood smear using a staining technique called “Giemsa” can also be done by one’s local or commercial labs to look for Babesia organisms in red blood cells; however, it is an insensitive test except during acute Babesia, particularly when fever is present.)

A final potentially useful test is the Babesia PCR (polymerase chain reaction). Unfortunately, in my experience it is also not a sensitive test and is the least useful of the three tests mentioned.

All three of these tests—Babesia IFA, FISH, PCR—are available through IgeneX, a laboratory specializing in Lyme disease and other tick-borne organisms. Medical Diagnostics Laboratory (MDL) has two of the tests—Babesia ELISA and PCR. Both labs are excellent and I utilize both regularly. (See the resources section for more information.) However, as mentioned, Babesia can frequently escape detection by diagnostic tests. Therefore, many times babesiois must be a clinical diagnosis made by physicians who are experienced in its detection and treatment.

How many Canadian people slipped through the cracks?



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