In what is thought to be the first study on the role of birds as Lyme disease hosts, researchers in Portugal have determined Blackbirds are a major carrier of the Lyme disease bacteria, with ramifications for Lyme disease prevention efforts worldwide. The scientists at the University of Coimbra studied the infection rates of a number of local bird species as well as studying the presence of ticks on native plants favored by these birds and found, to their surprise, an entirely new strain of Borrelia bacteria as yet uncategorized.
Lyme Disease Carried by Birds
Lyme disease bacteria exist in a reservoir of host animals, including white-footed mice, lizards, deer and birds but this is the first study to focus specifically on the contribution of the latter to the spread of the infection. Ticks feeding from birds become infected with bacteria but remain free of the Lyme disease symptoms seen in humans, dogs and horses. As birds have a wider migratory range than most other carriers of the bacteria it is particularly important to investigate their role in spreading the disease, especially given the effects of climate change and the ability of ticks to survive in a larger geographic area.
Lyme Disease in Portugal
The study, which was funded by the Foundation for Science and Technology (FCT), involved five researchers over three years looking into the spread of Lyme disease despite the rates of human cases in Portugal actually being fairly low. The first case was documented in the country in 1989 and around 35 cases are reported annually. Cláudia Norte, coordinator of the study, noted that it is important to be informed of the risks anyway, especially because diagnosis can be difficult ”due to the fact that early symptoms are similar to other diseases.”
Lyme Disease Awareness Vital, Portuguese Researcher Stresses
Norte goes on to say that because “more people travel to other countries, including in areas where prevalence is high […] Information is essential to take proper care.” Diagnosis is further problematized by the fact that tests do not detect all strains of the bacteria, including the newly documented strain Borrelia turdi found in the birds in this study. Without adequate treatment at an early stage, Norte says that “bacteria can spread throughout the body and cause serious injury at neurological, cardiac and articular levels.”
A New Strain of Lyme Disease Bacteria
The new strain of Borrelia was found after testing blood samples from birds abundant in Portugal. These 23 or so species commonly carry ticks as parasites, offering a blood meal and maintaining a reservoir of bacteria to pass on to new generations of ticks. Only the birds of the Turdus family were found to carry the Lyme disease bacteria, hence the naming of the new strain, Borrelia turdi. The scientists also looked at plants harvested at Tapada de Mafra and Mata do Choupal, monthly, for one year to assess seasonal variations in the abundance, distribution and infestation of ticks. It may be that such research allows for more effective tick control measures accounting for the fact that birds are significant hosts of Lyme disease, improved diagnostics that include antibody testing for Borrelia turdi, and better awareness of the risk of Lyme disease in Portugal.
Norte AC, Ramos JA, Gern L, Núncio MS, Lopes de Carvalho I., Birds as reservoirs for Borrelia burgdorferi s.l. in Western Europe: circulation of B. turdi and other genospecies in bird-tick cycles in Portugal, Environ Microbiol. 2013 Feb;15(2):386-97.