Coinfection rates of avian blood parasites increase with latitude in parapatric host species

Abstract

Animals are frequently coinfected with multiple parasites concurrently, and advances in our sampling of these complex intra-host parasite communities have revealed important ecological impacts on their hosts. However, the spatial distributions and environmental determinants of parasite coinfection remain infrequently studied. Here, we investigated the drivers of haemosporidian blood parasite coinfection in the Bicknell's thrush (Catharus bicknelli) and grey-cheeked thrush (Catharus minimus), parapatric sister species that occur across a broad latitudinal range in northern North America. Using 298 samples from across the distributions of these species, we found high overall infection (86%) and coinfection (41%) rates within host populations. Coinfection rates within populations were highly variable across sampling sites, ranging from 7 to 75%. Latitude was a more important predictor of coinfection frequency than host species identity, with coinfections becoming more abundant at higher latitudes. The 2 host species exhibited similar parasite faunas, and an analysis of the co-occurrence patterns among haemosporidians showed that host species identity was largely not a factor in structuring which parasites were found within coinfections. To our knowledge, this is the first study to illustrate a reverse latitudinal gradient in coinfection frequency in a eukaryotic parasite system. Further work is necessary to determine whether vector ecology or some other factor is the primary proximate driver of this pattern.

Insights into the Biology of Leucocytozoon Species (Haemosporida, Leucocytozoidae): Why Is There Slow Research Progress on Agents of Leucocytozoonosis?

“…In other words, some solely PCR-based reports of Leucocytozoon infections and co-infections might be due to the amplification of DNA from persistent sporozoites, including those injected by vectors, that are unable to initiate development if they appear in the wrong (resistant or partly resistant) avian host. It is still unclear if many reported co-infections of Leucocytozoon lineages in naturally infected birds [ 7 , 51 , 118 , 119 ] represent competent or incompetent (abortive) infections at the sporozoite and/or exo-erythrocytic meront stage. It is worth mentioning that some abortive haemosporidian infections at the megalomeront stage might be virulent and even lethal when they appear in non-adapted avian hosts [ 4 , 94 , 120 , 121 ].…”

“…Targeted molecular testing of such cases is needed for final taxonomic conclusions, but such studies remain rare [ 9 ]. This is a particularly important issue for understanding the pathology of Leucocytozoon species if co-infections are present [ 95 , 118 , 119 , 234 ].…”

“…Second, the molecular characterization of Leucocytozoon species is often confused because of common co-infections of parasites belonging to the same genus [ 7 , 10 , 38 , 40 , 42 , 105 , 118 , 119 , 254 , 256 , 257 , 259 , 260 , 261 , 262 , 263 , 268 , 270 , 272 , 273 , 274 ]. Microscopic examination of blood films from many naturally infected birds shows that infection with a single species of Leucocytozoon is rare.…”

“…It is worth noting that leucocytozoids are the dominant blood parasites in some areas of the Nearctic region [ 24 , 223 , 321 , 322 ]. These parasites are prevalent in New Zealand [ 35 , 92 , 160 ] and in cold mountain sites located at altitudes greater than 3000 m above sea level [ 48 , 49 , 50 , 119 , 228 ]. Leucocytozoids are also prevalent in the hot tropical regions of the New World [ 5 , 25 , 69 ], where they flourish in some bird species with prevalences of over 50% in passerines of some families [ 1 , 4 ] and prevalences of close to 20% in domestic chickens [ 29 ].…”