Migration and season explain tick prevalence in Brazilian birds

New insights on the Rickettsia-tick-wild bird associations in the Western Amazon, Brazil

Several studies have highlighted the importance of balancing wildlife and plant life to mitigate the spread of ticks and their pathogenic microorganisms. This balance is essential for preserving the health of wildlife, domestic animals, and, consequently, human populations. However, human activities, characterized by habitat destruction and fragmentation, have brought humans and domestic animals closer to wild bird populations, which act as dispersers of ticks of public health importance. In light of these challenges, this study aimed to determine the frequency of occurrence and abundance of tick species in wild birds in the upland forests of the southwestern Brazilian Amazon. Data were collected in two municipalities: Rio Branco (four urban forest fragments) and Manoel Urbano (an area of continuous forest in the Parque Estadual Chandless), both located in the state of Acre, Brazil. Birds were captured between May and September 2021 using 10 mist nets placed in five transects of each study area, resulting in a sampling effort of 1210 net hours. Captured birds were thoroughly inspected for tick infestation, and when found, they were removed using forceps. These ticks were identified using a stereomicroscope and specific taxonomic keys, as well as molecular analysis by PCR. We captured 315 birds, of which 95 (30.15 %) were infested with ticks in the larval and nymph stages. A total of 368 ticks belonging to the genus Amblyomma were collected. This included species such as Amblyomma coelebs, Amblyomma geayi, Amblyomma humerale, Amblyomma longirostre, Amblyomma nodosum, and Amblyomma maculatum sensu lato (s.l.). These results highlight 13 new associations between wild birds and ticks of the genus Amblyomma and reveal, for the first time, the presence of Amblyomma maculatum s.l. and rickettsiae from the Spotted Fever Group. These findings expand the knowledge of the epidemiology of ticks and rickettsial agents of public health importance in the region.

Seasonal dynamics of Amblyomma ticks in South America: A meta-analytical approach

In this study, we carried out a detailed analysis of the seasonality of ticks of the genus Amblyomma in the Neotropical region by means of a meta-analysis. Our aim was to identify temporal patterns and factors that influence the seasonality of these ectoparasites, considering different developmental stages (larvae, nymphs and adults) to provide a comprehensive understanding of the population dynamics of this group. To do this, we carried out a systematic review in databases such as Scopus and Web of Science. Studies that assessed the prevalence, abundance, or seasonality of Amblyomma ticks in the Neotropical region were included in our data collection. Despite our focus on the Neotropics, we only obtained data on South American populations. Multilevel meta-analytical models were used to test whether larvae, nymphs and adults of Amblyomma ticks show higher mean abundance, mean intensity and prevalence in the dry or in the rainy season. Our results validate that Amblyomma larvae, nymphs, and adults show distinct patterns of seasonality. During the dry season, larvae and nymphs occur more frequently, while adults predominate in the rainy season. We also observed variations in seasonal occurrence at the species level, highlighting the complexity and variability of these patterns. Thus, in summary, the data we provide here contributes to a better understanding on the temporal distribution of these ectoparasites, as well as the factors contributing for such distribution, thus providing subsidies for the development of more effective strategies for the control and prevention of tick-borne diseases. By showing research gaps in the literature, we also argue that further research on the seasonal patterns of ticks is needed to improve our understanding of the factors that influence the population dynamics of these parasites and to implementing more effective public health measures.

Environmental and ecological factors affecting tick infestation in wild birds of the Americas

The Americas hold the greatest bird diversity worldwide. Likewise, ectoparasite diversity is remarkable, including ticks of the Argasidae and Ixodidae families - commonly associated with birds. Considering that ticks have potential health implications for humans, animals, and ecosystems, we conducted a systematic review to evaluate the effects of bioclimatic, geographic variables, and bird species richness on tick infestation on wild birds across the Americas. We identified 72 articles that met our inclusion criteria and provided data on tick prevalence in wild birds. Using Generalized Additive Models, we assessed the effect of environmental factors, such as habitat type, climatic conditions, bird species richness, and geographic location, on tick infestation. Our findings show that most bird infestation case studies involved immature ticks, such as larvae or nymphs, while adult ticks represented only 13% of case studies. We found birds infested by ticks of the genera Amblyomma (68%), Ixodes (22%), Haemaphysalis (5%), Dermacentor (1%), and Rhipicephalus (0.8%) in twelve countries across the Americas. Our findings revealed that temperature variation and bird species richness were negatively associated with tick infestation, which also varied with geographic location, increasing in mid-latitudes but declining in extreme latitudes. Our results highlight the importance of understanding how environmental and bird community factors influence tick infestation in wild birds across the Americas and the dynamics of tick-borne diseases and their impact on biodiversity.

Migratory behaviour does not alter cophylogenetic congruence between avian hosts and their haemosporidian parasites

Parasites display various degrees of host specificity, reflecting different coevolutionary histories with their hosts. Avian hosts follow multiple migration patterns representing short but also long distances. As parasites infecting migratory birds are subjected to multiple environmental and biotic changes through their flyways, migration may disrupt or strengthen cophylogenetic congruence between hosts and parasites. On the one hand, parasites might adapt to a single migratory host, evolving to cope with the specific challenges associated with the multiple habitats occupied by the host. On the other, as migrants can introduce parasites into new habitats, higher rates of host switching could also disrupt cophylogenetic patterns. We analysed whether migratory behaviour shapes avian haemosporidian parasite–host cophylogenetic congruence by testing if contributions of host–parasite links to overall congruence differ among resident and short-, variable- and long-distance migrants globally and within South America only. On both scales, we found significant overall cophylogenetic congruence by testing whether overall congruence differed between haemosporidian lineages and bird species. However, we found no difference in contribution towards congruence among links involving resident vs migratory hosts in both models. Thus, migratory behaviour neither weakens nor strengthens bird–haemosporidian cophylogenetic congruence, suggesting that other avian host traits are more influential in generating phylogenetic congruence in this host–parasite system.

Haemosporidian taxonomic composition, network centrality and partner fidelity between resident and migratory avian hosts

Migration can modify interaction dynamics between parasites and their hosts with migrant hosts able to disperse parasites and impact local community transmission. Thus, studying the relationships among migratory hosts and their parasites is fundamental to elucidate how migration shapes host-parasite interactions. Avian haemosporidians are some of the most prevalent and diverse group of wildlife parasites and are also widely studied as models in ecological and evolutionary research. Here, we contrast partner fidelity, network centrality and parasite taxonomic composition among resident and non-resident avian hosts using presence/absence data on haemosporidians parasitic in South American birds as study model. We ran multilevel Bayesian models to assess the role of migration in determining partner fidelity (i.e., normalized degree) and centrality (i.e., weighted closeness) in host-parasite networks of avian hosts and their respective haemosporidian parasites. In addition, to evaluate parasite taxonomic composition, we performed permutational multivariate analyses of variance to quantify dissimilarity in haemosporidian lineages infecting different host migratory categories. We observed similar partner fidelity and parasite taxonomic composition among resident and migratory hosts. Conversely, we demonstrate that migratory hosts play a more central role in host-parasite networks than residents. However, when evaluating partially and fully migratory hosts separately, we observed that only partially migratory species presented higher network centrality when compared to resident birds. Therefore, migration does not lead to differences in both partner fidelity and parasite taxonomic composition. However, migratory behavior is positively associated with network centrality, indicating migratory hosts play more important roles in shaping host-parasite interactions and influence local transmission.