Traveling while diseased: Avian migration and Haemosporidian parasites
Relapse of otherwise latent haemosporidian infections and transmission peak occur in the spring, and there is evidence that many individuals of migratory Passeriformes are infected with haemosporidian parasites prior to travelling to, and returning from, wintering areas. Yet, we know little about how birds simultaneously deal with costly haemosporidian infections and the physiological demands of migration.
I am particularly interested in answering the following questions: 1) While in wintering grounds, do migratory birds lose infections acquired in the breeding grounds? 2) Prior to migration, do birds clear or suppress haemosporidian infections? 3) Once on their wintering grounds, do infections acquired on the breeding grounds relapse, or are parasites from the breeding grounds replaced by parasites from resident host assemblages? 4) What are the physiological costs of migrating while infected with haemosporidian parasites? 5) What are the carryover effects of infections acquired in wintering grounds? I am currently tackling questions #1–3 using data from bird captures of North American birds wintering in the Dominican Republic and in The Bahamas.
Estimating the effects of individual parasite lineages in host populations across space
Collaborator: Dr Robert E. Ricklefs
In the archipelago of the Lesser Antilles, there are several idiosyncrasies in how avian haemosporidian lineages are distributed. However, four lineages of avian malaria parasites are remarkably widespread, both in space and across host species. I use mathematical models to estimate individual infection probabilities for particular lineages, and estimate the relative contribution of host assemblage composition, island area, and parasite competition in the likelihood of infection. These models will provide robust estimates of how infection probabilities change across islands and host species, highlighting specific host populations under threat by these pathogens and guiding priorities on conservation and management of species.
Temporal dynamics of avian malaria parasites in the archipelago of the West Indies
The unique biogeography of the West Indian archipelago, located southeast of the North America in the Caribbean region, allows one to use island history to understand host-parasite interactions and their evolutionary relationships over time. In the Pleistocene, ca. 20 K yr. ago, sea level dropped up to 120 m due to the expansion of continental ice sheets, leading to the coalescence of several island masses in the archipelago. Organisms could freely disperse across islands within the past several thousand years using exposed land bridges, and tending to homogenize assemblages of hosts and their pathogens across islands currently isolated by seawater. I use the the geologic history of the islands as a natural experiment to determine parasite turnover rates over millennial time scales.
Co-infections of haemosporidian and trypanosome parasites in a North American songbird
Organisms in nature frequently have multiple parasitic infections, yet patterns of parasite co-occurrenceare poorly documented. I ask whether two common avian blood parasites, one haemosporidian and one trypanosome, affect each other’s occurrence in individuals of a single host species. I use molecular genotyping to survey protozoan parasites in the peripheral blood of yellow-breasted chats (Aves: Passeriformes: [Parulidae] Icteria virens) from the Ozarks of southern Missouri. I found a positive association between the occurrence of the haemosporidian and trypanosome parasites, such that infection by one parasite increases the probability of infection by the other. published at Parasitology.
Low prevalence of haemosporidian parasites of shorebirds in Argentina
Collaborators: Dr Robert E. Ricklefs; Graciela Escudero & Victor A.S. Penha
Migratory shorebirds (Charadriiformes) face physiological stress during migration and experience a wide range of vector-suitable habitats across their distributions, thought haemosporidian parasites (order Haemosporida) have been rarely detected in these species worldwide. We ask whether shorebirds that engage long-distance latitudinal migrations on the Western Hemisphere remain infection-free, even when wintering on sites where parasite transmission is known to occur. We test the hypothesis that parasite prevalence is higher in shorebirds wintering in inland areas associated with freshwater and abundant landbird populations, compared to shorebirds wintering in coastal habitats. We found that haemosporidian infections are rare in shorebirds even when these co-occur with landbird species in inland areas suitable for parasite transmission. published at Ardea.
Epidemiology of Cutaneous Leishmaniasis in human populations of Central Amazonia
Collaborators: Dr Gonçalo Ferraz, and Dr Fernando Abad-Franch.
Cutaneous leishmaniasis (CL) is a tropical neglected disease that occurs in Central and South America, as well as in some regions of the African continent and the Middle East. Ulcerative lesions that develop at or near the vector’s bite site typically characterize CL, which is caused by parasites of the genus Leishmania, and transmitted by phlebotominae sand flies. In South America, the disease cycle is mainly sylvatic, meaning that humans are accidental disease hosts. Generally, in forested areas, sand flies would feed on sloths, armadillos and other small mammals, and humans would get occasionally infected if they were exposed to habitats where both vectors and wild hosts are found. Since men are usually the ones that engage in activities that involve being in contact with habitats where transmission is likely, such as hunting and logging, disease incidence tends to be higher among males than their female counterparts. However, experimental infections in mice has also revealed that females, not only tend to develop the disease less often than males, but also present less severe lesions when clinical symptoms are present. Hence, one can ask whether male-biased disease incidence is solely due to differential exposure or is also a consequence of sex-related differences in the immune ability to cope with Leshmania spp. infection.
That was exactly the question I tackled for my MSc thesis research in the Instituto Nacional the Pesquisas da Amazônia. The study was just published on line in the journal Tropical Medicine and International Health, in which we investigated whether sex-biased CL incidence levels off when exposure time to CL vector habitats is comparable among sexes. We compared disease incidence between two populations from central Amazon: one composed by rural settlers, where exposure is male biased; and other composed by field researchers of the Biological Dynamics of Forest Fragments Project, where both males and females are similarly exposed to forested environments. Interestingly, at low levels of exposure disease incidence is higher among males in both populations, suggesting the existence of a sex-related and endocrine-mediated immunity against these parasitic infections. However, as exposure time increases, this suggested effect of higher immunity among females wears off, and disease incidence becomes comparable among sexes. Another relevant finding was that CL incidence among field researchers is eleven times higher than among rural settlers, which brings to attention a new disease risk group that deserves awareness. published at Tropical Medicine & International Health