Water quality and the incidence of Avian Malaria in the Western Cape, South Africa

Background/Question/Methods

Recent zoonotic epidemics have socio-economically impacted countries world-wide and affected public health and conservation efforts. Similarly, increasing human populations, particularly in Africa, are causing alterations to landscape integrity and disease epidemiology. Water quality and aquatic nutrient loads affect vector-borne disease prevalence by influencing the breeding success of the disease vectors. Such an influence on mosquito vectors is predicted to indirectly impact avian malaria prevalence. This study investigated the links between avian malaria prevalence in wetland passerine birds and water quality factors pertinent to the wetland site.

Nine hundred and seventy five (975) passerines were mist-netted and sampled from 26 separate wetland sites found along the coastal gradient of the Western Cape, South Africa. Blood smears were created from blood samples taken from each bird. Water quality measurements, including dissolved oxygen, temperature, electrical conductivity, salinity and pH, were taken at each wetland.

Results/Conclusions

One hundred and eighty three (19%) sampled birds were positive for avian malaria. One hundred and four (11%) individuals were infected with Plasmodium, 46 (5%) individuals were positive for Haemoproteus infection and 40 (4%) individuals were positive for Leucocytozoon infection. Fourteen birds (1%) exhibited a double infection of at least two haemosporidia. Salinity, electrical conductivity and temperature significantly influenced Leucocytozoon and Plasmodium prevalence. Site location in turn, was found to be influential to changing water quality.

These findings support previous research on malaria and emphasize the relationship between malarial epidemiology and the landscape in which it occurs. In the case of the avian malaria model, differing environmental factors proved influential for each species of haemosporidia, indicating that the pathogen species is a dictating factor. The influence of site location also highlights the dependence of vector-borne disease ecology upon vector biology, and vector tolerance to varying water quality.