“Understanding how ecological and behavioural factors shape parasite infections is key to predicting disease dynamics in wildlife,” said Mduduzi Ndlovu of the School of Biology and Environmental Sciences at the University of Mpumalanga. “The findings highlight the extraordinary diversity of Afrotropical bird pathogens and show that infection risk is shaped by a complex interplay of host ecology, behaviour and environment, offering new insights into the ecology and evolution of wildlife diseases.”
Described in the introduction by fellow Arghya Sengupta as “a rising star in African ecological sciences who is addressing knowledge gaps in species adaptation”, Ndlovu said: “Birds caught my attention growing up. I had an outdoor upbringing and caught and ate birds before I could identify them. I can’t remember when I didn’t know how to do that. I received huge amounts of knowledge from my great-grandparents.”
Ndlovu is now one of very few African ornithologists licensed to catch and ring all species.
He described his STIAS experience as “an opportunity to sit, eat and reflect on some of the things we love the most” – in his case that’s researching birds.
Bugs on the wing
He explained that there are 870 recorded bird species in South Africa and probably about a 1000 in southern Africa. This represents 8% of all the bird species diversity in the world. “But there is little research centred on southern Africa. Most of what we know is from the Northern Hemisphere.”
“Birds are found on nearly every continent,” he continued. “They adapt to different habitats. The migration pattern is the big thing – helping both to spread and escape infection. They can literally bring infections from one continent to another within a few days.”
And it’s the bugs (or pathogens) that the birds carry and can potentially spread to other species that are of interest to Ndlovu. This includes cellular/living parasites like protozoa, fungi and bacteria, and non-living or acellular parasites like viruses and prions. In multiple studies in and around South Africa’s Kruger National Park, he has investigated the prevalence, diversity and physiological impacts of avian blood parasites, including Haemoproteus, Plasmodium, Leucocytozoon, Trypanosoma and filarial nematodes.
Reservoirs of infection
“Screening more than 1000 birds representing over 80 species has revealed an overall infection prevalence of about 30% and more than 100 parasite lineages, over half of which are new to science,” he said.
“We are asking what the effect of the infection is on the bird host as well as what drives infection in the system – some of which may be key indicators in the next pandemic. It’s crucial for us to understand the crossover to other species and to humans.”
“Birds are essentially reservoirs of zoonosis potential,” he continued. “Pathogens circulate between the vector (a mosquito, for example) and the bird with some instances of crossover to other animals and people.” He used the iconic example of Oxpeckers – known as Vampire birds – commonly found in sub-Saharan Africa, who form an intimate connection with large mammals like buffaloes, rhinos, zebra and giraffe from whom they feed on ticks, dead skin and parasites.
The work has found that infection in birds is influenced by multiple factors including the birds’ habits and behaviours, weather patterns − especially rainfall and temperature (all now further impacted by climate change), the role of human habitats in the system, biogeography, host life-history traits and the landscape. “Interestingly, landscape and host are the primary drivers of infection. We would have thought temperature.”
“Parasite occurrence varied with host behaviour, foraging strata and movement patterns, and infections peaked during the wet season. Wet summers equal increased prevalence,” he added.
Ndlovu noted that malaria is of concern - Haemosporidian – the specific malaria parasite found in birds had an overall prevalence of 28.4% with a higher prevalence in birds found in groups compared to solitary birds.
In addition to looking for the presence of parasites, Ndlovu also studies the effect of the infections on the bird’s body (including body condition, mass and structure, and clinical signs of disease) and the bird’s immune response.
“We do both infection screening and genomic sequencing,” he said.
“Contrary to expectation, we have found that infections had little negative effect on body condition or physical stress indicators, suggesting tolerance in many hosts. Most bird’s body condition is not affected by blood parasites, but they have an elevated immune response. So, it seems they are in tune with evolution.”
“We can pick up active infection and test later to find no infection. Being able to clear infection is a good thing in the long run if the external stressors don’t change.”
The work has also compared invasive to native bird species finding that the native species have a higher prevalence of infection. “Comparing invasive house sparrows with native grey-headed sparrows revealed lower infection rates in the invader, supporting the enemy release hypothesis,” he said. (This hypothesis explains why invasive species thrive in new environments free from the pathogens usually encountered in their natural environment.)
Going forward, Ndlovu noted that the emerging zoonotic arboviruses of concern include West Nile and Usutu both of which are found in Red-Billed Oxpeckers and are known to be able to cross over to other species including humans. “West Nile is something humans can get from birds so it’s a cause for concern.”
“We need to know what we have and what will cross over so that we can prepare for possible future zoonotic pandemics,” he said.
Although there is not enough previous in-depth research to do detailed comparisons and some of the sample sizes are too small to make substantial conclusions, Ndlovu hopes that this work will lead to modelling that can predict emerging infections. “Ideally we can develop robust emerging-infection models and tracking tools,” he said. “I hope we can have a complete wildlife-disease tracking tool one day.”
In discussion, Ndlovu also described some of the challenges in the field. “We catch the birds via mist-nets and walk-in traps – using bird calls to lure them. There’s lots of waiting. But it’s a strictly controlled field. Taking birds from the nets is a skill and each bird requires different treatment methods. The health of the birds comes first, and no birds are lost in the research.”
“We also use rings and other technology that can be read and tracked anywhere in the world.”
In answer to a question, he also reflected on why so few African researchers are involved in this field and the need for the inclusion of more indigenous knowledge. “Children aren’t encouraged to study birds. It’s not well understood. And if you study them, then what – who employs a bird expert?”
“Licencing is also problematic. Many people have exceptional bird-identification skills but only have primary school education. The licencing process doesn’t test them in a way that shows their skills. This needs to change – we are missing out on indigenous knowledge. If it’s not in the formal sector it’s not recognised.”
“There’s a vast amount of local knowledge about birds. The knowledge has always been there,” he said.