First record of fatal Plasmodium relictum (GRW4) infection in a highly endangered Fatu Hiva monarch (Pomarea whitneyi) fledgling: a case report.

backgroundThe Fatu Hiva monarch (Pomarea whitneyi) is a Critically Endangered (IUCN) passerine species restricted to a single island in French Polynesia, with fewer than 20 individuals remaining. In the Pacific region, avian malaria caused by Plasmodium relictum lineage GRW4 is a major conservation concern because it has been linked to severe population declines and extinctions in Hawai'i and poses a documented threat to endemic birds in New Zealand. CASE PRESENTATION: On 17 June 2022, a recently fledged juvenile Fatu Hiva Monarch (Pomarea whitneyi) was found dead in its natural habitat on Fatu Hiva. A necropsy was performed on site in humid tropical conditions, with real-time online guidance from an expert based in Switzerland. Gross examination revealed severe emaciation, an empty gastrointestinal tract, diffuse pallor with scant intravascular blood and hepatosplenomegaly with dark discolouration. Despite advanced autolysis having occurred, cytologic tissue imprint and blood-smear assessment revealed high parasitaemia with intraerythrocytic developmental stages and abundant birefringent malarial pigment. Histopathology confirmed a hemozoin-producing haemosporidian infection due to the presence of widespread polarisation-positive and Prussian blue-negative intracytoplasmic pigment in erythrocytes and macrophages. Molecular testing was performed on dried blood pressed onto household filter paper, that had been stored and shipped at ambient temperature for several weeks. Nested cytochrome b polymerase chain reaction and sequencing confirmed a single infection with the GRW4 lineage of Plasmodium relictum.

conclusionsThis first confirmed fatal case of avian malaria in this critically depleted island endemic species highlights the urgent need to integrate disease surveillance and vector management into conservation planning. The results suggest that acute severe P. relictum (GRW4) infection was the proximate cause of death, likely occurring against a background of prolonged negative energy balance and chronic stress exposure. Although the direction of causality cannot be fully determined post-mortem, aggressive malaria prevention measures remain justified to avoid further demographic decline in the critically low Fatu Hiva monarch population. To effectively reduce risk, vector control measures must be combined with measures to enhance host resilience and continuous surveillance to monitor transmission and guide adaptive management. Furthermore, this case study shows that a scientifically defensible, lineage-level diagnosis can be achieved using simple, low-cost samples and techniques adapted for remote tropical fieldwork, even when carcass quality is compromised by warm, humid conditions.