# Anuran amphibian Hemoparasites over the Last Century: Advances, Challenges, and Future Prospects: A Systematic Review

## TL;DR

This review summarizes a century of research on blood parasites in frogs and toads, highlighting progress, gaps, and the need for better global studies.

## Contribution

The study provides a systematic review of hemoparasite research in anurans, identifying geographic and methodological gaps and suggesting ways to improve future research.

## Key findings

- Most studies focused on North and South America, with limited research in biodiverse tropical regions like Africa and the Amazon.
- Morphological methods dominated parasite identification, with few studies using molecular techniques.
- Protozoans like Hepatozoon and Trypanosoma were the most commonly reported parasites.

## Abstract

Over the last century, scientists have reported blood parasites in frogs and toads, but we still lack a clear picture of how common they are, where they occur, and what they mean for wildlife’s health. We reviewed 83 studies published between 1924 and 2024 to bring together what is known. Scientific activity has increased since the 2000s and has been concentrated in North and South America. Most studies used microscopy to search for and identify parasites in blood smears, and far fewer combined microscopy with DNA methods that improve detection. The parasites most often reported include protozoans in the groups Hepatozoon and Trypanosoma, as well as microfilariae. On the host side, studies focused on a few Anuran amphibians. Large gaps persist in tropical regions with high biodiversity, such as parts of Africa, Asia, and the Andes–Amazon area. Filling these gaps is important because these parasites can affect the health, survival, and reproduction of amphibians, which are key to healthy ecosystems. Our work highlights practical steps—strengthening local capacities, expanding sampling, and sharing clear methods—to monitor these infections and support conservation and environmental monitoring.

Hemoparasites are intracellular organisms that affect groups of vertebrates, including amphibians, yet their diversity, distribution, and ecological effects remain partially understood. This systematic review analyzed advances over the past one hundred years in the study of hemoparasites in anurans, emphasizing: (1) the geographical distribution of studies, (2) the diagnostic techniques employed, and (3) the diversity of parasites and hosts involved. To this end, 83 scientific articles published between 1924 and 2024 were reviewed, following PRISMA guidelines and within an adapted PICO framework. The results reveal a notable increase in publications since the 2000s, with a concentration in North and South America. Morphological studies predominated (69.9%), while only 22.9% combined morphological and molecular techniques and 9.6% used only molecular techniques. Protozoan genera such as Hepatozoon and Trypanosoma, as well as nematodes (microfilariae) of the family Filaroidea, were frequently reported (69.7%); on the host side, the most studied anuran families were Ranidae (34.6%), Hylidae (6.9%), and Bufonidae (21.5%). Important methodological gaps were evident, particularly biodiverse tropical regions such as Central Africa, Southeast Asia, the Andean-Amazon, and Central America. These findings underscore the need to strengthen local research capacities, expand sampling efforts, and standardize diagnostic protocols to advance knowledge of hemoparasite diversity, ecology, and their role in ecosystem health.