Illustration of a Harris's antelope squirrel looking through a microscope revealing a world of parasites.

Unveiling the Microscopic World of Antelope Squirrels: A New Parasite Species Discovered

Nico Varela in Science & Nature September 2025 • 4 min read.

"Scientists identify a novel species of Eimeria parasite in Harris's antelope squirrels, offering insights into the biodiversity and health of these desert rodents."

The vast and diverse world of parasites is often hidden from view, yet these organisms play a critical role in ecosystems. Recent research has uncovered a previously unknown species of parasite residing within Harris's antelope squirrels, adding another piece to the puzzle of biodiversity. This finding not only expands our knowledge of parasite species but also has implications for understanding the health and ecological interactions of these desert rodents.

Harris's antelope squirrels (Ammospermophilus harrisii) are active inhabitants of the arid landscapes of the southwestern United States and Mexico. These diurnal creatures, known for their year-round activity and omnivorous diets, thrive in rocky terrains. Despite their well-documented presence in these regions, the parasites that call these squirrels home have remained largely unexplored—until now.

A new study has identified and characterized a novel species of Eimeria, a type of parasitic coccidian, in Harris's antelope squirrels. Coccidia are single-celled, spore-forming parasites that commonly infect the intestinal tracts of animals. This discovery marks the first report of coccidia in this particular species of squirrel, offering valuable insights into the host-parasite relationships within this ecosystem.

What is Eimeria ammospermophili and How Was It Discovered?

Illustration of a Harris's antelope squirrel looking through a microscope revealing a world of parasites.

The newly identified parasite, named Eimeria ammospermophili, was described from a small percentage (7%) of Harris's antelope squirrels examined in Arizona. The sporulated oöcysts—the infective stage of the parasite—are ovoidal to ellipsoidal, measuring approximately 29.0 x 22.7 micrometers. These oöcysts possess a distinctive pitted, bi-layered wall, an oöcyst residuum (a leftover mass of material), and occasionally a polar granule. The sporocysts themselves are ellipsoidal, measuring around 11.0 x 7.9 micrometers, and contain a Stieda body (a structure involved in sporozoite release) and a sporocyst residuum.

Researchers collected fecal samples from live-trapped Harris's antelope squirrels in Usery Mountain Regional Park, Arizona, between February and September 2018. These samples were carefully processed using a solution of potassium dichromate (K2Cr2O7) to promote the sporulation of oöcysts. Microscopic examination then allowed for the identification and detailed characterization of the Eimeria species.

Sample Collection: Fecal samples were meticulously gathered from traps and handling bags.
Preservation: Samples were placed in vials containing a 2.0% aqueous solution of K2Cr2O7.
Screening: Centrifugal flotation in modified Sheather's solution was used to screen for coccidian oöcysts.
Sporulation: Samples with oöcysts were macerated in Petri dishes with a thin layer of 2.0% aqueous K2Cr2O7 and kept at room temperature for 5-12 days to allow sporulation.
Measurements: Thirty oöcysts were measured using a calibrated ocular micrometer.

In addition to the new species, the study also documented the presence of Eimeria vilasi in one of the examined squirrels. This represents the first time E. vilasi has been reported in Harris's antelope squirrels, expanding the known host range of this parasite. The oöcysts of E. vilasi found in the squirrels were consistent with previous descriptions of the species.

Why This Discovery Matters

This discovery of Eimeria ammospermophili and the new host record for Eimeria vilasi contribute to a broader understanding of parasite diversity and host-parasite interactions. As the first coccidian species described from Harris's antelope squirrels, it lays the groundwork for future research into the potential impacts of these parasites on squirrel health, population dynamics, and the overall desert ecosystem. Further investigations could explore the prevalence of these parasites in different squirrel populations, their effects on squirrel physiology and behavior, and their role in the transmission of other pathogens. This knowledge is crucial for effective wildlife management and conservation efforts.

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Everything You Need To Know

What is Eimeria ammospermophili, and how is it different from other Eimeria species?

Eimeria ammospermophili is a newly discovered species of parasitic coccidian identified in Harris's antelope squirrels. It differs from other Eimeria species in its unique morphological characteristics. The sporulated oocysts, the infective stage, are ovoidal to ellipsoidal, measuring approximately 29.0 x 22.7 micrometers, and feature a distinctive pitted, bi-layered wall, an oocyst residuum, and occasionally a polar granule. The sporocysts are ellipsoidal, around 11.0 x 7.9 micrometers, containing a Stieda body and a sporocyst residuum. These specific measurements and structural details distinguish Eimeria ammospermophili, highlighting its unique parasitic adaptation within Harris's antelope squirrels.

How was Eimeria ammospermophili discovered in Harris's antelope squirrels?

The discovery of Eimeria ammospermophili involved a multi-step process. Researchers collected fecal samples from live-trapped Harris's antelope squirrels in Usery Mountain Regional Park, Arizona. These samples were preserved in a 2.0% aqueous solution of potassium dichromate (K2Cr2O7) to promote sporulation. The samples were then screened using centrifugal flotation in modified Sheather's solution to find coccidian oocysts. Samples containing oocysts were kept at room temperature for 5-12 days to allow sporulation. Microscopic examination of these samples allowed for the identification and detailed characterization of the Eimeria species based on their morphology, leading to the discovery of the novel Eimeria ammospermophili.

What role do parasites like Eimeria ammospermophili play in the ecosystem of Harris's antelope squirrels?

Parasites such as Eimeria ammospermophili play a critical role in the ecosystem by influencing the health, behavior, and population dynamics of their hosts, Harris's antelope squirrels. While the specific impact is still under investigation, the presence of the parasite can affect the squirrels' physiology, potentially impacting their nutritional status, immune response, and overall fitness. Furthermore, the parasite's presence adds to the biodiversity of the ecosystem and can interact with other pathogens, influencing disease transmission and ecological interactions. Understanding these interactions is crucial for effective wildlife management and conservation efforts.

Besides Eimeria ammospermophili, what other parasite was found in the Harris's antelope squirrels, and what does this finding suggest?

Besides the novel Eimeria ammospermophili, the study also documented the presence of Eimeria vilasi in one of the examined Harris's antelope squirrels. This finding is significant as it marks the first reported occurrence of E. vilasi in this species of squirrel, expanding the known host range of this parasite. This suggests that the host-parasite relationships within the ecosystem of Harris's antelope squirrels are more complex than previously understood. It also highlights the importance of ongoing research to fully understand the diversity of parasites and their impact on wildlife health and ecosystem dynamics. It could indicate potential overlap and competition between Eimeria species within a single host.

What are the implications of the discovery of Eimeria ammospermophili and the first record of Eimeria vilasi for the conservation of Harris's antelope squirrels?

The discovery of Eimeria ammospermophili and the new host record for Eimeria vilasi have significant implications for the conservation of Harris's antelope squirrels. These findings provide a foundation for future research into the impacts of these parasites on squirrel health, population dynamics, and the overall desert ecosystem. Understanding the prevalence of these parasites, their effects on squirrel physiology and behavior, and their role in the transmission of other pathogens is crucial for effective wildlife management and conservation strategies. This knowledge can help in monitoring squirrel populations, assessing disease risks, and implementing appropriate measures to protect these animals and their habitat.