The AMA1 family of proteins has long fascinated parasitologists. These molecules sit at the apical tip of apicomplexan parasites, the group that includes the agents of malaria, cryptosporidiosis and toxoplasmosis, and they contribute to the invasion machinery that lets these organisms push their way into host cells. In Plasmodium, the malaria parasite, AMA1 has been extensively studied as a vaccine candidate because antibodies against it can block red blood cell invasion. Toxoplasma gondii carries several AMA1-like proteins, and previous work has shown that some of them are used at specific stages of the parasite’s life cycle. What has remained murky is the role of the sporozoite-specific member, sporoAMA1, which is predicted to be expressed when the parasite exists as a sporozoite inside the oocyst, the environmentally resistant stage shed in the feces of cats, the parasite’s definitive host.

To interrogate this protein, the team took a genetic approach, generating parasite lines in which the sporoAMA1 gene could be tagged and manipulated in its endogenous context. An early surprise came from the microscopy: when the researchers attempted to detect fluorescently tagged versions of the protein, the signal proved elusive, and endogenous tagging failed to yield detectable fluorescence. This kind of negative result is familiar to anyone working with low-abundance proteins in difficult-to-study life stages, and it underscores how technically demanding it is to study the sexual and environmental stages of T. gondii, which cannot be grown in standard cell culture the way the fast-replicating tachyzoite stage can.

However, the absence of a fluorescent signal did not mean the gene was silent. Using reverse transcription polymerase chain reaction, or RT-PCR, the researchers readily detected sporoAMA1 transcripts in bradyzoites, the slowly dividing stage that dwells inside tissue cysts during chronic infection; in the sexual stages that develop in the cat intestine; and in oocysts. The presence of messenger RNA across these stages suggested that the protein is genuinely expressed during the parts of the life cycle devoted to persistence and transmission, even if the protein itself is present at levels too low or in conformations too difficult to visualize with standard tagging strategies. The study also identified distinct forms of the sporoAMA1 protein across bradyzoites, sexual stages and oocysts, hinting at stage-specific processing or isoform usage that may fine-tune the protein’s function as the parasite transitions between environments as different as a host cell vacuole and the outside world.

The decisive experiments came from deleting or disrupting the gene and asking what happens to the parasite at each stage of its life cycle. In the tachyzoite stage, the rapidly dividing form responsible for acute disease, the answer was: essentially nothing. Parasites lacking functional sporoAMA1 grew normally in vitro, demonstrating that the protein is dispensable for the standard laboratory measures of tachyzoite fitness. This result is significant in itself, because it rules out a broad, housekeeping role in host-cell invasion during the acute phase and sharpens the question of why the parasite maintains this gene at all.

The answer emerged when the researchers turned to the chronic phase of infection. When mice were infected with parasites lacking sporoAMA1, the formation of tissue cysts was markedly impaired. Cyst formation is the process by which tachyzoites convert into bradyzoites and assemble the walled structures that can persist in brain and muscle tissue for the lifetime of the host. A reduced cyst formation rate means fewer persistent reservoirs of infection, and indeed the mutant parasites showed defects in establishing chronic infection. In practical terms, a parasite unable to express sporoAMA1 is a parasite that struggles to settle in for the long haul, which is precisely the strategy that makes T. gondii so successful in nature.

The defects did not stop at chronicity. The team also examined the parasite’s sexual cycle, which occurs exclusively in cats and culminates in the shedding of oocysts into the environment. Here again, loss of sporoAMA1 took a measurable toll: oocyst production was reduced, and the sporulation process, by which oocysts mature in the soil and become infectious to new hosts, was also inefficient. Oocyst yield and sporulation are the bottleneck steps of transmission for the foodborne and waterborne routes of toxoplasmosis, so a protein that influences both stages sits at a critical junction in the parasite’s epidemiology. Taken together, the phenotype of the sporoAMA1-deficient parasites traces a coherent arc: normal acute growth, defective chronic persistence, impaired sexual development, and compromised environmental transmission.

These findings reframe sporoAMA1 as a stage-dependent factor that links chronic infection and transmission, two phases of the parasite’s life that are often studied separately. The result also fits a broader pattern emerging from apicomplexan biology: different members of the AMA1 family appear to have been specialized for different life cycle stages and different host environments, rather than acting redundantly. For T. gondii, whose life cycle shuttles between asexual replication in intermediate hosts and sexual reproduction in cats, having a dedicated AMA1 protein for the sporozoite and sexual phases makes evolutionary sense, since the mechanical and immunological challenges of invading cells in the cat intestine or surviving sporulation in soil differ substantially from those faced by a tachyzoite in mouse blood.

The work also carries practical implications. Most current research into toxoplasmosis focuses on the tachyzoite stage because it is easy to culture, yet interventions aimed at blocking transmission would need to target the sexual and oocyst stages in cats or the sporozoite as it emerges from mature oocysts. A protein that is dispensable for tachyzoite growth but required for cyst formation, oocyst production and sporulation is an attractive candidate for such transmission-blocking strategies, whether through drugs, vaccines aimed at the definitive host, or genetic approaches to controlling oocyst shedding on farms and in the environment. The study’s demonstration that sporoAMA1 transcripts can be detected across bradyzoites, sexual stages and oocysts also provides researchers with a molecular handle for future work on stages that remain among the least accessible in the entire parasite.

As with any brief report, questions remain. The failure of endogenous tagging to produce detectable fluorescence leaves the precise subcellular localization of sporoAMA1 unresolved, and the distinct protein forms observed across stages invite deeper biochemical characterization. Whether the protein acts directly in invasion, in cyst wall biology, in oocyst wall assembly, or in some combination of these processes will require further study. Nevertheless, the core conclusion stands on solid genetic ground: removing sporoAMA1 leaves acute infection largely intact while undermining nearly every step that matters for persistence and spread. For a parasite whose global success rests on its ability to hide in tissue cysts and to seed the environment with hardy oocysts, that combination of vulnerabilities identifies sporoAMA1 as one of the more intriguing molecular targets to have emerged in toxoplasmosis research in recent years, and it offers a reminder that the most consequential stages of a parasite’s life are often the hardest ones to see in the laboratory.

Subject of Research: Stage-dependent function of the sporoAMA1 protein in chronic infection and transmission stages of Toxoplasma gondii

Article Title: Stage-dependent expression of sporoAMA1 links chronic infection and transmission in Toxoplasma gondii

Article References: Zhang, Z., Lin, Y., Xie, F., Xie, Y., Song, X., Liu, X., Suo, X., Tang, X., & Hu, D. (2026). Stage-dependent expression of sporoAMA1 links chronic infection and transmission in Toxoplasma gondii. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07650-4

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07650-4

Keywords: Toxoplasma gondii, sporoAMA1, AMA1 protein family, bradyzoites, tissue cysts, oocysts, sporulation, chronic infection, apicomplexan parasites, parasite transmission, host-cell invasion, Parasites & Vectors

Ethiopia’s stakes in this question are enormous. The country holds Africa’s largest livestock population, with a national herd of roughly 70.3 million cattle, 42.9 million sheep, 52.5 million goats and 8.1 million camels according to the Central Statistics Agency’s 2021 sample survey. Livestock supply animal protein, draft power for cultivation, transport, export earnings, organic fertiliser and household fuel, and they act as a financial buffer during crop failures. The sector contributes up to 40 percent of agricultural gross domestic product, nearly 20 percent of total GDP and about 20 percent of foreign exchange earnings. Any disease that quietly erodes calf growth therefore carries consequences that ripple through the national economy.

Coccidiosis is precisely such a disease. It is caused by Eimeria species, intracellular protozoa that invade and destroy the epithelial cells of the intestinal tract. Clinical cases present with diarrhoea, weight loss, fever, anorexia, emaciation and sometimes haemorrhagic dysentery and death. More insidiously, the majority of infections remain subclinical, yet they still reduce feed intake, impair feed conversion efficiency and slow weight gain. Subclinical cases account for more than 95 percent of total production losses attributed to the disease, and annual global losses have been estimated to exceed US$400 million. Affected calves may suffer growth retardation of up to two months, a delay that reshapes the lifetime productivity of a dairy animal.

More than a dozen Eimeria species have been described in cattle and buffalo, with Eimeria bovis, Eimeria zuernii and Eimeria auburnensis most frequently reported. E. bovis and E. zuernii are the most pathogenic, capable of severe disruption of intestinal absorption and substantial morbidity and mortality. The parasites display marked host specificity, restricting transmission largely to cattle. Calves acquire infection by ingesting sporulated oocysts shed in faeces, a process accelerated by communal housing, overcrowding and contaminated udders. The oocysts are environmentally formidable, surviving prolonged freezing at temperatures as low as minus 18 degrees Celsius and requiring only warmth and moisture to sporulate into their infective form over days to weeks.

The new study focused on Haramaya District, located roughly 500 kilometres east of Addis Ababa and 18 kilometres west of Harar, at altitudes between 1,600 and 2,100 metres. The area receives bimodal rainfall of approximately 492 to 866 millimetres annually, with temperatures ranging from 5.2 to 24 degrees Celsius, and mixed crop-livestock farming dominates. Haramaya town was purposively selected as the major urban dairy centre, while five surrounding kebeles, the local administrative units, were chosen by simple random sampling to represent peri-urban production systems. A preliminary census of all farms keeping calves under twelve months produced the sampling frame, from which individual calves were drawn by lottery, giving every eligible animal an equal chance of inclusion and minimising selection bias.

Fieldwork ran from November 2024 to May 2025, with sampling conducted during the dry season. Fresh faecal samples were collected directly from each calf, sealed in labelled leak-proof containers and transported in insulated cool boxes at roughly 4 to 8 degrees Celsius. In the laboratory, three grams of each sample were homogenised with 40 millilitres of sugar flotation solution of specific gravity 1.27, centrifuged at 1,500 revolutions per minute for five minutes, and the resulting surface film was examined microscopically at 40 times magnification for the characteristic oocysts. The sample size of 284 was calculated from an expected prevalence of 24.4 percent drawn from earlier work in the area, using standard epidemiological formulas for a 95 percent confidence interval.

The results showed that host characteristics and farm conditions mattered more than genetics or geography. Prevalence rose with age: calves aged six to under twelve months carried an infection rate of 27.3 percent, significantly higher than the 17.2 percent seen in calves younger than six months, a pattern the authors attribute to cumulative exposure to contaminated feed, water, bedding and animals over time. Calves in poor body condition showed a prevalence of 29.7 percent against 18.6 percent in those in good condition, though the cross-sectional design prevents any conclusion about whether malnutrition predisposed the animals to infection or the parasite drove them into decline. Farm hygiene produced the starkest contrast: 31.3 percent of calves on farms rated as poorly hygienic were positive, compared with 14.6 percent on well-kept farms.

Several expected risk factors, by contrast, proved statistically irrelevant. Sex was not associated with infection, suggesting male and female calves faced similar exposure. Breed made no significant difference, with crossbred Holstein Friesian crosses at 26.5 percent and local breeds at 21.3 percent, a finding consistent with the view that environmental and management conditions outweigh genetic susceptibility. Neither the management system, whether intensive housing or extensive free grazing, nor the individual kebele of origin was significantly linked to infection, implying that the crucial variable is not how a farm is organised but how cleanly it is run. Accumulated faeces, wet bedding, poor drainage and unhygienic feed and water troughs evidently matter more than the label attached to the production system.

The 22.5 percent prevalence sits squarely within the range reported across Ethiopia, matching figures from Dire Dawa, Wolaita Sodo, South Wollo, Bahir Dar and even Egypt, while remaining lower than rates of 62.5 percent in Asella and 68.1 percent in Addis Ababa and Debre Zeit. Earlier regional work has catalogued the local parasite fauna in detail, identifying six Eimeria species around Haramaya, with E. bovis and E. zuernii most common and mixed infections frequent. The present study, however, stopped at oocyst detection and did not identify species, so the reported figure should be read as the proportion of calves carrying detectable coccidia rather than as species-specific infection. The authors flag this as a key limitation and call for sporulation-based morphological identification and molecular characterisation, together with quantitative oocyst counts, in future work.

For farmers and veterinarians in East Hararghe, the practical message is unusually clear. Since hygiene status was the strongest modifiable predictor of infection, interventions targeting calf pen cleanliness, regular manure removal, dry and clean bedding, adequate drainage and well-maintained feeding and watering facilities could substantially cut exposure to Eimeria oocysts. Combined with routine health monitoring, attention to calf nutrition to protect body condition, and awareness that older calves accumulate exposure over months, such measures offer a low-cost path to reducing the hidden burden of subclinical coccidiosis. The authors recommend longitudinal follow-up studies with broader geographic coverage to clarify infection dynamics and quantify production losses, steps that would help convert these epidemiological findings into concrete gains for Ethiopia’s dairy-dependent rural households.

Subject of Research: Prevalence and risk factors of coccidiosis in calves in eastern Ethiopia

Article Title: Prevalence of Coccidiosis and Its Associated Risk Factors Among Calves in and Around Haramaya Town, Eastern Hararge, Oromia, Ethiopia

Article References: Jiru, B. T., & Emiru, A. Y. (2026). Prevalence of Coccidiosis and Its Associated Risk Factors Among Calves in and Around Haramaya Town, Eastern Hararge, Oromia, Ethiopia. Veterinary Medicine and Science, 12(5), Article e71245. https://doi.org/10.1002/vms3.71245

Image Credits: AI Generated

DOI: 10.1002/vms3.71245

Keywords: coccidiosis, Eimeria, calves, Ethiopia, livestock, parasitology, farm hygiene, veterinary epidemiology, dairy cattle, cross-sectional study, oocysts, body condition