Toxoplasma gondii is an obligate intracellular protozoan that cycles between felids, its only definitive hosts, and a vast range of warm-blooded intermediate hosts, including humans. Most infections are asymptomatic, but the parasite can cause devastating disease in immunocompromised individuals and severe congenital abnormalities when acquired during pregnancy. Humans typically become infected by eating tissue cysts in undercooked meat or by ingesting sporulated oocysts shed in cat faeces that contaminate soil, water, and food. Ground-foraging birds are considered excellent sentinels of environmental contamination because they peck in soil where oocysts persist, and because infection in birds is usually subclinical, allowing viable tissue cysts to accumulate in muscle and organs over long periods.

The research team, led by Ruth Ifeoluwapo Ayoade Akinbobola of the University of Abuja, collected brain, heart, and thigh muscle from 162 free-range birds: 102 chickens, 30 pigeons, and 30 guinea fowl drawn from all six area councils of the Federal Capital Territory. Sampling ran from August 2025 to February 2026, spanning both the rainy and dry seasons. The investigators used a semi-nested polymerase chain reaction targeting the B1 gene, a multicopy locus present in roughly 35 copies per parasite genome, which yields a characteristic amplicon of about 145 base pairs in the second round of amplification. Positive samples were then Sanger-sequenced and compared with reference sequences from GenBank.

The results showed that 22 of the 162 birds carried T. gondii DNA, an overall detection rate of 13.6 percent with a 95 percent confidence interval of 9.1 to 19.7 percent. Prevalence was highest in chickens at 16.7 percent, followed by pigeons at 10.0 percent and guinea fowl at 6.7 percent, though these interspecies differences were not statistically significant. Positives were spread across the territory: chickens tested positive in all six area councils, pigeons in Kuje and Gwagwalada, and guinea fowl in Bwari and Kwali. Council-level prevalence ranged from 7.4 percent in Abaji to 22.2 percent in Kuje, a geographic spread that was also not statistically significant, suggesting that exposure to the parasite is widespread rather than clustered in particular localities.

The single strongest association with infection was seasonal. Birds sampled during the rainy season, from August to October 2025, tested positive at a rate of 24.7 percent, compared with just 2.5 percent during the dry season from November 2025 to February 2026. This tenfold difference was highly significant, and rainy-season birds had approximately 13 times higher odds of PCR positivity, with an odds ratio of 12.78. Monthly prevalence declined steadily from 31.2 percent in August to zero in December and February. The pattern fits the biology of the parasite: T. gondii oocysts survive and sporulate far better in warm, moist conditions, while the desiccating Harmattan winds and low humidity of the dry season likely curtail environmental persistence. The authors caution, however, that sampling covered only seven months, so the seasonal pattern should be confirmed across a full annual cycle.

The study also found a striking metabolic signature of infection. PCR-positive chickens weighed significantly less than their PCR-negative counterparts, with mean body weights of 1,284.8 grams versus 1,819.4 grams, a difference that was highly significant. Similar directional differences appeared in pigeons and guinea fowl, though the small number of positive birds in those species, three and two respectively, meant the comparisons were descriptive rather than statistically testable. Notably, histopathological examination of brain and liver sections from 66 birds, including all 22 PCR-positive animals, failed to reveal tissue cysts or tachyzoites under the light microscope, a reminder that focal, low-burden infections can evade histological detection and that PCR positivity reflects parasite DNA rather than confirmed viable infection.

Genetic analysis of the parasite sequences added an intriguing dimension. Three high-quality B1 gene sequences, all from chickens and deposited in GenBank under accessions PZ576184, PZ576185, and PZ576186, shared 100 percent nucleotide identity with one another across a 108-base-pair conserved core region. In a neighbour-joining phylogenetic tree, they clustered with reference sequences from Egypt, Iran, Mexico, and India, and differed by only two to four nucleotides from previously reported chicken-derived sequences from Plateau State in north-central Nigeria. The authors are careful to interpret this correctly: the B1 locus is highly conserved across T. gondii populations worldwide, so this clustering reflects sequence conservation rather than evidence of shared recent ancestry or epidemiological connectivity. Higher-resolution tools such as multilocus sequence typing or whole-genome approaches would be needed to resolve lineage structure.

The detection in guinea fowl stands out as the study’s most novel contribution. Although viable T. gondii has previously been isolated from feral guinea fowl in Brazil, and clinical outbreaks have been documented in Brazil and the United States, molecular evidence of natural infection in this species had never been reported from Africa. This matters because guinea fowl, Numida meleagris, is an indigenous African bird and a widely consumed source of animal protein across the continent. Infected birds destined for the table could contribute to foodborne transmission where meat is inadequately cooked or improperly handled, particularly given that previous Nigerian research in Benue State demonstrated haplotype sharing among T. gondii sequences from free-range chickens, pigs, and seropositive pregnant women.

The FCT chicken prevalence of 16.7 percent sits within a broader African and global context. It is lower than the 30.6 percent reported in Benue State and far below the 83.3 percent documented in Plateau State, differences the authors attribute to variation in environmental oocyst contamination, cat density, climate, husbandry practices, and methodology, including the use of the more sensitive 529-base-pair repetitive element in some earlier studies. Regionally, the FCT figure exceeds the 9.5 percent reported from Libya, matches the 13.9 percent from Ghana, and falls well below the 79.0 percent from humid highland Kenya. Globally, it aligns with a pooled molecular prevalence of 18.7 percent for birds, confirming consistency with established avian toxoplasmosis epidemiology.

The authors frame their findings within a One Health perspective, arguing that free-range poultry deserve a place in zoonotic disease surveillance programmes in the Federal Capital Territory as sentinels of environmental contamination. They also suggest that food-safety education targeting pregnant women and immunocompromised individuals could be usefully timed around the rainy season, when infection pressure appears highest. At the same time, the study is candid about its limitations: sampling sites were purposively selected, many birds were obtained from live-bird markets where rearing history was unknown, tissue pooling precluded tissue-specific detection, and the B1 target is less sensitive than the 529-base-pair element, meaning the reported prevalence may be conservative. Even so, the message is clear: the parasite that silently infects billions of people is circulating among the birds of Nigeria’s capital, and the chickens pecking in village soil may be telling public health authorities something worth hearing.

Subject of Research: Molecular detection of Toxoplasma gondii in free-range avian hosts in Nigeria

Article Title: Molecular detection and partial B1 gene sequence analysis of Toxoplasma gondii in free-range chickens, pigeons, and guinea fowl from the Federal Capital Territory, Nigeria

Article References: Akinbobola, R. I. A., Akinbobola, J. S., Ejiofor, C. E., Jolayemi, K. O., Nafarnda, W. D., & Opara, M. N. (2026). Molecular detection and partial B1 gene sequence analysis of Toxoplasma gondii in free-range chickens, pigeons, and guinea fowl from the Federal Capital Territory, Nigeria. Discover Animals, 3(1), Article 90. https://doi.org/10.1007/s44338-026-00255-2

Image Credits: AI Generated

DOI: 10.1007/s44338-026-00255-2

Keywords: Toxoplasma gondii, free-range chickens, guinea fowl, pigeons, Nigeria, B1 gene, semi-nested PCR, zoonotic disease, One Health, food safety, avian toxoplasmosis, seasonal prevalence

T cell exhaustion was first characterized in the context of chronic viral infections, where researchers observed that T cells exposed to persistent antigen stimulation lost their ability to produce key inflammatory molecules such as interleukin-2 and tumour necrosis factor. Over time, these cells also lost cytotoxic function, the very machinery they use to kill infected or malignant cells. Cancer, particularly solid tumours, creates a similar situation of chronic antigen exposure. Tumour cells continuously present mutated or overexpressed proteins that T cells can recognize, but instead of a swift, decisive attack, the interaction stretches into months or years. This perpetual stimulation, combined with a suppressive tissue environment, drives T cells into increasingly dysfunctional states.

The tumour microenvironment amplifies this process through multiple converging pressures. Solid tumours are frequently hypoxic, meaning oxygen levels are low, which restricts the metabolic activity T cells require to sustain an energetic response. Nutrient competition is fierce, as rapidly dividing cancer cells consume glucose and amino acids such as glutamine, leaving T cells starved of fuel. Lactic acid secreted by tumours acidifies the surroundings and further impairs immune metabolism. On top of these metabolic constraints, tumour cells and associated stromal cells release immunosuppressive signalling molecules, including transforming growth factor beta and prostaglandins, while recruiting regulatory T cells and myeloid-derived suppressor cells that actively dampen immune attack. Each of these forces contributes to the progressive erosion of T cell function.

A crucial insight from recent research is that exhaustion is not a single uniform state but a spectrum of differentiation. Studies using single-cell RNA sequencing and T cell receptor tracking have revealed that exhausted populations contain both progenitor-like cells and terminally exhausted cells. Progenitor exhausted T cells retain a limited capacity to proliferate and can persist over time, serving as a reservoir from which other exhausted cells arise. Terminal exhausted cells, by contrast, are locked into a dysfunctional program marked by the loss of proliferative potential and reduced effector cytokine production. This distinction matters enormously for therapy, because checkpoint blockade immunotherapies appear to depend heavily on reinvigorating the progenitor compartment rather than resurrecting the terminal cells directly.

Central to the molecular identity of exhausted T cells is the transcription factor TOX, which becomes highly expressed as exhaustion deepens. TOX does not act alone; it works within broader gene regulatory networks that reshape the cell’s identity. Exhausted T cells express inhibitory receptors such as PD-1, TIM-3, LAG-3 and TIGIT on their surface, which serve as markers of the exhausted state and, in some cases, actively transmit suppressive signals. They also shift their metabolic profile, relying more heavily on fatty acid oxidation and oxidative phosphorylation rather than the glycolytic metabolism that characterizes robustly activated T cells. These changes are not merely consequences of a hostile environment; they reflect a fundamental reprogramming of cellular identity.

That reprogramming is epigenetic in nature, and this is one of the most consequential findings in the field. Exhausted T cells accumulate stable chromatin modifications that lock in their dysfunctional gene expression patterns. Enhancer regions that once supported the expression of effector molecules are remodelled and silenced, while new regulatory elements are opened to sustain inhibitory receptor expression. The result is a state that resists simple reversal. Even when the source of chronic antigen stimulation is removed, exhausted T cells often fail to return to their original functional program, because the epigenetic landscape that governed it has been irreversibly altered. This epigenetic rigidity helps explain why some patients respond spectacularly to immune checkpoint inhibitors while others derive little benefit.

Immune checkpoint blockade, exemplified by antibodies against PD-1 and CTLA-4, has transformed the treatment of melanoma, lung cancer, kidney cancer and several other malignancies. These therapies work in part by interrupting the inhibitory signals that exhaust T cells receive. Yet the overall response rates across cancer types remain far from universal, and the review underscores that the depth of exhaustion within a patient’s tumour infiltrating lymphocytes is a major determinant of success. Tumours with abundant progenitor exhausted T cells that still retain proliferative capacity tend to respond better, whereas tumours dominated by terminal exhaustion or lacking T cell infiltration altogether, sometimes described as cold tumours, respond poorly. This understanding has fuelled efforts to combine checkpoint inhibitors with other interventions that can broaden and deepen immune responses.

Among the most promising strategies is the combination of checkpoint blockade with therapies that reshape the tumour microenvironment itself. Agents that block transforming growth factor beta signalling, deplete regulatory T cells, or reprogramme myeloid suppressor cells may relieve some of the pressures driving exhaustion in the first place. Metabolic interventions, such as drugs that improve oxygen delivery or alter nutrient availability, represent another frontier. Oncolytic viruses and radiation therapy can convert cold tumours into inflamed ones by releasing tumour antigens and provoking innate immune activation, drawing fresh waves of T cells into the tumour that have not yet undergone exhaustion. Adoptive cell therapies, including chimeric antigen receptor T cells and tumour infiltrating lymphocyte therapy, introduce freshly armed immune cells but face the same risk of becoming exhausted once they encounter the suppressive tumour milieu, prompting efforts to engineer them with enhanced fitness and resistance to suppression.

Looking ahead, the review highlights the potential of manipulating the epigenetic and transcriptional programs that define exhaustion. Drugs targeting DNA methylation and histone modification are already approved for certain cancers, and researchers are investigating whether such agents can loosen the epigenetic locks that keep exhausted T cells dysfunctional. More precise approaches may one day selectively reprogramme the enhancer landscape of exhausted T cells, restoring effector function while preserving the cells’ tumour specificity. Single-cell and spatial profiling technologies continue to refine the map of exhaustion states within tumours, enabling clinicians to stratify patients according to the immunological character of their disease and to monitor how therapies shift T cell states over time.

Decoding T cell exhaustion in the tumour microenvironment is ultimately about recovering a lost weapon. The immune system already possesses cells capable of eliminating cancer; the challenge is that tumours have learned to wear them down through chronic stimulation and environmental hostility. By dissecting the transcriptional, epigenetic and metabolic architecture of exhaustion, researchers are converting what once seemed like an irreversible defeat into a set of addressable molecular mechanisms. Each layer of understanding brings the field closer to combination therapies that can prevent exhaustion, reverse it in its earlier stages, or work around it when it has become entrenched, offering new hope for patients whose cancers have so far resisted the immune system’s grasp.

Subject of Research: T cell exhaustion in the tumour microenvironment and its implications for cancer immunotherapy

Article Title: Decoding T cell exhaustion in the tumour microenvironment

Article References: Park, J. A., Im, J., & Hwang, S.-M. (2026). Decoding T cell exhaustion in the tumour microenvironment. Experimental & Molecular Medicine, 58(8), 2590-2602. https://doi.org/10.1038/s12276-026-01809-w

Image Credits: AI Generated

DOI: 10.1038/s12276-026-01809-w

Keywords: T cell exhaustion, tumour microenvironment, immunotherapy, PD-1, checkpoint blockade, TOX, epigenetics, cancer, inhibitory receptors, single-cell sequencing, Decoding, cell