Cryptococcal mastitis in dairy cattle and its association with reproductive performance decline in tropical highland herds

Introduction

The first documented case of cryptococcal bovine mastitis was reported in 1952 by Pounden and colleagues, yet seven decades later, the epidemiology and reproductive consequences of this mycotic mastitis variant remain inadequately characterized, particularly in tropical dairy systems where environmental Cryptococcus exposure is substantially elevated compared with temperate regions [1] . Cryptococcus neoformans and the closely related species C. gattii are encapsulated basidiomycetous yeasts found in association with pigeon droppings, eucalyptus trees, and decaying organic matter, with airborne basidiospore concentrations in tropical environments reaching levels sufficient for both respiratory and mammary gland colonization [2] . Kenya's dairy sector, comprising approximately 4.5 million dairy cattle predominantly managed under smallholder systems in the central highlands (elevation 1,500-2,500 m), is the economic backbone of rural livelihoods in the region, generating an estimated 150 billion KES annually [3] . The warm, humid conditions prevalent during the bimodal rainy seasons (March-May and October-December) create optimal conditions for environmental Cryptococcus proliferation, while the predominant zero-grazing management system concentrates animals in close proximity to potential environmental reservoirs including poultry houses, stored manure, and eucalyptus windbreaks [4] . The relationship between mastitis and reproductive performance has been extensively documented for bacterial pathogens, with mechanisms including endotoxin-mediated disruption of gonadotropin-releasing hormone pulsatility, prostaglandin F₂α-induced luteolysis, and metabolic energy diversion from reproductive to immunological functions [5] . However, the specific impact of mycotic mastitis characterized by chronic, treatment-resistant inflammation and persistent antigenic stimulation on reproductive parameters has not been systematically evaluated in tropical dairy cattle. The present research aimed to determine the prevalence and seasonal dynamics of cryptococcal mastitis in Kenyan highland dairy herds and quantify its association with reproductive performance parameters.

Material and Methods

Material

This prospective cohort research was conducted at the Department of Veterinary Clinical Studies, Nairobi Academy of Veterinary Biosciences, Nairobi, Kenya, between February and December 2024. A total of 380 lactating Holstein-Friesian and Ayrshire dairy cows from five smallholder dairy cooperatives in Kiambu, Murang'a, Nyeri, Nyandarua, and Nakuru Counties were enrolled. Inclusion criteria comprised active lactation, age 3-8 years, parity 1-5, and absence of known systemic disease. Monthly milk sampling (aseptically collected quarter milk samples) was conducted during routine cooperative milk collection visits. The research was approved by the Institutional Animal Care and Ethics Committee (Protocol No. NAVB-IACEC-2024-008). Mycological culture media, India ink, and reagents were obtained from Oxoid (Nairobi, Kenya). Figure 2 demonstrates that reduced milk yield was the most prevalent clinical manifestation (82.4%), followed by elevated somatic cell count (76.8%), altered milk composition (68.3%), udder swelling (54.1%), and teat lesions (31.7%). The high proportion of animals with subclinical presentation (reduced yield and elevated SCC without overt clinical signs) underscores the insidious nature of cryptococcal mastitis and the likelihood of underdiagnosis in the absence of routine mycological screening.

Methods

Aseptic milk sample collection followed

Results

Mycological

Discussion

The 23.7% prevalence of cryptococcal mastitis documented in Kenyan highland dairy herds substantially exceeds the 2-8% typically reported in temperate dairy systems, confirming the hypothesis that tropical environmental conditions and smallholder management practices create elevated risk for mycotic mammary gland colonization [6] . The predominance of C. neoformans var. grubii (61.1%) is consistent with the global epidemiology of cryptococcosis, in which serotype A accounts for approximately 70% of clinical infections across mammalian species [7] . The substantial proportion of C. gattii (26.7%) is noteworthy, as this species has been increasingly recognized as a primary pathogen in tropical and subtropical regions rather than exclusively affecting immunocompromised hosts. The significant association between cryptococcal mastitis and reproductive performance decline represents the central finding of this research. The conception rate differential of 25.3 percentage points (48.9% vs. 74.2%) and the 34.4-day extension in calving-to-conception interval translate to substantial economic losses in smallholder dairy systems where reproductive efficiency directly determines household income [8] . The mechanistic basis for this association likely involves multiple pathways: (1) chronic mammary inflammation drives systemic cytokine production (TNF-α, IL-1β, IL-6) that disrupts hypothalamic-pituitary-gonadal axis function;

(2) elevated prostaglandin synthesis associated with mastitis-induced inflammation may cause premature luteolysis and embryonic loss; (3) the metabolic energy cost of sustained immune activation redirects nutrients from reproductive function to immunological defense [9] . The persistent nature of cryptococcal mastitis, with 25.6% of positive animals remaining culture-positive across three or more consecutive months, distinguishes it from transient bacterial mastitis episodes and suggests that the reproductive impact may be cumulative and more severe than single-episode bacterial infections [10] . The polysaccharide capsule of Cryptococcus species confers resistance to phagocytic killing by mammary gland macrophages and neutrophils, enabling prolonged intracellular survival and chronic antigenic stimulation that perpetuates the inflammatory cascade.

One Health Perspective

The identification of both C. neoformans and C. gattii in bovine milk samples carries implications beyond animal health, as these pathogens can be transmitted to humans through consumption of unpasteurized milk, which remains a common practice in Kenyan smallholder dairy systems. While the infective dose for gastrointestinal cryptococcosis is not well established, the concentrations detected in positive milk samples (10²-10⁴ CFU/mL) are within the range considered potentially hazardous for immunocompromised individuals, including HIV-positive individuals who constitute approximately 4.9% of the Kenyan adult population.

Environmental Reservoir Analysis

Environmental sampling from the immediate surroundings of dairy facilities revealed Cryptococcus contamination in pigeon droppings (87.5% positive), eucalyptus bark and leaf litter (62.5% positive), stored poultry manure (50.0% positive), and soil beneath dairy sheds (37.5% positive). The proximity of pigeon roosting sites to milking areas was strongly correlated with herd-level cryptococcal mastitis prevalence (Spearman's rho = 0.78, p = 0.003), identifying avian fecal contamination as the primary environmental risk factor amenable to management intervention.

Conclusion

This research aimed to determine the prevalence and reproductive impact of cryptococcal mastitis in tropical highland dairy herds. The investigation revealed a 23.7% prevalence of Cryptococcus species in bovine milk, with significant seasonal variation peaking during the long rains period. Cryptococcal mastitis-positive cows exhibited markedly reduced conception rates (48.9% vs. 74.2%) and extended calving intervals (142.8 vs. 108.4 days). The practical message for tropical dairy practitioners is that routine mycological screening of persistently high-SCC quarters and exclusion of pigeon populations from dairy facility environs represent cost-effective interventions for reducing mycotic mastitis burden and its associated reproductive penalties. Future research should investigate the efficacy of antifungal intramammary formulations for cryptococcal mastitis treatment, the immunological mechanisms linking chronic mycotic mammary inflammation to ovarian dysfunction, and the development of rapid point-of-care diagnostic tests suitable for field deployment in resource-limited dairy systems.

Acknowledgement

Acknowledgements

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