Pathogenic Prototheca Species in Veterinary and Human Health

Prototheca spp. are unique, achlorophyllous unicellular algae that have emerged as opportunistic pathogens in both animals and humans. Five species, notably Prototheca wickerhamii, Prototheca zopfii genotypes I and II, Prototheca blaschkeae and Prototheca cutis, have been implicated in a spectrum of diseases ranging from bovine mastitis to human cutaneous, articular and systemic infections. In veterinary settings, Prototheca zopfii genotype II is a leading cause of acute mastitis, triggering severe inflammation, milk production losses and economic impact on dairy farms worldwide. In humans, infections are rare but often severe in immunocompromised hosts, with cutaneous lesions, arthritis or life-threatening disseminated disease. Diagnosis remains challenging owing to low awareness and the absence of rapid, specific laboratory assays. Treatment options are limited by intrinsic resistance to standard antifungals and high variability in drug susceptibility between species and even strains. Recent advances in genomics, cell biology and integrated omics have begun to elucidate host–pathogen interactions, pathogen evolution and metabolic pathways that underpin virulence. A One Health perspective emphasises the ecological resilience of Prototheca in environmental reservoirs, the potential for interspecies transmission and the urgent need for novel diagnostics, effective therapeutics and farm management strategies to mitigate both veterinary and public health risks.

Research from Nature Portfolio

Recent studies have delineated the molecular basis of Prototheca pathogenicity and evolutionary adaptation. In models of bovine mastitis, Prototheca zopfii genotype II was shown to invade mammary epithelial cells and macrophages, inducing mitochondrial-mediated apoptosis and a robust pro-inflammatory response characterised by upregulation of Bax, cytochrome-c, Apaf-1, caspase-9 and caspase-3 alongside downregulation of Bcl-2. This dual mechanism of inflammation and programmed cell death underlies tissue damage and clinical severity in infected glands. Complementing these findings, comparative organellar genome sequencing of Prototheca zopfii genotypes I and II revealed drastic compaction of mitochondrial and plastid genomes, loss of photosynthesis-related genes and absence of plastid-encoded RNA polymerases. Transcriptional activity of these reduced plastid genomes suggests nuclear-encoded compensatory mechanisms and offers insights into the evolutionary trajectory of pathogenic Prototheca spp. and their host-adapted lifestyle.

Pathogenic Prototheca Species in Veterinary and Human Health publication trend

The graph below shows the total number of articles in pathogenic prototheca species in veterinary and human health across all publications each year (not limited to Nature Index journals).

Technical terms

Protothecosis: Infection caused by Prototheca algae, manifesting in cutaneous, articular or systemic disease.

Unicellular achlorophyllous algae: Single-celled algae lacking chlorophyll, unable to photosynthesise, some species pathogenic to vertebrates.

Bovine mastitis: Inflammation of the cow’s mammary gland, often caused by bacterial or algal pathogens, leading to reduced milk yield and quality.

Genotype: Genetic variant within a species; in Prototheca zopfii, genotype II is associated with acute mastitis.

Mitochondrial apoptosis: Programmed cell death initiated by mitochondrial signalling, involving release of cytochrome-c and activation of caspases.

Algicidal: Capable of killing algal cells; contrasted with algistatic, which inhibits algal growth without necessarily killing cells.

One Health: An integrative approach recognising the interconnection between human, animal and environmental health in disease emergence and control.

References

1. Integration of transcriptomics, proteomics, and metabolomics data for the detection of the human pathogenic Prototheca wickerhamii from a One Health perspective. Frontiers in Cellular and Infection Microbiology (2023).
2. Drug Susceptibility Profiling of Prototheca Species Isolated from Cases of Human Protothecosis. Antimicrobial Agents and Chemotherapy (2023).
3. Prototheca Infections and Ecology from a One Health Perspective. Microorganisms (2022).
4. Prototheca zopfii genotype II induces mitochondrial apoptosis in models of bovine mastitis. Scientific Reports (2020).
5. Genome sequencing of Prototheca zopfii genotypes 1 and 2 provides evidence of a severe reduction in organellar genomes. Scientific Reports (2018).