pebrine

Pebrine is a contagious disease of the silkworm (Bombyx mori) caused by the microsporidian parasite Nosema bombycis. The infection primarily affects the larval stage, producing a characteristic speckled or “peppery” appearance of the cocoon, which gave the disease its name. Infected larvae may exhibit reduced appetite, stunted growth, and higher mortality, leading to severe losses in sericulture.

The disease was first described in the 18th century, but its etiology remained unknown until the mid‑19th century, when French chemist Louis Pasteur identified the microscopic spores as the cause. Pasteur’s work on pebrine, including the development of diagnostic microscopy and hygiene protocols, helped rescue the French silk industry and established foundational principles of epidemiology.

Transmission occurs vertically through infected eggs and horizontally via contaminated rearing equipment, food, and environmental spores. The parasite penetrates the mid‑gut epithelium, proliferates, and produces durable spores that persist in the environment for years. Diagnosis relies on microscopic examination of larval hemolymph or gut contents for the distinctive oval spores.

Control strategies focus on strict hygienic practices, selection of disease‑free breeding stock, and the destruction of infected material. Modern sericulture also employs resistant silkworm strains and, in some regions, controlled temperature regimes to inhibit spore germination. While pebrine incidence has declined in major silk‑producing countries, it remains a concern for small‑scale producers and for the preservation of heritage silkworm lines. Ongoing research aims to improve molecular diagnostics and develop integrated pest‑management approaches.