Mixed Infections in the Silkworm Bombyx mori L.: Pathogen Interactions, Disease Dynamics and Implications for Cocoon Productivity

Abstract

Sericulture represents an important agro-based industry that supports the livelihood of millions of farmers
worldwide, particularly in Asian countries such as India and China. The domesticated silkworm Bombyx mori
is highly susceptible to a wide range of pathogens, including viruses, bacteria, fungi and protozoa, which
significantly affect cocoon yield and silk quality. Among these disease conditions, mixed infections involving
two or more pathogens have emerged as a critical challenge in silkworm rearing systems. Mixed infections
frequently occur under field conditions due to environmental contamination, poor rearing hygiene and the
simultaneous presence of multiple pathogenic microorganisms. These infections often exhibit complex
interactions such as synergism, antagonism or competitive inhibition, which can alter disease severity and
host immune responses. Studies have demonstrated that combined infections involving pathogens such as B.
mori nucleopolyhedrovirus, cytoplasmic polyhedrosis virus, infectious flacherie virus and various bacterial
species can significantly increase larval mortality and reduce cocoon productivity compared with single
infections. The pathogenesis of mixed infections involves disruption of the silkworm midgut epithelium,
impairment of nutrient absorption, immune suppression and systemic spread of pathogens within the
host. Consequently, infected larvae exhibit reduced growth, prolonged larval duration and impaired silk
gland development, ultimately leading to substantial economic losses in sericulture. Understanding the
mechanisms underlying mixed pathogen interactions is therefore essential for developing effective disease
management strategies. This review synthesizes current knowledge on the occurrence, mechanisms, and
consequences of mixed infections in Bombyx mori. It also highlights host immune responses, pathogen
interactions, and their impact on silkworm physiology and productivity. Finally, the review discusses
emerging research directions, including molecular diagnostics, genomics-based resistance breeding and
integrated disease management approaches that could mitigate the impact of mixed infections and promote
sustainable sericulture production.