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Flacherie (literally: "flaccidness") is a disease of silkworms, caused by silkworms eating infected or contaminated mulberry leaves. Flacherie infected silkworms look weak and can die from this disease. Silkworm larvae that are about to die from Flacherie are a dark brown.

There are two kinds of flacherie: essentially, infectious (viral) flacherie and noninfectious (bouffee) flacherie. Both are technically a lethal diarrhea.

Bouffée flacherie is caused by heat waves (bouffée means "sudden heat spell" in French).

Viral flacherie is ultimately caused by infection with Bombyx mori infectious flacherie virus (BmIFV, Iflaviridae), Bombyx mori densovirus (BmDNV, Parvoviridae) or Bombyx mori cypovirus 1 (BmCPV-1, Reoviridae). This either alone or in combination with bacterial infection destroys the gut tissue. Bacterial pathogens contributing to infectious flaccherie are Serratia marcescens, and species of Streptococcus and Staphylococcus in the form known as thatte roga.

Louis Pasteur, who began his studies on silkworm diseases in 1865, was the first one able to recognize that mortality due to viral flacherie was caused by infection. (Priority, however, was claimed by Antoine Béchamp.[1]) Richard Gordon described the discovery: "The French silk industry was meanwhile plummeting from a 130 million to an 8 million francs annual income, because the silkworms had all caught pébrine, black pepper disease…He [Pasteur] went south from Paris to Alais, and rewarded them by discovering the silkworm epidemic to be inflicted by some sort of living microbe…Pasteur threw in another disease, flâcherie, silkworm diarrhoea. The cures for both were culling the insects which showed the peppery spots — the peasants bottled the silkworm moths in brandy, for display to the experts — and rigorous hygiene of the mulberry leaf."[2]


  1. ^ A. Béchamp, "La maladie microzymateuse des vers à soie et les granulations moléculaires", Comptes rendus de l'Académie des sciences, 67 (1868), p. 443, available on Gallica.
  2. ^ Richard Gordon. The Alarming History of Medicine: Amusing Anecdotes from Hippocrates to Heart Transplants. New York: St. Martin’s Press, 1993. p. 19.