Abstract
The following note describes modifications made in the Weigl method for cultivating rickettsiae and other small agents of disease within susceptible lice. Made primarily to facilitate isolations from diseased persons, they involve feeding larvae reared under sterile conditions on potentially infected blood.
The technique is essentially as follows. From 200-400 adult lice (Pediculus vesti-menti) are washed for 2 minutes in 60% alcohol and subsequently with sterile physiological saline. They are then enclosed in a cage (6 × 3 × 1 cm) covered on one side with a fine net and containing within it the piece of cloth recommended by Weigl. The caged lice are fed twice daily on a healthy nourisher whose skin is first sterilized with 70% alcohol. Between feedings the cages are kept in sterile paper boxes at 34°C. Under these circumstances, masses of eggs are laid on the cloth. These eggs are removed and washed first with 30% alcohol or other suitable weak disinfectant and then with sterile saline, bacterial sterility of the washed eggs being checked by culturing the last drops of the saline wash on nutrient agar. The: sterile eggs are dried on sterile paper and incubated at 34°C in sterile net-covered cages, 200-400 eggs per cage. The eggs hatch after 4 to 6 days and the larvae are then ready for use.
When used to isolate rickettsiae or other agents of disease from a patient, such a cage of larvae is fed sterilely and twice daily over a period of four to twelve days, depending on the disease being investigated. To do this, the net side of the cage is attached to the sterilized skin on the medial side of the forearm or shank. Sterilization is affected with ether followed by 70% alcohol, care being taken to be sure that the alcohol has completely evaporated before feeding begins. Bacterial sterility is routinely checked by seeding larval excrement to agar plates.
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