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Updated: Jun 19, 2026
An Electroporation Method to Transform Rickettsia spp. with a Fluorescent Protein-Expressing Shuttle Vector in Tick Cell Lines
Published on: October 11, 2022
EXPERIMENTS ON THE CONVERSION OF TYPHUS STRAINS
1Laboratory of the American Hospital, Mexico City, and the Institute of Hygiene, Popotla, Mexico.
Abstract:
TWO TYPES OF STRAINS OF TYPHUS VIRUS ARE OBSERVED IN MEXICO: first the murine type which is obtained from wild rats in nature, from isolated endemic cases, and from cases during short epidemic outbreaks, and second, the epidemic type of strains which is obtained from long standing serious epidemics. Some of these epidemic strains correspond entirely to strains of historic Old World typhus. Other strains which in their experimental behavior are intermediate between these two types of strains were isolated from the same epidemic. A method is described by which these epidemic non-orchitic strains can be converted into murine strains regularly causing scrotal lesion in guinea pigs and a highly fatal disease in rats. The same results were obtained with an Old World strain of epidemic typhus. The method, which consists of daily blood injections into intraperitoneally inoculated rats, is based on the observation that Rickettsia prowazeki multiplies only within cells which come in constant or frequent contact with fresh blood. It is concluded from our experiments that there does not exist any real difference between the virus of historic Old World typhus and the murine New World typhus. Both are considered to be of murine origin. The murine strains represent the original form of the virus of typhus, whereas the epidemic strains are the result of a prolonged propagation in the cycle man-louse-man.
Insights
Murine typhus and epidemic typhus strains are not distinct. A novel method converts epidemic strains into murine strains, suggesting both originate from murine sources.
Area of Science:
- Microbiology
- Infectious Diseases
- Epidemiology
Background:
- Typhus fever presents as murine and epidemic types in Mexico.
- Epidemic strains can resemble historic Old World typhus strains.
- Intermediate strains have been isolated from epidemics.
Purpose of the Study:
- To investigate the relationship between murine and epidemic typhus strains.
- To develop a method for converting epidemic typhus strains into murine strains.
- To determine the origin of typhus virus strains.
Main Methods:
- Daily blood injections into intraperitoneally inoculated rats were used.
- This method leverages the multiplication of Rickettsia prowazeki in cells with frequent blood contact.
- Experimental conversion of epidemic non-orchitic strains to murine strains was performed.
Main Results:
- Epidemic strains were successfully converted into murine strains, causing scrotal lesions in guinea pigs and fatal disease in rats.
- This conversion was also achieved with an Old World epidemic typhus strain.
- The experimental manipulation demonstrated the plasticity of typhus strains.
Conclusions:
- There is no fundamental difference between Old World and New World typhus viruses.
- Both typhus types are considered to be of murine origin.
- Murine strains represent the original form, while epidemic strains result from human-to-human transmission cycles.
