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Francisella tularensis: No Evidence for Transovarial Transmission in the Tularemia Tick Vectors Dermacentor reticulatus and Ixodes ricinus.

Genchi M, Prati P, Vicari N, Manfredini A, Sacchi L, Clementi E, Bandi C, Epis S, Fabbi M - PLoS ONE (2015)

Bottom Line: Transmission electron microscopy and fluorescence in situ hybridization showed F. tularensis within oocytes.However, cultures and bioassays of eggs and larvae were negative; in addition, microscopy techniques revealed bacterial degeneration/death in the oocytes.We can speculate that Francisella does not have a defined reservoir, but that rather various biological niches (e.g. ticks, rodents), that allow the bacterium to persist in the environment.

View Article: PubMed Central - PubMed

Affiliation: National Reference Laboratory for Tularemia, Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna "Bruno Ubertini", Pavia, Italy.

ABSTRACT

Background: Tularemia is a zoonosis caused by the Francisella tularensis, a highly infectious Gram-negative coccobacillus. Due to easy dissemination, multiple routes of infection, high environmental contamination and morbidity and mortality rates, Francisella is considered a potential bioterrorism threat and classified as a category A select agent by the CDC. Tick bites are among the most prevalent modes of transmission, and ticks have been indicated as a possible reservoir, although their reservoir competence has yet to be defined. Tick-borne transmission of F. tularensis was recognized in 1923, and transstadial transmission has been demonstrated in several tick species. Studies on transovarial transmission, however, have reported conflicting results.

Objective: The aim of this study was to evaluate the role of ticks as reservoirs for Francisella, assessing the transovarial transmission of F. tularensis subsp. holarctica in ticks, using experimentally-infected females of Dermacentor reticulatus and Ixodes ricinus.

Results: Transmission electron microscopy and fluorescence in situ hybridization showed F. tularensis within oocytes. However, cultures and bioassays of eggs and larvae were negative; in addition, microscopy techniques revealed bacterial degeneration/death in the oocytes.

Conclusions: These results suggest that bacterial death might occur in oocytes, preventing the transovarial transmission of Francisella. We can speculate that Francisella does not have a defined reservoir, but that rather various biological niches (e.g. ticks, rodents), that allow the bacterium to persist in the environment. Our results, suggesting that ticks are not competent for the bacterium vertical transmission, are congruent with this view.

No MeSH data available.


Related in: MedlinePlus

TEM micrographs of Ixodes ricinus pre-vitellogenic oocyte after feeding on guinea pigs infected with F. tularensis subsp. holarctica.The morphology of some inclusions is typical of a Gram-negative bacterium, and their size is congruent with that of bacteria from the Francisella genus. m: mithocondrium, b: bacterium. Scale bar: A 0.22 μm, B 1.1 μm.
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pone.0133593.g003: TEM micrographs of Ixodes ricinus pre-vitellogenic oocyte after feeding on guinea pigs infected with F. tularensis subsp. holarctica.The morphology of some inclusions is typical of a Gram-negative bacterium, and their size is congruent with that of bacteria from the Francisella genus. m: mithocondrium, b: bacterium. Scale bar: A 0.22 μm, B 1.1 μm.

Mentions: TEM examination of D. reticulatus and I. ricinus ovaries during and at the end of oviposition showed that the oocytes contain Gram-negative coccobacillar bacteria of approximately 0.4 μm, referable to F. tularensis (Fig 3).


Francisella tularensis: No Evidence for Transovarial Transmission in the Tularemia Tick Vectors Dermacentor reticulatus and Ixodes ricinus.

Genchi M, Prati P, Vicari N, Manfredini A, Sacchi L, Clementi E, Bandi C, Epis S, Fabbi M - PLoS ONE (2015)

TEM micrographs of Ixodes ricinus pre-vitellogenic oocyte after feeding on guinea pigs infected with F. tularensis subsp. holarctica.The morphology of some inclusions is typical of a Gram-negative bacterium, and their size is congruent with that of bacteria from the Francisella genus. m: mithocondrium, b: bacterium. Scale bar: A 0.22 μm, B 1.1 μm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4526560&req=5

pone.0133593.g003: TEM micrographs of Ixodes ricinus pre-vitellogenic oocyte after feeding on guinea pigs infected with F. tularensis subsp. holarctica.The morphology of some inclusions is typical of a Gram-negative bacterium, and their size is congruent with that of bacteria from the Francisella genus. m: mithocondrium, b: bacterium. Scale bar: A 0.22 μm, B 1.1 μm.
Mentions: TEM examination of D. reticulatus and I. ricinus ovaries during and at the end of oviposition showed that the oocytes contain Gram-negative coccobacillar bacteria of approximately 0.4 μm, referable to F. tularensis (Fig 3).

Bottom Line: Transmission electron microscopy and fluorescence in situ hybridization showed F. tularensis within oocytes.However, cultures and bioassays of eggs and larvae were negative; in addition, microscopy techniques revealed bacterial degeneration/death in the oocytes.We can speculate that Francisella does not have a defined reservoir, but that rather various biological niches (e.g. ticks, rodents), that allow the bacterium to persist in the environment.

View Article: PubMed Central - PubMed

Affiliation: National Reference Laboratory for Tularemia, Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna "Bruno Ubertini", Pavia, Italy.

ABSTRACT

Background: Tularemia is a zoonosis caused by the Francisella tularensis, a highly infectious Gram-negative coccobacillus. Due to easy dissemination, multiple routes of infection, high environmental contamination and morbidity and mortality rates, Francisella is considered a potential bioterrorism threat and classified as a category A select agent by the CDC. Tick bites are among the most prevalent modes of transmission, and ticks have been indicated as a possible reservoir, although their reservoir competence has yet to be defined. Tick-borne transmission of F. tularensis was recognized in 1923, and transstadial transmission has been demonstrated in several tick species. Studies on transovarial transmission, however, have reported conflicting results.

Objective: The aim of this study was to evaluate the role of ticks as reservoirs for Francisella, assessing the transovarial transmission of F. tularensis subsp. holarctica in ticks, using experimentally-infected females of Dermacentor reticulatus and Ixodes ricinus.

Results: Transmission electron microscopy and fluorescence in situ hybridization showed F. tularensis within oocytes. However, cultures and bioassays of eggs and larvae were negative; in addition, microscopy techniques revealed bacterial degeneration/death in the oocytes.

Conclusions: These results suggest that bacterial death might occur in oocytes, preventing the transovarial transmission of Francisella. We can speculate that Francisella does not have a defined reservoir, but that rather various biological niches (e.g. ticks, rodents), that allow the bacterium to persist in the environment. Our results, suggesting that ticks are not competent for the bacterium vertical transmission, are congruent with this view.

No MeSH data available.


Related in: MedlinePlus