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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

FISH staining with a probe specific for Francisella tularensis in Dermacentor reticulatus oocytes after feeding on guinea pigs infected with F. tularensis subsp. holarctica.(A) Image obtained from light transmission; (B) Overlay image with blue signal for F. tularensis (23S rRNA probe for F. tularensis labelled with the fluorochrome Cy5) and red signal for universal eubacterial probe EUB338; (C) 23S rRNA probe for all F. tularensis; (D) universal eubacterial probe EUB338. Scale bar: 200 μm.
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pone.0133593.g005: FISH staining with a probe specific for Francisella tularensis in Dermacentor reticulatus oocytes after feeding on guinea pigs infected with F. tularensis subsp. holarctica.(A) Image obtained from light transmission; (B) Overlay image with blue signal for F. tularensis (23S rRNA probe for F. tularensis labelled with the fluorochrome Cy5) and red signal for universal eubacterial probe EUB338; (C) 23S rRNA probe for all F. tularensis; (D) universal eubacterial probe EUB338. Scale bar: 200 μm.

Mentions: In both tick species, FISH staining using the probe specific for F. tularensis revealed brightly stained bodies in in the oocytes, but also in the salivary glands (Figs 5 and 6).


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)

FISH staining with a probe specific for Francisella tularensis in Dermacentor reticulatus oocytes after feeding on guinea pigs infected with F. tularensis subsp. holarctica.(A) Image obtained from light transmission; (B) Overlay image with blue signal for F. tularensis (23S rRNA probe for F. tularensis labelled with the fluorochrome Cy5) and red signal for universal eubacterial probe EUB338; (C) 23S rRNA probe for all F. tularensis; (D) universal eubacterial probe EUB338. Scale bar: 200 μm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0133593.g005: FISH staining with a probe specific for Francisella tularensis in Dermacentor reticulatus oocytes after feeding on guinea pigs infected with F. tularensis subsp. holarctica.(A) Image obtained from light transmission; (B) Overlay image with blue signal for F. tularensis (23S rRNA probe for F. tularensis labelled with the fluorochrome Cy5) and red signal for universal eubacterial probe EUB338; (C) 23S rRNA probe for all F. tularensis; (D) universal eubacterial probe EUB338. Scale bar: 200 μm.
Mentions: In both tick species, FISH staining using the probe specific for F. tularensis revealed brightly stained bodies in in the oocytes, but also in the salivary glands (Figs 5 and 6).

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