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Parasites & vectors2013; 6(1); 306; doi: 10.1186/1756-3305-6-306

Amblyomma cajennense is an intrastadial biological vector of Theileria equi.

Abstract: The apicomplexan hemoprotozoan parasite Theileria equi is one of the etiologic agents causing equine piroplasmosis, a disease of equines that is endemic throughout large parts of the world. Before 2009 the United States had been considered to be free of this parasite. Occasional cases had occurred but there was no evidence for endemic vector-borne transmission in the U.S. until a 2009 outbreak in Texas in which Dermacentor variabilis and Amblyomma cajennense were implicated as vectors. Although D. variabilis has previously been shown to be a competent laboratory vector, studies suggested A. cajennense was not a competent transstadial vector, even though the presence of this tick species on horses in South American is epidemiologicaly correlated with higher a prevalence of infection. In this study we tested the transstadial and intrastadial vector competence of D. variabilis and A. cajennense for T. equi. Methods: A tick passaged T. equi strain from the Texas outbreak and ticks colonized from engorged females collected off horses on the outbreak ranch in Texas were used for these studies. Nymph or adult ticks were fed on infected horses and transmission fed on naïve horses. Infections were tracked with PCR and serology, dissected tick tissues were tested with PCR. Results: A. cajennense transmitted T. equi intrastadially when adult ticks acquired infection by feeding on an infected horse, and transmitted to a naïve host on subsequent reattachment and feeding. D. variabilis failed to transmit in the same experiment. Transstadial transmission was not successful for either tick species. PCR on DNA isolated from eggs of females that had fed on an infected horse suggests that there is no transovarial passage of this parasite by either tick species. Conclusions: This work confirms that ticks from the Texas population of A. cajennense are competent intrastadial vectors of T. equi. We propose that the most likely natural mode of transmission for this parasite/vector combination in the Texas outbreak would have been biological transmission resulting from adult male ticks moving between infected and uninfected horses. The intrastadial mode of transmission should be considered as one equally possible scenario whenever implicating vectors of T. equi.
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Publication Date: 2013-10-23 PubMed ID: 24499587PubMed Central: PMC4028807DOI: 10.1186/1756-3305-6-306Google Scholar: Lookup
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  • Non-P.H.S.

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research article discusses a study conducted to test the capacity of two tick species in transmitting the Theileria equi parasite, a causative agent of equine piroplasmosis. The study revealed that the Amblyomma cajennense tick is a competent intrastadial vector of the parasite.

Research Context

  • The cause of concern in the study is Theileria equi, an apicomplexan hemoprotozoan parasite leading to equine piroplasmosis, a disease affecting horses.
  • Though the United States was considered free of this parasite until 2009, an outbreak in Texas revealed Dermacentor variabilis and Amblyomma cajennense ticks as potential vectors.
  • Previous studies have indicated D. variabilis as a competent laboratory vector. However, initial studies suggested A. cajennense may not be a competent transstadial vector, despite being linked with higher infection rates in South America.

Study Approach and Methodology

  • The researchers used a T. equi strain passed through ticks during the Texas outbreak and ticks cultivated from engorged females gathered from horses on the outbreak ranch for the tests.
  • They fed nymph or adult ticks on infected horses and then allowed them to feed on naïve horses. This was done to monitor the transmission of the parasite.
  • The presence of infections was tracked through Polymerase Chain Reaction (PCR) and serology (study of blood serums).

Findings of the Study

  • A. cajennense ticks acted as intrastadial vectors, successfully transmitting T. equi when the adult ticks fed on an infected horse, and transferred it to a naïve host upon subsequent reattachment and feeding.
  • In the same experiment, D. variabilis failed to transmit the parasite, and transstadial transmission was found unsuccessful in both tick species.
  • Further PCR tests on DNA isolated from the offspring of females that had fed on an infected host suggested that neither of the tick species passes this parasite through their eggs (transovarial transmission).

Conclusion

  • Findings provided validation that the Texas population of A. cajennense ticks could efficiently transmit T. equi on an intrastadial basis.
  • The authors propose that the most plausible explanation for the breakout in Texas was the biological transmission of the parasite via adult male ticks moving between infected and uninfected horses.
  • The study strongly affirms that the capability for intrastadial transmission should be viewed as an equally likely possibility for vectors of T. equi.

Cite This Article

APA
Scoles GA, Ueti MW. (2013). Amblyomma cajennense is an intrastadial biological vector of Theileria equi. Parasit Vectors, 6(1), 306. https://doi.org/10.1186/1756-3305-6-306

Publication

Parasites & vectors
ISSN: 1756-3305
NlmUniqueID: 101462774
Country: England
Language: English
Volume: 6
Issue: 1
Pages: 306

Researcher Affiliations

Scoles, Glen A
  • USDA, ARS, Animal Disease Research Unit, 3003 ADBF, Washington State University, Pullman, WA 99164, USA. Scoles@vetmed.wsu.edu.
Ueti, Massaro W

    MeSH Terms

    • Animals
    • Disease Vectors
    • Female
    • Horse Diseases / parasitology
    • Horse Diseases / transmission
    • Horses
    • Ixodidae / parasitology
    • Male
    • Polymerase Chain Reaction
    • Texas
    • Theileria / genetics
    • Theileria / isolation & purification
    • Theileriasis / parasitology
    • Theileriasis / transmission

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    This article has been cited 10 times.
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