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Infectivity of three Anaplasma marginale isolates for Dermacentor andersoni
Abstract:
Three isolates of Anaplasma marginale--Virginia (VAM), Illinois (IAM), and Florida (FAM)--were compared for infectivity for Dermacentor andersoni. The isolates were selected, in part, because of a tail-like appendage that has been demonstrated in the VAM and IAM, but not in the FAM. Ticks were exposed to the isolates as nymphs either naturally by feeding on a calf with anaplasmosis or artificially by percutaneous inoculation with infected bovine erythrocytes. They were examined for infectivity after molting to the adult stage by determining their capability to transmit the disease to susceptible calves and by demonstrating colonies in tick gut sections. Only those ticks exposed to the VAM proved to be infected with A marginale; ticks naturally exposed and those artificially infected with this isolate transmitted the disease to susceptible calves. Colonies of A marginale were observed only in gut tissues of ticks naturally infected with VAM. The IAM (appendage present) and FAM (appendage absent) could not be found in ticks exposed by either method, indicating that factors other than the presence of inclusion appendages may be involved in infection of ticks by A marginale.
Insights
Only the Virginia isolate of Anaplasma marginale infected Dermacentor andersoni ticks, enabling disease transmission. Other isolates, regardless of appendage presence, did not infect ticks, suggesting other factors are involved.
Area of Science:
- Veterinary Entomology
- Molecular Pathogenesis
- Tick-borne Diseases
Background:
- Anaplasma marginale causes anaplasmosis, a significant cattle disease.
- Tick vectors, such as Dermacentor andersoni, are crucial for Anaplasma marginale transmission.
- Morphological variations, like tail-like appendages in some A. marginale isolates, have been observed but their role in tick infectivity is unclear.
Purpose of the Study:
- To compare the infectivity of three Anaplasma marginale isolates (Virginia, Illinois, Florida) for Dermacentor andersoni ticks.
- To investigate the role of morphological features, specifically tail-like appendages, in tick infection by A. marginale.
Main Methods:
- Dermacentor andersoni nymphs were exposed to three Anaplasma marginale isolates (VAM, IAM, FAM) via natural feeding on infected calves or artificial inoculation.
- Adult ticks were assessed for infectivity by their ability to transmit anaplasmosis to susceptible calves.
- Tick gut sections were examined for the presence of Anaplasma marginale colonies.
Main Results:
- Only ticks exposed to the Virginia isolate (VAM) became infected with Anaplasma marginale.
- Both naturally and artificially infected VAM-exposed ticks transmitted anaplasmosis to susceptible calves.
- Anaplasma marginale colonies were exclusively observed in the gut tissues of ticks naturally infected with VAM.
- Ticks exposed to Illinois (IAM) and Florida (FAM) isolates showed no signs of infection, irrespective of the exposure method or the presence/absence of appendages.
Conclusions:
- The infectivity of Anaplasma marginale for Dermacentor andersoni is isolate-specific.
- The presence or absence of tail-like appendages does not appear to be the determining factor for tick infection by Anaplasma marginale.
- Additional factors beyond observed morphology likely influence the ability of Anaplasma marginale to infect and be maintained in tick vectors.