Treating Ticks With Antibiotics Inhibits Their Reproduction

UC Irvine professor Dr. Alan G. Barbour and researchers Jianmin Zhong and Algimantas Jasinskas found that certain antibiotics reduced the number of bacteria in ticks, and this was associated with retarded growth in immature ticks and reduce reproduction by adult females.

“The significance is that control of ticks as vectors of disease and as pests for humans, pets and agricultural animals might be achieved by targeting inborn bacteria that the ticks depend on for achieving full growth and reproduction,” Barbour said.

The yearlong study focused on the lone star tick, Amblyomma americanum, which is common in the southern and eastern United States and transmits erhlichiosis and other infections to humans and other animals. All of the ticks of this species have bacteria that appear to live symbiotically with the arthropod and are passed from one generation to the next.

The bacteria are found at highest concentrations in nymphs that have not quite reached adulthood and in engorged females. Ticks were divided into three groups and injected either with the antibiotics rifampin or tetracycline, or with a buffer that contained no antibiotics. In the groups that got antibiotics, the nymphs gained less weight than control ticks, and the females took longer to lay eggs, hatched fewer eggs and produced fewer viable larvae.

Because the bacteria are only distantly related to humans and other vertebrates, compounds that selectively inhibit or kill the bacteria could be identified and taken as a supplement by at-risk animals as part of an integrated pest management program. The compounds would then be passed through the blood to feeding ticks. This may provide an improvement over current use of pesticides that target ticks directly but also may be toxic to vertebrates and beneficial insects.

Barbour, Zhong and Jasinskas conducted the research under the auspices of the Department of Microbiology and Molecular Genetics, Department of Medicine and the Pacific-Southwest Center for Biodefense and Emerging Infections at UCI. Zhong also is affiliated with the Department of Biological Sciences at California State University Humboldt.