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Ants use vaccination to fight fungal infections

Lasius Neglectus uses a process very similar to our own vaccination technique to reduce risk of infection by a fungus. Picture credit: April Nobile / http://www.AntWeb.org

Vaccinations work on the principle that intentionally introducing weakened or dead infectious agents into the human body, triggers our immune system to generate the antibodies necessary to fight any actual infection that we could face in future. But a new study published in the open access journal PLoS Biology on April 3rd, has shown that such vaccination happens in ants too when a fungus infects their society.

Social immunization has been observed before in ant and termite colonies. Earlier studies by some of the authors of this current study, showed that uninfected ants exposed to fungus “treated” nest mates, had increased survival rates when faced with the same infection sometime later. But it was not clear whether that was due to active immunity, where the untreated, but exposed, ant itself generates the necessary antibodies to fight off pathogens, or passive immunity, where the antibodies generated by the treated ants were transferred to the exposed nest mates, or through some other means.

To answer that question, ants of the species Lasius Neglectus were “treated” with the fungus species Metarhizium anisopliae that was used as the infecting agent. Each of these “treated” ants were kept in contact with uninfected ants over a period of 5 days.

By using a red fluorescent label on the fungus, which helped the authors keep track of where the fungal spores traveled, this study established that uninfected ants who lick the treated ants to clean them, ended up with small doses of the fungus themselves. The fungus was found on the antennae and legs “suggesting that nest mates pick up the pathogen from the fungus-exposed individual during grooming”, the study says.

But to learn if it is indeed active immunity of the previously uninfected ants, rather than passive immunity, that led to increased protection, the team exposed some uninfected ants to a treated ant two days after the initial “treatment”, by which time the fungus loses the ability to be transferred. Such later exposed ants, showed no evidence of increased protection. This confirmed that it was the fungus itself that acted as a trigger for the immune system.

As a final confirmation that the immune system of the ants were activated, the study measured the gene expression of previously known anti-fungal and anti-bacterial genes. As expected, the expression of the anti-fungal genes increased significantly when compared to expression of anti-bacterial genes which did not show any change.

When queried as to the impact of the study in the human fight against diseases, “We have extended epidemiological models that are also used to model disease spread in human societies. By adding the effects of active and passive social immunisation in societies, these same effects can also be addressed in human societies by using our model.”, said Prof.Sylvia Kremer, one of the authors of the study, in an email response.

Reference: Konrad M, Vyleta ML, Theis FJ, Stock M, Tragust S, et al. (2012) Social Transfer of Pathogenic Fungus Promotes Active Immunisation in Ant Colonies. PLoS Biol 10(4): e1001300. doi:10.1371/journal.pbio.1001300

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