0 Female Pheromones and Infection May Affect Tick Behavior

Image: Researcher drags white
flannel to collect questing ticks. 

Recently I came across an abstract for the paper, "The correlation between tick (Ixodes persulcatus Sch.) questing behaviour and synganglion neuronal responses to odours".

I'm looking forward to reading the full text, as the abstract demonstrates two findings on tick behavior which may reveal who is more likely to be bitten by ticks.

In this experiment, the taiga tick or Ixodes persulcatus is used - a tick common in parts of Russia. It is unknown if other Ixodes ticks would respond to the same odors the same way, and I think the same experiment should be conducted in Western Europe and North America with local Ixodes ticks to see if there would be a similar outcome.

The researchers experimented with seeing which odors would attract and repel ticks, focusing on seeing how ticks respond to synthetic hormones and insecticides/acaricides. Osmopherone®, Osmopherine®, DEET®, ethanol, and water were placed in a simple maze, and changes in their synganglia - basically their entire central nervous system, as ticks do not have a brain as we think of one - were measured to reflect whether they were attracted, repelled, or neutral to the specific odor tested.

Also, researchers tested which odors were most likely to encourage the maximum height ticks could reach during questing behavior by placing ticks on glass rods which were held at a 75 degree angle.

Two notable findings came from these experiments:

1. Ticks were, as expected, repelled by DEET® and ethanol. It's good to have further confirmation that DEET® works as a repellent. But what was interesting is that ticks were totally neutral to Osmopherone® and water - and attracted to Osmopherine® .
   
   
2. Questing ticks were studied not only for their attraction to certain odors but were tested for whether or not they were infected with Borrelia burgdorferi sensu lato and tickborne encephalitis virus. It was found that not only did those ticks which were most attracted to Osmopherine® reach the highest questing height - but also those ticks which were infected with Borrelia burgdorferi sensu lato were more likely to reach the highest questing height.
   

What is the difference between Osmopherone® and Osmopherine®? Osmopherone® is a synthetic sex pheromone that is meant to mirror the scent human males give off. Osmopherine® is a synthetic sex pheromone that is meant to mirror the scent human females give off. Each of these pheromones are found in their natural form on people and are not an obvious smell people give off - they are registered on a subconscious level and may act as an attractant to the opposite sex.

In these experiments, it appears the female sex pheromone, Osmopherine®, attracts ticks, and ticks infected with Borrelia burgdorferi sensu lato are more likely to have the highest questing height in a laboratory.

What is not known is whether or not the same behavior occurs in the wild, outside a lab - and how much other factors may play into ticks' behavior when questing. Different ticks have different behavior in the wild to begin with, such as Amblyomma americanum tends to be more aggressive in searching out a blood meal and Ixodes scapularis is a more passive questing tick.

Ticks are already attracted to the source of their blood meal through detecting heat and carbon dioxide (CO₂) given off by exhalation. One thing I would hope the full text of this article would explain is how the presence of warm blooded, CO₂ exhaling researchers was shielded so they did not have any influence on these ticks. It may be that these indicators of the next potential dinner may play a bigger role than the gender of the potential host in front of them and whether or not the tick is currently infected with Borrelia burgdorferi s.l. 

Certainly more research is needed to determine what the case is in the wild, but in the meantime these findings provide one with more food for thought as to how a tick host's gender and the tick's state of infection might play a role in tick behavior.

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0 Lyme Disease Presents Differently In Women Compared To Men

Recently, Lauren A. Crowder, M.P.H. reported observations on some differences between women and men in response to Lyme disease in a poster at the International Conference on Emerging Infectious Diseases.

The short story: Women with Lyme disease display more clinical symptoms than do men with the disease and also are less likely to seroconvert following treatment, according to findings from a prospective cohort study involving 77 patients.


The study revealed the following observations:

• Significantly more women than men reported joint pain, muscle pain, headache, back pain, heart palpitations, nausea, vomiting, anxiety, numbness and tingling, and changes in vision during at least one of six preplanned study visits with a physician.
• At the initial study visit, a similar proportion of men and women (about 60% of each) tested negative for Lyme disease using the Centers for Disease Control and Prevention’s recommended two-tier testing criteria for serodiagnosis. At the first post-treatment interview, 70% of women who tested negative at the first pre-treatment visit remained negative, compared with only 35% of the men who initially tested negative.

Read more about this Lyme Disease Foundation funded study here:
http://www.internalmedicinenews.com/news/infectious-diseases/single-article/lyme-disease-presents-differently-in-men-and-women/1bf48578d5.html

And see the original source with study here:

SEE page 151 of ICEID 2012 Abstracts
March 11-14, 2012 | Hyatt Regency Atlanta | Atlanta, Georgia
(PDF) http://www.iceid.org/images/iceid_2012_finalprogram_final.pdf

Board 264. Another Difference between Boys and Girls: Sex-Based Differences in Lyme Disease.
L.A. Crowder, A. Rebman, V. Yedlin, M. Soloski, J.N. Aucott; Lyme Disease Research Foundation of Maryland, Lutherville, MD, USA, Johns Hopkins University, School of Medicine, Baltimore, MD, USA.

This isn't the first time, however, that someone observed a difference between men and women's immune responses in relation to Borrelia burgdorferi.

Let's take the time machine back to Sweden, in 2004...

Lyme borreliosis reinfection: might it be explained by a gender difference in immune response?
Sara Jarefors, Louise Bennet, Elin You, Pia Forsberg, Christina Ekerfelt, Johan Berglund, and Jan Ernerudh
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1782288/

This study had a different goal than Ms. Crowder's in that it was intended to measure the difference in immunological response between people of both genders who had only been infected once and those who had been reinfected with Lyme disease within a five year period.

The findings relevant to women in this case:

"...for the immunological response there were major differences between men and women. The women displayed higher spontaneous secretion of all cytokines measured, i.e. IL-4, IL-6, IL-10, IFN-γ and TNF-α. Spontaneous secretion, at an infection-free time-point, reflects the habitual immune status and may suggest what type of immunological defence an individual generally displays. For instance, allergy has been considered a Th2-type related condition and, accordingly, atopic individuals have higher spontaneous IL-4 expression than non-atopic controls.

Women of reproductive age are believed to handle infections better than men, having a stronger tendency to show Th1-type responses and expression of higher levels of pro-inflammatory cytokines, and they also develop higher antibody titres than men when vaccinated. However, the female immune response fluctuates with the menstrual cycle. In general, oestrogen has a stimulatory effect on the immune system whereas testosterone acts as a suppressor. When women enter the menopause their levels of oestrogen decrease and thereby the stimulatory effect diminishes, leading to an altered immune status. All except one of the women in our study were postmenopausal, and this could be a factor explaining why more women than men became reinfected with B. burgdorferi."

And...

"Serology was not performed on the individuals in this study because, at the time of EM diagnosis, only 30–40% of patients displayed antibodies to Borrelia. Studies following patients with culture-confirmed EM have shown that, although antibodies can be detected 10–20 years after initial infection, titres decline gradually during the first year."

A paper which cited the previous one discusses the functions of IL-10 in relationship to Borrelia burgdorferi:

Interleukin-10 alters effector functions of multiple genes induced by Borrelia burgdorferi in macrophages to regulate Lyme disease inflammation.
Gautam A, Dixit S, Philipp MT, Singh SR, Morici LA, Kaushal D, Dennis VA.

Source: http://www.ncbi.nlm.nih.gov/pubmed/21947773

To sum it up: IL-10 (an interleukin) which is produced in higher amounts in women than it is in men, is responsible for inhibiting the actions of some genes in Borrelia burgdorferi - but it is also responsible for empowering the actions of some genes, too.

What implication this has on infection in different genders remains to be seen and requires more study.

But what is already known about the role of inflammation in the presence of Borrelia burgdorferi is important to take note of here: Inflammation facilitates Borrelia burgdorferi's adaptation to its host; it stimulates antigenic variation and it leads to increased spirochetal burden in mice. So if this applies to humans: All that pain, swelling, and inflammation patients feel? It is good for the spirochetes, and it is bad for you.

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