In this study, Theodos et. al.
(1991) looked at the effect of sand fly saliva on the effectiveness of Leishmania infections. Researchers focused on the sand fly vectors
Lutzomiya longipalpis and Phlebotomus papatasi and two species of Leishmania, Leishmania major and Leishmania Mexicana amazonensis. Researchers suggest that the sand fly
saliva contains calcitonin gene-related peptidss, or CGRP, which prevents the
production of H202 by host macrophages. They also suggest that the saliva could be
preventing the macrophages from presenting antigens against Leishmania.
In the first part of this study
researchers tested the affect of the saliva on five different mice strains, one
susceptible mouse strain, one mouse that is intermediately susceptible, and
three strains that are genetically resistant.
The mice were injected with either L.
major or with L. major and lysate
of ½ of a salivary gland of L.
longipalpis. The disease was most
pronounced in two of the resistant strains, which were then used for the other
tests. When the mice were injected with
1/10 of a salivary gland the lesion was significantly larger than the
control. Researchers then tested the
effect of the saliva on L. Mexicana
amazonensis and the results showed once again an increased infection in two
of the mice strains. The effect of P. papatasi saliva was also tested and
showed similar results to the saliva from L.
longipalpis. The final part to this
study tested whether or not the sand fly vectors introduces material that
enhances infection when they are probing the skin while they are looking for
blood. The mice were anesthetized and
shaved at their posterior end and were exposed to the bites of L. longipalpis. The mice were then injected with L. major in the area they were bitten. The
results showed that the lesions developed quicker and the infection was more
severe then in the mice that were not bitten by the sand fly.
I thought this was a very
interesting article because it touches on something that I discussed in my
first article about possibly finding a better cure for espundia caused by Leishmania braziliensis. The article by Theodos et. al. (1991)
suggests that it may be possible to vaccinate people against leishmaniasis by
creating a vaccine against whatever is in the saliva that supports the survival
of the parasite. This would rid the need
of using antimony compounds to try and kill off the parasite. It would be interesting to see if the saliva
is necessary for other strains of the parasite to survive. It would also be interesting to know whether
this occurs with other parasites and vectors, where a specific vector in some
way enhances the survival and course of infection of a given parasite. It’s hard to believe that something as simple
as saliva can have such a large effect on the survival of this parasite.
Theodos, C. M., J. M. C. Ribeiro, and R. G. Titus. 1991.
Analysis of Enhancing Effect of Sand Fly Saliva on Leishmania Infection in Mice.
Infection and Immunity. 59(5): 1592-1598.
It is very interesting that the contents of the saliva can determine the makeup of a vaccine. Finding a vaccine that works would be very beneficial to the environment without the need for antimony compounds to kill off the sandfly.
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