Leishmaniasis, a skin infection caused by
Leishmania parasites, develops when an infected sand fly bites the skin of a
mammal, transmitting both sand fly saliva and single-celled Leishmania
The bite can then turn into a raised red lesion and, in some
cases, form an open ulcer that then becomes infected with bacteria.
Sores in the nose and mouth can also cause complications.
‘Saliva from a species of the fly responsible for transmitting leishmaniasis can be used to vaccinate mice against the infection.’
A vaccine against cutaneous leishmaniasis may be spitting distance away.
Saliva from a species of the fly responsible for transmitting
leishmaniasis can be used to vaccinate mice against the infection,
researchers have shown. The new study, published in PLOS Neglected Tropical Diseases
also found that humans with cutaneous leishmaniasis tend to have lower
levels of antibodies against this sand fly saliva than others living in
areas where the infection is endemic.
In Brazil, one
of 10 countries where 75% of cutaneous leishmaniasis cases are
concentrated, the infection is generally caused by Leishmania
braziliesis, and is transmitted by the sand flies Lutzomyia intermedia
and Lutzomyia whitmani
. Previous work showed that immunity to proteins in Lu. intermedia
saliva exacerbated leishmaniasis, spurring an increased immune reaction to infected sand fly bites.
In the new work, Camil de Oliveira and Aldina Barral of the
Instituto Gonçalo Moniz, Fundação Oswaldo Cruz in Brazil, with
colleagues, tested the effect of immunity to the other major sand fly, Lu. whitmani
, on leishmaniasis. They removed the salivary glands from Lu. whitmani
flies collected in Brazil and used the tissue to immunize mice three
The researchers showed that the immunized mice immunized
developed antibodies to four distinct proteins in the saliva. When the
mice were then infected with L. braziliesis
, injected through a
needle at the same time as sand fly saliva, the immunized mice did not
develop lesions, while control mice did. Moreover, the immunized mice
had lowed levels of parasites at the injection sites and higher levels
of certain immune molecules.
To find out whether the results might have relevance in humans, the team tested for the natural presence of antibodies against Lu. whitmani
saliva in nearly 300 people from Corte de Pedra, Brazil, some of whom
had active cutaneous leishmaniasis, others who had subclinical
infections not causing lesions, and others with no history of infection.
They detected the antibodies in all three groups of people, but
patients with cutaneous lesions had the lowest levels. The results in
both humans and mice are quite distinct from what was previously
discovered using Lu. intermedia
saliva. However, both studies
have yet to be replicated using live sand fly bites, a critical next
step since injected compounds don't fully replicate the natural bite.
"Our results reinforce the importance of investigating the
immunomodulatory effect of saliva from different species of closely
related sand flies," the authors say. "Together, our data reinforce the
possibility of employing sand fly salivary molecules as components for a
leishmaniasis vaccine," they add.