Parasite Pursuit: Sand fly coughs up leishmania protozoan's secrets of prolifera

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http://www.sciencenews.org/articles/20040724/fob6.asp

 

 

Week of July 24, 2004; Vol. 166, No. 4 , p. 53

 

Parasite Pursuit: Sand fly coughs up leishmania protozoan's secrets of

proliferation

 

Nathan Seppa

 

Leishmania, a tropical parasite carried by sand flies, spreads

prolifically to mammals by forcing the flies to regurgitate as they

bite their prey, a new study finds.

 

While still in the sand fly, the parasite secretes—and then multiplies

in—a gel that obstructs the fly's throat. When the fly bites a person

or another mammal to feed on blood, the insect is forced to expel the

parasite-laden blob of gel into the victim's bloodstream, the

researchers report in the July 22 Nature. Inside the new host, the gel

appears to promote the parasite's survival.

 

A fly remains infected for life. So, by obstructing the sand fly's

digestive tract, the parasite could also be forcing the insect to take

more blood meals than normal, prompting more bites and hence greater

spread, hypothesizes Matthew E. Rogers, a parasitologist at the

University of Liverpool in England.

 

He and his colleagues studied Leishmania mexicana, a New World species

that causes skin lesions and disfigurement if untreated. Other more

dangerous species of the leishmania protozoan parasite can cause

internal-organ damage and death.

 

To ascertain the importance of the gel itself, the scientists exposed

some mice to leishmania via either the bites of infected sand flies or

laboratory injection of a solution containing the parasites but not

the gel. Leishmania delivered by a single sand fly bite caused skin

lesions much sooner than the injected parasites did. Fly saliva and

the gel accompanying the parasite boost the virulence of the ensuing

infection, Rogers says.

 

In a subsequent test, the scientists compared leishmania injected

along with the gel against the parasite injected with saliva. They

determined that the gel results in a more virulent infection.

 

Rogers and his coworkers also found that the active ingredient in the

gel is a compound called filamentous proteophosphoglycan (fPPG), a

protein coated with sugar molecules. Without fPPG, the gel doesn't

boost the virulence of an infection. However, the mechanism by which

fPPG helps the parasite thrive in its new host remains under

investigation, Rogers says.

 

The compound might tamper with the immune system of the mammalian host

by activating certain chemical signals or shutting down others, says

Jesus G. Valenzuela, a biochemist at the National Institute of Allergy

and Infectious Diseases (NIAID) in Rockville, Md.

 

Shaden Kamhawi, a medical entomologist also at NIAID, says the new

research " is great, because we really don't know the intricacies of

what's going on [in leishmania] transmission. "

 

Such details might provide leads for researchers working to develop a

vaccine containing components of saliva and the gel, Rogers says. No

anti-leishmania vaccine is currently beyond the experimental stage

(SN: 8/11/01, p. 85: Available to rs at

http://www.sciencenews.org/articles/20010811/fob6.asp).

 

Roughly 12 million people worldwide are infected with leishmania

parasites. The lethal species in the Leishmania genus—which can cause

fevers, anemia, and organ damage—are most prevalent in India, Sudan,

and Brazil.

 

Drugs for leishmaniasis can be expensive, and some must be regularly

injected for weeks or months.

 

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References:

 

Rogers, M.E., et al. 2004. Transmission of cutaneous leishmaniasis by

sand flies is enhanced by regurgitation of fPPG. Nature 430(July

22):463-467. Abstract available at http://dx.doi.org/10.1038/nature02675.

 

Further Readings:

 

Kamhawi, S., et al. 2000. Protection against cutaneous Leishmaniasis

resulting from bites of uninfected sand flies. Science 290(Nov.

17):1351-1354. Available at

http://www.sciencemag.org/cgi/content/full/290/5495/1351.

 

Sacks, D.L., et al. 2000. The role of phosphoglycans in

Leishmania-sand fly interactions. Proceedings of the National Academy

of Sciences 97(Jan. 4)):406-411. Available at

http://www.pnas.org/cgi/content/full/97/1/406.

 

Schubert, C. 2001. Insect-saliva vaccine thwarts parasite. Science

News 160(Aug. 11):85. Available to rs at

http://www.sciencenews.org/articles/20010811/fob6.asp.

 

Stierhof, Y.-D. . . . M.E. Rogers, et al. 1999. Filamentous

proteophosphoglycan secretes by Leishmania promastigotes forms

gel-like three-dimensional networks that obstruct the digestive tract

of infected sandfly vectors. European Journal of Cell Biology

78(October):675-689. Abstract.

 

Valenzuela, J.G. . . . S. Kamhawi, et al. 2001. Toward a defined

anti-Leishmania vaccine targeting vector antigens: Characterization of

a protective salivary protein. Journal of Experimental Medicine

194(Aug. 6):331-342. Available at

http://www.jem.org/cgi/content/full/194/3/331.

 

The Web site of the International Leishmania Network can be found at

http://www.bdt.org.br/leishnet/.

 

Additional information about leishmaniasis can be found at

http://www.cdc.gov/travel/diseases/leishmaniasis.htm.

 

Sources:

 

Shaden Kamhawi

National Institute of Allergy and Infectious Diseases

Laboratory of Parasitic Diseases

National Institutes of Health

4 Center Drive

Bethesda, MD 20892

 

Matthew E. Rogers

Liverpool School of Tropical Medicine

Pembroke Place

Liverpool L3 5AQ

United Kingdom

 

Jesus G. Valenzuela

National Institute of Allergy and Infectious Diseases

Laboratory of Malaria and Vector Research

12735 Twinbrook Parkway

Room 2E22C

Rockville, MD 20852

 

 

 

From Science News, Vol. 166, No. 4, July 24, 2004, p. 53.