Biology Reference
In-Depth Information
Symbionts of tsetse flies (
Glossina
species), which are vectors of both animal
and human African sleeping sickness, have been transformed (
Richards 1993,
Cheng and Aksoy 1999, Aksoy et al. 2001, 2008, Hurwitz et al. 2011a
). Proposals
have been made to release tsetse flies carrying transgenic symbionts so the
released flies could replace or outcompete native populations, but fail to trans-
mit the disease. Because the host range of these bacteria is narrow, horizontal
transfer (HT) of the transformed bacteria is less likely. One of the symbionts,
Sodalis
, can be cultured and genetically modified (
Aksoy et al. 2008
).
Sodalis
is
a secondary symbiont that is found in the hemolymph, midgut, and milk gland
and is transmitted vertically through the milk glands. Because
Sodalis
is in prox-
imity to the trypanosome parasite and is resistant to proteins produced by the
trypanosome, paratransgenic
Sodalis
can be introduced by injection and poten-
tially reduce transmission of the disease-causing agent. The endemic
Sodalis
could be eliminated with specific antibiotics without eliminating the essential
Wigglesworthia
symbiont. Deployment of the paratransgenic tsetse flies could
be achieved using a drive system to replace wild flies with the flies unable to
vector the trypanosome. An alternative is to use the SIT in order to eliminate
wild-type tsetse and follow it with releases of paratransgenic flies that cannot
transmit the pathogen.
Extracellular bacteria isolated from the gut of the walnut husk fly,
Rhagoletis
completa
, was transformed with enhanced green fluorescent protein (GFP) and
zeomycin resistance genes (
Peloquin et al. 2000
). This modified bacterium in the-
ory could deliver proteins into the gut that could enhance the nutrition of the
flies, improving their vigor and competitiveness for potential SIT programs.
Ren et al. (2008)
discovered, cloned, and characterized a densovirus able
to infect the mosquito
Anopheles gambiae
, and introduced the GFP gene into
the virus. The virions were highly infectious and disseminated to and expressed
GFP in the midgut, fat body, and ovaries.
Ren et al. (2008)
concluded that this
virus could be used as part of a paratransgenic malaria-control strategy if anti-
Plasmodium
peptides or insect-specific toxins could be introduced into the virus.
Cirimotich et al. (2011)
found a naturally occurring
Enterobacter
in wild
An. gam-
biae
populations in Zambia. The bacterium “renders the mosquito resistant to
infection with the human malaria parasite
Plasmodium falciparum
by interfering
with parasite development before invasion of the midgut epithelium.” The ques-
tion is: Can this bacterium be transmitted to wild
An. gambiae
populations else-
where to prevent malaria transmission?
Sand flies (Psychodidae) transmit leishmaniasis (also known as kala azar), causing
nearly 100,000 deaths per year in the Indian state of Bihar (
Hurwitz et al. 2011a
).
