Biology Reference
In-Depth Information
DDT resistance in the sand fly
Phlebotomus argentipes
makes it difficult to manage
the vector.
Bacillus subtilis
, a commensal bacterium found in the gut of the sand
fly, was transformed using GFP and added to the food of the larvae. The bacteria
were transstadially transmitted and adults emerging from the treated food carried
large numbers of modified bacteria in their gut lumens. This indicates that para-
transgenic manipulation of the sand fly is possible once genes are discovered that
can kill or inactivate the leishmaniasis-causing pathogen.
Rio et al. (2004)
outlined the requirements for use of paratransgenesis for
control of human or animal disease (
Table 14.4
). As you can see, paratransgen-
esis projects require extensive efforts in both development and risk assessment.
14.5.3 Viral Vectors
Several types of viruses have been modified to serve as vectors in insects or
insect cells (
Burns 2000, Carlson et al. 2000, Olson 2000
, Terzian et al. 2000,
Webb 2000
). In some cases, these viruses are intended to yield stable transfor-
mation, but others are expected to result in a short-term transformation of the
infected tissues.
Nuclear polyhedrosis viruses (NPVs), also known as baculoviruses, have double-
stranded, circular DNA genomes contained within a rod-shaped protein coat.
Table 14.4: Requirements for Effective Control of Human or Animal Disease by
Paratransgenesis in Arthropods.
l
Naturally occurring symbionts must be isolated and cultured.
l
Transmission mode and population dynamics of the symbiont throughout the host life cycle should be
known.
l
A transformation system that produces stable phenotypes is needed.
l
Anti-pathogenic genes (transgenes) such as antimicrobial peptides or transmission-blocking monoclonal
antibodies should be identified, cloned, and evaluated.
l
Transgenes are expressed by the symbiont without fitness costs.
l
It is possible to insert the transgenic symbiont into hosts (lacking normal symbionts).
l
The transgene products are produced in the tissues or organs that can affect the pathogen.
l
The potential emergence of resistance by the pathogen to the transgene product should be evaluated.
l
The repopulated insects (with the transgenic symbiont) should be as fit as the wild-type insect hosts.
l
An effective gene-driven mechanism(s) should be available to replace field populations with the
paratransgenic insects.
l
An assessment of the potential spread of the transgenic symbionts and barriers to dispersal to nontarget
species should be conducted.
l
An in-depth analysis of the potential for harmful effects of symbionts or of transgene products to humans
and animals should be conducted.
l
Any implementation project should be evaluated for environmental impacts.
Modified from Rio et al. (2004).
