Mia Arreola

May 1, 2008

Parasites and Pestilence

Humbio 153


Proposal Outline: Schistosomiasis


Project: Furthering research and developing methods to prevent Schistosomiasis




The limitations of using chemotherapy against schistosomiasis, a parasitic disease which should be considered a consequence of a chronic infection, are steering scientists in the direction of prevention. In particular, chemotherapy does not affect transmission of the infection or the high re-infection rates and so limits the success by demanding frequently re-scheduled mass treatments. For this reason, a complementary approach that can be integrated and could sustain chemotherapy-based control programs, vaccination, is very much needed. The rationale is that drug treatment would provide short-term reduction of worm burdens and vaccination would provide the long-term protective immune response. Vaccination can either be targeted towards the prevention of infection or to the reduction of parasite fecundity.   Schistosome eggs are responsible for both pathology and transmission, a vaccine targeted on parasite fecundity and egg viability also appears to be entirely relevant.


Specific Aims


The main purpose of this project is to shed light on the experimental chemoprophylaxis taking place in mice in the form of oral anti-penetration agents in hopes to find the method that would have the best chance of working in humans.  Although there is doubt to whether the findings and successes in these experiments can be extrapolated to the much more complex human species, an attack on schistosomiasis from a different angle must be taken if we want to reduce the numbers of those infected.  The ultimate aim of expanding this sort of preventative research in humans is to come up with an effective vaccine.  The current treatment using Praziquantel is safe and highly effective in curing an infected patient, yet it does not prevent the patient from being re-infected when re-exposed.  Rapid infection demands continuing treatment and drug delivery which requires an elaborate and reliable infrastructure and many of the developing countries affected by schistosomiasis lack this type of infrastructure.  Vaccines have proven to be an excellent means of cost-effective control of many infectious diseases, and hopefully this success may be applied to the case of schistosomiasis in the near future.




-Why addressing schistosomiasis is important

            -description of schistosomiasis

            -disease burden of schistosomiasis

                        -morbidity vs. mortality statistics


-Description of fluke

            -epidemiology of schistosome (eg. Life cycle, intermediate host, etc.)

            -symptoms of schistosomiasis

            -burden of the disease (DALY and sequelae)


-Current treatment


                        -safe and effective in curing infection, but unable to prevent reinfection

                        -explain not optimum treatment for people living in endemic areas


-Present the difficulties of other preventative measures

            -why the ecological intervention technique may not be the best method

                        -introducing/augmenting existing crayfish populations

                        -problems with eliminating, avoiding, and/or controlling the snail


                        -Gopo Berry researched by Dr. Chidzere of Zimbabwe; the berry could be

used in the control of the freshwater snails that carry the schistosomiasis parasite(?)


            -why targeting the design of new dam and irrigation schemes is not best method

-good design has potential to minimize the contact between snails and the local population as well as the colonization of snails in the water

                        -not cost-effective to alter the already constructed irrigation schemes

                        -it is impossible to keep people out of snail infested waters, especially

                        when livelihood depends on it (eg. Japan and rice)



Study designs for follow up research in humans


-Preventative drugs/medicines

-Anti penetration agents

                        -Cremophor/Castor oil used to prevent cercarial penetration

                        -Praziquantel moderately effective in blocking cercarial penetration, but

                        effect dependent on the vehicle used to administer the drug

                                    -Salafsky et al: ̉Schistosoma mansoni: experimental

                                    chemoprophylaxis in mice using oral anti-penetration agents