A MOLECULAR APPROACH TO THE EPIDEMIOLOGY OF GIARDIA DUODENALIS IN A PERUVIAN SHANTYTOWN.

Hoover PJ, Reed C, Sturbaum GD, Gilman R, Sterling CR

Giardia duodenalis is a protozoan parasite that causes severe diarrhea, abdominal pain and rapid weight loss.  As the most common intestinal parasite of humans in developed countries, G. duodenalis has been named in several U.S. outbreaks occurring in daycare centers and small communities. The situation, however, is far worse in developing countries where living conditions are often crowded and sanitation is poor.  In fact, these conditions create an environment where people are continually exposed to infection. This setting has proven especially devastating for children, whose immune systems are not developed enough to fight off repeated G. duodenalis infections. Sadly, children with multiple infections early in life do not develop equally with their age-matched counterparts.  While infectious from person to person, controversy remains as to whether or not the organism is transmissible from animals to humans.  Furthermore, transmission patterns within an endemic community are poorly understood.  This study attempts to provide insight into these issues by examining an endemic locality in Peru.

Because the organism is passed in the feces, stool samples were collected from 12 households and their dogs living in a shantytown outside of Lima, Peru from May 20 to July 31, 2001.  Households consisted of five to nine members, and their ages ranged from 0 to 58 years. Eighty-one individuals and four dogs participated.  Participants were asked to give one fecal sample each week of the study.  Samples were microscopically screened for G. duodenalis, and positive fecal samples were purified using differential centrifugation techniques.  G. duodenalis DNA was extracted from purified samples using a QIAamp DNA Stool Mini Kit.  To identify different strains of G. duodenalis affecting the shantytown, a genomic region variable among G. duodenalis strains was analyzed. The 16S-rRNA gene was targeted utilizing the polymerase chain reaction and primers RH4 and RH11.  A 292-bp product was produced from positive samples and sequenced to compare strains.  Infections were tracked graphically taking into consideration each participant’s age, infection duration, and the infecting G. duodenalis strain.

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