Giardiasis in Leon, Nicaragua : prevalence and protection

Abstract

Giardia intestinalis is endemic in Nicaragua and affects children early in their lives. Infected individuals may be asymptomatic or suffer from acute or chronic diarrhea, malabsorption and weight loss. The prevalence of Giardia intestinalis infection in the population of León-Nicaragua was investigated. The presence of Giardia specific secretory antibodies was correlated with protection against disease. Parasite proteins as powerful immunogens were evaluated.

By microscopic examination of stool samples, we found G. intestinalis cysts in 15.9 % of the tested material. Giardia was most prevalent in the youngest age group, close to 30 % in children less than 5 years old. The presence of the parasite could be correlated to poor socioeconomic conditions. In a subsequent study a prevalence of 15.6 % of anti-Giardia antibodies in milk was detected in lactating women.

The protective effect of milk anti-Giardia antibodies against G. intestinalis infection was studied in 307 children aged 1 week to 2 years. Giardia cysts were found in stools of 36.1 % of infants. Among infected children, 24 (21.6 %) acquired the infection before the age of 6 months. Sixty-five children (58.8 %) presented multiples episodes of giardiasis during the first two years of life. Of 24 children infected early in life, 23 (96 %) were born to mothers lacking specific antibodies in milk. These children also developed more severe diarrhea. There was a significant difference between children born to mothers with and without antibodies with respect to the age at which the first Giardia infection was acquired (p=0.036).

Milk and saliva samples from a group of 100 lactating women living in the same area were tested for the presence of Giardia specific antibodies. Anti-Giardia antibodies were seen in 59 % of milk samples and 52 % of saliva samples. Milk antibodies gave stronger reactions than saliva and most of them reacted with surface and flagella components. Secretory anti-Giardia antibodies recognized up to 16 different proteins in the molecular weight region between 20 and 165 kDa. Differences among samples were mostly quantitative. Selected anti-Giardia positive milk samples were tested with recombinant Giardia proteins alpha-1 giardin, alpha-enolase, arginine deiminase (ADI) ornithine carbamoyl transferase (OCT), and VSP4EX. All tested milk samples reacted with the recombinant antigens.

Specific reactivity of milk antibodies with the ventral flagellae of the parasite was observed. Milk antibodies showed a similar reactivity to a reference anti-tubulin antibody previously generated and shown to recognize Giardia ventral flagella. The 50 kDa target tubulin immunogen has also the mobility of Giardia beta tubulin in polyacrylamide gel electrophoresis and isoclectric focusing of cytoskeleton parasite preparations.

In conclusion, Giardia intestinalis is frequent among the population of León-Nicaragua and children born to immune mothers are at lower risk of getting giardiasis. Milk and saliva anti-Giardia antibodies found in Nicaragua women recognized Giardia immunogens such as VSPs, alpha-giardins as well as OCT, ADI and enolase. These antigens can be important in the development of immunodiagnostic tools and vaccines. During Giardia infection antitubulin secretory antibodies are also produced recognizing the ventral flagella of the parasite.