However, if the illness is acute or symptoms persist and medications are needed to treat it, a nitroimidazole medication is used such as metronidazole, tinidazole, secnidazole or ornidazole.The World Health Organization and Infectious Disease Society of America recommend metronidazole as first line therapy. The US CDC lists metronidazole, tinidazole, and nitazoxanide as effective first-line therapies; of these three, only nitazoxanide and tinidazole are approved for the treatment of giardiasis by the US FDA. A meta-analysis done by the Cochrane Collaboration found that compared to the standard of metronidazole, albendazole had equivalent efficacy while having fewer side effects, such as gastrointestinal or neurologic issues. Other meta-analyses have reached similar conclusions. Both medications need a five to 10 day long course; albendazole is taken once a day, while metronidazole needs to be taken three times a day. The evidence for comparing metronidazole to other alternatives such as mebendazole, tinidazole or nitazoxanide was felt to be of very low quality. While tinidazole has side effects and efficacy similar to those of metronidazole, it is administered with a single dose.Resistance has been seen clinically to both nitroimidazoles and albendazole, but not nitazoxanide, though nitazoxanide resistance has been induced in research laboratories. The exact mechanism of resistance to all of these medications is not well understood. In the case of nitroimidazole-resistant strains of Giardia, other drugs are available which have showed efficacy in treatment including quinacrine, nitazoxanide, bacitracin zinc, furazolidone and paromomycin.
Additionally, peristalsis and the renewal of enterocytes provide further protection against parasites. Nitric oxide production
Nitric oxide does not kill the parasite, but it inhibits the growth of trophozoites as well as excystation and encystation. Innate immune system
Lectin pathway of complement
The lectin pathway of complement is activated by mannose-binding lectin (MBL) which binds to N-acetylglucosamine. N-acetylglucosamine is a ligand for MBL and is present on the surface of Giardia. The classical pathway of complement
The classical pathway of complement is activated by antibodies specific against Giardia. Adaptive immune system
Antibodies
Antibodies inhibit parasite replication and also induce parasite death via the classical pathway of complement.Infection with Giardia typically results in a strong antibody response against the parasite. While IgG is made in significant amounts, IgA is believed to be more important in parasite control. IgA is the most abundant isotype in intestinal secretions, and it is also the dominant isotype in mothers milk. Antibodies in mothers milk protect children against giardiasis (passive immunization). T cells
The major aspect of adaptive immune responses is the T cell response. Giardia is an extracellular pathogen. Therefore CD4+ helper T cells are primarily responsible for this protective effect.One role of helper T cells is to promote antibody production and isotype switching. Other roles include cytokine production (Il-4,IL-9) to help recruit other effector cells of the immune response. Diagnosis
According to the CDC, detection of antigens on the surface of organisms in stool specimens is the current test of choice for diagnosis of giardiasis and provides increased sensitivity over more common microscopy techniques.