Xenodiagnosis is used in the diagnosis of a disease that is transmitted by the bite of a
Xenodiagnosis is used in the diagnosis of Chagas disease, which is caused by Trypanosoma cruzi, a hemoflagellate. There are four morphologic forms of hemoflagellates. In man, they may be intracellular, in which they are called leishmanial forms; or, they may be located extracellularly in the blood, in which they are called trypanosomes. The insect vectors may have leptomonads (promastigotes) or crithidial (epimastigote) forms. Leishmaniasis (cutaneous, mucocutaneous/and visceral) only has the leishmania, intracellular forms present in man. In Mrican trypanosomiasis, only the extracellular, or trypanosomal form, is present in man. Chagas disease has both the intracellular (leishmanial) and extracellular (trypanosomal) forms. Chagas disease is rampant in South America and is the major cause of progressive hea failure and death in that area. T cruzi is a flagellated protozoan that is transmitted to man by the bite of the Reduviid bug, or kissing bug, which usually occurs during the night. Sholy after the bite, the bug defecates on the wound site and the sleeping host rubs the organisms into the wound. Periorbital inflammation develops, which is called Romana's sign. Trypanosomes circulate in the blood and leishmanial forms invade (1) the reticuloendothelial cells, producing hepatosplenomegaly; (2) the hea muscle, causing myocarditis and arrhythmias; (3) the brain, producing a meningoencephalitis; and (4) into the gastrointestinal tract, where the leishmania destroy the ganglion cells in the distal esophagus and rectum to produce acquired achalasia and Hirschsprung disease, respectively. Laboratory diagnosis is made by (1) finding trypanosomes in the blood, (2) finding leishmanial forms in tissue, (3) culture, (4) serology, and (5) xenodiagnosis. Xenodiagnosis is a method of inoculation in which sterile Reduviid bugs are fed or offered the blood of an infected patient. After a few weeks, the bug's intestinal contents are examined for presence or absence of the organism. Only 5% of patients die in the acute stage of hea failure, whereas in chronic disease, hea failure is a common cause of death. Nifuimox is the drug of choice.
Body louse
Deer tick
Reduviid bug
Mosquito
parasitology