From the Guidelines
Diagnosing Chagas Disease on a Blood Smear
Chagas disease can be diagnosed on a blood smear by performing a thick and thin blood film examination using Giemsa stain, as recommended by the Infectious Diseases Society of America and the American Society for Microbiology 1.
- The diagnosis is typically made by identifying the presence of Trypanosoma cruzi parasites, which can appear as curved or C-shaped organisms with a distinctive kinetoplast.
- A thorough examination of the blood smear should be performed, particularly during the acute phase of the disease when parasitemia is highest.
- In some cases, a buffy coat smear or a concentration technique may be used to enhance the detection of parasites.
- It is essential to note that a negative blood smear does not rule out the diagnosis, and additional tests such as PCR or serology may be necessary to confirm the diagnosis, especially during the latent and chronic stages of the disease when parasitemia is very low 1.
The standard method for diagnosis of American trypanosomiasis during the acute phase of infection is microscopy of Giemsa-stained thick and thin blood or buffy coat films, since extracellular trypanosomes will be present at this time 1.
On stained preparations, the motile trypomastigote forms typically adopt a “C” shape and can be differentiated from the similar-appearing trypomastigotes of Trypanosoma brucei by the presence in T. cruzi of a large posterior kinetoplast 1.
Serology by commercially available enzyme-linked immunoassay (ELISA) kits is of greatest use during the latent and chronic stages of disease when parasites are no longer easily detected in peripheral blood preparations by microscopy 1.
Positive ELISA results are considered evidence of active infection and would exclude potential blood/tissue donors who test positive from acting as donors, as the infection has been shown to be transmitted by transfusion and transplantation 1.
It's worth noting that the diagnosis of Chagas disease can also be established by microscopic examination of tissue aspirates or biopsies, and culture in Novy-MacNeal-Nicolle medium or similar media of any appropriate blood or tissue specimen during the acute and chronic stages can add to the sensitivity of laboratory diagnosis 1.
However, live trypanosomes are highly infectious and specimens must be handled with care using “standard precautions” for the handling of blood and body fluids 1.
In summary, diagnosing Chagas disease on a blood smear involves a combination of microscopy, serology, and PCR, and it's crucial to consider the stage of the disease and the limitations of each diagnostic method 1.
From the Research
Diagnosing Chagas Disease on a Blood Smear
The diagnosis of Chagas disease on a blood smear is typically performed by detecting the presence of the parasite Trypanosoma cruzi.
- The parasite can be detected in blood smear samples using a microscope 2.
- Trained microscopists are required to detect the parasites in blood smear samples, which can be a time-consuming and expensive process 2.
- A machine learning approach has been proposed to automate the detection of T. cruzi in blood smear samples using mobile phone images 2.
- The use of rapid diagnostic tests (RDTs) has also been explored for the detection of chronic T. cruzi infections, which can provide results within an hour and do not require cold storage 3.
Laboratory Diagnosis Techniques
Several laboratory diagnosis techniques are available for Chagas disease, including:
- Direct techniques, which detect the presence of the parasite in different types of samples 4.
- Indirect techniques, which detect immune specific response against T. cruzi antigens 4.
- Molecular techniques, which detect parasite genetic material 4.
- Immunoassay techniques, such as ELISA, which detect IgG antibodies directed against T. cruzi antigens 4.
Blood Donor Screening
Blood donor screening for Chagas disease is important to prevent transmission of the disease through blood transfusion.