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New diagnostic tools for leishmaniasis are tested


19/02/2020

Fiocruz Minas

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A research by Fiocruz Minas has shown that Lamp, the test used to detect a series of infectious diseases, can also be used to diagnose human visceral leishmaniasis. The study by the PCPP, the Group of Clinical Researches and Public Policies on Infectious and Parasitic Diseases, was recently published in the BioMed Research International magazine.

To verify the efficacy of the Lamp test, the researchers used the technique on blood samples that had already been submitted to traditional diagnostic methods. A total of 219 samples were employed, of which 114 had been drawn from patients already diagnosed with visceral leishmaniasis and 105 had tested negative for the disease. Comparing the results of Lamp and of the exams done before, researchers verified a concordance of 98% among the positive and the negative samples.

“We obtained high sensitivity, which is the test’s ability to properly identify individuals with the disease, as well as high specificity, the test’s ability to correctly identify subjects who do not have the disease”. That is, Lamp has proven to be a diagnostic technique with pretty high accuracy, showing it can be employed in the diagnosis of human visceral leishmaniasis”, states the researcher Daniel Moreira de Avelar.

The Ministry of Health currently recommends some types of diagnostic tests for visceral leishmaniasis, including the parasite test, serology tests, and molecular tests. According to the researcher, however, these methods have some limitations that may make it difficult to diagnose the disease early.

“The parasite test has low sensitivity, in addition to being very invasive, meaning it must be done at hospitals or reference centers. Many patients must cover long distances in order to have access to this test. Serology tests work well in people with a good immune response, but immunosuppressed patients, for instance, do not respond well, due to their deficient production of antibodies. Molecular tests, on the other hand, offer high precision, but usually depend on equipment that is not always available everywhere”, explains Avelar.

According to him, the Lamp is an isothermal test: all the reactions required to detect the diseases can take place within a single temperature range. It is different from PCR, a type of molecular test that requires temperature variation, and therefore depends on costly equipment and well-structured laboratories.

“The Lamp test can be used with simple tools, such as bain-marie”, he says. “This makes it easier to implement in smaller laboratories”.

Cutaneous leishmaniasis

The efficacy of the Lamp test is also being tested for the detection of cutaneous leishmaniasis. A study to be published soon has shown that the technique associated to material collected with swabs yielded results very similar to those obtained through biopsy.

“The advantage is, when the Lamp test is adopted, we can use swabs to collect material, and it is much less invasive and painful for the patient. This also means that the procedure can be made in small laboratories”, highlights the researcher.

The studies that focus on the evaluation of new diagnostic techniques carried out by Fiocruz Minas are in line with the recommendations of the WHO regarding the criteria that should be observed when recommending new methodologies.

“The WHO states that the tests must be sensitive, specific, fast, sturdy, easy to make and able to be executed wherever the sick people are. They must also be made in real time, use as little equipment as possible, and sample collection must be non-invasive. We have attempted to guarantee these criteria in our studies”, he says.

Disease

Leishmaniasis can be of two main types: cutaneous, when it involves the skin and the mucosas; and visceral, when it attacks internal organs such as liver and spleen. The disease is caused by parasitic protozoans that mainly use rodents and dogs as hosts, and are transmitted to humans by female sandflies.

The main symptom of cutaneous leishmaniasis is the appearance of ulcers in the skin. The ulcer usually begins small, round-shaped, deep, red, and progressively grows as days go by. However, when the parasite infects the mucosa of the contaminated subject, the ulcers appear in the nose, in the mouth, or, in more serious cases, in the throat and in the larynx.

Visceral leishmaniasis is a systemic infectious disease characterised by long-term fever, enlarged spleen and liver, weight loss, weakness, low muscle strength, anemia and other symptoms.

There is currently no vaccine against human leishmaniasis. The most common steps taken to fight the disease are based on the control of vectors and reservoirs, individual protection, early diagnosis and treatment of sick people, environmental handling and health education.

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