Parasites responsible for leishmaniasis are mainly acquired from the skin, explains researcher Dr. Carlos Henrique Costa

Publicação: 9 de October de 2018

Recent researches prove that blood is not the main source of parasites for sand flies. New information brings a significant breakthrough in understanding leishmaniasis

To effectively control the disease, in addition to curing the patients, it is also necessary to understand and break the parasite’s transmission cycle

A recent study entitled “Skin parasite landscape determines host infectiousness in visceral leishmaniasis” published on Nature Journal, describes that scientists at York University discovered that parasites responsible for leishmaniasis are mainly acquired from the skin, not from a person’s blood.

Professor and physician Dr. Carlos Henrique Nery Costa, coordinator of the Laboratory of Leishmaniasis of the Federal University of Piauí, a world reference, explains that this is not exactly a finding.  “In Teresina (PI), we had already checked similar signs in people with kala-azar. What researchers at the University of York have observed in this study is that there is a heterogeneous distribution of the Leishmania infantum amastigote in the skin of mice, suggesting, by mathematical modelling, that the transmission is through the skin”, he says.  Still according to the professor, Greek researchers at the University of Thessaly had already verified the presence of the parasite in the epidermis and in the upper layers of the dermis of symptomatic dogs. “Our studies in Teresina pointed out that the number of circulating parasites in the blood is very small and insufficient to transmit the disease.  However, the study also showed a small number of parasites in the skin of patients, but still capable of infecting sandflies, the disease’s transmitters”, he signs. To him, this finding explains this contradiction, since parasites are unevenly distributed in the skin, where some areas may have and others have less parasites.

Professor Carlos Costa said the new information will help understanding the disease’s transmission cycle, as well as identifying infecting people and animals within a community. However, it is still not possible to tell which areas of the skin transmit the parasites, a process that would allow to point more accurately which individuals are capable of transmitting the disease.  “This way, the new information reaffirms that blood is not the main responsible for the transmission of leishmaniasis, such as discovered in 2016, but do not exactly point where we should look for the parasite in human or animal skin,” he recalls.

Sacrifice of leishmaniasis-infected dogs

Currently, once the disease is diagnosed in dogs, the most common recommendation is the sacrifice of the animal.  Asked if this reality could be changed with the new information, the teacher says that the study does not help because it does not address the issue directly. However, he argues that there are studies performed in Teresina that clearly show that there are no links between the results of the exam conducted with dogs and the chances of disease transmission to the insects. “We reaffirm that eliminating dogs as a control strategy is not correct”, he stresses.

Still on this topic, the researcher describes this year’s publication, reiterated at the 54th edition of the Congress of the Brazilian Society of Tropical Medicine (MedTrop), with the participation of Dr. Wilhelm Werneck and other researchers. According to this new study, the best qualified method to help in the control of the disease is the regular use of collars impregnated with deltamethrin, that can be distributed by the Government. “This, in experimental studies has proved capable of reducing the transmission of the disease”, he adds.

Use of mathematical models

In the article published in Nature Journal, professor Jon Pitchford, from the University of York’s Biology and Mathematics Department, stated that the application of mathematics can help solve important problems in medicine. In 2013, the SBMT already drew attention to the subject in the article Mathematical model promises to contribute to combating leishmaniasis. To Dr. Carlos Henrique, combining mathematics, data analysis standards, with laboratory work to better understand the ecology, epidemiology and evolution of leishmaniasis should be stimulated. According to him, understanding the various aspects of communicable diseases, whether their spatial or temporal distribution for predicting occasions of transmission is always a very useful tool that helps control diseases. “The use of mathematical modeling in the biomedical field has been increasingly recognized. I will repeat the aphorism about its use in communicable diseases: They should be used as a light pole, not for scientists to lean against, as a drunk man would, but to enlighten the path for new ideas”, he says.

Brazilian research in the field of leishmaniasis

According to the Coordinator of the Leishmaniasis Laboratory, Brazilian research in the field are quite advanced and Brazil has made important contributions in the disclosure of a series of factors of the disease and has collaborated with several countries, besides publishing several articles on the topic. “Brazil has a very strong contribution in the various fields of the leishmaniasis. But we are still in debt: we must find a less toxic drug of oral use and a vaccine. In addition, researchers still do not know how to handle the severe form of the disease more effectively and how it leads to death”, he acknowledges. A significant number of patients, from 5 to 10%, which are in specific and appropriate treatment unfortunately will evolve to death.

Disease transmission cycle

To effectively control the disease, besides curing patients, also it is necessary to understand and break the parasite’s transmission cycle, a very difficult task, in the opinion of the expert, because leishmaniasis is a metaxenic disease, meaning it has vectors as reservoirs and they have no fixed location for the development of the larvae, as mosquitoes in water, as the flies, proliferate in gardens or in pens, since all they need is organic matter, as manure or compost. That is, they are spread over wide areas in cities and in the wild. The interruption of the transmission chain would be more effective by combating the vector. In the past DDT was used, but it was outlawed. Currently there are some insecticides for residual use, but the few evidences about their action are not enough to build a program using them.

In the opinion of Dr. Carlos Henrique, it lacks to streamline the program and rank municipalities, as the Ministry of Health is trying to do. “After that, we must redo insecticides tests, with collars or other methods to figure out how to stop the transmission. In my view, the most promising at the moment is the use of collars and investments in vaccines, which is also difficult, since the organism is quite complex”, he concludes.

Genes may help in the treatment of visceral leishmaniasis in BrazilA research team in collaboration with the University of Glasgow, the Federal University of Piauí and the Universidade Estadual de Montes Claros, found that the absence of four particular genes in the parasite Leishmania infantum in Brazil makes it less susceptible to an oral medication called miltefosine. The study may help doctors to predict the results of drug treatment. The results may lead to a new prognostic test able to predict which patients will respond well to treatment and which require alternative solutions.