Chagas Disease in Mexico: The Transmission and Distribution

Mexico is the country with the highest number of vectors that transmit Chagas disease. It is a silent disease that causes, in low-income people in rural areas, inflammation of a single eyelid, fever, and heart failure. April 14, World Chagas Disease Day.

Chagas Disease in Mexico: The Transmission and Distribution
The bedbug: April 14, World Chagas Disease Day. Image by Cicero7 from Pixabay

Mexico is the endemic country for Chagas disease. Its incidence is estimated at 1,100,000 infected people, but almost 30 million could be at risk of contracting it, says Paz María Salazar Schettino, a scientist at the School of Medicine (FM).

The Chagas disease mainly affects the heart, causing 14,000 deaths a year mainly in South America, and primarily damages the population living in rural areas, because that is where the transmitters are found, which are the triatomine bugs that transmit the Trypanosoma cruzi parasite.

Not all people develop Chagas disease, only approximately 30 percent of those infected. As for the transmitters, in a study carried out in the state of Veracruz, only 10 percent of them were found to have the parasite.

This pathology in the acute phase can go unnoticed, since on many occasions there is only fever and consequently it is not treated, so that after several years there is dilated cardiac insufficiency, even death, in some cases sudden.

Mexico is the country with the most proven transmitters of this disease: two species of intra-domiciliary bedbugs (living inside houses) and thirteen peri-domiciliary (outside). In the southern cone, there is only one important one: Triatoma infestans.

For example, in the Huasteca, Triatoma dimidiata is abundant and infects mainly children and the elderly; "we have a red focus for this transmitter in that area", where we found infants with cardiomyopathy, as in the altiplano, with the other intra-domiciliary transmitter, Triatoma barberi.

Characteristics of Chagas disease

World Chagas Disease Day is celebrated on April 14 to raise awareness of this neglected disorder. It was first celebrated in 2020, following the approval and endorsement received by the World Health Assembly at the World Health Organization in May 2019.

This year the ephemeris aims to give visibility and attention to the importance of improving early detection, achieving expanded diagnostic coverage, and equitable access to clinical care.

This disease was discovered in 1909 by Dr. Carlos Chagas, a Brazilian physician and malaria expert, who once saw bedbugs crawling up and down the walls of houses. He checked them and in the defecation of the triatomine, he saw a parasite that he named Schizotrypanum cruzi (Trypanosoma cruzi).

The parasite enters the human organism in the feces of the bedbug; this type of transmission is known as "rural Chagas disease". In the beginning, there is the so-called acute phase, characterized by fever, inflammation of only one eye (known as Romaña's sign), the so-called Chagoma of inoculation (pink to red inflammatory reaction of hard consistency that coincides with the area of the bite and inoculation of the parasite), and inflammation of the ganglions.

Without treatment and over the years, a problem manifests itself mainly in the heart. That is why it is known as the silent disease or the disease of oblivion, because it goes on for a long time without manifesting itself and because it especially affects low-income people in rural areas. This period is called the indeterminate period or chronic asymptomatic phase, during which the parasite gradually produces lesions inside the organism.

It is also transmitted through blood, transfusions, and organ transplants; this is known as "urban Chagas disease". The infection can also be transmitted orally, when consuming, for example, sugar cane juice; "this has been studied in other countries, although it has not been described in Mexico". It can also be transmitted during pregnancy.

Although Trypanosoma cruzi can cause damage to other organs such as the esophagus, colon, or gall bladder, the most frequent is heart failure and sudden death, as when a soccer player is playing a game and suddenly falls lifeless. In Mexico we see many places where deaths from heart failure and infarction are reported; it is not known how many are due to Chagas disease. Many studies are needed to have exact figures.

Treatment with Benznidazole or Nifurtimox is effective in the acute phase and it is possible to cure this disease. However, in the chronic phase it is only possible to administer antiarrhythmic drugs, among others, "because the arrhythmias are the most annoying for the patient", but the cardiac tissue is already destroyed.

Prevention of Chagas disease

In rural areas where there are houses built with palm roofs, sticks, mud walls, and dirt floors, the highest frequency of infected people are found.

Having firm floors helps to reduce the incidence of the disease: home improvement is important because some bedbugs live mainly on the floor and walls; health education is also of utmost importance, in addition to the use of insecticides where peri-domiciliary transmitters are found.

It is also important to use screens on doors and windows so that the transmitter does not enter the house during the night; follow hygiene measures in the preparation of food and beverages and have a blood test before any transfusion.

The behavior of Chagas disease

According to the World Health Organization, 25% of the total population of Central and South America is at risk of contracting the infection. There are one million cases each year and more than 45,000 people die in the same period. Of the 16 million people infected, 2 to 3 million already present the complications of the chronic stage and, in about 3 million, the Trypanosoma is still in the incubation period.

Although there is no consistent epidemiological follow-up of Chagas disease in Mexico, it is estimated that about 28 million people are at risk, mainly in rural areas where marginalization and lack of health services are the norms. However, it has been reported that in some urban or suburban areas of the cities of Oaxaca and Cuernavaca the prevalence of the infection is high.

The distribution of the disease is related to the distribution of the bedbug, which covers three-quarters of the southern region, in semiarid areas below 1,800 meters above sea level. Nonetheless, research to define specific risk areas in each state began years ago and for some specialists in the field, Chagas is the most important parasitological disease in Mexico.

Control of Chagas disease

The parasite induces an autoimmune reaction, so the possibility of finding a vaccine is remote since instead of attacking the Trypanosoma, it would attack the cells themselves. Furthermore, Chagas disease is not recognized by the country's health authorities, so it is not possible to organize fumigation campaigns in high-risk areas. In conclusion, the only weapon available is education for prevention.