'We can no longer eradicate the dengue mosquito,' says biologist.

Marco Weissheimer, On the 21 - On May 4th, the Minister of Health, Arthur Chioro, confirmed that the country is facing a dengue epidemic. According to a survey by the Ministry of Health, there were 745.957 cases up to April 18th, and this number is expected to increase. According to Chioro, the epidemic is concentrated in seven states, which have more than 300 cases per 100 inhabitants: São Paulo, Acre, Goiás, Mato Grosso do Sul, Tocantins, Rio Grande do Norte, and Paraná. São Paulo currently accounts for 73% of the 229 confirmed dengue deaths in the country up to that week. These numbers show that, contrary to what many people believed until recently, dengue is not a disease that chooses social class to manifest itself.

"The dengue mosquito is extremely democratic. Wherever there is a place that accumulates water, it will settle, whether in a favela or an upper-class neighborhood," says Carmen Silvia Gomes, a biologist with the State Dengue Control Program at the State Center for Health Surveillance (CEVS), linked to the State Health Secretariat, in an interview with Sul21. Carmen Gomes analyzes the evolution of dengue in Rio Grande do Sul in recent years and defends the importance of public participation in controlling the Aedes aegypti mosquito, the vector of the disease.

"We can no longer eradicate the presence of the dengue mosquito. What we need to try to do is keep this infestation level as low as possible to hinder the transmission of the virus. If each person looks at their living and working spaces, identifies possible breeding grounds for the mosquito and eliminates them, we will be taking a big step towards tackling this disease," says the biologist from the Health Department.

Sul21: What is the history of dengue fever in Rio Grande do Sul? Since when has the state been on the map for this disease?

Carmen Silvia Gomes: The presence of the Aedes aegypti mosquito in Rio Grande do Sul was first detected in 1995 in the municipality of Caxias do Sul. From then on, the State Health Department began surveillance work on this vector. Since then, we have observed that, from the moment the municipalities managed to structure themselves and create surveillance teams to do house-to-house work, the number of cities that detected the presence of Aedes aegypti increased considerably. Today we have 149 municipalities in the state with identified mosquitoes. This increase in the number of municipalities is related to several factors. One of them is the resistance of part of the population to change their habits. Many people insist, for example, on keeping those saucers under flowerpots. In cemeteries, people often still keep water in vases and glasses to place flowers on graves. We also have the increase in the number of PET bottles that end up serving as a container for something. All this ends up favoring the increase in mosquito breeding grounds.
Another important factor is related to the Aedes aegypti egg, which usually remains viable for up to a year. Therefore, this egg can often be easily transported from one municipality to another and from one state to another. All these factors contribute to the mosquito's dispersal.

Sul21: Are there environmental issues, such as deforestation and climate change, that influence this mosquito dispersal process and explain its greater presence in certain areas, as is the case, for example, in the northwestern region of Rio Grande do Sul?

Carmen Silvia Gomes: Climate is a significant influence. The issue in the northwest region is also related to its proximity to Argentina, a country that also has the presence of Aedes aegypti and cases of dengue fever. Summer, high temperatures, and rainfall also contribute to an increase in the population, as they create ideal conditions for mosquito proliferation. Since the female mosquito usually lays her eggs in containers that are mostly inside homes, we have to put the environmental aspect into perspective. Of course, deforestation, for example, can influence other factors such as rainfall patterns and temperature, but it is not as directly related to the increase in the mosquito population.

Sul21: In your opinion, is the explosion of dengue cases in São Paulo this year related to the water crisis the state is experiencing?

Carmen Silvia Gomes: The fundamental problem with dengue fever is that this disease requires constant surveillance. Surveillance and control efforts must be carried out in each municipality year-round to keep mosquito populations at very low levels, which hinders the transmission of the virus.

Sul21: What would be considered very low levels? Is that quantifiable?

Carmen Silvia Gomes: Yes. From the moment a house-to-house visit is made, an infestation index is determined. A low level is when, out of every hundred houses, only one shows the presence of the vector. When the work is not carried out properly throughout the year, it becomes very difficult to maintain these very low levels during the summer, when the mosquito population increases. This is without mentioning the fact that during this period people travel a lot, going from one state to another and often carrying the virus from one state to another, creating the conditions to trigger an epidemic. Dengue epidemics, when they occur, have this explosive characteristic. When it arises, there are many cases.

Unlike the common mosquito, which bites at night, generally when a person is sleeping, the female Aedes aegypti usually bites during the day. When it lands on someone to feed, that person ends up moving and the female goes to another. There, it sucks a little more blood, the person moves, and the process repeats. This passage of the same mosquito through several people helps to understand the explosive nature of these dengue epidemics worldwide.

Sul21: What is your daily work routine like here at the Surveillance Center in relation to dengue control?

Carmen Silvia Gomes: The State Center for Health Surveillance (CEVS) coordinates the State Program for the Control of Aedes aegypti and Dengue Fever. The state has 19 regional health coordination centers, and each of them has an environmental surveillance unit that coordinates dengue-related actions in its municipalities. The CEVS is responsible for supervising the work carried out by the municipalities, providing necessary support when requested, supplying inputs (insecticides, machinery, and personal protective equipment), and providing training and capacity building for the health agents involved in these actions.

Sul21: Does the increase in the number of municipalities with dengue cases in recent years indicate, in addition to behavioral problems in the population, the existence of problems in the work of inspection and control by the public authorities?

Carmen Silvia Gomes: It's a combination of things that needs to be analyzed. Beyond the behavioral issue, there's the problem of maintaining these teams of agents working in the municipalities. Often, the municipality has difficulties in how to hire and pay these agents. Sometimes these contracts are for fixed periods of four or six months. When this happens, the work is often interrupted. Furthermore, as municipalities become more structured, cases begin to appear. If you don't look for them, you won't find the presence of dengue vectors. From the moment there's a team that goes into the field, visits house to house, collects larvae, and identifies the presence of the vector, we have an indication that the municipality is working. From this discovery, control actions follow, using insecticides or mechanical control.

The Ministry of Health annually allocates resources to the area of ​​health surveillance, which the municipality can use for specific actions. The state also makes some allocations during periods when there is assessed to be greater vulnerability, such as in the summer. When an epidemic occurs in a region, a task force is assembled with the presence of state agents who support the control work of the municipalities.

Sul21: What are the indicators used to define an epidemic scenario?

Carmen Silvia Gomes: This varies greatly. For example, we can have a case of a municipality that has never had an epidemic and suddenly registers 5, 10, or 15 cases. This situation could constitute an epidemic. But that's not the most important thing. The important thing is to determine whether or not the municipality has the presence of Aedes aegypti. If it does, it presents a risk of having a dengue epidemic. Another important factor is knowing if the virus is circulating. If so, from the first case onwards, the actions that are triggered are the same regardless of whether there are 2, 3, or 4 cases. This is from the point of view of environmental control. Obviously, from the point of view of treating infected people, it is different for the municipality to have 3 or 100 cases.

Sul21: To date, there have been two deaths from dengue fever recorded in Rio Grande do Sul. What factors can cause fatalities in cases of dengue? Is delayed diagnosis one of them?

Carmen Silvia Gomes: Yes. Because dengue fever has symptoms very similar to the flu, people often feel better and think they are well. When a person is diagnosed with dengue, they need to return to the health center for evaluation. In some situations—I'm not saying these are the cases in the two deaths in the state—people end up feeling better and don't return to the health center. Then they end up developing a hemorrhagic condition that can lead to death.

Sul21: Until quite recently, there was a common belief that dengue fever was something that affected poor people, those living in the outskirts of cities, and impoverished areas. Reality seems to have disproved that idea, doesn't it? The Southeast region now leads the ranking for dengue fever cases in Brazil.

Carmen Silvia Gomes: Absolutely. The dengue mosquito is extremely democratic. Wherever there is a place that accumulates water, it will settle, whether in a favela or an upper-class neighborhood. If a person keeps any container with water in their yard, they will be breeding the mosquito and running the risk of becoming infected.

Sul21: There are several reports of resistance, in some sectors of the population, when receiving visits from health agents responsible for inspection, prevention, and control. Is this happening?

Carmen Silvia Gomes: Yes, this is a reflection of the violence. People are afraid to let someone they don't know into their homes. This is also one of the obstacles faced by surveillance work. This needs to be addressed very thoroughly with the population, who need to be well-informed about these actions. The Porto Alegre City Hall provided a phone number some time ago through which people could check the health agent's identification number. But there is a lot of resistance, yes. There are people who don't open their doors and don't let the agent in.

People already know that dengue fever is transmitted by a mosquito. And most also know what to do to avoid the presence of this mosquito. The presence of health agents in homes is more to verify the existence of possible water deposits that could breed mosquitoes. The population often expects the agent to come to their home so that they can take action that should be taken by each of us. If each of us takes care of our own space and doesn't allow these types of breeding grounds, we won't need the presence of health agents in our homes.

Sul21: Is the dengue mosquito very different from the traditional mosquito we have here in Rio Grande do Sul?

Carmen Silvia Gomes: It has some characteristics that are different from those of the common mosquito and can be easily identified. It has white-striped legs, which is a characteristic of this species. This, by itself, does not mean that it is Aedes aegypti, but it is an indication that it could be. For accurate identification, it needs to be taken to a laboratory. A person who is not trained is not able to make this identification with the naked eye.

Sul21: What is your assessment of the evolution of dengue fever in Rio Grande do Sul in recent years? Is this problem getting worse, or is it not possible to say?

Carmen Silvia Gomes: The state of Rio Grande do Sul experienced its first dengue epidemic in 2007. Before that, the country was already facing this problem. The overall situation in the country will always end up being reflected in the states. If we have epidemic outbreaks in certain states, the chance of having an epidemic here also increases. We have the issue of travel that I already mentioned. It is also important to point out that dengue is caused by four different serotypes, meaning a person can have dengue four times. There is dengue one, dengue two, dengue three, and dengue four. This numbering is not a scale of severity, just an identification of the different types. When a person is infected by one type, they end up developing antibodies for that specific type, but remain vulnerable to the other three. And when they are successively infected by two different serotypes, the chance of developing the hemorrhagic form the second time is very high.

Over the years, the work has improved in the sense that municipalities have begun to structure themselves to carry out surveillance. From the moment we have this structured surveillance system and the mosquito is already distributed throughout the territory, we will be constantly encountering it. We can no longer eradicate the presence of the dengue mosquito. What we need to try to do is keep this infestation level as low as possible to hinder the transmission of the virus.

Sul21: Is there any type of biological control that can be used to reduce the mosquito population?

Carmen Silvia Gomes: Biological control is one of the control alternatives for several pest species, but in the case of Aedes aegypti, it is a very expensive product. Today, it is used when resistance to chemical products is detected in the mosquito. It is a bacterium that is placed in the water and ingested by the mosquito larva, causing paralysis of its digestive tract. In some states, the Ministry of Health distributes the biological product because resistance to chemical products has already been detected. Here in Rio Grande do Sul, it is not used.

Sul21: Last week, the Minister of Health admitted the existence of an epidemic in seven states of the country. Could Rio Grande do Sul be added to this map?

Carmen Silvia Gomes: Yes. From the moment the vector is present, the risk exists. Now, we are beginning a cold season and, automatically, the cases are already starting to decrease. All the epidemics we've had here in the state occurred during this period of April and May, which coincides with the end of the holidays. The trend is for a decrease in cases, but whenever the vector is present, there is a risk of viral circulation. In winter, we have the false idea that mosquitoes disappear, but the cold doesn't eliminate them. There is a natural decrease in the population, but they don't disappear.

Finally, I would like to draw attention to the importance of the population in this surveillance and control process. If each person looks at their living and working spaces, identifies potential breeding grounds for the mosquito and eliminates them, we will be taking a big step towards tackling this disease. The participation of the population in this work is extremely important.