Oropouche fever is associated with cases of microcephaly in babies; understand the warning

Researchers at the Evandro Chagas Institute (IEC), associated with the Ministry of Health (MS), have found evidence that oropouche fever, a disease transmitted by mosquitoes, can be passed from mother to baby during pregnancy. In light of the discovery, the ministry issued a technical note this weekend recommending that states and municipalities increase their vigilance regarding the possibility of this type of transmission, known as vertical transmission.

The alert was issued after the IEC identified the presence of antibodies against the virus in four babies born with microcephaly, as well as genetic material from the oropouche virus in a stillborn fetus at 30 weeks of gestation.

The ministry highlights that the findings are evidence of vertical transmission of the virus, but the limitations of the study do not allow confirmation that infection during pregnancy is the cause of neurological malformations in babies.

Studies with newborns were conducted last month, when the institution analyzed serum and cerebrospinal fluid samples (a type of fluid that protects the brain and spinal cord), collected to investigate arboviruses that can affect the nervous system, but with negative results for other infections, such as zika and chikungunya.

In addition to ruling out the possibility of these diseases, the presence of other possible causes of microcephaly, such as toxoplasmosis or syphilis infections, was not identified in the mothers.

Thus, they detected the presence of IgM class antibodies against the oropouche virus in four of the babies with microcephaly, three of them at one day of age and one at 27 days.

This month, laboratory investigations in a case of fetal death, at 30 weeks of gestation, identified genetic material of the OROV virus in the umbilical cord blood, placenta and several fetal organs, including brain tissue, liver, kidneys, lungs, heart and spleen of the fetus.

“This is evidence of the occurrence of vertical transmission of the virus. Laboratory analyses and epidemiological and clinical data are being carried out for the conclusion and final classification of this case,” the ministry said in the note.

Animal studies

Research carried out on animals infected by viruses from the same serological group as Orthobunyavirus Peribunyaviridae (OROV), the virus that causes oropouche fever, and transmitted by mosquitoes of the same genus, proved that there is vertical transmission in these agents, which can cause abortions and fetal malformations.

Given these data, the ministry states that the possibility of transmission of the oropouche virus from mother to baby has been considered since the first outbreaks recorded in Brazil. However, the ministry highlights that, to date, there is no solid scientific evidence to confirm transmission or its effects.

Relationship with microcephaly

According to Pedro Vasconcelos, a researcher at the IEC and one of those involved in the investigation, although tests that demonstrate the presence of viral antigens are still needed to confirm this, there is a high chance that the oropouche virus is, in fact, the cause of the documented cases of microcephaly. “Because the finding of the IgM antibody in the central system is highly indicative of infection at the site, that is, that the virus penetrated, infected and induced the formation of antibodies in the region,” he states.

The investigation revives concerns about the history of the Zika virus, another arbovirus. Previously a rarity, microcephaly became common in several parts of Brazil in 2015. In the first few months, the scientific community was still unaware, but there was a link between the virus and the disease, which resulted in the birth of more than 4,000 babies with the malformation in the country.

Clinical investigations revealed that most mothers of newborns with microcephaly reported symptoms of a viral infection early in pregnancy, leading to suspicion of Zika. According to the ministry, between 2015 and 2017, 4,595 live births with the congenital malformation were recorded.

Oropouche, on the other hand, is a completely different virus, says Vasconcelos. First, although the sand fly, the vector of oropouche, is widely distributed, it is less associated with disease transmission than the Aedes mosquito, which transmits Zika. This and other characteristics lead the researcher to believe that there is a possibility of an outbreak, but not on the same scale as the one that began in 2015. However, he emphasizes: “the impact should be smaller, but not insignificant.”

Furthermore, while the presence of viral antigens in people’s brains was demonstrated in the case of Zika virus, this confirmation was only possible in one case of oropouche. Therefore, the next steps in the study are to identify the antigens, conduct experiments with animals and actively search for cases of oropouche fever in pregnant women, to examine the presence of similar cases.

Number of cases

The Ministry of Health had already issued a warning about the increase and spread of oropouche fever in Brazil in May. This is because the number of diagnoses of the disease increased fivefold between 2023 and 2024.

According to the agency, up to epidemiological week 27 of 2024, 7,044 cases of the disease were confirmed in Brazil, with autochthonous, that is, local, transmission in 16 federative units and with the probable site of infection under investigation in another three, as per the list below.

States with confirmed cases of oropouche:

• Amazonas
• Rondônia
• Bahia
• Holy Spirit
• Acre
• Roraima
• Santa Catarina
• Minas Gerais
• For
• Rio de Janeiro
• Piauí
• Mato Grosso
• Pernambuco
• Amapá
• Maranhao
• Tocantins

UFs with local transmission under investigation

• Ceara
• Paraná
• Mato Grosso do Sul

Previously, the registration of cases was concentrated primarily in the North Region, which draws attention to the spread of the disease.

What is oropouche fever?

Oropouche fever is a disease caused by an arbovirus (virus transmitted by mosquito species) called Orthobunyavirus Peribunyaviridae (OROV). Transmitted to humans mainly by the bite of Culicoides paraensis, known as the sandfly or sandfly, this virus was detected in Brazil in the 1960s from a blood sample taken from a sloth captured during the construction of the Belém-Brasília highway.

Since then, isolated cases and outbreaks have been reported in Brazil, mainly in the Amazon region. Cases and outbreaks have also been reported in other countries in Central and South America (Panama, Argentina, Bolivia, Ecuador, Peru and Venezuela).

How does transmission occur?

There are two types of disease transmission cycles:

Wild cycle: in this cycle, animals such as sloths and monkeys are the hosts of the virus. Some types of mosquitoes, such as Coquilletti diavenezuelensis and Aedes serratus, can also carry the virus, but the maruim is considered the main transmitter in this cycle.

Urban cycle: in the urban cycle, humans are the main hosts of the virus. The maruim is also the main vector, but some cases may also be associated with Culex quinquefasciatus, commonly found in urban environments.

Symptoms

The symptoms of oropouche fever are similar to those of dengue and chikungunya: headache, muscle pain, joint pain, nausea and diarrhea.

In addition to being transmitted by different mosquitoes, which in the case of dengue fever is Aedes aegypti, the diseases differ in the evolution of the clinical picture.

While patients diagnosed with dengue fever may develop severe abdominal pain and, in more severe cases, internal bleeding, such symptoms are not seen in oropouche fever.

In the case of oropouche, specifically, the most severe cases may involve impairment of the central nervous system, causing aseptic meningitis and meningoencephalitis, especially in immunocompromised patients.

Recommendations

As protective measures for pregnant women, the Ministry of Health recommends:

Avoid areas where there are a lot of insects (mosquitoes and midges) if possible, and use fine mesh screens on doors and windows;

Wear clothes that cover most of your body and apply repellent to exposed areas of your skin;

Keep the house clean, including cleaning the land and animal breeding areas, and collecting leaves and fruit that fall to the ground;

If there are confirmed cases in your area, follow the guidance of local health authorities to reduce the risk of transmission.

In the technical note, the body also recommends that public managers intensify surveillance of the following cases:

Outcomes of pregnancy and assessment and monitoring of the baby in women with suspected arboviruses during pregnancy, with sample collection and completion of the notification form;

Abortion, fetal death and congenital neurological malformations, with collection of serum, blood, cord blood, cerebrospinal fluid and tissue samples to investigate markers of OROV infection.

Information from Estadão Content