A little-known virus spreads in South America: What is Oropouche fever?

Produced by: Science Popularization China

Author: Yang Cihan (PhD in Biology)

Producer: China Science Expo

Recently, South America, more than 15,000 kilometers away from us, is experiencing an outbreak of a serious viral disease, Oropouche fever.

According to CCTV News, according to the latest data released by the Amazon State Health Monitoring Foundation in Brazil, there have been 1,674 confirmed cases of Oropouche fever in the state from January to February 2024. On March 1, the Amazon State Government confirmed that an Oropouche fever outbreak had occurred in the state.

According to ScienceAdviser, as of June 2024, Brazil has reported 5,530 cases of Oropouche fever, more than six times the number of cases in the whole of 2023. The epidemic is gradually expanding, and the disease has also been found in areas far away from the rainforest, such as Bolivia, Colombia and Cuba.

In fact, this is not the first outbreak of the disease. There have been more than 30 outbreaks, with more than 500,000 people infected. Oropouche fever is the second largest vector-borne infectious disease in Brazil. Compared with previous outbreaks, the scope and impact of this outbreak have increased significantly. Currently, Oropouche fever is mainly prevalent in Central America (Panama, Trinidad and Tobago) and South America (Brazil and Peru). It is estimated that 5 million people in the Americas may live under the threat of the disease.

Oropouche in America

(Image source: International Travel Health Advisory Network)

The pathogen that causes Oropouche fever

Oropouche fever is a viral disease caused by Oropouche virus (OROV), which is mainly transmitted by bites of blood-sucking insects such as mosquitoes and midges. The viral genome consists of three segments of single-stranded negative-sense RNA. The virus particles are spherical with a diameter of about 80-110nm. It belongs to the Orthobunyavirus genus of the Peribunyaviridae family.

The virus was first isolated in 1955 from the blood of a febrile forestry worker and was named after the village of Vega de Oropouche where the patient lived.

midge

(Image source: Bugguide)

mosquito

(Photo source: veer photo gallery)

Spread and Popularity

Researchers have found traces of the virus in vector mosquitoes collected in the wild, as well as sloths and other animals. At present, the transmission of Oropouche virus is divided into two types of cycles. The first is the jungle cycle, in which mammals (three-toed sloths, non-human primates and rodents) and birds are the natural reservoir hosts of the virus, and its transmission vector is still uncertain. The second is the urban cycle, in which humans are the only known vertebrate host. The main transmission vectors in the urban cycle are Culicoides paraensis and Culex quinquefasciatus.

There is currently no evidence that the virus can be transmitted horizontally between people. It is worth noting that humans may be an important hub between the two types of circulation. There is evidence that the virus is usually caused by infected people with a history of living in forest areas and in the viremic period entering urban areas, which leads to the urban circulation of the virus.

The transmission of Oropouche virus is divided into sylvatic and urban cycles

(Photo source: drawn by the author)

Symptoms and treatment

Symptoms of Oropouche virus infection are similar to those of dengue fever, with clinical symptoms beginning 4-8 days (or 3-12 days) after infection. The onset of illness is sudden, usually accompanied by fever, headache, joint stiffness, pain, chills, and sometimes persistent nausea and vomiting, which can last up to 5-7 days. Severe clinical manifestations are rare, but may lead to aseptic meningitis.

Most cases will recover within seven days, but some patients may take weeks to recover. Because the symptoms of Oropouche fever are similar to those of other arbovirus infections and the infected can recover on their own, it is often misdiagnosed or ignored in clinical practice, thus underestimating its prevalence, leading to sudden outbreaks and epidemics. Currently, no specific antiviral drugs or vaccines for this virus have been developed for clinical use.

This type of virus was found in my country

The orthobunyaviruses currently discovered in my country and transmitted by mosquitoes and midges include Tahyna virus (TAHV), Batai virus (BATV), Akabane virus (AKAV), Oya virus (OYAV), Cat Que virus (CQV), Manzanilla virus (MANV) and Ebinur lake virus (EBIV).

The first three viruses are widely distributed in my country, among which Tashina virus is mainly concentrated in the northwest of my country. In 2009, 5 confirmed cases of TAHV infection were found in Golmud, Qinghai Province. The main clinical features were fever, 80% of the patients showed pharyngitis, in addition to fatigue, loss of appetite, joint pain and headache. All symptoms can be recovered within 2-3 days.

The distribution and host range of the Batai virus is even wider. The virus can be found in mosquitoes or animals in Yunnan, Inner Mongolia and Zhejiang, but no human cases related to it have been found in my country.

After the Akaba virus was first isolated from mosquito and midge samples collected in Shanghai, my country in 1998, the virus was also isolated from mosquitoes or animals in Hunan, Guangxi and Yunnan. The results of serological surveys showed that Akaba virus antibodies are widely present in the sera of cattle and sheep in China.

Pigs are the main mammalian hosts of Oya virus, Cat Que virus and Manzanilla virus, which have been found in mosquitoes in Yunnan, Guangzhou, Hunan, Sichuan and other places. Lake Aibi virus was isolated from mosquito samples in the Lake Aibi area of ​​Xinjiang. Although no human infection cases have been found in my country, laboratory evaluation has shown that these viruses are potentially pathogenic to humans or animals.

How to prevent it?

The prevalence of Oropouche fever has once again reminded us that we need to pay attention to the prevention of arboviruses in our daily lives. First of all, we need to be aware that the infection and transmission of arboviruses are inseparable from vectors, mainly including mosquitoes, ticks, midges, fleas and other blood-sucking insects. Therefore, in daily life and outdoor activities, such as in park grass, scenic woodlands, riverside and other places, we must always pay attention to mosquito and tick prevention, and be careful of midges that are smaller than mosquitoes.

It is recommended to wear light-colored long-sleeved shirts and long pants when doing outdoor activities, or spray mosquito repellent in time, and tie up your trouser legs when walking in the grass. When living at home, use mosquito nets, screen doors and screen windows to reduce the entry of mosquitoes, keep the surrounding area clean and hygienic, clean up stagnant water and wet garbage, and reduce the breeding of insect vectors.

tick

(Photo source: veer photo gallery)

References:

1.A little-known virus on the rise in South America could overwhelm health systems.

2.Travassos da Rosa JF, de Souza WM, Pinheiro FP, Figueiredo ML, Cardoso JF, Acrani GO, Nunes MRT. Oropouche Virus: Clinical, Epidemiological, and Molecular Aspects of a Neglected Orthobunyavirus. Am J Trop Med Hyg. 2017 May;96(5):1019-1030.

3. Xia Han, Yuan Zhiming. 2023. Discovery, distribution and response of arboviruses in my country over the past 70 years[J]. Chinese Journal of Schistosomiasis Control, 35(05): 427-436+450.

4. Fu Shihong, Sun Xiaohong, Wang Huanyu, et al. 2005. Molecular biological identification of the first isolated Batai virus in my country[J]. Chinese Journal of Experimental and Clinical Virology, 19(04): 331-334.

5. Lü Z, Fu S, Lü X, et al. 2011. Biological characteristics and molecular evolution analysis of the Tahyna virus strain isolated for the first time in China[J]. Acta Virologica Sinica, 27(02): 97-102.