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Yellow fever – Brazil Disease outbreak news 24 November 2017, WHO

Between July and mid-October 2017, a total of 71 suspected yellow fever cases were reported in São Paulo State, Brazil. Of these, two were confirmed, six are under investigation, and 63 were ruled out. The two confirmed cases (one of which was fatal) were reported from Itatiba from 17 September through 7 October 2017.

From July to early November, 580 epizootics in non-human primates (NHPs) were reported in São Paulo State, with an increase in the number of cases reported from 10 September 2017. Of these, 120 were confirmed for yellow fever, 233 are under investigation, 74 were classified as undetermined, and 153 were ruled out. The highest number of epizootics was registered in the health surveillance area of Campinas, where epizootic episodes were reported for the first time in the municipalities of Campo Limpo Paulista (in the week ending 23 September 2017), Atibaia (in the week ending 30 September 2017), and Jarinu (in the week ending 14 October 2017). Epizootics in NHPs were also recently reported in large parks located within the urban area of São Paulo City (in the week ending 14 October 2017).

Public health response

The detection of two confirmed yellow fever human cases and epizootics in the state of São Paulo, as well as confirmed yellow fever epizootics in the urban area of São Paulo City, prompted national authorities to begin vaccination campaigns in areas previously considered not at risk for yellow fever transmission. In addition, state and municipality health authorities are strengthening health care services and carrying out risk communication activities.

WHO risk assessment

These are the first human cases of yellow fever that have been reported in Brazil since June 2017. These cases, alongside the occurrence of epizootics in the urban area of São Paulo City and in municipalities that were previously considered not at risk for yellow fever, are a public health concern. Although Brazilian health authorities have swiftly implemented a series of public health measures in response to this event, including mass vaccination campaigns, it may take some time to reach optimal coverage in these areas given the large number of susceptible individuals. Currently, the number of unvaccinated people in São Paulo City remains high at around 10 million. If yellow fever transmission continues to spread to areas that were previously considered not at risk for yellow fever, ensuring the availability of vaccine and implementing control measures would pose significant challenges.

To date, there has been no evidence of transmission by Aedes aegypti in relation to this outbreak in Brazil which began in 2016. Although entomological studies conducted in selected municipalities of São Paulo revealed low levels of Ae. aegypti and Aedes albopictus infestation (pupa index range: 0% – 3.1%), the risk of sustained arbovirus transmission is ever present.

The risk of spread at the regional level is considered to be low given the high vaccination coverage in neighbouring countries; however, the detection of a human case of yellow fever in Oiapoque, the border river between French Guiana and Brazil in August 2017 by French health authorities indicates that the risk of regional spread exists. The risk at the global level is considered to be low and limited only to unvaccinated travellers returning from affected areas. Travelers who return home while infected with yellow fever virus may increase the risk of establishing local cycles of yellow fever transmission in areas where the competent vector is present.

WHO continues to monitor the epidemiological situation and assess the risk according to the latest available information.

WHO advice

Advice to travellers planning to visit areas at risk for yellow fever transmission in Brazil includes receiving yellow fever vaccine at least 10 days prior to traveling, following measures to avoid mosquito bites, and being aware of yellow fever symptoms and signs. WHO continues to promote health seeking behaviour when travelers are in and when they have returned from an area at risk for yellow fever transmission.

As per Annex 7 of the International Health Regulations (2005), a single dose of yellow fever vaccine is sufficient to confer sustained immunity and life-long protection against yellow fever disease. Booster doses of yellow fever vaccine are not needed. If, on medical grounds, a traveler cannot be vaccinated against yellow fever, this must be certified by the relevant authorities as per Annex 6 and Annex 7 of the International Health Regulations (2005).

The WHO Secretariat does not recommend any restrictions on travel or trade with/to Brazil according to the information currently available for this event.

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Ongoing surveillance and vaccination are key to prevent yellow fever outbreak in humans

November 6, 2017

A combination of continuous monitoring of mosquitoes and non-human primate deaths, along with laboratory tests and increased vaccination, is crucial to prevent human cases of yellow fever in places where the virus is transmitted. Findings from a brief research report are published in Annals of Internal Medicine.

Yellow fever is a virus found in South America and Africa that is transmitted by infected mosquitoes. Transmission typically occurs in wild animals, but occasionally spills over to humans entering forest regions. Still, urban transmission is rare, mainly due to vaccination. Recently, concerns about reemergence of urban yellow fever have grown because of the reappearance and rapid spread of A aegypti (a type of mosquito that may carry yellow fever) in the urban environment. Further, immunization coverage for yellow fever is insufficient because it is usually administered to high-risk populations.

Researchers from the Instituto Goncalo Moniz studied the 2017 epizootic outbreak (outbreak within animals) of yellow fever in Salvador, Brazil to determine the risk for human disease. The researchers studied the temporal and spatial distribution of the yellow fever virus outbreak affecting non-human primates (small monkeys) in Salvador, by geocoding the places where the monkeys were found dead. They also collected mosquitoes at such places to investigate potential vectors. The authors found that cases of yellow fever in non-human primates in densely urbanized areas posed a considerable risk for disease resurgence in humans because of the high prevalence of the A aegypti and A albopictus mosquitoes. Salvador has long been an epicenter of dengue transmission and more recently of Zika and chikungunya viruses, all with A aegypti as the main vector.

The authors conclude that surveillance and increased vaccination, even among those not considered at high risk for infection, could help to prevent human cases of yellow fever in Brazil.

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Yellow fever virus found in semen of Brazilian patient

SHOW CITATION

October 27, 2017

Researchers in Brazil recently detected yellow fever virus RNA in urine and semen samples from a convalescent patient in Brazil.

Yellow fever is normally detected in blood, but urine has been used to confirm yellow fever infection in humans, researchers from two universities and a research institute in São Paulo noted in their report. But yellow fever was not among the 27 viruses previously identified to persist in semen.

The researchers said their findings “suggest that semen can be a useful clinical material for diagnosis of yellow fever and indicate the need for testing urine and semen samples from patients with advanced disease.”

“Such testing could improve diagnostics, reduce false-negative results and strengthen the reliability of epidemiologic data during ongoing and future outbreaks,” they wrote in Emerging Infectious Diseases.

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A recent yellow fever outbreak in Brazil was fueled by cases among monkeys in the Amazon basin and other tropical forests in Brazil, rather than person-to-person transmission involving mosquitoes. Following a large vaccination campaign, Brazil declared an end to the outbreak in September.

According to the researchers, there were 792 confirmed cases and 274 deaths in the Brazilian outbreak as of July 10. Their report summarized the case of a man aged 65 years from São Paulo who was not vaccinated against yellow fever.

According to the researchers, the man had traveled to the southeastern Brazilian state of Minas Gerais on Dec. 28, not long after the first cases of yellow fever were detected there. About a week later, he traveled to a rural area north of São Paulo. Three days after that, on Jan. 6, he began experiencing symptoms of infection, including fever, chills, body pain and nausea, according to the researchers.

More severe symptoms developed, and the man was admitted to several different hospitals over the next few weeks, according to the report. On Jan. 16, he was admitted to a reference hospital for infectious diseases in São Paulo. Serum samples taken there were negative for yellow fever, but a urine sample obtained 10 days after symptom onset was positive for the virus, the researchers reported.

Urine and semen samples taken on Jan. 27 also were positive for yellow fever virus by qRT-PCR. The researchers tested the urine sample to evaluate infectivity and isolated the virus in cell culture, confirming virus integrity. They confirmed infectivity after a second virus passage. The researchers did not mention testing the semen sample for viable virus. – by Gerard Gallagher

Disclosures: The authors report no relevant financial disclosures.

PERSPECTIVE

PERSPECTIVE

The detection of yellow fever virus in urine and semen when it is undetectable in blood suggests an additional approach to making a yellow fever diagnosis. Viable virus in urine and evidence of virus in semen raises a question about the risk for sexual transmission. It also raises the question about possible effects that yellow fever virus infection might have on male fertility as it does with infection by the related Zika virus. These results are from a single case. Considerably more cases need to be studied to determine how frequently yellow fever virus is shed in urine and semen and for low long before any firm conclusions can be drawn.

Thomas M. Yuill, PhD

ProMED virus diseases moderator
Professor emeritus, department of pathobiological sciences and department of forest and wildlife ecology
University of Wisconsin-Madison

Disclosure: Yuill reports no relevant financial disclosures.

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