May 29th, 2019 – The African country of Uganda reported various disease outbreaks in 2017 and 2018, and according to new information from the Ugandan Ministry of Health, the yellow fever virus has become endemic.
Uganda notified the World Health Organization (WHO) that they have declared a yellow fever outbreak on May 6, 2019, following laboratory confirmations from the Uganda Virus Research Institute (UVRI).
Following that declaration, various yellow fever outbreaks were confirmed in the Northern and Central regions of Uganda, on May 14, 2019.
To better understand this outbreak, a national rapid response team was constituted and dispatched to the affected Uganda districts to conduct further investigations to support the response activities.
This is because Uganda has a history of outbreaks, such as in 2016.
The yellow fever outbreak of 2016 was likely sylvatic and transmitted to a susceptible population probably by mosquito bites during farming in forest and swampy areas.
To reduce this outbreak, a reactive yellow fever vaccination campaign was conducted in 3 districts, including Kalangala, Masaka, and Ruukunguri.
One of the affected districts during this outbreak was located along the border with the Democratic Republic of the Congo and South Sudan. Since there are frequent population movements between these countries, there is a potential for the international spread of the yellow fever virus, says the WHO.
Yellow fever is a viral disease that is transmitted by certain types of mosquitoes. The infection can cause illness which ranges from a fever with aches and pains to severe liver disease with bleeding and yellowing skin and it can spread rapidly.
However, yellow fever can be prevented by a single vaccine dose, says the US Centers for Disease Control and Prevention (CDC).
The CDC’s Advisory Committee on Immunization Practices published a recommendation in 2015 that 1 dose of yellow fever vaccine provides long-lasting protection and is adequate for most travelers.
In reaction to Uganda's outbreak declaration, the CDC updated its vaccination suggestions when visiting Uganda on May 16, 2019. The recommended vaccinesnow include the MMR, Routine Vaccines and the yellow fever vaccine.
In the USA, the Stamaril vaccine is approved and has a clinical efficacy profile similar to the YF-VAX vaccine, and is available at select locations.
“Rabid bats have been reported from every state except Hawaii,” Emily Pieracci, DVM, MPH,a veterinarian in the CDC’s Rabies Branch, said during a telebriefing. “While the majority of bats in the wild do not carry rabies, you cannot tell which bats have rabies just by looking at them.”
Pieracci said many people may not know bats can spread rabies.
Bats are the leading cause of rabies in the U.S.
“For example, we have had several large groups of people exposed to bats in university dorms, camping lodges and schools.”
According to Pieracci and colleagues, data from 1938 to 2018 show a steady decline in human rabies cases caused by dog bites, whereas bats surpassed raccoons in 2015 as the leading cause of human rabies infections in the U.S. Bats accounted for 62 (70%) of 89 human rabies cases between 1960 and 2018, according to the study.
Further, mass bat exposures also are on the rise, according to Pieracci. These are instances where 10 or more people are exposed to a potentially rabid bat. With the coming summer months, Pieracci and colleagues warned that increased time spent outdoors — in campgrounds, parks or yards — will expose large groups of people to potential interactions with bats.
“People may not realize that bats carry rabies, so they may not see their medical provider after touching or handling a bat,” CDC Principal Deputy Director Anne Schuchat, MD, said in the briefing. “Bat bites are smaller than the top of a pencil eraser, and so they can go unnoticed. This is a problem, because rabies is deadly once symptoms start. Recognizing the risk and getting treatment fast is important.”
In 2017 and 2018, an average of 55,000 Americans received post-exposure prophylaxis (PEP) for potential rabies exposure each year, according to the findings. Schuchat noted that 70% of Americans who died from rabies in the U.S. were infected by bats.
Globally, rabies causes around 59,000 deaths each year, including approximately two in the U.S., according to Pieracci and colleagues.
“The bottom line is rabies continues to be a threat in the U.S. and abroad, and people should see their health care professionals if they think they've been bitten or scratched by an animal and before symptoms occur,” Schuchat said. “An ounce of prevention can go a long way.”
Researchers identified numerous clinical and laboratory predictors of mortality in patients with yellow fever, including higher RNA plasma viral load, according to findings reported in The Lancet Infectious Diseases.
“Although only 10% to 50% of patients infected with yellow fever virus develop symptoms, yellow fever virus infection is recognized as a very severe disease, with associated mortality as high as 50% in symptomatic patients,” Esper G. Kallas, MD, PhD, from the Clinical Hospital at the University of São Paolo, and colleagues wrote.
Kallas and colleagues’ observational cohort study included adult patients aged 18 years or older with yellow fever who were admitted to the hospital between Jan. 11, 2018, and May 10, 2018. The final analysis included 76 patients with yellow fever virus, confirmed either through detectable yellow fever virus RNA in blood or at autopsy.
The researchers reported that 36% of patients died within 60 days after hospital admission. According to the findings, risk factors associated with higher mortality included older age; male sex; higher leukocyte and neutrophil counts; higher alanine aminotransferase, aspartate transaminase, bilirubin and creatinine; prolonged prothrombin time; and higher yellow fever virus RNA plasma viral load.
Of the 11 patients with neutrophil counts of 4,000 cells/mL or greater and viral loads of 5.1 log10 copies/mL or greater, 100% died compared with 11% of the 27 patients with neutrophil counts of less than 4,000 cells/mL and viral loads of less than 5.1 log10 copies/mL, the researchers reported.
“Our findings have several implications for the care of patients with yellow fever virus,” Kallas and colleagues wrote. “Identification of poor outcome markers could help guide resource allocation and strategies to provide intensive care for patients with potentially severe disease, supporting a rational approach during disease outbreaks. Medical services and intensive care units can be overwhelmed during the peak of epidemics and decision-making referral algorithms might take advantage of simple clinical and laboratory evaluation.”
In a related editorial, Annelies Wilder-Smith, MD, PhD, DTM&H, MIH, professor of emerging infectious diseases at the London School of Hygiene & Tropical Medicine, and colleagues explained that some of the study findings from Kallas and colleagues are “as expected.”
“Older age is also associated with more severe outcomes in other flavivirus infections, including Japanese encephalitis and West Nile encephalitis,” they wrote. “However, a potential novel finding is the higher viral load associated with fatal outcomes, suggesting a possible causative role, as has been shown in a hamster model. This finding has implications for improving understanding of the pathogenesis of severe disease and the potential role of early antiviral treatment in mitigating severity.”