In illnesses, distinguishing between yellow fever and dengue fever is vital. While both are viral infections spread by mosquitoes, they differ significantly in severity, geographic distribution, and preventive strategies.

Dengue fever, known as break-bone fever, has surged globally, particularly in tropical regions. In contrast, yellow fever poses a significant threat in specific endemic areas like Africa and South America.

This article delves into their nuances, exploring epidemiology, symptoms, diagnosis, and management. Understanding these differences is crucial for accurate diagnosis and effective public health responses. Explore further to equip yourself with essential knowledge to combat these diseases.

What exactly are those two diseases and why should we differentiate them 

To break it down, we can start by defining the two diseases.

Dengue fever, also known as break-bone fever, is a viral illness transmitted by a mosquito called Aedes aegypti, particularly prevalent in tropical and subtropical regions.¹

Yellow fever may share some similarities to dengue but it is an entirely different disease. It is a viral disease that is also transmitted by the bite of infected Aedes or Haemagogus species of mosquitoes. These mosquito are found in both urban and rural environments. It has the potential to cause epidemics, but fortunately, we have developed a vaccine which prevents the disease.²

Dengue cases have surged globally, with reported cases from the WHO jumping from 505,430 in 2000 to 5.2 million in 2019, though the true figures are likely higher due to under-reporting. Estimates suggest 390 million infections annually, with 96 million showing clinical symptoms.

Endemic in over 100 countries, dengue disproportionately affects regions like the Americas, South-East Asia, and the Western Pacific. It's spreading to new areas, including Europe, with significant outbreaks recorded in various countries in 2019. As of 2021, dengue remains a concern in numerous countries, including Brazil, India, and Vietnam.¹

In 2023, approximately 34 African nations and 13 countries in Central and South America are identified as having either endemic regions or endemic status for yellow fever. According to a modelling analysis using African data sources, the estimated toll of severe yellow fever cases in 2013 ranged from 84,000 to 170,000, with 29,000 to 60,000 resulting in fatalities.³

Differentiating between dengue fever and yellow fever is crucial due to their varying severity, mortality rates, and geographic distributions. Yellow fever presents a more severe threat with higher mortality rates, primarily affecting Africa and South America. Dengue fever, more widespread globally, tends to cause milder symptoms but does still have the risk of causing severe disease. Accurate diagnosis is essential for appropriate treatment and effective public health responses, aiding in outbreak control.

How do we get the disease 

We may often associate these diseases with mosquitos, but in fact the symptoms are caused by viruses damaging our bodies. These viruses spend a portion of their life cycle inside the bodies of mosquitoes before they are transmitted to our bodies through an infected mosquito bite.

Both diseases are in most times transmitted by the same species of mosquitoes that is the Aedes, specifically Aedes aegypti or Aedes albopictus for Dengue. These mosquitoes have a preference for biting humans and can be found both indoors and outdoors, particularly near areas where people reside. They are known carriers of diseases such as dengue, chikungunya, and Zika, and they are active throughout the day and night.

Typically, they lay their eggs in standing water found in containers like buckets, bowls, animal dishes, flower pots, and vases. When they bite an infected person, they can become carriers of the virus themselves, transmitting it to others through subsequent bites.⁴

Yellow fever is transmitted by Aedes aegypti mosquito, when the infection occurs in urban settings, it can be transmitted by another species called Haemagogus when the infection occurs in rural settings such as jungles and mountains.⁵

Yellow fever transmission occurs in three main environments: the jungle (sylvatic), intermediate (savannah), and urban.²

In the jungle, the virus circulates between non-human primates and forest-dwelling mosquitoes, potentially infecting humans who enter these areas.²

In African border regions, an intermediate cycle facilitates transmission from monkeys to humans or between humans via mosquitoes.²

The urban cycle involves transmission between humans and urban mosquitoes. Infected individuals from jungle or savannah areas can introduce the virus into urban regions, where it can spread among human populations through mosquito bites.²

Symptoms and clinical presentation: what does infection look like?

While many individuals infected with dengue remain asymptomatic, those who exhibit symptoms typically experience a combination of high fever, headache, body pains, nausea, and skin rash. The majority tend to recover within 1 to 2 weeks without complications. However, in certain cases, the illness can progress to severe dengue, requiring hospitalization and specialized medical attention. 

Dengue typically manifests as mild or asymptomatic in most individuals, with recovery occurring within 1–2 weeks. However, rarely it can progress to a severe form, potentially resulting in fatality.¹

Symptoms, if present, usually emerge 4–10 days post-infection and endure for 2–7 days. These may present as a high fever (reaching 40°C/104°F), intense headache, eye pain, muscle and joint discomfort, nausea, vomiting, swollen glands, and a rash. Those who experience a secondary infection face an elevated risk of severe dengue.¹

Severe dengue symptoms often surface after the fever has subsided and can include severe abdominal pain, persistent vomiting, rapid breathing, bleeding gums or nose, fatigue, restlessness, blood in vomit or stool, excessive thirst, cold and pale skin, and weakness. Prompt medical attention is crucial for individuals experiencing these severe symptoms.¹

Even after resolution, recovering patients may experience fatigue for several weeks.¹

Yellow fever on the other hand can present with a wide range of symptoms and severity. 

Many individuals may not exhibit symptoms; however, when symptoms do manifest, they typically include fever, prominent backache, headache, muscle pain, loss of appetite, and nausea or vomiting. In most cases, symptoms disappear after 3–4 days.²

However, a minority of patients progress to a more critical phase within a day of symptom resolution. In this phase, there is a resurgence of high fever with involvement of multiple organs notably the liver and kidneys. Jaundice, indicated by yellowing of the skin and eyes, hence the term "yellow fever," along with darkened urine and abdominal discomfort with vomiting, are common manifestations. Bleeding may also occur from various sites such as the mouth, nose, eyes, or stomach. Tragically, half of individuals in this stage succumb to the illness within a span of 7–10 days.²

Cardiovascular effects: why is this important?

We've outlined the severe symptoms of Dengue and tellow fever, now we'll address their life-threatening cardiovascular complications.

Starting with a study that included 73 confirmed cases of yellow fever, with a median age of 48 years. Different types of cardiac complications were noted, such as myocardial fibrosis, cardiomyocyte hypertrophy, endothelial alterations, fibre necrosis, viral myocarditis, and secondary myocarditis among patients, these cardiac insults in severe yellow fever were the results of multiple factors like direct virus damage, endothelial cell injury and inflammatory responses.⁷

In contrast, while cardiac complications in dengue fever cases are uncommon, instances of asymptomatic cardiac involvement have been observed. Acute myocarditis (which is acute inflammation of the heart muscle) stands as the primary cardiac pathology noted in severe dengue cases. The initial cardiovascular symptoms usually present as tachycardia (fast heart rate).

Additionally, a range of other abnormalities, including bradycardia (low heart rate), hypotension(low blood pressure), myocarditis- inflammation of the heart muscle-, pericarditis -inflammation of the membrane covering the heart-myocardial depression leading to heart failure symptoms, arrhythmias (which are disturbances of the heart’s rhythm), have been documented within the spectrum of associated cardiovascular manifestations.⁸

It is important to recognise these complication as early as possible to prevent multiple organ failure and fatality, and this is a challenging subject for doctors as these symptoms are often subtle., For that reason it is wise for doctors to keep those atypical manifestations at mind while dealing with a suspected dengue case.⁸

How do doctors confirm the diagnosis

Most labs or health care centres offer blood tests that can detect either the viruses themselves or the bodies specific immune response for the virus.

In dengue fever, people with suspicious symptoms and a travel history to areas endemic with the virus are offered certain tests starting with Nucleic acid amplification tests (NAATs) which is the preferred diagnostic method for suspected cases. It is most accurate performed on serum collected within 7 days of symptom onset. Detecting viral genetic material in a single serum sample confirms the diagnosis, alongside a relevant clinical and travel history.⁶

IgM antibody testing is crucial for identifying additional infections but can show false results because it may detect activity from other viruses of the same family like Zika. Another test called MAC-ELISA or commonly referred to as just ELISA can detect antibodies in later stages of illness, while for early presentations, testing should include both viral detection (rRT-PCR or NS1) and IgM.⁶

Diagnosing yellow fever poses challenges, particularly in its initial phases, as it closely resembles several other severe illnesses such as malaria, leptospirosis, viral hepatitis, various hemorrhagic fevers, flavivirus infections like dengue, and cases of poisoning.³

During the early stages of the disease, polymerase chain reaction (PCR) testing on blood samples may occasionally reveal the presence of the virus. However, in later stages, identifying antibodies becomes imperative, requiring tests like ELISA and PRNT.³

Treatment and management

What to do when you feel symptoms, and what does treatment look like?

If you fear you might have contracted an infection, seeking medical advice is the wisest thing to do, leave it to the experts! They will begin by taking your medical history and conducting a physical examination, followed by a confirmatory blood test to gain a clear picture of what is going on.

If you contract dengue fever, it's essential to take certain steps to alleviate symptoms and aid recovery. These include getting ample rest, staying hydrated by drinking plenty of fluids, using paracetamol to manage pain, avoiding non-steroidal anti-inflammatory drugs like ibuprofen and aspirin, and closely monitoring for any signs of severe symptoms. If severe symptoms are detected, it's crucial to seek medical attention promptly.¹

In case of tellow fever, infections can lead to severe illness and may prove fatal. Timely supportive care provided in hospital settings significantly increases the chances of survival. Although there is no targeted antiviral medication available at present, offering specialized care to address dehydration, fever, and liver and kidney dysfunction can significantly improve patient outcomes.

Additionally, any associated bacterial infections can be effectively managed through the administration of appropriate antibiotics. Also, patients with active infection must stay under mosquito nets to prevent further spread of the virus.²

What about prevention and control

Mosquitoes that transmit dengue fever are most active during daylight hours. To minimize the risk of contracting dengue, it's crucial to protect yourself by wearing clothing that covers as much skin as possible, using mosquito nets—preferably treated with insect repellent—especially during daytime sleeping, installing window screens and applying mosquito repellents.¹

Currently, only one vaccine, Dengvaxia, has been approved and licensed in select countries. However, this vaccine provides protection only to individuals who have previously been infected with dengue. Several other vaccine candidates for dengue fever are currently undergoing evaluation.¹

Contrasting with dengue fever, Vaccination against yellow fever stands as the foremost measure in prevention. Halting outbreaks depends on widespread immunization across the population. Fortunately, the yellow fever vaccine is both safe and cost-effective, conferring lifelong immunity with just a single dose. Additionally, individuals who recover from yellow fever gain lifelong protection.²

In scenarios where vaccination coverage is insufficient or immediate access to the vaccine is lacking, mosquito control comes into place. This involves eradicating breeding grounds for mosquitoes and using insecticides to eliminate adult mosquitoes and larvae in areas with dense mosquito populations.²

Summary

In summary, distinguishing between dengue fever and yellow fever is crucial due to their differing severity, mortality rates, and geographic distributions. Early diagnosis and appropriate management are vital in both diseases to prevent complications and improve outcomes. While dengue fever often presents milder symptoms, it can progress to severe cases, especially in secondary infections, necessitating hospitalization. 

Yellow fever poses a more severe threat, particularly in later stages, with higher mortality rates. Strategies for prevention and control are essential to mitigate the cardiovascular impact of both diseases. 

Vaccination stands as a key preventive measure for yellow fever, while mosquito control measures play a vital role in preventing transmission for both diseases. Continued research into new vaccine candidates for dengue fever offers hope for improved prevention in the future. 

By understanding the distinct characteristics of each disease and implementing targeted interventions, we can effectively reduce morbidity and mortality rates associated with these mosquito-borne illnesses.