Overview

Vector-borne disease is a bacterial or viral infection transmitted by a vector, primarily mosquitoes. Vector-borne diseases raise the global health burden, mainly in tropical and subtropical regions, causing alarming statistics of 700,000 deaths each year. Some examples of the most well-known vector-borne diseases include malaria, dengue fever, Zika virus fever, chikungunya fever, and West Nile fever. In this review, we will focus on two of the most common mosquito-borne diseases, Chikungunya and Dengue fever, further looking into their differences in manifestations and epidemiology.  

Chikungunya and dengue fever explained

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that belongs to the Togaviridae family. The virus is mainly transmitted by mosquitoes of the Aedes spp., primarily Aedes aegypti and Aedes albopictus, in urbanised areas.¹ CHIKV is classified as an Arthritogenic virus, as it induces musculoskeletal inflammations, resulting in symptoms such as joint pains, muscle aches, and rashes associated with high fever.^1,2 Other alphaviruses with similar clinical symptoms are Barmah Forest virus, Ross River virus and Mayaro virus.³ In recent years, CHIKV outbreaks have been seen everywhere in the world, predominantly in tropical areas of Asia, Australia and Africa, where mosquitoes inhabit.^1,3 

Similarly, dengue virus disease (DENV) is another significant mosquito-borne disease. DENV is a type of flavivirus originating from the Flaviviridae family. The infection is caused by any of the four serotypes of the virus: DENV-1, DENV-2, DENV-3, and DENV-4. DENV is also transmitted by female mosquitos of Aedes aegypti and Aedes albopictus.⁴ The manifestations of dengue usually do not last more than a week. Despite that, the symptoms may evolve or change abruptly within a short timeframe, transitioning into either mild or fatal conditions.⁵ DENV infections are often characterised by hemorrhagic fever, rashes, nausea, and muscle and joint aches, while most of infections are asymptomatic.⁴ The resemblance in clinical manifestations between CHIKV and DENV infections is why they are often misdiagnosed. DENV has a greater distribution than CHIKV, affecting approximately 390 million people worldwide. DENV gives rise to endemic and hyperendemic conditions, primarily in urbanised tropical regions across multiple continents, including Asia, America, Australia and Africa.⁵

Epidemiology and outbreak patterns of chikungunya and dengue 

CHIKV was initially isolated from Tanzania, Africa, in 1952. Since then, its prevalence has expanded in Asia, with sporadic cases and minor outbreaks reported throughout Southeast Asia and African countries until the massive flare-up in the Indian Oceans Islands of Réunion in 2006.³ Mutations were found in the viral sequence isolated from the Reunion island epidemic, contributing to an increased transmission rate.¹ From then on, CHIKV gained prevalence in developed countries, specifically the Western countries, when an increase in imported cases was reported due to Western travellers (Europeans and Americans) carrying the CHIKV infection back to their home country upon their return from epidemic regions.³ Eventually, CHIKV began to spread to Western nations, with sporadic and epidemic cases reported in countries such as Italy, America and Brazil. To date, CHIKV infections can be found anywhere in the world as a result of advancements in cross-border global travel and climate change. Global warming-induced climate change promotes the expansion of vector range towards subtropical and temperate regions, thus provoking the occurrence of sudden flare-ups in populations where mosquito control is not well-established.¹  

DENV infection had its first immense blow-up in Indonesia and Egypt in the late eighteenth century. Then, dengue epidemics were reported in several countries across Africa throughout the eighteenth to twentieth century.⁶ Massive globalisation, urban growth, and the rise in human population after World War II attributed to the expansion in the geographical range of the Aedes spp., thus contributing to the rapid dissemination of the virus.⁵ This rapid spread started from the dengue pandemic in Southeast Asia in the 1950s. In the subsequent years, dengue fever epidemics became an annual event for all Southeast Asia countries, including Malaysia, Thailand, Indonesia, Philippines, Laos, etc..⁶Continuous developments in modern transportation and urbanisation throughout the years further enhanced the vector transmission, leading to major outbreaks being intermittently reported in various continents involving, America, Africa, Asia and Australia.⁵ Recent years, DENV infections have been circulating in an endemic-epidemic cycle across 100 countries worldwide, with Asia contributing to 70% of all infected cases. 

CHIKV and DENV infections have the same transmission patterns as they are both transmitted by the mosquito vector,  Aedes spp. They generally inhabit subtropical and tropical regions, especially during the rainy season, as accumulated precipitates contribute to the formation of stagnant waters, creating a habitat for breeding.⁷ In recent years, several factors such as urbanisation, climate change and globalisation have contributed to the spread of CHIKV and DENV to new temperate regions that were initially disease-free.⁸

The scale and frequency of CHIKV outbreaks are significantly smaller than DENV outbreaks, where occasional flare-ups were only reported in Africa and Asia.¹ Meanwhile, DENV is hyperendemic across various countries, with ~400 million cases reported each year.⁴

Clinical manifestations and complications

There is a vast overlap in the clinical presentations and the geographical distribution of chikungunya and dengue. Thus, it is rather difficult for your doctor to differentiate between the two just by examining the symptoms presented.¹Therefore, differential diagnosis becomes necessary for an accurate diagnosis of the disease. Some factors that are taken into consideration when making the diagnosis include the person’s travel history and their place of residence. 

Most cases of CHIKV infections are symptomatic; it is extremely rare for the infection to be asymptomatic (~3% to 28% of all infections).¹ The clinical features of chikungunya include: 

• Fever 
• Rashes
• Polyarthralgia (pain in multiple joints) 
• Headache 
• Myalgia (muscle aches) 
• Nausea and vomiting 
• Arthritis
• Conjunctivitis

The incubation period of chikungunya fever takes about 3 to 7 days. Severe complications such as encephalitis, meningitis, and persistent arthralgia may develop in elderly people aged 65 and above, newborns, and individuals with other underlying medical conditions such as diabetes, cardiovascular diseases, etc.¹

Dengue, on the other hand, is also a febrile illness with an incubation period of about 5 to 7 days. In contrast to chikungunya, most cases of dengue are asymptomatic (up to 75%).⁴ For cases where symptoms are present, they will typically go away within two weeks. However, some people might experience acute worsening of the disease, subsequently leading to the development of severe dengue, such as dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS). DHF is characterised by leaky blood vessels, a significant drop in platelet counts and increased red blood cell levels. If this condition persists, DSS will ensue, leading to shock, haemorrhagic complications and multi-organ failure, potentially leading to death. Some people will develop rare neurological, renal and hepatic complications like encephalitis, meningitis, hepatitis, kidney failure and pancreatitis.^4,6 

Common manifestations of dengue are very similar to those of chikungunya fever which include: 

• Fever
• Headache 
• Muscle and joint pain
• Nausea and vomiting
• Rashes
• Pain behind the eyes. 

Treatment and prevention of chikungunya and dengue

There is currently no cure for both chikungunya and dengue. People with mild symptoms are encouraged to get sufficient rest, fluids and if needed, over-the-counter (OTC) medications for the relief of symptoms. 

People who have developed severe dengue or those who are contracted with the disease while having other underlying morbidities usually require hospitalisation for constant monitoring in case of life-threatening conditions. Hospitalised individuals will be given supportive care, including intravenous (IV) drips and blood transfusion, and they will be constantly monitored should there be signs of the development of associated complications.⁴ Do bear in mind that some OTC painkillers and anti-inflammatory drugs such as ibuprofen, aspirin and naproxen are not encouraged for dengue patients as they may induce haemorrhagic complications. Implementing dengue vaccines like Dengvaxia in countries with dengue endemic is greatly encouraged to prevent the widespread infection. 

The same goes for chikungunya patients, but lethal conditions are relatively rare in chikungunya-affected individuals. However, people with severe joint issues might have to undergo physiotherapy to regain joint mobility, whereas intravenous immunoglobulin is used for the management of neurological complications associated with CHIKV infections.⁹

Summary

Chikungunya and dengue fever highly resemble each other regarding their transmission route, pattern, and symptoms. As both viruses are transmitted via the same mosquito species, the Aedes spp., both infections are prevalent in pretty much the same tropical regions, except dengue fever covers a larger area and can transmit faster than chikungunya, resulting in it causing the largest spread among all mosquito-borne diseases worldwide. CHIKV and DENV cases often spike during the rainy seasons when Aedes mosquitoes are highly abundant, and the breeding period is extensively promoted due to increased precipitation. 

There is currently no direct cure for both chikungunya and dengue fevers. Treatments are generally targeted at relieving symptoms. To readers, it is crucial to be vigilant and aware of the symptoms associated with these infections, especially when these symptoms arise after paying a visit to CHIKV and DENV-endemic countries, and seek medical care promptly to avoid the risk of developing severe complications.