Dengue

Data as of October 2023

NCCID Disease Debriefs provide Canadian public health practitioners and clinicians with up-to-date reviews of essential information on prominent infectious diseases for Canadian public health practice. While not a formal literature review, information is gathered from key sources including the Public Health Agency of Canada (PHAC), the USA Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO) and peer-reviewed literature.

This disease debrief was prepared and updated by NCCID staff.  Questions, comments, and suggestions regarding this disease brief are most welcome and can be sent to nccid@manitoba.ca.

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Questions Addressed in this debrief:

  1. What are important characteristics of dengue?
  2. What is the current risk for Canadians from dengue?
  3. What is the prevalence of dengue in Canada?
  4. What measures should be taken for a suspected dengue case or contact?

What are important characteristics of dengue?

Characteristics and Causes

Dengue is a viral infection caused by the bite of infected Aedes mosquitoes (Ae. aegypti or Ae. albopictus). There are four serotypes of dengue virus (DENV): DENV-1, DENV-2, DENV-3 or DENV-4. When a mosquito bites a human who has any one of the DENV serotypes, the mosquito becomes infected. The infected mosquito can then spread the virus to other humans through biting them.

Dengue is most often found in tropical and subtropical regions. However, mosquitoes carrying the virus may adapt to new environments due to climate change and the consequences of the 2023 El Niño phenomena increasing temperatures, rainfall, and humidity.

Symptoms

About 1 in 4 people with dengue will get sick. In general, most people have no or mild symptoms and recover within one to two weeks.

Mild symptoms of dengue may be confused with other illnesses that cause flu-like symptoms. The most common symptom of dengue is a sudden onset of high fever (40°C/ 104°F) for three to five days. The fever is usually accompanied by at least two of the following symptoms:

Severity and Complications

About 1 in 20 people infected with a dengue virus will experience complications and develop severe dengue. Severe dengue occurs when blood vessels become damaged and platelet levels drop. This can lead to internal bleeding, organ failure, and shock.

Individuals who are infected with dengue for a second time are at a greater risk of developing severe dengue.

Severe dengue, also known as dengue haemorrhagic fever, often comes 24-48 hours after a high fever has passed. Symptoms of severe dengue may include:

  • persistent vomiting
  • severe stomach pain
  • bleeding from gums or nose 
  • blood in urine, stools, or vomit
  • difficult or rapid breathing
  • feeling tired, weak, restless, or irritable
  • being very thirsty
  • pale and cold skin

Severe dengue can be fatal within hours and requires immediate hospital care.

Transmission

Dengue has a human-to-mosquito-to-human transmission cycle. After a mosquito bites a person infected with a dengue virus, the virus replicates and spreads in the mosquito’s tissues and salivary glands. Approximately 8-12 days after ingesting the virus, the infected mosquito can then spread the virus to other humans by biting them. The infected mosquito can continue to transmit the virus for the rest of its lifetime.

The female Aedes aegypti (yellow fever) mosquito is the primary vector that carries and transmits the dengue virus to humans. The Aedes albopictus (tiger or forest mosquito) is a secondary vector for dengue in Asia.

Dengue does not spread directly from person-to-person except on rare occasions through blood transfusions or organ donations.

Prevention and Control

The best way to prevent dengue is by reducing the number of mosquito breeding sites. If the number of breeding sites is reduced, there will be fewer emerging adult mosquitoes to transmit the dengue virus.

The Aedes aegypti mosquitoes lay their eggs in water-filled containers and prefer to live in urban areas near humans. The eggs hatch when in contact with water.

To limit the number of adult mosquitoes emerging from the egg/larva/pupa stage, cover or properly discard water-filled containers. Any remaining water-filled containers should be emptied, cleaned, and scrubbed once a week to remove mosquito eggs.

Indoor breeding sites for Aedes aegypti mosquitoes can include:

  • Bottles, plastic containers
  • Water storage tanks (domestic drinking water, bathroom, etc.,)
  • Flower pots
  • Ant traps

Outdoor breeding sites can include:

  • Discarded bottles, containers, tins
  • Drums for filling water
  • Boats, equipment
  • Leaves of various plants
  • Tree holes, potholes, and holes from construction sites
  • Tree seeds

Personal and Household Protection

Aedes aegypti mosquitoes feed on humans during the day, especially early in the morning and in the evening before dusk. In regions at risk of dengue, it is important to:

Vaccines

The first dengue vaccine (Dengvaxia®) was licensed in Mexico in 2015 for people aged 9 to 45 years. It is now licensed in 20 countries for individuals living in areas where dengue is endemic. The dengue vaccine is not approved for use in Canada.

The World Health Organization recommends only giving Dengvaxia® to people who previously had dengue.

Treatment

There is no specific treatment for dengue.

Acetaminophen (paracetamol) is often used for treating fever and pain symptoms. It is not recommended to take aspirin, ibuprofen, or other non-steroidal anti-inflammatory drugs as they can increase the risk of bleeding.

Patients with symptoms of severe dengue are advised to go to a hospital immediately. Severe dengue is a medical emergency.Centers for Disease Control and Prevention (CDC) – Dengue Symptoms and Treatment

Epidemiology

General

Over the past two decades, the global incidence of dengue has increased ten-fold from 500,000 million cases in 2000 to a peak of 5.2 million in 2019. While there was a slight decline in cases during the COVID-19 pandemic between the years 2020 and 2022, cases significantly increased again in 2023 and spread to regions previously unaffected by the virus. Dengue transmission follows a cyclic epidemic pattern with outbreaks expected to occur every 3 to 4 years.

Almost half of the world’s population live in areas where there is a risk of contracting dengue. Dengue is endemic in over 100 countries in five of the six WHO Regions: the Americas, Africa, Easter Mediterranean, South-East Asia, and Western Pacific. It is most common in urban and semi-urban areas in tropical and subtropical regions.

As the climate crisis drives warming temperatures and shifts in rainfall patterns, dengue is suspected to become endemic in the southern United States of America, southern Europe, and parts of Africa in the next 10 years.

WHO Region of the Americas

The Region of the Americas has seen a significant increase in dengue over the past decade. Between 2010 and 2019, approximately 17.5 million dengue cases were reported in the Region, with the previous historical high at 3.18 million cases in 2019. Cases declined slightly between the year 2020-2022 due to the COVID-19 pandemic; however, peaked to a historical high at 4.1 million suspected cases (cumulative incidence of 419 cases per 100,000 population) between January 1 and December 11, 2023, including 6,710 severe cases and 2,049 deaths. Until November 12, 2023, 45% (n= 1,895,122) of the total suspected cases were laboratory confirmed.

There are currently 46 countries and territories in the Region of the Americas that systematically report dengue data to the World Health Organization. During the epidemiological week (EW) 48 (November 26 – December 2, 2023), the highest number of suspected dengue cases in the Region was reported in Brazil (n = 2,909,404; 1,359 cases per 100,000 population), followed by Peru (n= 271,279; 813 cases per 100,000 population), and Mexico (n = 235,616; 179 cases per 100,000 population).

All four DENV serotypes are co-circulating in nine countries with the Region of the Americas: Brazil, Colombia, Costa Rica, Guatemala, Honduras, Mexico, Nicaragua, Panama, and Venezuela. DENV-1 and DENV-2 have been the predominant serotypes detected in the Region of the Americas, however, there has been an increase in the frequency of detection for DENV-3 and DENV-4 in 2023.

Canada

In Canada, there have been no locally acquired dengue cases reported. All reported cases of dengue in Canada have been among travellers returning from areas with dengue.

United States of America

In 2023, there were 2,343 dengue cases reported across 52 jurisdictions; of which, 1,347 were travel associated and 996 were locally acquired. Of the locally acquired cases, the highest numbers occurred in Puerto Rico, followed by the southern states Florida, California, and Texas.

Incubation Period

The average incubation period begins 4–10 days after infection and last for 2–7 days.

What is the current risk for Canadians from dengue?

The risk of contracting dengue in Canada is low. All travelers are at risk of dengue if travelling to areas where dengue is endemic.

What is the prevalence of dengue in Canada?

In Canada, approximately 200-300 cases of dengue are imported each year. All cases have been among travellers returning from countries where dengue is present.

What measures should be taken for a suspected dengue case or contact?

Individuals are advised to see a healthcare provider if symptoms of dengue develop while travelling or after return to Canada. A healthcare provider will make an accurate diagnosis based on travel history, symptoms, and laboratory testing.

Case Definition

Identifying and Reporting

Dengue is not a nationally notifiable disease in Canada.

Laboratory Testing

The National Microbiology Laboratory (NML) of PHAC provides four reference diagnostic services for dengue: molecular testing by real-time reverse transcriptase polymerase chain reaction (RT-PCR); serological testing of both dengue-specific immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies by Enzyme-Linked Immunosorbent Assay (ELISA); and serological testing of antibodies by Plaque Reduction Neutralization Test (PRNT)*. All four testing methods require serum specimens, although, molecular testing can also be performed on plasma or cerebral spinal fluid (CSF).

The testing turnaround time at NML is 21 calendar days for RT-PCR and 14 calendar days for dengue-specific IgM/IgG ELISA. For PRNT, the testing turnaround time is 21 calendar days after the completion of preliminary ELISA testing.

*Testing by PRNT at NML is only performed for reactive (positive) results from dengue-specific IgM/IgG ELISA. Non-reactive (negative) ELISA samples will not be tested by PRNT.

Laboratory Interpretation

Positive RT-PCR test results are indicative of a current dengue diagnosis. RT-PCR results are classified as positive if any of the four dengue serotype targets are detected in their respective singleplex assays and if the cycle threshold (Ct) value falls within the pre-established target for the specific assay/serotype.

Past or present exposure to dengue is indicated by the detection of IgG antibodies in a dengue-specific IgG antibody test. A dengue case is considered “confirmed” if there is a fourfold or greater rise in neutralizing antibody tire, or seroconversion in paired sera.

Detection of IgM antibodies is indicative of exposure to dengue at an undetermined time. It is important to note, however, that detection of IgM alone is not sufficient for confirmation of acute infection as IgM antibodies may remain in serum for one year or longer following exposure to the virus.