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VECTOR-BORNE DISEASES

OUTLINE

• Define vector-borne diseases (VBD)

• Overall burden

• Vectors

• Types of vector-borne diseases

• VBD’s currently affecting global populations

• Dengue Fever

• Malaria

VECTOR-BORNE DISEASES

• Vector-borne diseases (VBDs) are human illnesses that are transmitted by the

bite of an infected arthropod species

• Many are bloodsucking insects that ingest disease-producing microorganisms

during a blood meal from an infected host (human or animal) and later

transmit them into a new host during their next blood meal

• Disease can result from transmission of parasites, viruses, or bacteria

• Since 2014, major outbreaks of dengue, malaria, chikungunya, yellow fever, and

Zika virus have afflicted populations, claimed lives and overwhelmed health

systems in many countries

GLOBAL BURDEN

• Account for more than 17% of all infectious diseases

• More than 1 billion are infected and more than 700,000 people die annually

• More than half the world at risk

• The burden of these diseases is highest in tropical and subtropical areas

• Affect the poorest populations

• Lack of access to adequate housing, safe drinking water, and sanitation

• Malnourished people and those with weakened immunity are especially

susceptible

FACTORS FOR DISTRIBUTION OF VECTOR-BORNE DISEASES

• Determined by demographic, environmental, and social factors

• Global travel and trade, unplanned urbanization and environmental challenges such as climate change can impact on pathogen transmission

• Can result in longer transmission season or more intense

• Can cause diseases to emerge in countries where previously not found

• Variation in temperature and rainfall can affect vector-borne disease transmission

• Growth of urban slums, lacking reliable piped water or adequate solid waste management

TYPES OF VECTORS

Aedes Anopheles Culex

Dengue fever Malaria West Nile fever

Chikungunya Lymphatic filariasis Japanese encephalitis

Yellow Fever Lymphatic filariasis

Zika Virus

Rift Valley fever

Mosquitoes most commonly known vector

OTHER VECTORS

• Other vectors include:

• Ticks (Lyme disease, Tularemia, Crimean-Congo hemorrhagic fever, Tick-borne encephalitis, & Q fever)

• Triatomine bugs (Chagas disease)

• Tsetse flies (African sleeping sickness)

• Fleas (Plague, Rocky Mountain Spotted Fever)

• Lice (Typhus and louse-borne relapsing fever)

• Sandflies (Leishmaniasis)

• Freshwater snails (Schistosomiasis)

VECTOR-BORNE DISEASES

DENGUE FEVER

DENGUE FEVER

• Severe, flu-like illness

• Symptoms: high fever, severe headaches, muscle and joint pains, nausea,

vomiting, swollen glands or rash.

• Dengue itself is rarely fatal

• Severe dengue, however, is a potentially fatal complication

• Symptoms: low temperature, severe abdominal pains, rapid breathing, bleeding

gums and blood in vomit

DENGUE SEROTYPES

• Four known serotypes of dengue virus (DENV 1 to 4).

• Recovery from infection by one provides lifelong immunity against that

particular serotype

• However, subsequent infections by other serotypes increase the risk of developing

severe dengue

DENGUE FEVER BURDEN

• More than 2.5 billion people – over 40% of the world’s population –at risk

• More than 100 million dengue infections worldwide annually

• An estimated 500,000 people with severe dengue require hospitalization

annually

• Large proportion are children

• About 2.5% of those affected die

DENGUE FEVER BURDEN

• Most rapidly spreading mosquito-borne viral disease in the world

• In the past half century, incidence has increased 30-fold

• Geographical expansion to new countries

• In the present decade, from urban to rural settings

Countries at Risk for Dengue Infection

DURING 2008 -2011

Dengue Cases by Year – The Americas Region

DENGUE FEVER TRANSMISSION

• Primary vector: Aedes aegypti

• Transmitted through the bites of infected female mosquitoes

• Ae. Aegypti lives in urban habitats

• Breeds in man-made containers

• Daytime feeder

• Peak times are early morning and evening before dusk

• Travelers play an essential role in the spread of dengue

• Can carry new dengue strains into areas where mosquitoes can transmit infection

DENGUE FEVER TREATMENT

• No effective antiviral medications

• In severe dengue, critical to maintain the patient’s body fluid volume

• One commercial vaccine is available (Dengvaxia)

• Approved for use in 20 countries

• Several restrictions due to increased risk of severe dengue

• Offers protection for people who have already had dengue at least once

• It increases the risk of severe infection in children who were never infected, when they were vaccinated.

DENGUE FEVER PREVENTION

• Primary method: combating mosquitoes by:

• Preventing mosquitoes from accessing egg-laying habitats

• Disposing solid waste properly, removing artificial man-made habitats

• Covering and emptying containers weekly

• Personal household protection measures

• Window screens, long-sleeved clothes, repellents, and insecticide treated materials

• Applying insecticides

VECTOR-BORNE DISEASES

MALARIA

MALARIA

• Parasitic disease

• 5 types of Plasmodium that cause malaria

• P. falciparum is the most deadly

• Symptoms appear approximately 10 - 15 days after infection

• First symptoms are nonspecific: Fever, headache, chills

• If not treated within 24 hours, P. falciparum malaria can progress to severe

illness, often leading to death.

MALARIA

• Children with severe malaria frequently can develop any of the following

symptoms:

• Severe anemia, respiratory distress, or cerebral malaria

• In adults, multi-organ failure is also frequent

MALARIA BURDEN

• In 2017, there were about 219 million cases of malaria and an estimated

435,000 deaths

• In 2012 there were about 207 million cases of malaria and an estimated 627,000

deaths

• In 2017, cases have increased by 6%, however,, deaths have declined 31% since 2012

MALARIA BURDEN

• Malaria transmission occurs in 97 countries,

• Approximately 3.4 billion people at risk

• The disease burden is heavily concentrated in sub-Saharan Africa,

• An estimated 90% of malaria deaths

• 4/10 malaria-related deaths occur in the two highest burden countries: the

Democratic Republic of the Congo and Nigeria

MALARIA TRANSMISSION

• Transmitted by female Anopheles mosquitoes

• Active mainly between dusk and dawn

• 60 known species of Anopheles that can transmit malaria

• Disease transmission more intense where the mosquito species has a long

lifespan and a habit of biting only humans

MALARIA TREATMENT

• Antimalarial drugs

• Chemoprophylaxis for travelers

• Intermittent preventative treatment for pregnant women and infants living in

endemic areas

• Since 2012, WHO has recommended malarial chemoprevention in Sub-Saharan

Africa to children under 5 during the high transmission season.

MALARIA VACCINE

• RTS,S/AS01 (RTS,S)

• Shows partial protection against malaria in young children

• Acts against P. falciparum

• Prevented 4 in 10 cases of malaria over a 4-year period

• Due to its success, introduced in three other Sub-Saharan African countries

during 2019

• Ghana, Kenya, and Malawi

WHO MALARIA RESPONSE

• WHO Global Technical Strategy for Malaria 2016-2030

• Technical framework for all malaria-endemic countries

• Guide and support regional and country programs towards malaria control and

elimination

• Global Targets

• Reducing malaria case incidence and mortality rates by at least 90% by 2030

• Eliminating malaria in at least 35 countries by 2030

• Preventing a resurgence of malaria in all countries that are malaria-free

THANK YOU