31. Epidemiology and prevention of haematogenic and lymphogenic infections

Vector-borne diseases

Infections transmitted by the bite of infected arthropods like:
- Flies
  - Sleeping sickness
- Mosquitoes
  - Malaria
  - Yellow fever
  - Zika
  - Dengue fever
  - West Nile fever
- Ticks
  - Lyme disease
  - Tick-borne encephalitis
  - Q fever
  - Tularaemia
- Lice
- Fleas
  - The plague
The infection can be located inside the vector or outside
Arthropods are cold-blooded and are therefore very sensitive to changes in the climate
- Climate change changes their habitat -> can make areas previously spared from these diseases become affected
Prevention
- Protective clothing
- Insect repellant
- Regularly examine the skin for ticks
- Avoid endemic areas
- Remove ticks safely
- Insect nets

Lyme disease

Borrelia burgdorferi, afzelii and garinii
Epidemiology
- Endemic in most of Europe, most in central and eastern European countries
Transmission
- By bite of the Ixodes tick
Reservoir
- Many small mammals
- Ground-feeding birds
Symptoms
- Target-shaped rash (erythema migrans)
- Myocarditis
- Neuroborreliosis
- Lyme arthritis
Prevention
- No vaccine
- Avoiding tick bites
- Early removal of attached ticks

Tick-borne encephalitis

An arbovirus (= transmitted by arthopod) and a flavivirus (= the genus it belongs to)
Epidemiology
- Endemic in areas of Europe and Asia
- Most cases occur during the summer
Transmission
- By bite of the Ixodes tick
Reservoir
- Small rodents
Clinical features
- Few infected people get sick
- Illness is worst in elderly
- Neurological symptoms, sometimes permanent
Prevention
- Vaccine exists
- Avoiding tick bites
- Early removal of attached ticks

Malaria

Parasites of the genus plasmodium
- Plasmodium falciparum – most severe
- Plasmodium ovale
- Plasmodium vivax
Epidemiology
- Most cases are in Africa, especially Nigeria and Congo
- Major cause of death in developing countries
Transmission
- By mosquitoes (Anopheles species)
- Entomologic inoculation rate = how many infectious mosquitoes bites per person per year
  - A measure of transmission intensity
  - High if above 50
  - The higher the EIR, the greater the burden of malaria
- Rarely by blood transfusion, needle sharing, etc.
Reservoir
- No animal reservoir
- Only lives in humans
Risk groups for severe disease
- Pregnant women
- Children and infants
- HIV infected
Prevention
- Chemoprophylaxis:
  - For travellers to malaria endemic countries
  - For high-risk residents of endemic countries
- Kill mosquitoes
- Insect nets
- Clothes that cover the body
- Mosquito repellent
Vaccine
- Name: RTS,S
- Very recent (2019)
- Against plasmodium falciparum

Crimean-Congo haemorrhagic fever (CCHF)

Tick-borne relapsing fever

West Nile virus

A flavivirus
Epidemiology
- Originated from Africa, now present worldwide
Reservoir
- Birds
Transmission
- Mosquitoes
Symptoms
- Often asymptomatic
- Most commonly mild infection flu-like symptoms and rash
- Rarely meningitis or encephalitis
Prevention
- Protect against mosquito bites

Japanese encephalitis

Zika virus

Yellow fever

Yellow fever virus, a flavivirus
Transmission by mosquito
Occurs in Sub-Saharan Africa and South America
Infants and children are at highest risk
Clinical features
- Most patients experience mild symptoms
- 15% develop serious disease
  - Haematemesis
  - Bloody diarrhoea
  - Jaundice
  - Organ failure
Prevention
- Vaccine
  - Reccomended for those travelling to or living in areas with yellow fever transmission
- Protection against mosquito bites

Lymphatic filariasis