Virus 2 (RNA): Arboviral Infections (Dengue, etc.) Flashcards
What is the definition of an arboviruses and which arboviruses exist?
Arboviruses:
- (ArBo = ARthropod BOrne) arthropod vectors -> most have reservoirs in mammals/birds
- high proportion of asymptomatic cases
- tend to agglutinate red blood cells
Which clinical syndromes do arboviruses cause?
Three clinical syndromes associated with arboviruses:
FAR - fever, arthralgia, rash
VHF - viral heamorrhagic fever
CNS - central nervous system syndrome (encephalitis)
VHF can be caused by arboviruses. Which viruses cause VHF without transmission from arthropod vector, i.e. person to person spread?
- Arthropods:
- Dengue and Yellow Fever
- Chikungunya
- Zika
- Japanese Encephalitis
- Arthropods and bodily fluids:
- Crimean-Congo and Rift Valley
- Only direct transmission
- Ebola
- Marburg
- Lassa
How many people are affected by Dengue and how is it spread?
- 100 million cases per year
- 2.5 billion at risk
- Reservoir humans
- Vector Aedes msoquito
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What does the Aedes mosquito look like?
What are some of the factors contributing to the spread of Dengue since WWII?
- every country between tropics of Capricorn and Cancer
- Poor vector control and expansion of vector species affected
- Reintroduction of insect into Central and South America
- Intercontinental transport of car tyres containing Aedes eggs
- Overcrowing of refugee and urban populations
- Increased human travel
What are the clinical features of Dengue?
- Classically use of WHO classification of Dengue Fever (DF) and Dengue Haemorrhagic Fever (DHF; 4 subtypes) used
- Superseded by newer classification but still in use
- Three phases:
- Febrile phase:
- high fever 2 - 7 days with generalised aches and rash
- Critical pahse:
- decrease in temp. most of those with dengue without warning signs will recover.
- Recovery phase:
- Patient improves, vital signs normalise, GI symptoms subside and appetite returns. At times, bradycardia and generalised pruritus
- Febrile phase:
What is a positive tourniquet test?
A BP cuff inflated to half way between systolic and diastolic pressure for 5 min produces 20 or more petechiae in a 2.5cm square on the forearm
How is the new WHO classification of Dengue different?
Patients are now described as having dengue +/- warnings signs of severe dengue
Warnings signs:
- Abdo pain or tenderness
- Persistent vomiting
- Clinical fluid accumulation
- Mucosal bleeding
- lathargy or restlessness
- Liver enlargment >2cm
Patients with sever dengue:
- shock or fluid accumulation with respiratory distress due to plasma leakage
- Sever oragn impairment
How do we diagnose Dengue?
Leucopenia and thrombocytopenia common
- Rapid testing for NS1 antigen and IgM and IgG levels in critical and recovery phase
- Must be followed up by viral PCR if positive
- Haematocrit can show whether plasma leakage
How do we manage Dengue patients?
- Patients without warning signs
- Rehydration and paracetamol
- Do not prescribe NSAID
- With warning signs/significant co-morbidities
- Hospitalise
- Paracetamol
- Start hydration, monitor for good urine output and monitor HCT
- Sever dengue:
- Emergency resuscitation with fluids and oxygen
- USe frusemide or fresh whole blood if needed
In Dengue Fever, what does antibody dependent enhancement (ADE) refer to?
There are four types of dengue virus, DV-1, DV-2, DV-3, DV-4. Infection with any one type results in protection against that type for life. However if a second type infects the person later, then the consequent disease is likely to be far more severe than expected and may progress to DHF and DSS.
Many hold that ADE is the cause of this. When a person is infected with a different strain of virus the body quickly reacts by producing a massive antibody response to the original infecting strain. These antibodies coat the new virus but, instead of destroying the new strain, they facilitate its entry into macrophages.
Here the new strain multiplies rapidly and can evoke a powerful pro-inflammatory response with an explosive release of inflammatory cytokines. It is this unbridled outpouring of cytokine proteins that cause a subsequent DHF/DSS.
How do we prevent Dengue?
Vector control of Aedes mosquito
How is chikungunya transmitted and where is it prevalent?
Aedes and Culex mosquito
- Several outbreaks over last two decades, with millions affected (1.4 million in India outbreak for example)
What are the clinical features of chikungunya?
- Chikungunya means stooped posture in Makonde language
- Multiple joint pain that may persist for months, in 33% for at least 4 months
- Fever (with rigors and chills), arthralgia (100% of patients), rash
- Atypical presentations:
- Myocarditis
- Hepatitis
- Neurological manifestation
- Ocular presentations
What is the difference between African and Asian chikungunya?
How do we diagnose and treat chikungunya?
- No specific treatment - same as dengue, so not necessarily important to differentiate between the two
- Chloroquine can be used
How can we differentiate between dengue and chikungunya?
very difficult
leucopaenia, neutropaenia and thrombocytopaenia more common in dengue
Where do we find Zika virus and how is it transmitted?
- Aedes transmission
- Trasnpacental
- Sexual transmission
What are the clinical features of Zika virus?
- only 20% symptomatic
- Headache, oedema, vomiting, diarrhoea
How do we diagnose and treat Zika patients?
- In the UK only test those with a relevant travel history
- Virus detection:
- RT-PCR - blood (for 7 days after infection); Urine for up to 3 weeks after infection
- Amniotic fluid
- Serology:
- IgM/IgG
- Cross-reaction
- Previous flavi infection
What is congenital zika syndrome?
How do we screen pregnant woman with potential Zika?
Where can Japanese Encephalitis (JE) be found and how is it transmitted?
- Most important cause of encephalitis epidemics worldwide
- Mostly found in Asia, Japan and Pacific
- Flavivirus transmitted by Culex mosquito
- Reservoir is birds with pigs amplifying virus – often occurs in paddy fields and flood planes. Typically seasonal.
What are the clinical features of JE?
- Most – 99% – are asymptomatic and have +serology with no disease
- Non-specific febrile illness that can be respiratory/GI in nature – then go on to develop drowsiness/coma
- Seizure/status, focal neurological signs, parkinsonism, chorea-type movement, aseptic meningitis, polio-like flaccid paralysis are all possible presentations.
How do we diagnose JE?
Investigations
- CSF – viral picture
- Serology/CSF/rapid tests for IgM
- PCR
