Lower Respiratory Infection = Viral Flashcards
What is viral bronchiolitis and how is it related to repsiratory synctial virus?
Bronchiolitis – disease restricted to children, mostly <2 yr
- Bronchioles narrow, inflammation and swelling blocks them, restricting air passage and causing epithelial death
- 75% of cases due to Respiratory syncytial virus (RSV)
What is the respiratory synctial virus (form of bronchiolitis)? Discuss its viral characteristics, transmission, epidemiology and clinical features
Family: Parymxoviruses (ssRNA, enveloped)
- 2 major strains: group A and B
- 2 envelope spikes: G and F proteins
G protein – attachment to cell
F (fusion) – initiated entry into cell, also causes fusion of host cells –> syncytia
- Transmitted through droplets, contaminated hands
- Outbreaks in winter
- Virus infects upper and lower respiratory tract
- Incubation period 4-5 days, clinical signs follow
> Infants – can be particularly severe, peak mortality 3 months
Symptoms: rapid respiratory rate, cough, cyanosis, bronchiolitis and pneumonia
- Children and adults – less severe, upper respiratory tract only, cold-like illness
- Treatment – in children, supportive: rehydration, bronchodilators and hospitalisation if needed, oxygen
- Vaccine – at present none available
- Prophylaxis with monoclonal antibody (palivizumab) in high risk children <2 yr (passive immunity)
- Preterm babies, congenital malformations of the heart and airways
What is viral pneumonia
- Many viruses cause pneumonia
- Healthy individuals are at risk
- Most of the viruses have surface molecules that attach specifically to epithelium
- Even if virus doesn’t cause pneumonia, damage to epithelium may result in secondary bacterial pneumonia
- Look at: Parainfluenza virus Influenza virus Measles virus
What is parainfluenza virus - Pneumonia
Family: Paramyxoviruses (ssRNA, enveloped)
Parainfluenza virus – 2 envelope spikes:
> Haemagglutinin-neuraminidase (HN)
> Fusion protein (F)
- Spread through respiratory droplets and infect respiratory epithelium
- 4 types based on different antigens (serotypes)
- Parainfluenza 1-3 – pneumonia, pharyngitis, bronchiolitis and croup Croup – in children <5 yr, acute laryngo-tracheo-bronchiolitis
> Narrow airway, harsh barking cough = croup
- Parainfluenza 4 – less common, cold-like symptoms –> no vaccine
What is influenza?
- Influenza is an acute respiratory tract infection that usually occurs in epidemics
- fever, cough, running nose
- Compare with the common cold which is less severe: no fever, runny nose –> different viruses
- Family: Orthomyxoviruses, ssRNA, enveloped •
- 3 types: A, B, C, based on proteins inside capsid
Influenza Virus Strains:
- Type A - moderate to severe illness: all age groups, humans and other animals, reservoir birds –> causes epidemics, occasional pandemics
- Type B - milder disease • primarily affects children & elderly, humans only –> causes epidemics
- Type C – rarely reported in humans • no epidemics • minor respiratory illness
What are the antigenic properties for Influenza?
The major surface antigens are the glycoproteins (spikes)
– haemagglutinin (HA)
– neuraminidase (NA)
- These two surface glycoproteins are important antigens that determine antigenic variation and are targets for host immunity
- Type A is antigenically highly variable (most epidemics)
- Type B can show antigenic changes and some epidemics
- Type C is antigenically stable causing mild illness
Antigenic drift (can occur in all types –> A,B)
- Minor change in viral antigens
- Changes occur because of point mutation in genes
- Same subtype; can cause epidemic
Antigenic Shift (type A only)
- Major change resulting in new subtype
- Caused by exchange of gene segments
- Co-infection of a host with different viral strains from different species (human and animal)
- Antigen genes recombine –> cause epidemics and pandemic
Influenza A nomenclature? Influenza pathogenesis? Clinical features?
Nomenclature
Based on glycoprotein combinations
- H, Haemagglutinin –> gain entry, attach to sialic acid
- N, neuraminidase – since new virions take cell membrane, N cleaves sialic acid of virion membranes and infected cells
- H = 18 (H1-H18)
- N = 9 (N1-N9)
Pathogenesis
- Respiratory transmission of virus through droplets
- Replication in respiratory epithelium with subsequent destruction of cells
- Viraemia rarely occurs
- Virus shed in respiratory secretions for 5-10 days
Clinical Features
- Incubation period 2 days (range 1-4 days)
- 50% of infected persons develop classic symptoms –> Abrupt onset of fever, myalgia, sore throat, non-productive cough, headache
- Fever usually lasts 3 days as do systemic symptoms
- Respiratory symptoms typically last another 3-4 days
- The cough and weakness may persist for 1-3 weeks
- Children may have higher fever and higher incidence of GI manifestations such as vomiting
Complications
- Pneumonia
> secondary bacterial – most common
> primary influenza viral – less common
- Myocarditis
- Mortality < 1/1000 cases usually in elderly
- In pandemics severe disease may occur healthy young adults
What is the epidemiology of Lower respiratory tract infections?
- Epidemiology of influenza is closely associated with antigenic changes – drift and shift
- Incidence peaks during the winter with periodic outbreaks due to antigenic changes
- High susceptibility to a particular antigenic change can result in an epidemic
- Antigenic shift in influenza type A is thought to occur because related influenza A viruses circulate in animal and bird populations
- Influenza outbreaks occur in waves with the period between epidemic waves of influenza A being 2-3 years
- Every 10-40 years when a new subtype of influenza A appears a pandemic results
- H1NI = spanish (severe)
- H2N2 = asian (Severe)
- H3N2 = hong kong (moderate_
- H5N1 is particularly virulent –> avian flu
What is the influenza vaccination?
- Influenza vaccine prevents morbidity and mortality by:
Preventing infection and Attenuating disease
- Changing antigenic nature of the virus creates a problem in vaccine production
> Vaccine gives protection only against strains in vaccine and also against related strains
>WHO has worldwide surveillance centres to monitor viral antigenic changes
>The southern hemisphere gets a few more months as the epidemics are evident first in the northern winter
Being in the Southern hemisphere has an advantage –> Because of the changing nature of the viruses vaccination is only effective for about 1 year
- Influenza vaccines in Australia are inactivated virus
- Prepared from purified influenza virus made in hens eggs (allergy to eggs is contraindicated)
- Significant market with many different manufacturers
- Influenza vaccination is broadly recommended in the population there are some groups specifically targeted
>65 year, pregnancy, Indigenous people, those suffering from chronic illness, health care workers, etc (see Immunisation Handbook)
What is measles? Describe it pathogenesis, clinical features and complications
Measles virus: ssRNA genome, enveloped,
- Paramyxoviridae family
- Highly infectious, with 99% of population infected prior to vaccine - asymptomatic or subclinical infection rare
- After infection, complete life-long resistance
- Before a vaccine became available, measles killed 7–8 million children each year worldwide.
Pathogenesis
- Transmitted by respiratory droplets
- Virus enters in the upper/lower respiratory tract or conjunctiva and spreads to sub-epithelial and local lymphatic tissues
- During the next few days, there is a primary viraemia: virus spreads and multiplies in lymphoid tissues (inc. spleen, respiratory tract)
- Secondary viraemia, ~5 days after the infection, virus disseminates to a variety of epithelial sites including the skin, kidney, and bladder
- Does not replicate at site of entry
- Replicates systemetically and then returns in large numbers to entry surface and replicates further and is shed
Clinical features
- After 9-10 days post infection: acute, respiratory illness with a runny nose, fever and cough, and conjunctivitis
- Patient is highly infectious with large amoutnt of virus being shed in respiratory infections
- Koplik spots appear inside cheek and shortly afterwards –> the maculopapular rash is seen, first on the face, then down the body to extremities
Treatment
- Antiviral Ribavirin may be used; MMR vaccine
What is aspergillosis? What are its causative agents and clinical features?
Fungal infection of the respiratory tract is usually associated with immunocompromised individuals
- Immune suppressive treatment
- Concomitant disease
Most medically important: Aspergillosis fumigatus and Aspergillosis flavus
- Do not form part of the normal flora
- Spores inhaled and able to cause a range of diseases
Allergic bronchopulmonary aspergillosis
- allergic irritation to antigens in lungs, in asthma patients
Aspergilloma
- A fungal ball of growth in lung cavitis, form pre-existing condition, no invasion of tissue but can cause respiratory problems
- Disseminated disease in immunocompromised patients –> high mortality as limited number and toxicity of antifungal agents
