68. Characteristics of influenza viruses, epidemiology of influenza (Zoon.).

Question 1

Influenza types?

Answer 1

Orthomyxoviridae

• Alphainfluenzavirus genus: Influenza A virus
• Betainfluenzavirus genus: Influenza B virus
• Gammainfluenzavirus genus: Influenza C virus
• Isavirus genus ➝ infectious salmon anaemia
• Quaranjavirus genus: Quaranfil virus, Johnston Atoll virus ➝ human, bird, arbovirus
• Thogotovirus genus: Thogoto virus, Dhori virus ➝ human, sheep, arbovirus

Question 2

Influenza virus A history?

Answer 2

Alphainfluenzavirus: Influenza A virus

• History

‣ Spanish flu, 1918

‣ Seasonal and pandemic influenzas in humans

‣ Influenza in domestic animals

Question 3

Occurence and causative agent of Influenza virus A?

Answer 3

Occurrence: worldwide, variable prevalence and types of strains

• Causative agent: ssRNA

• 8 genome segment, helical nucleocapsid, envelope
• Proteins (coded in separate segments)

‣ PA, PB1, PB2 (RNA dependent RNA polymerase)

‣ NP (Nucleopeptide), M1 (Matrix protein) ➝ genus-specific antigens, conserved genes/proteins

‣ M2 (matrix protein) ➝ ion channel for decapsidation

‣ HA (haemagglutinin) ➝ antireceptor protein (attachment to the host cell sialic acid receptor), 18 serotypes, protease

cleavage for receptor-mediated endocytosis

‣ NA (neuraminidase) ➝ role in release and spread by digesting the cell surface sialic acid receptors, 11 serotypes

Question 4

Resistance of Influenza A?

Answer 4

Resistance

• relatively good,
• drying out,
• high temperature,
• UV light,
• detergents inactivate,
• human infection

Question 5

Host Spectrum of Influenza A?

Answer 5

Host spectrum

‣ Determined by HA protein

‣ Natural hosts: (wild) birds

‣ Relative host-adaptation to certain mammalian hosts ➝ human, swine, horse ➝ transmission between host of same

species

‣ Accidental hosts ➝ mainly avian strains in mammals, high dose infections, serious clinical signs can occur, no

transmission

Question 6

Antigenicity of Influenza A?

Answer 6

Antigenicity

‣ HA and NA together determine serotype

‣ Hypervariable genes ➝ serials of point mutations, antigenic drift (seasonal influenzas)

‣ Segmented genome ➝ simultaneous infections (segment reassortment)

‣ Strain identification codes (e.g. influenza A, chicken, Hong Kong)

Question 7

Influenza in other mammals?

Answer 7

Influenza in other mammals

• Dog

• 2004 USA ➝ outbreak in greyhounds (H3N8)

‣ Adaptation to dog and transmission between dogs

‣ Frequent subclinical infections, mainly in USA

• China, South Korea ➝ H3N2 from poultry meat
• Thailand ➝ H5N1 from birds

‣ Fever, haemorrhagic pneumonia, high mortality

• Ferret, milk, martin, fox ➝ rarely clinical signs
• Cat, tiger, leopard ➝ rarely H5N1, from dead birds
• Domestic cats resistant to human seasonal influenzas
• Successful experimental infections with HPAIV H5N1
• Natural H5N1 infections were reported

• Seals, whales

• Both sides at the shores of Atlantic Ocean
• From bird faeces: H4N5, H7N7, H4N6, H13N2
• Respiratory signs, pneumonia, mortality

Question 8

Human Influenza worldwide occurence?

Answer 8

Human influenza

Human Influenza

• Worldwide
• Mainly Influenza A virus, but B is also frequent
• Larger pandemics during history
• H1N1 1918 Spanish flu (swine, human)
• H2N2 1957 Singapore (duck HA, NA and BP1 segment)
• H3N2 1968 Hong Kong (duck, H3 and PB1 segment)
• H1N1 1977 China, Soviet Union
• H5N1 1997 Hong Kong (goose, duck, quail hybrid)
• H1N1 2009 Mexico, USA then worldwide (triple hybrid, 5 segment swine, 2 avian, 1 human origin)

Question 9

Seasonal influenza and epidemiology, symptoms of Human influenza?

Answer 9

• Seasonal influenza mainly in Autumn/Winter
• Epidemiology and symptoms
• Transmission: direct contact, airborne
• Incubation: 1-3 days
• Fever, loss of appetite, depression, headache, muscle pain, nasal discharge, sneezing, coughing, sometimes pneumonia

Question 10

Diagnosis and treatment of human influenza?

Answer 10

• Diagnosis

• Seasonality, spread (outbreaks)
• Symptoms
• Lab tests: RT-PCR, isolation, serology (paired sera)

• Treatment

• Patients should stay at home, rest, drink, optional Oseltamivir
• If bronchitis or pneumonia develop ➝ AB therapy

Question 11

Prevention and vaccination of Human Influenza?

Answer 11

• Prevention: avoid cold, personal hygiene and immunisation
• Vaccination
• Risk groups: physicians, paramedics, nurses
• Patients with CV or respiratory diseases, pregnant women, elderly

• Human influenza vaccines

• Produced in eggs or in cell lines ➝ Inactivated
• Trivalent (H1N1, H3N2 and B) ➝ strains are updated yearly
• 1x before season, type-specific protection, duration: 6-12 months
• Novel vaccines

Question 12

Zoonotic influenza?

Answer 12

Zoonotic Influenza

• Avian origin, direct host switch is rare
• No adaptation: severe, even deadly disease in infected individuals (human-to-human transmission is rare)
• Risk groups
• Occupation: vets
• Farmers living in close contact with animals (hygiene)
• Prevention: observe hygiene measures
• Occurrence: low chance in EU and developed countries
• Risk
• General population: very low
• Occupation risk groups: low
• Transmitted by swine: risk higher because of adaptation opportunity, but rare