Lecture 7: respiratory diseases and pandemics Flashcards
How many people die of infectious diseases worldwide?
One in four. Half of those die of viruses
What were the reasons the SARS pandemic was easily controlled?
The reason for containment of the SARS outbreak was twofold:
- Disease symptoms with SARS occurred before people became infectious. The reason for this is that the virus primarily replicated in the lower airways. The replication in the lower airways also explains the more serious disease.
- There was no airborne route of infection.
Which virus families are similar in etiology?
For a number of virus families, the picture is quite the same. Influenzaviruses, paramyxoviruses, pneumovirus and coronaviruses are all present in world animals, in particular birds and bats. In these reservoir hosts there is an incredible diversity of these viruses circulating. The animals do not suffer from these viruses as these viruses have co-evolved with their host for thousands or maybe millions of years. Occasionally these wild animals transmit their virus to domestic animals, where they can spread wildly. This also increases the chance that humans get exposed. This is when zoonotic infections happen. For influenzaviruses, paramyxoviruses, pneumovirus and coronaviruses zoonotic infections happen rather frequently. A lot of animals also harbour endemic viruses in humans. All of these viruses can be traced back to their animal reservoir host.
How many seasonal coronaviruses are there?
There are four seasonal coronaviruses, which all cause mild respiratory illnesses in humans in winter. Currently we have SARS-CoV-2, which can cause more severe respiratory illness in humans.
What was done to combat the SARS epidemic?
To combat the SARS epidemic by coordinating three global networks: the existing global outbreak alert response network of epidemiologists, it brought together a group of medical doctors to share experiences on how to best treat patients with SARS and a group of researchers to determine the etiology of SARS.
What did the etiological team find about SARS?
Later in the outbreak it became clear that although it was related to viruses from bats, the outbreak originated from ferrets and raccoon dogs in a live animal market.
What did the clinical team find for SARS?
From the clinical network, it became clear that simple hygiene measures like hand washing and face mask wearing were sufficient to limit infection. It was further shown by epidemiologists and modellers that if we reduce the contact rate between patients and stop moving people around in hospitals that the reproductive number of infections could be brought back very rapidly. This led countries to very strictly adhere to hygiene rules, diagnostic testing and quarantining people in hospitals to stop the outbreak.
What makes SARS-CoV-2 more difficult to control than SARS?
- It replicates in the lower airways
- It can be asymptomatic
- Might be airborne, but lecturer thinks this evidence is very weak.
What did we learn about paramyxo- and pneumoviruses?
There are eight paramyxo- and pneumoviruses. These viruses also originate in bats and reach humans through different animals (e.g. horses and pigs). These viruses have a very high case-fatality rate. The intervention is at the level of domestic animals (pigs and horses). As pigs and horses get infected by roaming under the trees where fruit bats live, a useful intervention is removing the fruit bats from these trees. You can also keep the domestic animals away from the bats.
Where do flu viruses originate from and how do they reach humans?
In contrast to corona-, paramyxo- and pneumovirusses, flu viruses originate from birds (ducks, geese, swans, gulls) instead of bats. In September-October chances that a random duck or goose has the flu are 20-30%. They don’t suffer from the flu, but occasionally spread the virus to poultry. Wild birds excrete the virus in their faeces and e.g. chickens that roam outside will pick at the faeces and get infected. Outside pigs will also eat the bird faeces and get infected.
What is the critical difference between zoonotic viruses and pandemic viruses?
The critical difference between a zoonotic virus and a pandemic virus is that pandemic viruses can transmit from human to human, whereas most zoonotic infections can’t.
Why can’t virologists predict if a zoonotic virus can become a pandemic?
Because it is not known what makes a virus transmissible from human to human.
Why would it be useful to predict if a zoonotic virus can become a pandemic virus?
Because a pandemic zoonotic virus can spread very quickly, like the swine flu in 2009. Here, the world was lucky that the virus was not very virulent.
Are all flu pandemics equally dangerous?
No. Flu pandemics can vary enormously in severity. However, if you combine the seasonal flu deaths and compare those to the last few pandemic flus, the seasonal flu has killed more people.
Why can there be a flu epidemic every year and can people get sick even when they’ve been previously exposed or vaccinated?
On the surface of a influenza virus, there are two proteins: hemagglutinin (attachment protein) and neuraminidase (allows virus to release from infected cells). There are 16 hemagglutinin variants and nine neuraminidase variants in wild birds (reservoir). This means that there are 9*16=144 antigenic subtypes of flu. These subtypes are defined based on antibody responses. This is why a pandemic influenza can emerge in a population that already has had a flu epidemic/exposure.
