Emerging Infectious Diseases

The slides for this lecture aren't actually online yet, so I'm just going to make do with my own shitty notes. Hold on tight...

Influenza

Influenza is often seen as a common, relatively mild illness, but it has also been responsible for some major pandemics around the world. The only type of influenza responsible for pandemics is influenza A, as it can skip species and mutate in order to evade immunity from the population as a whole. Migrating birds are common vectors for influenza, as are pigs, as they have receptors for both bird and human influenza. The main types of mutations include reassortment, where packets of nucleic acid are swapped between human and animal viruses, and adaptation, in which enough mutations occur within the virus for it to be unrecognisable by human immune systems. The 1918 Spanish Flu was a result of viral adaptation.

Most influenza deaths are in the young and in the elderly. However, there are some exceptions. In 1918, there were also a lot of deaths in young adults, possibly because people of this age group were exposed to poor conditions when fighting in the war. In the 2009 swine flu pandemic, there was a peak in the 40-60-year-old age group, but the elderly were not too badly affected. It has been speculated that this is because the swine flu was similar enough to some earlier strains circulating between 1918 and 1957 for the elderly to have immunity.

The most likely candidates for future pandemics are H5N1, H7N9 and H3N2. H5N1 is mainly spread by bird migration and transport, whereas H7N9 is associated with contact with songbirds. H7N9 is mostly confined to China. It has evolved in southern China to produce a strain that is more pathogenic in birds, but it remains to be seen exactly how pathogenic this strain is in humans.

Coronaviruses

SARS

SARS is a bat virus that obtained a mutation that increased its human transmission. Bats can pass on SARS to civic cats, which in turn can pass it on to us. Thankfully, SARS is not that great at human transmission, requiring close contact for its spread. Furthermore, it is most infectious during the second week when patients are showing symptoms. As such, SARS can be readily controlled by quarantine and hygiene.

MERS

MERS, or Middle Eastern Respiratory Syndrome, may also originate from bats. Camels are the intermediate host for this virus. As you might expect from the name, most cases of MERS are in the Middle East, particularly in people with close contact with camels.

Exotic arboviruses

The good thing about arboviruses, or insect-borne viruses, is that you need that particular insect in order for the disease to spread. As such, controlling mosquito breeding can be very helpful in stopping the spread of the disease. The bad thing is that we have some of these mosquitoes in Australia: Aedes aegypti is found in northern Queensland, and Aedes albopictus is found in the Torres Strait Islands. Outbreaks of Dengue fever have occurred in northern Queensland due to the presence of Aedes aegypti.

Zika virus

Zika virus is primarily transmitted by Aedes aegypti and Aedes albopictus. Zika used to cycle between apes and these mosquitoes, but now it cycles between humans and mosquitoes. Zika can also be transmitted from human-to-human, either transplacentally, sexually or via blood transfusion. The incubation period of Zika virus is around 2 weeks, after which mild symptoms such as headache, fever and rash usually occur. Even though Zika is normally mild, it can have disastrous neurological and fetal complications. In congenital Zika syndrome, there is microcephaly (small brain due to tissue destruction), retinal damage and musculoskeletal problems.

Chikungunya

Chikungunya fever has symptoms similar to Ross River Virus, such as aches, headaches and fever. It is mainly transmitted by Aedes aegypti, but there have been some mutations that allow it to be transmitted by Aedes albopictus as well.

Nipah virus

Nipah virus originates from bats, but can be passed on to pigs and then to humans. It was originally found in Singapore and Malaysia, but there have also been outbreaks in Bangladesh and India. Symptoms include encephalitis and pneumonia, which are obviously pretty nasty, but as Nipah virus has limited person-to-person transmission, you're likely to be safe if you avoid bats.

Other viruses

Other viruses that were mentioned during the lecture include Lassa virus (from rodents), Ebola and Marburg viruses (from bats) and Congo-Crimean haemorrhagic fever (CCHF). However, the lecturer didn't go into much more detail, so that's pretty much all I'm going to say about them.