|Pandas and tigers: Delectably adorable but tragically endangered.|
Endangered animals must overcome many obstacles to avoid extinction. Habitat loss, poaching, reduced genetic diversity -- what else could possibly go wrong?
The answer: Canine distemper virus (CDV)!!!
Paramyxo, our old friend... We've come to talk of you again.
(The Sound of Distemper)
A CDV outbreak is sweeping Chinese wildlife centers. So far, two giant pandas have succumbed to the disease, and two more infected pandas remain in critical condition. There are also 1,600 pandas in the wild that are at risk for the disease. Despite the panic, giant pandas are not our biggest concern. Pandas have incredible immune systems such that the CDV fatality rate in pandas is 10% compared to the usual 50% in adult dogs.
A study suggest that the extremely endangered Amur tiger (also known as the Siberian tiger) may be the most vulnerable to CDV. They live in small groups of up to 25 tigers. Such a small population could be wiped out by a CDV outbreak. Interestingly, the researchers' proposed solution also involve with population size: Separating groups so that each tiger would live alone would make an outbreak unsustainable.
This ties into major themes in viral eradication. Basic (R0) and effective reproduction rates (R) and population thresholds are crucial in determining the sustainability of an outbreak. For instance, if tigers were alone, then R, the average number of tigers that an infected tiger would infect, would be zero. Therefore, the outbreak would start and end with one tiger.
The math checks out. Unfortunately, the feasibility of this plan does not compute. Do we really want to isolate tigers from each other? Let's not forget that small populations also have increased risk of extinction (a theme from island biogeography!). This CDV outbreak is a reminder of the havoc viruses can wreak upon entire species, and how difficult it can be to contain them.
-- Tina Ju