WEBVTT - Could the Bird Flu Cause a Human Pandemic? 0:00:01.890 --> 0:00:07.870 Welcome to BrainStuff, a production of iHeartRadio. Hey BrainStuff, Lauren 0:00:07.890 --> 0:00:12.640 Vogelbaum here. Over the past several years, you've probably seen 0:00:12.720 --> 0:00:16.160 news stories with dire warnings about the avian flu or 0:00:16.200 --> 0:00:20.310 bird flu. This refers to a highly infectious disease that 0:00:20.450 --> 0:00:24.070 swept through both wild bird and poultry populations all over 0:00:24.090 --> 0:00:28.140 the world. The virus doesn't pass to humans easily, but 0:00:28.270 --> 0:00:30.860 when it does, it kills at a rate much higher 0:00:30.960 --> 0:00:34.900 than other strains of influenza. But what exactly is the 0:00:34.940 --> 0:00:37.400 bird flu, and how is it different from the seasonal 0:00:37.440 --> 0:00:41.320 flus that come around every year? Today, let's talk about 0:00:41.420 --> 0:00:44.870 how the bird flu works, why it's considered unlikely to 0:00:44.930 --> 0:00:48.409 cause an epidemic in humans, and why disease control centers 0:00:48.490 --> 0:00:51.750 are nonetheless watching it closely and working to contain it. 0:00:53.170 --> 0:00:56.330 But first up, let's talk about how viruses work in general. 0:00:57.210 --> 0:01:01.990 A virus particle, or virion, is not a cell. The 0:01:02.050 --> 0:01:06.000 cells in our bodies, and bacteria cells, are living entities 0:01:06.110 --> 0:01:11.179 with the ability to eat, grow, and reproduce. Viruses are 0:01:11.260 --> 0:01:15.459 nothing like that. A virus is a microscopic packet that 0:01:15.520 --> 0:01:18.540 contains a set of genetic instructions wrapped up in a 0:01:18.580 --> 0:01:21.880 protective layer of protein that sometimes with a protective layer 0:01:21.920 --> 0:01:26.250 of lipid around that. Viruses cannot reproduce on their own. 0:01:26.610 --> 0:01:29.009 They have to hijack a living cell to do that 0:01:29.069 --> 0:01:32.830 work for them. This process destroys the cells and makes 0:01:32.910 --> 0:01:37.450 people and other animals sick. Viruses usually enter an animal's 0:01:37.490 --> 0:01:40.810 body through the mouth, mucous membranes, or breaks in the skin. 0:01:41.530 --> 0:01:45.230 Then they infect specific cells, depending on the type of virus. 0:01:45.970 --> 0:01:48.930 For example, cold sores are caused by the herpes virus 0:01:49.030 --> 0:01:52.470 attacking cells in the lips. Other viruses, like the measles, 0:01:52.550 --> 0:01:55.310 can be widely damaging because they attack cells in the 0:01:55.350 --> 0:01:59.440 immune system. A virus particle will attach to the surface 0:01:59.560 --> 0:02:03.060 of whatever host cell and inject its genetic instructions into 0:02:03.100 --> 0:02:07.600 that cell. The virus's code recruits the cell's enzymes to 0:02:07.780 --> 0:02:11.440 make and assemble the parts for many new virus particles. 0:02:12.580 --> 0:02:15.240 Once assembled, the new viruses then break out of the 0:02:15.280 --> 0:02:18.160 host cell, killing it in the process, and go on 0:02:18.210 --> 0:02:22.650 to attack other cells and continue the cycle. Influenza is 0:02:22.690 --> 0:02:25.750 a specific type of virus that attacks the respiratory system 0:02:25.930 --> 0:02:30.070 of birds and some mammals. It can cause fevers, sore throats, 0:02:30.190 --> 0:02:33.030 and congestion as your body works to fight and flush 0:02:33.090 --> 0:02:36.010 out the virus. If it attacks muscle cells, it can 0:02:36.030 --> 0:02:40.910 also cause muscle aches. There are four basic types, or genera, 0:02:41.010 --> 0:02:44.940 of influenza virus, called A, B, C, and D, each 0:02:45.040 --> 0:02:50.650 with multiple subtypes, or lineages, and strains. In general, viruses 0:02:50.710 --> 0:02:53.930 mutate pretty often. That's why a new flu vaccine comes 0:02:54.010 --> 0:02:56.670 out every year, to help protect you from the specific 0:02:56.730 --> 0:03:00.570 strains that have developed and spread. All four types of 0:03:00.650 --> 0:03:04.510 influenza can infect humans, but influenza A causes the most 0:03:04.610 --> 0:03:08.250 serious illnesses and seasonal epidemics, and is the only type 0:03:08.310 --> 0:03:13.410 known to have caused pandemics. We identify subtypes of influenza 0:03:13.440 --> 0:03:15.960 A based on the specific proteins that they have on 0:03:16.000 --> 0:03:21.060 their surfaces. These proteins are antigens, that is, particles that 0:03:21.100 --> 0:03:23.560 your immune system uses to tell whether something is a 0:03:23.680 --> 0:03:28.359 friend or foe. Influenza A has two kinds of surface proteins, 0:03:28.580 --> 0:03:33.070 hemagglutinin and neuraminidase, and each has a bunch of numbered subtypes. 0:03:34.010 --> 0:03:39.030 That's why influenza A viruses have names like H1N1, which 0:03:39.090 --> 0:03:40.950 was the flu that caused the pandemic of 1918, or H3N2, 0:03:40.970 --> 0:03:48.810 which caused the pandemic of 1968. The strain that's commonly 0:03:48.870 --> 0:03:53.070 referred to as the bird flu is H5N1. It first 0:03:53.130 --> 0:03:55.970 cropped up in 1996, and we'll get more into its 0:03:56.010 --> 0:04:00.300 history here in a minute. But, okay, how do new 0:04:00.340 --> 0:04:05.080 strains develop in the first place? Like many viruses, influenza 0:04:05.140 --> 0:04:10.800 can mutate through antigenic drift or shift. In antigenic drift, 0:04:11.040 --> 0:04:14.990 small changes occur to a virus's surface proteins as it reproduces. 0:04:16.070 --> 0:04:19.050 This is happening all the time, and these small changes 0:04:19.170 --> 0:04:22.050 can add up enough that your immune system eventually won't 0:04:22.089 --> 0:04:25.210 be able to recognize the virus anymore, and the virus 0:04:25.250 --> 0:04:28.810 will thus be able to infect you again. Iterations of 0:04:28.870 --> 0:04:34.279 both H1N1 and H3N2 still circulate as yearly seasonal flus 0:04:34.339 --> 0:04:37.500 because of this, and hence new flu vaccines come out 0:04:37.580 --> 0:04:43.570 every year. But an antigenic shift sudden, major changes occur 0:04:43.650 --> 0:04:46.400 that create a whole new subtype of the virus that 0:04:46.740 --> 0:04:50.719 basically no one has immunity to because it's new or novel. 0:04:51.900 --> 0:04:54.659 Although of course the coronavirus is not a type of influenza, 0:04:55.000 --> 0:04:59.630 this is what happened with COVID-19. It was novel. Being 0:04:59.650 --> 0:05:02.349 that these viruses are new, new vaccines have to be 0:05:02.390 --> 0:05:06.310 developed in order to help fight them. Antigenic shift is 0:05:06.320 --> 0:05:08.950 a lot more rare, but it can happen when two 0:05:09.050 --> 0:05:12.810 different strains of influenza encounter each other in a single animal, 0:05:13.230 --> 0:05:17.370 and the viruses swap some segments of their DNA. This 0:05:17.410 --> 0:05:21.370 is called reassortment, and the novel viruses it can create 0:05:21.490 --> 0:05:25.960 can be especially dangerous. For example, the aforementioned flu pandemic 0:05:26.000 --> 0:05:29.080 of 68 was caused by a reassortment of a human 0:05:29.120 --> 0:05:33.539 strain and an avian strain. And the 2009 swine flu 0:05:33.580 --> 0:05:37.099 pandemic was caused by a triple reassortment of swine, human, 0:05:37.300 --> 0:05:43.070 and avian strains. Now, birds can carry every known subtype 0:05:43.190 --> 0:05:47.470 of influenza A. But when scientists talk about avian strains 0:05:47.529 --> 0:05:51.089 of the flu, they usually mean varieties that exist mostly 0:05:51.330 --> 0:05:55.670 or entirely in birds, not in people. Most of the time, 0:05:55.850 --> 0:05:59.870 birds can't transmit the flu directly to people. They first 0:05:59.930 --> 0:06:03.950 infect pigs, horses, and other non-human mammals that can also 0:06:03.990 --> 0:06:08.839 contract human flu strains. Reassortment in those other mammals can 0:06:08.860 --> 0:06:14.140 then create novel strains capable of infecting humans. Many wild 0:06:14.180 --> 0:06:17.660 birds carry avian flu viruses in their intestines but don't 0:06:17.760 --> 0:06:21.260 actually get sick from them. However, they can shed the 0:06:21.300 --> 0:06:26.290 virus in their droppings, saliva, and other bodily fluids. Domesticated 0:06:26.350 --> 0:06:28.770 birds like chickens can get sick when they come into 0:06:28.810 --> 0:06:33.789 contact with contaminated water, feed, or soil. Avian flu strains 0:06:33.890 --> 0:06:38.900 aren't always dangerous, even to poultry. Low pathogenic strains cause 0:06:38.980 --> 0:06:42.820 very mild symptoms, like ruffled feathers and reduced egg production. 0:06:43.940 --> 0:06:47.650 High pathogenic strains, however, can be deadly. They can have 0:06:47.670 --> 0:06:52.010 a mortality rate in poultry approaching 100%. Birds that do 0:06:52.050 --> 0:06:54.589 survive can continue to shed the virus in their droppings 0:06:54.670 --> 0:06:57.909 for several days after recovering, which helps the virus continue 0:06:57.930 --> 0:07:03.030 to spread. Farmers can protect their birds by frequently disinfecting 0:07:03.089 --> 0:07:07.000 their clothing, shoes, and equipment, by keeping domestic birds away 0:07:07.060 --> 0:07:10.070 from wild birds as much as possible, and by working 0:07:10.090 --> 0:07:13.850 to quarantine birds that may be infected. By doing so, 0:07:14.090 --> 0:07:17.670 they're not just protecting their birds or their livelihood, they're 0:07:17.710 --> 0:07:23.040 also protecting human health. Because, in rare cases, avian flu 0:07:23.240 --> 0:07:27.280 can spread to humans. Since people have no immunity to 0:07:27.320 --> 0:07:31.240 these strains, they can be especially deadly. And that's what 0:07:31.320 --> 0:07:34.970 happened with H5N1. And we're going to get into the 0:07:35.030 --> 0:07:37.110 story of that, but first we're going to get into 0:07:37.150 --> 0:07:46.260 a quick break for a word from our sponsor. So, 0:07:46.720 --> 0:07:52.060 in 1996, researchers identified a highly pathogenic avian influenza in 0:07:52.080 --> 0:07:56.560 domestic waterfowl in southern China. The next year, health officials 0:07:56.600 --> 0:07:59.660 in Hong Kong reported that, for the first time, it 0:07:59.700 --> 0:08:03.410 appeared that this virus had moved directly from birds to people, 0:08:03.730 --> 0:08:07.870 instead of moving through a second species. The virus caused 0:08:07.990 --> 0:08:11.830 typical flu symptoms, but could also cause eye infections, pneumonia, 0:08:11.970 --> 0:08:18.150 and acute respiratory distress. Tests confirmed that influenza A H5N1 0:08:18.350 --> 0:08:23.170 was completely new to humans. And thus, what's now often 0:08:23.230 --> 0:08:27.570 simply called the bird flu was born. At the time, 0:08:27.570 --> 0:08:31.130 18 people infected with the virus were hospitalized, and six 0:08:31.150 --> 0:08:34.390 of them died. The Hong Kong government, alarmed at the 0:08:34.410 --> 0:08:38.360 potential threat of an epidemic or even pandemic, took drastic steps. 0:08:39.120 --> 0:08:41.820 In about three days, the government destroyed some one and 0:08:41.840 --> 0:08:46.740 a half million birds, the country's entire poultry population. Although 0:08:46.760 --> 0:08:49.780 this might sound extreme, many health experts think that Hong 0:08:49.800 --> 0:08:54.680 Kong's actions prevented an influenza pandemic that year. After that, 0:08:54.880 --> 0:09:00.439 the H5N1 strain appeared to lay dormant until 2003. Then, 0:09:00.559 --> 0:09:04.059 government officials in Vietnam and Thailand began to report infections 0:09:04.160 --> 0:09:08.350 in birds and people. About 100 million birds died in 0:09:08.470 --> 0:09:12.449 Asia in 2003-2004, either as a result of the disease 0:09:12.650 --> 0:09:15.970 or as part of efforts to stop its spread. In 0:09:16.070 --> 0:09:19.750 fall of 2005, the disease spread to Eastern Europe, likely 0:09:19.790 --> 0:09:23.990 due to migrating birds. By the following January, several people 0:09:24.050 --> 0:09:27.630 in Turkey had contracted the disease, most likely from contact 0:09:27.650 --> 0:09:32.000 with dead birds. Health officials found Nigerian birds infected with 0:09:32.020 --> 0:09:36.520 the disease in early 2006. Relatively few humans have ever 0:09:36.600 --> 0:09:41.719 contracted H5N1, and most who did had extended direct contact 0:09:41.740 --> 0:09:47.280 with infected birds. However, of the over 860 people confirmed 0:09:47.340 --> 0:09:51.420 to have contracted the virus, over 50% have died, which 0:09:51.620 --> 0:09:56.570 is a wildly high fatality rate. Previous influenza pandemics have 0:09:56.650 --> 0:10:00.910 killed an estimated 0.1 to 2.5%. percent of the people 0:10:00.960 --> 0:10:04.980 they infected. And now, some researchers think that 50 percent 0:10:05.080 --> 0:10:08.140 is an overestimate of the bird flu's true fatality rate 0:10:08.200 --> 0:10:12.380 in humans, but relatively conservative estimates have put it somewhere 0:10:12.440 --> 0:10:14.059 from 14 to 33 percent, which is still wildly high. 0:10:18.570 --> 0:10:22.090 Since that first decade, the bird flu has mutated, forming 0:10:22.150 --> 0:10:26.630 a few recognized subtypes, and spread around the world. Every 0:10:26.670 --> 0:10:29.800 few years, it's caused outbreaks in both wild birds and 0:10:29.900 --> 0:10:34.320 poultry in different places, plus occasional infections in humans and 0:10:34.380 --> 0:10:40.100 other mammals. Then, in 2021, a new strain of H5N1 0:10:40.300 --> 0:10:43.579 caused what's called a panzootic. That's the term for a 0:10:43.600 --> 0:10:47.630 pandemic in wild animals, in this case wild birds. This 0:10:47.830 --> 0:10:52.990 panzootic continues today. Reports of die-off events involving sometimes tens 0:10:53.030 --> 0:10:56.930 of thousands of birds come in every month. And the 0:10:56.950 --> 0:11:00.429 bird flu has been observed transmitting from mammal to mammal. 0:11:01.650 --> 0:11:05.030 In 2024, researchers found that it was making dairy cattle 0:11:05.130 --> 0:11:08.390 in Texas sick. There have since been outbreaks in cattle 0:11:08.450 --> 0:11:11.290 in at least 17 U.S. states, causing a lot of 0:11:11.390 --> 0:11:15.380 stress and financial loss for dairy farmers. Other mammals that 0:11:15.400 --> 0:11:19.810 have contracted H5N1 include farmed mink in Europe, domestic cats, 0:11:20.190 --> 0:11:24.330 and wild animals like bears, raccoons, rodents, and even South 0:11:24.350 --> 0:11:31.010 American sea lions. Notably, human-to-human transmission has been extremely rare, 0:11:31.880 --> 0:11:35.960 which has left some people wondering whether scientists have overreacted 0:11:36.059 --> 0:11:40.620 to the H5N1 bird flu. But public health officials have 0:11:40.679 --> 0:11:44.520 several concerns about it. There's that high mortality rate and 0:11:44.580 --> 0:11:47.380 the fact that in the past, it's killed young adults 0:11:47.540 --> 0:11:51.099 in otherwise good health. Also, controlling the spread of it 0:11:51.240 --> 0:11:54.780 is difficult because lots of wild and migratory birds can 0:11:54.820 --> 0:11:59.079 carry it. And given its recent spillover into different mammals, 0:11:59.380 --> 0:12:03.400 the virus is clearly changing. Whether those changes will wind 0:12:03.480 --> 0:12:06.600 up making it more dangerous to humans is anybody's guess, 0:12:07.059 --> 0:12:11.910 but researchers are closely following the situation. But to cause 0:12:11.990 --> 0:12:14.429 a pandemic in humans, the bird flu would have to 0:12:14.500 --> 0:12:17.680 mutate in a few ways to become better at traveling 0:12:17.720 --> 0:12:21.320 through the air, better at binding to human respiratory cells, 0:12:21.840 --> 0:12:26.960 and better at hijacking mammalian host cells in general. Unfortunately, 0:12:27.240 --> 0:12:30.140 the more interaction that humans have with the virus through 0:12:30.220 --> 0:12:34.400 infected wild and domestic animals, the more opportunities the virus 0:12:34.460 --> 0:12:39.580 has to undergo reassortment and antigenic shift. This is one 0:12:39.620 --> 0:12:41.480 of the many reasons why it's good to get the 0:12:41.500 --> 0:12:44.660 seasonal flu vaccine every year if you can. It can't 0:12:44.700 --> 0:12:47.080 protect you against the bird flu, but it will lower 0:12:47.120 --> 0:12:50.620 the possibility of human and avian flu viruses interacting with 0:12:50.640 --> 0:12:54.830 each other in your body. Speaking of vaccines, there are 0:12:54.890 --> 0:12:58.350 vaccines for humans to protect against the bird flu. At 0:12:58.429 --> 0:13:01.070 least 50 have been approved by different regulators around the 0:13:01.110 --> 0:13:05.510 world for use in different circumstances. And there are plans 0:13:05.570 --> 0:13:08.230 in place by bodies like the World Health Organization to 0:13:08.550 --> 0:13:10.760 to help make sure that everyone would have access to 0:13:10.800 --> 0:13:14.920 vaccines in case of a pandemic. Researchers are also working 0:13:14.960 --> 0:13:18.300 on improving bird flu vaccines for non-human animals to help 0:13:18.340 --> 0:13:22.870 stop the spread. You can help protect yourself and, you know, 0:13:23.070 --> 0:13:27.010 all of humanity by avoiding contact with wild animals, alive 0:13:27.110 --> 0:13:31.490 or dead, and by keeping any pet cats indoors. If 0:13:31.530 --> 0:13:33.910 you have a backyard flock of chickens, ensure that they're 0:13:33.929 --> 0:13:38.010 fully enclosed, away from wild birds and their droppings. If 0:13:38.030 --> 0:13:40.550 you work with animals, you probably know more about this 0:13:40.600 --> 0:13:44.800 than I do, but always practice good sanitation, like handwashing 0:13:44.980 --> 0:13:49.800 and frequent cleaning of equipment, clothing, and shoes. Also, the 0:13:49.820 --> 0:13:52.980 spread of H5N1 to farm animals is a great reminder 0:13:53.020 --> 0:13:57.000 for us all to practice food safety. Cook meat, and 0:13:57.120 --> 0:14:01.040 especially poultry, to a safe temperature, and opt for pasteurized 0:14:01.100 --> 0:14:06.220 milk instead of raw milk. Pasteurization inactivates viruses like influenza 0:14:06.460 --> 0:14:09.540 and kills bacteria, and thus prevents you from getting sick 0:14:09.620 --> 0:14:14.660 from all kinds of potential pathogens. Basically, we're not ready 0:14:14.760 --> 0:14:17.780 for a bird flu pandemic. We're never really ready for 0:14:17.800 --> 0:14:21.880 a pandemic. But science is working on it, and you 0:14:21.900 --> 0:14:29.040 can help. Today's episode is based on the article, How 0:14:29.080 --> 0:14:32.440 Bird Flu Works, on HowStuffWorks.com, written by Tracy V. Wilson. 0:14:33.330 --> 0:14:35.870 BrainStuff is a production of iHeart Podcasts in partnership with 0:14:35.890 --> 0:14:39.660 HowStuffWorks.com and is produced by Tyler Klang. For more shows 0:14:39.700 --> 0:14:43.740 from iHeart Podcasts, visit the iHeartRadio app, Apple Podcasts, or 0:14:43.820 --> 0:14:45.570 wherever you listen to your favorite shows.