Lack of Sunlight

Lack of Sunlight

When the poultry sheds are eventually scooped out, some of the scrapings—about one million tons per year—are fed to American cattle,¹⁷⁹² and some are spread upon cropland as fertilizer. Out in the open air, combined with the sanitizing rays of the sun, the tons of manure rapidly dry and the fecal micro-organism rapidly die.¹⁷⁹³ Inside dimly lit sheds, however, human pathogens like Salmonella¹⁷⁹⁴ and Campylobacter¹⁷⁹⁵ thrive in the moist litter. So may viruses like H5N1.

Transmission experiments with chickens reveal that the spread of H5N1 is predominantly via the fecal-oral route rather than in respiratory droplets. H5N1 can survive in wet feces for weeks, but at ambient temperatures is inactivated as soon as the feces dry out.¹⁷⁹⁶ In an outdoor, free-range setting, then, the spread of bird flu viruses like H5N1 would be expected to be relatively inefficient.

In countries like Thailand, the combination of tropical heat and crowded confinement necessitates “evaporative cooling” in poultry sheds, which uses large fans and a water mist to cool down the birds during the hot season. Although this reduces heat stress, the high level of humidity ensures that the litter is kept moist, which may facilitate the spread of pathogens like bird flu. So-called “evap houses” increase flock survival, but may increase virus survival as well.¹⁷⁹⁷

Farther north in China, some poultry flocks may be outdoors most of the year but taken inside during the cold winter months, offering researchers a unique opportunity to compare bird flu activity in flocks confined indoors versus those let outside. Indeed, bird flu outbreaks are more likely to occur when the birds are crammed inside. Although this may be due to other factors, such as increased viral survival at colder temperatures, the FAO blames in part the winter confinement.¹⁷⁹⁸ Increased crowding indoors with suboptimal ventilation,¹⁷⁹⁹ combined with less solar radiation across the Earth’s surface,¹⁸⁰⁰ may be why the human flu season flips every year between the north and south hemispheres following the winter.

“Birds that are housed indoors year-round should be considered more susceptible to infectious diseases,” an avian virus textbook reads, “because of decreased air quality, the accumulation of pathogens in a restricted environment, and the lack of exposure to sunlight. These factors function collectively to decrease a bird’s natural resistance to disease.”¹⁸⁰¹

The absence of adequate ventilation and sunlight inherent to intensive confinement is a powerful combination for the spread of influenza. Perhaps the best studied illustration of the danger of crowded enclosed spaces in human medicine was a commercial airline flight in 1977 that was stuck on a tarmac for more than four hours due to a mechanical failure—while a young woman lay prostrate in the back of the cabin feverishly coughing with the flu. Within three days, nearly three out of four of the remaining passengers were destined to share in her pain.¹⁸⁰² Laboratory studies on animals show the same thing—decreased air exchange is strongly associated with increased influenza infection rate.¹⁸⁰³

Lessons can be learned from past pandemics. In 1918, as Boston hospitals filled beyond capacity, a tent hospital was set up in nearby Brookline. Though exposing ailing patients to the chilly Boston autumn was condemned by Bostonians as “barbarous and cruel,” it turned out that the fresh breeze and sunshine seemed to afford the lucky overflow patients far better odds of survival than those inside the overcrowded, poorly ventilated hospitals.¹⁸⁰⁴

A study of the 1957–58 pandemic demonstrated the potential role of sunlight. Ultraviolet rays damage genetic material. That’s why we get a sunburn: The ultraviolet light in the sun’s rays damages DNA in our skin, triggering the inflammation that manifests as redness and pain.¹⁸⁰⁵ Ultraviolet lights, then, have been used in tuberculosis wards to kill off some of the TB bugs coughed into the air. To see if influenza could be killed in the same way, researchers compared influenza rates in patients in TB buildings with UV lights to patients in TB buildings without UV lights during the pandemic. In the rooms without UV, 19% got the flu; in rooms with the UV lights only 2% became infected, a statistically significant difference.¹⁸⁰⁶ This suggests that sunlight may help sanitize influenza virus from the air, highlighting the increased risk of crowding poultry indoors. For flocks raised outdoors, according to the FAO, the natural UV rays of the sun may “destroy any residual virus.”¹⁸⁰⁷

If sunlight has such a disinfectant quality, why doesn’t the industry install windows to allow some natural sunlight to perhaps cut down on airborne fecal pollutants? More light means chickens become more active, which means, as one poultry industry trade journal describes, “birds burn energy on activity rather than on growth and development.” Natural lighting has a negative impact on “feed conversion.”¹⁸⁰⁸ In other words, the animals “waste” energy on moving instead of just growing fatter to reach slaughter weight faster. According to Broiler Industry, “It is obvious that the light supplied by sunshine during the day and normal darkness at night is the most inferior of any lighting program.”¹⁸⁰⁹