Barnyard Pestilence

Many human infectious diseases originated in domesticated animals, a study has shown.

Of 25 diseases that have historically caused high mortality in human beings, many probably or possibly reached humans from domesticated animals, according to an article published in Nature in 2007. The main ones among so-called temperate diseases are diphtheria, influenza A, measles, mumps, pertussis, rotavirus, smallpox and tuberculosis. Three others probably came from apes (hepatitis B) or rodents (plague and typhus), the review says.

Among the important tropical diseases, the article said, domestic animal origins can be ruled out for 6 of the 10: AIDS, dengue fever, vivax malaria and yellow fever, all derived from wild primates; cholera, from aquatic algae and invertebrates; and falciparum malaria, from birds.

The strong links to domestic animals for the temperate diseases is tied to the rise of agriculture 11,000 years ago, which brought humans into frequent contact with animals.

C.CLAIBORNE RAY




Where a Shark Winters

Basking sharks, those slow-moving creatures that are second in size only to whale sharks, spend their summers and falls in surface waters feeding on plankton blooms. But their winter whereabouts have been a bit of a mystery.

For a long time, scientists thought that the sharks must hibernate in deep waters to conserve energy at a time when there was little plankton around. But that idea was disproved by satellitetagging studies of sharks in the eastern side of the North Atlantic, which showed that they moved seasonally within the region’s temperate waters.

Now a new tagging study of sharks in the western North Atlantic, where the seasonal changes in the ocean are greater, has shown that they migrate much farther - into tropical waters and even across the equator. The sharks travel at depths of up to 914 meters, sometimes remaining in deep waters for weeks or months.

Gregory B.Skomal of the Massachusetts Division of Marine Fisheries and colleagues attached satellite tags to 25 sharks off Cape Cod, and received data on depth, water temperature and light levels from 18 of them. Their findings are published in Current Biology.

HENRY FOUNTAIN

A new study reveals the winter migrations of basking sharks.


Summer Suicides

Greenland has one of the highest suicide rates in the world, and according to a new study suicides peak in the long, bright days of summer.

The study, published online in BMC Psychiatry, looked at 1,351 suicides from 1968 to 2002 and found that the concentration of suicides in the summer was greater north of the Arctic Circle than south. The highest concentration of summer suicides was in the northernmost inhabited region, where the sun remains above the horizon for four months.

The reasons for the summer increase are unclear. Alcohol consumption is associated with suicide, but there was no significant variation in alcohol sales over the course of the year. Major depression was uncommon, and most of the suicides appeared to be impulsive.

The authors speculate that sleeplessness might lead to delirium and suicide. The lead author, Dr.Karin S.Bjorksten of the Karolinska Institute, said that the mechanism may involve disruptions in the sleep cycle and an imbalance in the neurotransmitter serotonin, which is released in greater amounts in bright light. “A lack of sleep may be the key,’’ she said. “It’s very dangerous when people don’t sleep enough.’’

NICHOLAS BAKALAR