Rats #7: Disease vectors throughout history

Since the Great Plague, after which the Black rat (rattus rattus) was ruthlessly hunted and killed off in millions, this species has declined to near non-existence in Europe, though it still thrives in the USA and Africa. The Brown rat (rattus norvegicus) – just as big a disease carrier, didn’t arrive in Europe until the 18th century. 

They are also excellent swimmers and may have entered new regions through self-propelled swimming. The naturalist Pallas reportedly saw great hordes of Brown rats swimming across the Volga river in 1727, from the Asian to the European side, arriving in modern-day Russia. Migrating rats can swim up to half a mile and survive by treading water for three days. Brown rats are more aggressive creatures than their black counterparts and quickly established their superiority all over Europe.

The Volga River, site of a massive rat crossing from Asia to Europe. Image labeled for reuse.

Rats may well like to live in waste dumps and sewers but they are not naturally dirty creatures and are highly intelligent. In many ways it seems that humanity’s war on them is very one sided. Untold millions of rats are ruthlessly exterminated by us, yet the same cannot be said of them where we are concerned. Each time in history that some kind of plague has broken out, rats became the fall guys. During the Byzantine dynasty there occurred the ‘Plague of Justinian’ where up to 10,000 people a week were dying.

The fact is that rats themselves rarely succumb to the disease carried by their fleas. But when they do die, the fleas have to look for other bodies, like humans, to live on, which can happen at epidemic proportions. This happened periodically in history as far back as biblical times, and the flea-born disease is especially scary because the rupturing and decay of blood vessels beneath the skin cause it to gradually turn black, hence the "black death."

Labeled for reuse, by Mikael Häggström
Public domain, via Wikimedia Commons

China experienced Bubonic plague in 1330, from where it was carried west to the Crimea. By 1347 it had reached Europe via seafarers. Before it died down again, from Russia to the Mediterranean Sea 25 million people had died. Some 1,000 villages in England were wiped out by the disease.

The Bubonic plague re-appeared in 1665, when 17,440 people died during the ‘great plague of London,’ and in the 1860’s another outbreak in the Far East led to the deaths of 12,600,000 people all the way across to America. Plague outbreaks weren't limited to early times; Los Angeles had a major outbreak in 1925 and Vietnam saw tens of thousands of cases during the 1960’s. India suffered an outbreak in 1992.


Rats do carry other fatal diseases as well. The Hanta virus, Weil’s disease, Tuberculosis, Listeria and Q fever are all carried by them and easily passed on to humans via household pets. This is one cause for rats being seen as vermin.

In our case, for the most part disease isn't the main cause for concern. It's their constant gnawing and digging that I don't want. And the fact that my very DNA seems to have an aversion to them.

Hats off to Writeedge.com where I discovered much of what I know about rats.

http://writedge.com/why-do-people-hate-rats/

The rat series
Rats #1: Rats!

Rats #2: Rats and human co-evolution

Rats #3: Part of the English language

Rats#4: Biology basics and what’s in rat poison

Rats #5: Rat behavior

Rats #6: Causing very real damage

Rats #7: Disease vectors throughout history

Rats #8: The Dirty Secret: Rats in Our Neighborhood

Rats #9: Good riddance at The Eggplant

Rats #6: Causing very real damage

Norway rats consume and contaminate foodstuffs and animal feed. They may damage crops in fields prior to and during harvest, and during processing and storage. Rats also damage containers and packaging materials in which foods and feed are stored.

Rats cause structural damage to buildings by burrowing and gnawing. Our neighbor has found small holes gnawed through 2x6 boards (the wide way!) and are so small it looks like just the skinniest of snakes could pass through. However, her exterminator told her that they were definitely rat holes.

Rats undermine building foundations and slabs, cause settling in roads and railroad track beds, and damage the banks of irrigation canals and levees. Or in our case, they've excavated a large amount of gravel and sand, and I'm surprised we haven't seen any obvious chicken coop foundation settling.

Rats also may gnaw on electrical wires (one could only hope they get as far as the copper part) or water pipes, either in structures or below ground. They damage structures further by gnawing openings through doors, window sills, walls, ceilings, and floors. Considerable damage to insulated structures can occur as a result of rat burrowing and nesting in walls and attics. And then there's the smell of both rodent urine and dead rodents if poison suddenly caught up with them while nesting.

The "three now cosmopolitan commensal rodent pest species" (the brown rat, the black rat and the house mouse) have been dispersed in association with humans, partly on sailing ships in the Age of Exploration. Together with with a fourth rat species in the Pacific, the Polynesian rat (Rattus exulans), they have severely damaged island biotas around the world. 

For example, when the black rat reached Lord Howe Island in 1918, over 40 percent of the terrestrial bird species of the island, including the Lord Howe fantail, became extinct within ten years. Similar destruction has been seen on Midway Island (1943) and Big South Cape Island (1962). Conservation projects can, with careful planning, completely eradicate these pest rodents from islands using an anticoagulant rodenticide such as brodifacoum. This approach has been successful on the island of Lundy in the United Kingdom, where the eradication of an estimated 40,000 brown rats is giving populations of Manx shearwater and Atlantic puffin a chance to recover from near-extinction. From wikipedia. When I was traveling around New Zealand, we heard a lot about the destruction of ground-dwelling birds such as the iconic kiwi. The rats had eggs for breakfast, baby birds for lunch and the occassional youngster for dinner.

Lord Howe Island, image used with permission. 

The ship or wharf rat has contributed to the extinction of many species of wildlife including birds, small mammals, reptiles, invertebrates, and plants, especially on islands. True rats are omnivorous and capable of eating a wide range of plant and animal foods. True rats have a very high birth rate. When introduced to a new area, they quickly reproduce to take advantage of the new food supply. In particular, they prey on the eggs and young of forest birds, which on isolated islands often have no other predators and thus have no fear of predators. Some experts believe that rats are to blame for between 40 percent and 60 percent of all seabird and reptile extinctions, with 90 percent of those occurring on islands. Thus man has indirectly caused the extinction of many species by accidentally introducing rats to new areas.

We're not facing extinction of anything in our back-yard situation, but in the wake of all this destruction, planning their death didn't seem so harmful.

Rats #1: Rats!

Rats #2: Rats and human co-evolution

Rats #3: Part of the English language

Rats#4: Biology basics and what’s in rat poison

Rats #5: Rat behavior

Rats #6: Causing very real damage

Rats #7: Disease vectors throughout history

Rats #8: The dirty secret, rats in our neighborhood

Rats #9: Good riddance at The Eggplant

Rats #5: Rat behavior

I found that learning about rat behavior and habits particularly helpful as I tried to understand, outsmart, outgun and defeat the critters living under our chicken coop.

Norway rats (most likely the type we have) are primarily nocturnal. They usually become active about dusk, when they begin to seek food and water. Some may be active during daylight hours when rat populations are high. In our case, we believe we only had two. Consistent with normal behavior, neighbor Matt said that he saw our duo of rat squatters from his kitchen window in the evening.

Rats have poor eyesight (and they’re nocturnal, evolution is a joker) relying more on their hearing and their excellent senses of smell, taste and touch. They are considered color-blind. Therefore, for safety reasons, baits can be dyed distinctive colors without causing avoidance by rats. The baits we bought are green, I’d make them blaze (hunter) orange.

Rats use their keen sense of smell to locate food items and to recognize other rats. Their sense of taste is excellent, and they can detect some contaminants in their food at levels as low as 0.5 parts per million. That’s freaky good, kinda like a supertaster.

Norway rats usually construct nests in below-ground burrows or at ground level. In our case, the burrow was under the storage area of our coop. 

One of the many openings to the underground burrow within the run of our chicken coop.

Nests may be lined with shredded paper, cloth, or other fibrous material. Litters of six to 12 young are born 21 to 23 days after conception. Newborn rats are hairless and their eyes are closed, but they grow rapidly. They can eat solid food at two and a half to three weeks. They become completely independent at about three to four weeks and reach reproductive maturity at three months of age.

Females may come into heat every four or five days, and they may mate within a day or two after a litter is born. Breeding often peaks in spring and fall, with reproductive activity declining during the heat of summer and often stopping completely in winter, depending on habitat. These seasonal trends are most pronounced in more severe climates. The average female rat has four to six litters per year and may successfully wean 20 or more offspring annually.

Studies indicate that during daily activities, a rat normally travels an area averaging 100 to 150 feet in diameter. Rats seldom travel farther than 300 feet from their burrows to obtain food or water. Rats constantly explore and learn about their environment, memorizing the locations of pathways, obstacles, food and water, shelter, and other elements in their domain. They quickly detect and tend to avoid new objects placed into a familiar environment. Thus, objects such as traps and bait stations often are avoided for several days or more following their initial placement.

Knowing all of this can be helpful when planning a rat removal or extermination program.

Rats #1: Rats!

Rats #2: Rats and human co-evolution

Rats #3: Part of the English language

Rats#4: Biology basics and what’s in rat poison

Rats #5: Rat behavior

Rats #6: Causing very real damage

Rats #7: Disease vectors throughout history

Rats #8: The dirty secret, rats in our neighborhood

Rats #9: Good riddance at The Eggplant

Source Internet Center for Wildlife Damage Management