Hantavirus, Arenavirus, Ebola Virus, Hemorrhagic Fever. These are all names you may have stumbled across in the news in the past few years, as the media reported the severe illness or even death of people in the United States or elsewhere in the world. The articles may very well have terrified you, as is normal whenever we seem to be faced with new and life-threatening diseases.
However, how "new" are some of these diseases? Is it possible that they really are ancient diseases that only now are being discovered for what they are? I believe that this is the case. For example, Hantavirus Pulmonary Syndrome was given this name as recently as mid-1993, after an outbreak of an unknown disease caused the death of a large number of people in the southwestern U.S. Intense study of those affected led to the isolation of a specific virus that was the cause, a virus previously unknown to science, but which now has been shown to have caused the deaths of many people well before 1993, as tissue samples of deceased persons who had died from "unknown causes" are studied with the new disease knowledge at hand.
While our main purpose here is to discuss Hantavirus and Arenavirus, I at least want to mention Ebola Virus, also called Ebola Hemorrhagic Fever. This disease is not in the United States, but certainly was made famous by a movie called "Outbreak", which, in a somewhat fictional manner, spoke to the disease outbreaks in Africa that have killed so many people in a rather gruesome way. Ebola, Hantavirus, Arenavirus, and many other viral diseases are referred to as "Viral Hemorrhagic Fevers, as one of the symptoms of the disease in its late stages may be bleeding, bloody vomiting, or bloody diarrhea. Ebola Virus is still not well understood, and the reservoir of the disease is not know for certain, but it is believed to reside in animals, most likely monkeys, and can be passed to humans in blood or saliva from these infected animals, and from an infected person to other people in the same route.
Hantavirus Pulmonary Syndrome (HPS) became widespread news in 1993, when 23 people living in the "Four Corners" area of the southwestern United States came down with severe respiratory illness, and around 20 of them died. From this outbreak a great deal of knowledge was gained. The disease pathogen was identified as a virus of a type known as hantaviruses, of which there are many strains throughout the world. Since this was a new strain of these viruses, and it had no name given to it, it was justly named the "Sin Nombre Virus". Sin Nombre is, of course, Spanish for "without a name", and this name has stayed with it.
Sin Nombre Virus is by far our most common strain throughout the United States, and the reason is because it is associated with a rodent species that also is common throughout much of the country. That rodent is called The Deer Mouse - Peromyscus maniculatus - the principal reservoir or host animal for this virus strain that is so dangerous. In fact, most kinds of rodents are reservoirs for various kinds of hantavirus or other viruses, but many of them are of no consequence to humans, or would cause only mild disease. Others may be more virulent, and it is the Sin Nombre strain that is the worst of the hantaviruses, with about a 35% mortality rate.
In the United States the principal strains of hantavirus are:
About 10 other species of mice or rats have been tested and found positive for various strains of hantavirus, including Meadow Mice (Voles), harvest mice, pinon mice, and chipmunks. However, those listed above are considered to be the species responsible for spreading the disease to humans.
More recently a new disease name began to make headlines, and this is the Arenavirus. In 1999 and 2000 three residents of California were affected and died from this disease, also spread by association with rodents. With this particular virus, however, the primary culprit is called the Wood Rat, or Pack Rat - Neotoma spp. - also a common rodent living in semi-rural areas. There are nine species of Wood Rats in the United States, and some kinds occur in almost every state.
How dangerous is Hantavirus to people?
Initially, like so many diseases, symptoms of infection by Hantavirus or Arenavirus may be similar to many other things - headache, fever, nausea, diarrhea, abdominal pain. These may not begin for anywhere from one to five weeks after exposure to the virus, which we will discuss more in a moment. Once these initial symptoms begin, it may be only a few days later that the more serious, or late symptoms are felt - coughing, shortness of breath, and a tight feeling around the chest, all caused by the lungs filling with fluids.
Even with this horrifying scenario, Hantavirus and Arenavirus are considered rare diseases, and easily avoided with basic sanitary precautions. It also is helpful to put the hazard from these diseases into perspective, and the following are some statistics about them:
How is Hantavirus or Arenavirus transmitted to people?
A great deal of study on these diseases has been done in the past 7 years, and it is believed that HPS and Arenavirus are transmitted to people in one principal way - through inhalation of "aerosolized" dust or droplets containing rodent feces or urine that are infected with the virus. The rodent excretes the virus with its waste material, and as the surfaces dry the virus remains in the dust on the surface. If this is disturbed in some way and becomes airborne it is possible for us to inhale the pathogens, and they rest in our lungs where they begin their work.
It also is possible for humans to become infected by direct contact with infected rodents, either by contact with an open break in the skin, a rodent bite, or touching the mouth with fingers or objects that may be carrying the virus. However, hantavirus and arenavirus apparently are NOT transmitted in any of the following ways:
Normally, it is felt that a scenario for infection would go somewhat like this. Infected rodents are living within a structure, and in the course of that lifestyle they produce a great deal of fecal matter and urine, and are not particularly discriminating about where it lands. Mice tend to urinate as they are walking. Rats may produce up to 25,000 droppings each year. The surface then dries, but the viruses that were deposited there may be alive and well for a very long time, as they encapsulate themselves for survival through harsh times. If this happens to be a cabin in a rural area, as often happens, Deer Mice may move in in large numbers when the owners of the cabin are not there, perhaps for the entire winter.
Once people come back to reoccupy the structure they notice all the rodent droppings laying around, and instinctively grab the broom or vacuum cleaner to remove the mess. This is the worst thing to do, for by sweeping or vacuuming you may quickly create dust that carries the virus into your lungs. In the Four Corners region of the southwest United States, where the initial outbreak of Sin Nombre Virus occurred, the weather had been drier than usual, creating dustier conditions. Human activity in and around the dens of Deer Mice then exposed these people to higher than normal levels of contaminated dust.
How do I avoid exposure to Hantavirus or Arenavirus?
Since the sole route of these pathogens into humans is by way of infected mice and their waste products, avoiding the diseases consists of two primary measures:
An expert on the control of birds and rodents is Dr. Bobby Corrigan, of Purdue University, and it is his recommendation that we never directly contact rodents, pest birds, or their unsanitary conditions. If you trap rodents you should wear gloves and other protective clothing when removing them, as well as while cleaning up after them. It has long been known that birds, bats, and rodents pass disease agents in their urine and feces. Over 40 diseases are associated with pigeons, starlings, and sparrows, many of them respiratory problems that are contracted from inhaling infected fecal dust.
So, step #1 is to keep rodents from living in your structures or on your property. Even though they are a part of Nature, and it may be cute to see them, we truly may be competing with them for our health. Wood Rats, the vectors of Arenavirus, generally stay outdoors, and their nests may be large, visible piles of sticks and debris with the living quarters inside. These should be eliminated, while wearing safety clothing that will be discussed in a few minutes. Deer Mice also are generally outdoor rodents, but when buildings are left unoccupied for long periods they may move in. Even our "domestic" rodents - the House Mouse, Norway Rat, and Roof Rat - while not associated with hantavirus, can and do carry disease pathogens in their waste products. For example, a serious condition called Lymphocytic choriomeningitis is a viral disease spread by the House Mouse.
Rodent exclusion also is a vital step, for once the rodents are eliminated from your home or office you would like them to stay out, rather than repeating the process. Rodent exclusion techniques also are covered in the BugInfo article on Rats.
Should you be camping or enjoying other activities in the outdoors these same general guidelines would be appropriate. While they are downright cute, burrowing chipmunks and squirrels and other rodents are not the best of companions. In California it is burrowing rodents, particularly squirrels, that serve as the primary reservoir for Bubonic Plague, also called Black Death. Put away foods at night, keep tents sealed while you are away from them or while sleeping, and don't leave tidbits around just to attract the cute little things. Potato Chips probably aren't the healthiest things for native animals anyhow.
How should I clean up an area contaminated by rodents?
Your main considerations, in avoiding nasty diseases spread by rodents, is to avoid touching surfaces with your bare skin, and to avoid inhaling airborne dust from the surfaces. Again, you may want to consider calling a licensed professional from the pest control industry in your area. Generally, you can then have someone evaluate your situation who is trained in the control of rodents, has received information on proper cleanup of potentially contaminated environments, and already has and wears the appropriate protective equipment.
Should you choose to tackle the cleanup yourself the following steps have been recommended by many of the knowledgeable people in the industry and from universities.
This is some basic information about Hantavirus and Arenavirus, and rodent control in general. There is a great deal of information available on the Internet, and good, factual, accurate information can be found on sites provided by The Centers for Disease Control (CDC), State or County Health Departments, and the medical community.