This document summarizes key information about rodent biology and health risks associated with rodent infestations. It discusses the identification and behaviors of common commensal rodent species like house mice and rats. It also outlines several diseases that can be transmitted by rodents or their fleas, including hantavirus, leptospirosis, rat bite fever, typhus, and plague. The document stresses the importance of thorough sanitation and rodent control to prevent the spread of diseases.

1. RODENT BIOLOGY
AS PART OF AN ADVANCED IPM PLAN

2. COMMENSAL RODENT FACTS
• Rodents are a diverse type of animal and many types of rodents are considered pest species.
• The most particular of these rodent species are rats and mice.
• While gophers and other non-commensal rodents can be invasive and of large concern, some of the
most problematic structural pests include rats and mice.
• Several species of rats and mice are considered commensal pests because of their dependence on
humans.

3. RODENT IDENTIFICATION
• Between rats and mice, rats are the larger of the two species.
• Obvious differences can be noted between them with regards to their appearance as well.
• A rat pup can be about the same size as an adult mouse, making identification difficult, but mice have
much smaller ears in relation to their heads.
• This could help to identify a caught rodent, but if there is still doubt identification can be made by
looking at the tail.
• Rats have a tail that is longer than their bodies, especially in the young, but mice have a tail that is
almost always equal in length to their bodies.

4. THE HOUSE MOUSE
• The more common species of mouse encountered in homes is the house mouse (Mus domestics).
• While mice usually don’t stray more than 10 – 30 feet from the nest on average, they can in some cases go as
far as 50 feet for food. 50 feet is not however typical, and when mice are entering a structure it can usually be
traced back with the entry point very close to the areas of activity.
• Mice living within a structure are more complicated however, and careful distinctions should be made as to
the current level, and type of activity.
• Mice, unlike rats do not require a water source. Mice receive water from the food they eat and are sustained
even from the driest foods.
• This is why liquid rodent baits for mice are ill-advised solutions. Rats on the other hand require water
constantly and liquid baits can be a beneficial tool for their control.
• Interior treatments for the house mouse should focus on trapping the majority of the population, removing
food sources, and excluding areas of entry into the structure.
• Outside, smaller mouse specific bait stations can be used and areas of harborage corrected.
• This means that bushy plants close to the structure and more specifically close to entry points should be trimmed or
removed to prevent nesting close to the structure.

5. THE HOUSE MOUSE
• House mice have 4-7 pups per litter on average according to studies.
• This number is significant because mice are able to mate in as little as 5 weeks and up to 8 times per
year.
• They reproduce quickly and if a large majority of the population is living and nesting within a structure
fumigation may be required to control them, or a relatively large number of traps combined with a
diligent integrated pest management plan.
• In the case of mice living inside of a structure the most reasonable and least intrusive method for
control is trapping.
• Properly placed traps should be able to catch eliminate the entire population.
• Only in rare cases is fumigation ever required. Fumigations should be reserved for those rare cases that
it is appropriate, and necessary.

6. RATS
• There are two types of rats common in Southern California and they typically tend to be the most common in the world.
• Norway rats are relatively large blunt nosed rodents that most often make burrows outside, with food and harborage close by.
• Roof rats on the other hand are slightly smaller, forage much larger areas, and have pointed noses.
• The forage area for Norway rats is roughly 100 – 300 feet from their nest with roof rats foraging up to 450 ft. Norway rats are often
seen or found closer to the ground where they make their burrows but roof rats can be seen in all areas from the ground to the
roofline, and in trees.
• Bait station and trap placement may differ such as is the case when bait stations are placed close to Norway rat burrows.
• Stations are most effective however when placed between food and harborage. Therefore, placement should be made only after a
thorough assessment of the property is made.
• While bait stations can be effective alone for Norway rats, baiting the individual burrows is sometimes helpful.
• The burrows are essentially where the rats live, and filling their burrows with tracking powder eliminates them at their source.
• The product works very simplistically. As rats lick the product off of themselves, they ingest it, and it contains a poison.
• They can’t avoid it because it’s in their burrow. Norway rats have much larger litters than roof rats and house mice. Their litters are
on average 8-12 pups, but house mice average 4-7 and roof rats average 4-8. Rats in general have 4-7 litters per year for roof rats and
4-8 litters per year for Norway rats.
• Treating the burrows helps with the younger rats since they tend to stay with the mother until they reach maturity.

7. THIGMOTAXIS
• All 3 species of commensal rodents are thigmotactic. Thigmotaxis is when an organism uses touch to identify
its path or direction.
• As a result of rodents being thigmotactic they can be found moving along vertical surfaces such as walls. Traps
should therefore most often be placed along these vertical surfaces inside, and bait stations can be placed
along exterior walls and fences for enhanced levels of control.
• This small but significant bit of information can be used to identify failed control methods. In many cases
traps are used unsuccessfully because they are placed in the open center of an area.
• Rats rarely forage away from the areas near walls and other areas they provide the touch stimulus.
• When they do forage away from walls and other areas where they can touch, it is because they have
developed a familiarity with the area.
• In this case however setting traps in an area away from vertical surfaces such as the center of a room is still ill-advised.
• Those traps placed openly in the center of an open area are less likely to catch anything.

8. RAT TEETH
• Rats also chew regularly on items of little consequence to them such as electrical wires, and prefer food that is
crunchy such as dog and cat food.
• This creates an obvious problem for those customers with pets, but likewise an obvious IPM minded control solution.
• Customers should control the access that rodents may have to any kind of animal feed.
• This is often accomplished by emptying and putting away animal feeding bowls, and storing the inventory in rat proof
containers.
• Dog and cat food usually comes in paper bags that rodents can easily eat their way into, therefore storage inside of a
metal cabinet or transferring the food to a metal trashcan with a lid is highly recommended.
• Rodents are forced to sharpen and fine down their teeth as their teeth continue to grow throughout their life
cycle.
• This makes crunchy items such as dog and cat food highly desirable to rodents.
• This small piece of pertinent information provides a level of insight that can add tremendously to any rodent control
plan.

9. HEALTH ASSOCIATED ISSUES
• Rodents also pose severe health concerns.
• The first of which involves allergens.
• Some studies have shown that the urine of mice can cause asthma and other similar conditions.
• Similar theories exist in regards to rodent droppings, and hairs causing allergens.
• Many people however do have allergies to different types of animal hairs including dog, cat, rabbit, and others.
It seems reasonable to assume then that allergies to hairs found on rodents, and left behind may cause some
type of allergy in some people.
• Cleaning, and sanitation is considered the most viable solution in cases of believed allergen presence in
addition to controlling the rodent problem.

10. HANTAVIRUS
• There are several hantavirus strains, but the one of most importance is referred to as HPS, hantavirus pulmonary syndrome.
• HPS has been implicated in several high profile instances, such as a string of cases in 1993 near the four corners states where it was
referred to as the "sin nombre" virus, or in 2012 where a campsite at Yosemite National Park saw several campers become ill as a
result of the virus.
• Before the incident in 1993 hantavirus hadn't been found in the United States, but upon further review it was determined that earlier
cases did exist, but we're simply unidentified or misidentified.
• Hantavirus strains had been previously found in Europe, but the American strains affect the lungs, and the respiratory system while
European strains cause hemorrhagic fever with renal syndrome (HFRS).
• Hantavirus is zoonotic, which means that it is a pathogen spread from animals to people. It does not spread from person to person.
• The primary host of the HIPS pathogen is the deer mouse.
• The commensal rodent species such as the house mouse, roof rat, and Norway rat have not been shown to carry the strain that
causes HPS, but the Norway rat has been shown to carry other strains that can cause hemorrhagic fevers and renal failure.
• Exposure to rodent feces, urine, blood and saliva are the most common means of transfer from rodent to human for hantavirus.
• The best method of controlling exposure therefore comes from controlling the rodent problem and decontaminating suspected areas.
• Hantavirus generally dies outside of the body of rodents within 48 hours, therefore removing active rodent populations becomes important, and
sustained sanitation adds a second level of control in the case of unknown recurring infestations.
• Sanitizing should always be done with all possible vectors of disease included however, not just the suspected issue.
• Cleaning and exclusion should be done in a manner that allows for control of all possible rodent caused health issues.

11. LEPTOSPIROSIS
• Bacteria from the genus leptospira are what cause the illness.
• Leptospirosis has been shown to cause meningitis which is a type of swelling around the brain stem. It can also cause liver failure, kidney
damage, and respiratory distress.
• These conditions are all serious and can lead to death. The bacteria is usually spread by contact with rodent urine, but if the contamination
spreads to pets, or livestock infection can occur as a result of exposure to the urine of otherwise domesticated animals.
• Some pets can be vaccinated, and in cases where this is appropriate it is recommended.
• Removal of rodents, and rodent evidence is suggested, but care should be taken with water supplies that may be contaminated, and surfaces
that can have rodent urine on them.
• The methods of cleaning, sanitation, and removal are important since the primary route of infection is through the skin, membranes, or into
open cuts, and sores on the body.
• Water sources however do become contaminated, as well as food preparation surfaces, and dinnerware as a result of rodents crossing them.
• This means that infection is also common from ingestion.
• Proper disinfecting techniques include the use of sanitizers, and may require a lot of scrubbing and ‘elbow grease'. Contaminated water and
food or feed should be discarded and not used.
• Larger water sources such as lakes, rivers and ponds are beyond the scope of pest control technicians and not mentioned here.

12. RAT BITE FEVER
• Rat bite fever is another condition associated with rodent infestations. In spite of the name it is not always the result of a
bite from a rodent.
• It can also occur as a result of consuming contaminated food and water. As a result of ingestion the normal symptoms of
vomiting and sore throat may be more severe.
• The other symptoms include fever, swollen lymph nodes, joint pain, muscle pain, headaches and rash, as well as localized
swelling and even ulcers in the areas of rodent bites or scratches.
• Streptobacillary RBF is one of the two types of rat bite fever and has an onset at about 3-10 days, but in some cases won’t
show for up to 3 weeks.
• This makes a diagnosis more difficult, since the original exposure may not be remembered. Streptobacillary RBF is the type
most associated with aches and pains.
• The second type is Spirillary RBF which has symptoms appearing within 7-21 days.
• Spirillary RBF is most associated with swelling around the bite or wound, ulcers in the infected area, and a fever that may
come and go.
• Rat bite fever however is not a major medical concern is rarely diagnosed in the United States.

13. ENDEMIC TYPHUS
• While many insects are considered vectors of disease, fleas are of particular importance with regards to rats.
• Rats, and several other urban animal species are known carriers of the bacteria that causes endemic typhus, sometimes
referred to as murine typhus (Rickettsia typhus).
• As rats enter a structure or sometimes nest close to it, they bring fleas with them. The fleas then enter the structure, or get
onto those that come outside.
• These fleas that get onto unsuspecting people have often contracted the typhus causing bacteria and can spread it to those
unsuspecting people.
• The infection generally occurs when fecal matter from fleas gets into a flea bite, or through the skin in some other way.
• Many people scratching the bites don't realize they are infecting themselves by forcing the fecal matter into these areas.
• Symptoms include headaches, fevers, muscle pain, joint pain, nausea and vomiting. Some people will develop rashes and
neurological signs such as confusion.
• These symptoms can cause a misdiagnosis since they resemble other similar, and dissimilar conditions.

14. PLAGUE
• Plague is another bacterial condition often contracted from fleas that are brought onto a property or
into a structure by infected animals such as rats.
• This can however be more troublesome because if pneumonia develops in a human host the condition
can then be spread from person to person.
• Likewise, flea bites are not the only way of contracting it. Contact with any bodily fluid from infected
animals can lead to contracting the serious condition that is identified by fever, chills, muscle aches and
swollen lymph nodes that are referred to as buboes.
• These buboes are the reason that the condition is sometimes referred to as the bubonic plague.

15. MITES
• Rat and bird mites are secondary pests that can often cause grief for a home owner and a pest control
technician.
• When rodents and birds leave a structure these insects are sometimes left behind.
• They then move into the human occupied portion of the structure and attack unsuspecting people and pets.
• In many cases rodents continue to bring more of these insects, and a less than complete rodent control plan
may provide for an ongoing infestation of secondary pests.
• Therefore, thorough exclusion is recommended, removal of all nesting material, and at least one application
of a proper miticide.
• If mite infestations continue it is more likely that an exclusion plan has failed, or nesting material was left
behind.
• The application of the miticide is to give clients immediate relief, and is not a complete solution by itself.