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Definition

An organism that lives on the outer surface of another organism, its host, and which does not contribute to the survival of the host.

Clinical Signs

In cases where infestation is present may observe any of the following:

• Intense itching with intermittent or persistent scratching.
• Loss of hair, ulcerated skin, abrasions or scabs seen most commonly on the neck and back of shoulders.

Flea infestation

• May see actual fleas on the rat, or may see and indication of their presence by droppings of digested blood on the rat’s skin which may seem to appear like particles of dirt.

Lice infestation

• May see light tan, brown, or reddish color “dots” on skin or the presence of silvery colored nits attached to hair shafts.

Mite infestation

• May see a fine bran like substance on the skin and fur. In sarcoptid or sarcoptid like species crusted red or yellowish lesions may be seen on the auricle or pinna of the ear and on the nose; along with small reddish bumps to tail, genitals, and feet.

*Note: for additional information on recognizing various signs of pain or discomfort refer to: Signs of Pain In Rats.

Etiology

Ectoparasites are those which live on skin or attach to hair follicles. The following listed external parasites are those that most often affect rats.

Lice (class arachnids) are of two orders, the mallophaga which are of a species that bite or chew, and the order of Anoplura (family Pediculidae) which are a species that suckle blood. The order of Anoplura which infest domestic animals is what is most often seen in rats.

Polyplax spinulosa (spined rat louse) is a type of lice that causes hair loss and pruritus (itching). It can sometimes be detected by the silvery colored nits attached to the hair.

Lice are species specific, meaning they do not cross from one species to another. They will spend their entire life cycle, approximately 14 to 21 days, from egg to nymph to adult on the host. They obtain nutrition by sucking blood, which in turn can cause anemia to the rat. They are also able to transmit the parasite Hemobartonella muris, leading to a disease similar to tick fever.

Mites are also classified as arachnids, however, unlike lice they are considered host specific meaning that with certain species of mites, if the desired host is not available, they may cross to another species.

The tropical mite Liponyssus bacoti (synonym:  Ornithonyssus bacoti) is round in shape and appears dark when engorged with blood. They can survive on fomites (e.g, bedding, litter), and only stay on an animal when they are feeding. They are one of the species of mites that will also bite other animals including humans.

Demodex spp., and Notoedres muris (a sarcoptid-like mite), both transmit mange. Deomodex spp. can be found anywhere on the skin but are primarily found on hair follicles and sebaceous glands of the ears. Notoedres muris (also termed the ear mange mite) burrows into skin, and presents as yellowish crusty appearing warts on edges of ears and nose, or can appear on other extremities as reddened bumps. Both of these are not often seen in the domestic pet rat.

Sarcoptes scabiei varieties while not host-specific per se do possess some host specific preference and physiologic differences do exist between varieties. Rats can be infested with a variety of sarcoptes mite; however, they do not give their owners their type of mange. Human infestation is with a different variety of scabies mite than what is found on animals’.
Should your pet rat be infested with a sarcoptic mite and have close contact with you, it can get under your skin and cause itching and skin irritation. However, the mite dies in a couple of days and does not reproduce. They may cause you to itch for several days, but you do not need to be treated with special medication to kill them. Until your rat is treated effectively and its environment cleaned continued infestation will be a source of discomfort for your rat and an annoyance to you. For more information on scabies in humans see The CDC Fact Sheet.

The Radfordia ensifera is a fur mite that can cause dermatitis. It may occasionally be seen as white specks of dust on hair follicles. This type of mite is most commonly seen in rats. It produces intense itching, and leads to scabs most frequently seen on the shoulders, neck, and face of the rat. The rat fur mite and mange mite do not infest humans or other animals.

Mites under normal conditions are commensal in small numbers and do not tend to be bothersome to their host. It is when the rat is stressed, has a decreased immunity due to other illnesses, and/or is unable to keep the numbers reduced by normal grooming that causes the mites to flourish in numbers. Inattention to proper husbandry, a rat that is ill, or giving ineffective treatment can lead to reinfestation, and dermatitis. On the average the entire life cycle of the mite beginning with the eggs which hatch in about seven days through the larval, nymphal, and adult stages requires approximately 23 days to complete. It is therefore important to maintain care and follow through with treatment(s) prescribed.

Fleas, of which thousands of species are recognized worldwide, affect human and animal. The specie that most commonly affects animals, and humans, is Ctenocephalides felis. It causes severe irritation and can be responsible for flea allergy dermatitis. Fleas go through developmental stages before becoming adults. It is the adult fleas, which appear as 1-5mm, laterally flattened, wingless insects that infest the animals fur. Reinfestation can occur if care is not taken to include the surrounding environment of the animal when treating. The deposited eggs on the host by the adult female flea can fall from the host to the surrounding environment, go through development, emerge as young adults either moving back to the host, or to a newly acquired host.
Flea infestation can be determined by the actual presence of fleas or by flea excreta seen as digested droppings of blood appearing as black dots. These black dots when dissolved on paper, or placed in water, will appear red.
This species of flea, Ctenocephalides felis, is also responsible for the transmission of Murine typhus by Rickettsia typhi, a type of febrile disease in both man and small mammals, and principally seen in the southern coastal climates.
Treatment for flea infestation should include the home, the rat’s environment and any other animals living in the home.

Transmission of all the above ectoparasites can be by host to host or fomites to host. Fortunately with proper husbandry and persistent treatment they do not have to pose a problem.

For information on hypersensitivity, allergic contact dermatitis, see Dermatitis/Eczema.

Figures

Photos and Case Histories Involving Parasite Infestation

• Fig. 1:  Signs of mite infestation.
• Fig. 2:  Sarcopetes Mange photos and case history.
• Fig. 3:  Lice and case history.
• Fig. 4:  Ectoparasite slides and descriptions courtesy of
  University of Missouri Research Animal Diagnostic Laboratory

Diagnostics

Skin scrapings for possible parasites can be done, however, parasites may still be present even though the scrapings are negative.

Treatment

For information regarding dosages and usage of the following medications refer to the section Anti-infectives in the Rat Medication Guide.

Mites and lice

Ivermectin (sold as horse worming paste) given orally: brands Equimec in Australia, Equimectrin, Equalvan, Rotectin 1, and Zimecterin in the U.S., where the active ingredient ivermectin is - 1.87%.
Treatment with oral or topical dosing noted to be less stressful to rats and mice. Rare incidences of adverse reactions have been reported when ivermectin has been given by injection in rats.

For treatment specific to stubborn demodectic , notoedres, and sarcoptid mite infestation

Ivermectin or topical treatment of Mitaban (amitraz) may be considered. It is recommended to discuss the proper use of Mitaban with your vet before attempting to use. Ivermectin is considered to have a wider margin of safety.

Fleas and lice

Topical dosing with Advantage (orange labeled package for cats/kittens 9 pounds and under).

Fleas, mites (other than demodectic mites), and lice

Topical dosing with selamectin (Revolution), a derivative of ivermectin, labeled for use in kittens.
The topical application of selamectin, as directed, is less stressful for rats than other injectable treatments.

Alternative treatment for mites, lice and fleas

A spray or shampoo sold for small animals such as rats, mice or hamsters , or that which is safe for kittens or puppies 2 weeks of age containing 0.05 % or 0.06 % pyrethrin can be used for rats every 7 days for 4 weeks. Discuss with veterinarian if intending to use in conjunction with ivermectin, or selamectin.

In Addition To Treatments Above:

Treat all rats at the same time, clean all cages including bedding and toys thoroughly. Disinfecting with bleach can be very effective, but be sure to rinse cage and articles well and allow to dry before returning rats to their cage.

Clip toenails of rear feet to prevent increased trauma to lesions from scratching.

If irritation to skin from scratching is observed, an application of a Vitamin E cream, or Polysporin ointment, or Neomycin Plus anesthetic cream may help relieve and prevent further secondary infection from occurring.

If there continues to be skin irritation, inflammation, or weeping lesions, systemic antimicrobials may need to be started. See your veterinarian.

Nursing Care

• When treating adult rats weighing between 300 to 500 grams with ivermectin (sold as horse worming paste where the active ingredient ivermectin is - 1.87%) orally: give a small amount equivalent to a grain of uncooked rice. Dose once a week, for at least 3 weeks. For rats that are younger or those under 300 g, split dose by half and dose once a week for at least 3 weeks.

*NOTE*
Contribution by C.Himsel-Daly DVM

There is no need to decant ivermectin paste if in the original tube, decanting any fluid would concentrate the drug and thus raise the concentration in a volumetric dose, thus potentiating a toxicity.
If in opening the original tube of paste and found to have a drip of fluid at the end of the tube, before the actual paste emerges, all that is required is to express the tube, discard that bit of paste until uniform in consistency, and dose according to the veterinarian’s recommendation. If the paste has been dispensed in another container, then mix thoroughly before dosing. Paste tends to be a less accurate dosing method than using the parenteral product.
Fortunately the paste has a wide margin of safety.*

• Continue treatment as prescribed.
• Keep toe nails clipped on a regular basis making sure not to cut the quick. Keep styptic on hand if bleeding occurs.
• Repeat cage and article disinfecting at least once a week.
• Remove and discard articles made of wood.

Outcomes

• Free of parasite infestation.
• Free of inflammation and irritation of skin.

Prevention

• Maintain rats overall general health.
• Use of prepackaged processed litter, and the freezing of litter prior to using may be of help.

  *Please note*
  CareFRESH poly bags have been connected with other parasite (particularly mites) infestations in the past. Also the CareFRESH big bags have been noted to have a row of holes in the top of the bag which has allowed entrance into packs while stored in some pet stores and feed/tack stores. It is best to freeze this type of litter/bedding before using in cages.

• The freezing of prepackaged or mixed foods and rat blocks prior to feeding, is recommended.
• Provide a clean cage environment.
• Quarantine all new rats for a minimum of three weeks and treat for infestation or infections if present prior to introducing to existing colony.
• When holding or playing with rats other than your own, it is recommended that you wash and change clothes prior to handling your own rats.

References

• Arlian, L., Runyan, R., & Estes, S. (1984). Cross infestivity of Sarcoptes scabiei. J Am Acad Dermatol, 10(6), 979-86.

Posted on June 29, 2003, 10:20, Last updated on April 8, 2010, 14:04 | Integumentary / Skin