Mesostigmatid mites are blood-sucking parasitic mites found in wild rodent populations. Periodically they can also become a problem for laboratory rodent colonies, particularly when building construction or renovations disturb colonies of commensal building rodents that had been acting as hosts. Mesostigmatid mites infest both rats and mice and, unlike the more common rodent fur mites Myobia , Myocoptes , and Radfordia sp. They easily penetrate barrier caging systems, including individually ventilated cages, thus circumventing the usual precautions to protect rodents from infection. The two mites reported in laboratory rodent colonies, Ornithonyssus bacoti and Laelaps echidnina , also bite humans and have the potential to transmit zoonotic diseases.

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Mesostigmatid mites are blood-sucking parasitic mites found in wild rodent populations. Periodically they can also become a problem for laboratory rodent colonies, particularly when building construction or renovations disturb colonies of commensal building rodents that had been acting as hosts.

Mesostigmatid mites infest both rats and mice and, unlike the more common rodent fur mites Myobia , Myocoptes , and Radfordia sp. They easily penetrate barrier caging systems, including individually ventilated cages, thus circumventing the usual precautions to protect rodents from infection.

The two mites reported in laboratory rodent colonies, Ornithonyssus bacoti and Laelaps echidnina , also bite humans and have the potential to transmit zoonotic diseases. Once the mites gain access to a colony, eradication requires elimination of commensal rodent reservoirs in addition to insecticide treatment of both the laboratory rodents and the environment.

In view of the undesirability of insecticide use in the animal facility, it is advisable to investigate the effectiveness of preventive treatments, such as environmental application of insect growth regulators or silica-based products. The overall health status of laboratory rodent colonies has improved over the last 20 years such that organisms prevalent in the past—such as Sendai virus, mouse cytomegalovirus, mouse adenovirus 1 and 2, reovirus 3, polyomavirus, and pneumonia virus of mice—are increasingly rare in modern barrier facilities Clifford a , b ; Jacoby ; Livingston ; Schoondermarkvan de Ven et al.

Pathogen-free rodents are readily available from vendors, and widespread use of barrier caging systems in concert with sterilized equipment, high-efficiency particulate air HEPA — filtered air cabinets, protective clothing, and disinfection help keep pathogens out Brielmeier et al.

Regular health surveillance Livingston helps to detect excluded organisms, and should there be an outbreak, mites and pinworms are variously susceptible to treatment with parasiticides such as avermectins, pyrethroids, and benzimidazoles Baumans et al. Also in the event of an outbreak, the rederivation of valuable genetic lines is possible through embryo transfer Baker ; Reetz et al. But despite the technological and therapeutic tools available, it would be a mistake to become complacent.

Mice carry pathogens that may remain undetected in barrier housing due to low prevalence and inefficient transmission to bedding sentinels Besselsen et al. In addition, there is the threat of contamination from wild rodent populations, which harbor a wide variety of rodent pathogens Becker et al.

In this article I review published information on mesostigmatid mites, which have a wild rodent reservoir and cause sporadic problems in laboratory animal facilities, particularly during building renovations. I also provide additional comments and suggestions based on personal experience with several mesostigmatid mite outbreaks at a large academic institution. Mesostigmatid mites are a large order of highly mobile mites, class Arachnida, subclass Acari, order Mesostigmata.

Most are predators of other mites, but three genera are ectoparasites of mammals and birds: Liponyssoides, Laelaps syn. Haemogamasus, Echinolaelaps , and Ornithonyssus Baker ; Flynn Among laboratory rodents, they usually parasitize the Norwegian rat Rattus norvegicus and black rat Rattus rattus , but they also readily infest mice.

Wild rodents are hosts to Liponyssoides sanguineus house mouse mite , Laelaps echidnina spiny rat mite , Laelaps pontiger syn.

Haemogamasus pontiger , and Ornithonyssus bacoti tropical rat mite. Rodents may also be accidental hosts to O. Bdellonyssys bacoti, Liponyssys bacoti Flynn has the widest host range, parasitizing a variety of domestic and wild mammals and birds, and is the most commonly reported mesostigmatid mite both in laboratory rodent colonies Chu and Couto ; Cole et al. Mites are distinguishable from insects as the adults have eight legs and never have wings.

All mesostigmatid mites are dorsoventrally flattened in the body idiosome and head gnathostome , and have four pairs of jointed legs attached to the anterior half of the body.

Both males and females have a single dorsal shield thickened chitinous area ; males usually have one ventral shield and females three: sternal, genital, and anal. Females are readily identifiable by the characteristic arrangement of their ventral shields together with the number and arrangement of setae hair-like extensions Figure 1. Ventral aspect of female Ornithonyssus bacoti top and Laelaps echidnina bottom. The three chitinized shields—sternal 1 , genital 2 , and anal 3 —and setae 4 are often used for identification.

Laelaps spp. The female L. Liponyssoides sp. They are only weakly sclerotized and semitransparent, appearing white when unengorged and red-brown when engorged. Compared with Ornithonyssus, Liponyssoides has much sparser and shorter setae and its genital shield is broader and rounder than the narrow tapering genital shield of Ornithonyssus sp. Baker et al. The mesostigmatid mite life cycle consists of an egg, six-legged larva, and two eight-legged nymph stages before adulthood.

Only the first nymphal and adult stages feed on blood and serum Laelaps sp. Infestations in laboratory animal colonies most likely originate with wild rodents that transmit their mite populations to laboratory mice via commensal mice living in the building.

Pigeon or chicken colonies may also harbor Ornithonyssus bursa or O. At our institution the first report of an infestation was from a laboratory that housed experimental mice for short periods and that showed evidence of commensal rodents. The experimental mice transferred the infection back to their housing facility and, despite apparently successful treatment of the affected mice and facility, four other housing facilities were subsequently infested over a period of 2 years JW personal observation.

Building demolition and renovations or removal of commensal rodents are particularly high-risk periods and can result in new laboratory rodent mite infestations as the mites travel in search of new hosts. Renovations therefore require coordinated treatment to prevent infestation of adjacent rodent facilities when sites harboring commensal rodents are demolished.

Treatment of the environment for mites should precede vermin eradication, which should in turn be coordinated with demolition. Cage barrier systems NRC are commonly used in research institutions as a means to exclude unwanted pathogens. Unlike barriers at the room or facility level that depend on limiting access to a few highly trained individuals, barriers at the cage level allow facility access by multiple personnel while still protecting the laboratory rodents.

Whether the institution uses individually ventilated or static caging with filter tops, the effect is the same: barrier cages protect the rodents inside from commonly encountered rodent pathogens while they remain closed Brielmeier et al. In the case of mesostigmatid mites, however, the cage barrier system breaks down.

These blood-sucking mites live in the environment adjacent to their rodent hosts and are freely mobile Baker ; Flynn Indeed, we have observed them leaving occupied, closed cages on individually ventilated racks after cage treatments JW personal observation. Disturbances to existing rodent hosts e. Once established, they colonize the environment adjacent to the rodent and, due to their small size 0.

Reports of mesostigmatid mite infestations in laboratory rodent facilities have generally been uncommon in the last 2 decades. Recently, however, several institutions have reported infestations with O.

Both O. When laboratory rodents are infested, personnel who have contact with materials or equipment used in the animal facility or who handle the infested animals may be bitten Kelaher et al. There is considerable evidence that rat mites carry and have the potential to transmit a number of pathogens. Experiments have shown that Ornithonyssus bacoti transmits Rickettsia akari rickettsialpox; Phillip , Francisella pestis plague; Yamada , Coxsackie virus Schwab et al. Researchers have also documented O.

Lopatina Iu et al. Kim et al. Reeves et al. In addition, O. Rat mites thus can transmit several zoonotic diseases, and both O. There are, however, sporadic but persistent reports of cases of rat bite dermatitis caused by O. Severe rat mite infestations cause debility and anemia in rodents French ; Harris and Stockton ; Keefe et al. The first sign of a mesostigmatid mite infestation is usually a complaint of bites among personnel who work with the laboratory rodents.

Follow-up investigation reveals the presence of mites as tiny moving black dots on the animal or in the cage, most easily visible against a pale background, such as a cage filter; indeed, where cages have filter tops, their close examination proves to be a good way to detect an infestation. In our institution, sticky insect traps were inefficient as a diagnostic tool; instead, in each of our outbreaks the diagnosis of mites came from animal handlers who had either been bitten or had observed the mites on themselves or on cage tops.

Sticky traps placed on or adjacent to the racks remained negative even after confirmation of the presence of mites in the cages presumably because the mites did not venture far from their rodent hosts. The traps proved more useful for determining the extent of an outbreak after the fact: trapping mites from previously undiagnosed positive cages after administering mite-repelling permethrin cage treatments JW personal observation.

Permanent elimination of mesostigmatid mite infestations requires a coordinated and sustained effort to eliminate both mites and rodent vermin reservoirs. In our experience, although individual facility treatments were successful, further outbreaks subsequently occurred in other rodent facilities. These were likely due to the transfer of infested rodents before discovery of the outbreak, undiscovered commensal rodent reservoirs, or mites that escaped during early treatments before we learned to sequence our environmental and cage treatments JW personal observation.

The use of insecticides is contraindicated in animal facilities, but the zoonotic potential of mesostigmatid mites requires extraordinary measures. Permethrin is a more stable synthetic analog of pyrethrum, which was originally derived from chrysanthemum cinerariaefolium flowers; it acts as a neurotoxin, prolonging sodium channel activation and causing repetitive firing of peripheral nerves and eventual paralysis in insects Narahashi It is also an insect repellent Mencke and is available impregnated into clothing for that purpose Faulde et al.

Any treatment plan should start with environmental treatments. As mentioned above, we have observed mites exiting ventilated rack cages after permethrin was placed inside to treat infested mice JW personal observation , so treatment of cages without first treating the environment can result in the establishment of escaped mites on rodents outside the treated area.

Unlike animal treatments, environmental treatments that can result in personnel exposure usually require application by a licensed pest control professional. Operatives should work inward from the periphery of the risk area toward the center to prevent mites escaping to untreated areas.

To avoid reinfestation, they should treat all areas occupied by rodents or rodent equipment, including support areas, investigator laboratories, and procedure areas. In addition, treatments should address potential locations for colonies of escaped rodents, such as inside poorly sealed animal facility doors, biosafety cabinets, and ventilation ducts.

Prevention, particularly in laboratory housing areas or during high-risk periods such as building renovation, is unquestionably preferable to treatment. Given the undesirability of insecticides, alternatives include physical methods such as silica-based products and biological methods such as insect growth regulators.

Insect growth regulators fall into two categories, nonsteroidal ecdysteroid agonists that mimic the action of molting hormones and cause accelerated and incomplete molting, and juvenile hormone chemical analogs that inhibit maturation Dhadialla et al. Juvenile hormone analogs are registered with the Environmental Protection Agency EPA as biopesticides and approved for indoor use they are also effective against the German cockroach Atkinson et al. The EPA reports no evidence of toxicity in nontarget species EPA , but it is advisable to avoid exposure of Drosophila melanogaster colonies and mice or cell lines that use ecdysone-inducible gene expression systems No et al.

There is no published information on the use of insect growth regulators IGRs to prevent mesostigmatid mite infestations in animal facilities. We chose to add them to our pest control program for a number of reasons, not least of which was our previous inability to prevent further infestations in distant areas despite apparently successful cage and environment insecticide treatments.

Product literature suggested IGRs would have no impact on research and were effective against many insect and mite species, and applications could take place during regularly scheduled visits, which made them relatively inexpensive. In the 12 months since we added it to our pest control program, we have remained free of rat mites and have observed no untoward effects JW personal observation. Environmental application of silica aerogel has been effective for controlling rat mite infestations in homes Ebeling and, as it is not likely to have a research impact, could also be a candidate for environmental control of insect and mobile mite pests in laboratory animal facilities.

Mesostigmatid mites are present on wild rodents and thus may migrate to commensal rodents. Laboratory rodent colonies are at increased risk of infestation if they are exposed to infested commensal rodents e. Once an infestation is diagnosed in laboratory rodents, eradication requires removal of commensal rodent reservoirs and widespread treatment of both the environment and the mice. Pyrethrins appear to be safe and effective for both cage and environmental use.

Failure to eliminate the commensal rodent reservoir or to prevent mite migration during treatments may result in repeated infestations or in new infestations at sites distant from the original problem.


House-mouse mite

Liponyssoides sanguineus is a species of mite that infests the house mouse Mus musculus. It can transmit human disease, [2] is associated with causing rodent mite dermatitis in humans [3] and is noted for carrying Rickettsia akari , which causes rickettsialpox. It was formerly known as Allodermanyssus sanguineus. From Wikipedia, the free encyclopedia. Liponyssoides sanguineus Scientific classification Kingdom: Animalia. Vector Borne Zoonotic Dis. Comparative Parasitology.







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