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Review of related literature
[Tuesday, April 04, 2006]
REVIEW OF LITERATED LITERATURE
General Information on Rodents Under Study
Mus sp. are small, scaly-tailed mouse with a distinct notch in the cutting surface of upper incisors (seen best in side view). The hairs are short and the ears are moderately large and naked and are colored pale brown (Burnie, 2000). They have long tails that have very little fur and have circular rows of scales (annulations). An adult weighs 17-25 grams and this species ranges from 65 to 95 mm long from the tip of their nose to the end of their body, their tails are 60 to 105 mm long. The house mouse (Mus musculus) tends to have longer tails and darker fur when living closely with humans. They have habitats that are generally considered to be in proximity to humans—in houses, barns, granaries, etc. Buildings, cultivated fields and other wooden areas are also some examples of their natural habitat (Ballenger, 1999).
With a very minimal estrous cycle of 4-6 days, females can give birth to 5-10 litters in just a week’s time. They can produce more than 10 families a year (Burnie, 2000).
it is of significant importance to note its peculiar behavior when commensally inhabiting with humans, where it is considered both territorial and colonial, as opposed to its non-territoriality in the wild. Aggression within the colony or so-called family group is rare; however, the defense of the territory itself is seen for all of the individuals of that territory (Ballenger, 1999).
Rattus sp. is a rather large member of the mouse family. Males are usually larger than females. The teeth of this rodent species have one pair of distinctive chisel shaped incisors with hard yellow enamel on front surfaces. It has a blunt muzzle with long whiskers and medium ears. It has a shaggy bristly fur that is colored gray to brown on the dorsal side of the animal and white to gray on the ventral side. The tail is short, scaly and shorter than the body. Rattus species body weight ranges from 200-480 grams (Burnie, 2000).
Rattus sp. was native to forests and brushy areas. However, in the modern setting, brown rats have found ample and more preferable habitats alongside the rapid expansion of the human population. They inhabit such diverse places as garbage dumps, sewers, open fields and woodlands, and basements. At present, every port may contain such a number of them so that they can be noted to occur anywhere that humans are located (Armitage, 2004).
Viewing its reproduction, several factors account for the successful inhabitation and rapid population growth of Rattus sp. Its being polygynandrous allows it to breed in large groups and also allows the female to mate with as many as five hundred competing males just after its estrous period of six hours. Also, it is not a seasonal breeder technically. With an average of seven times of giving birth per year, the females enter a very short gestation period of 22 to 24 days (Calhoun, 1962).
Furthermore, Silver (1927) noted its nocturnal, burrowing and foraging behavior to add to its attributed success to flourish in number. New packs can start in a network of burrows after a couple establishes a nest in a previously unoccupied area. With males being dominant in a noted group, nests are constructed with any of the efficient foraged materials such as leaves, garbage, and twigs.
Brown rats (Rattus norvegicus) spread diseases. Compared to mice, they are large and aggressive due to the fact that they will attack if they are cornered. Getting rid of rats is difficult as they are clever enough to avoid traps and are wary of poisoned foods (Burnie, 2000).
Common Parasites of Rodents
In a survey done by Jueco (1983) in 2 species of rats namely Rattus norvegicus and Rattus rattus mindanesis and 1 species of mice, Mus musculus collected from several provinces in Luzon and Visayas, 15 out of 36 species of ectoparasites isolated were known to be transmissible to man. In another study conducted by Eduardo and Mercado (1981) it was noted that from 500 Rattus norvegicus collected from various marketplaces in Manila , 7 species of ectoparasites were isolated namely Laelaps nutalli having the highest rate of infection (70.8%) followed by Polypax spinulosa (27%), Radfordia lemnina (24.8%), Xenopsylla cheopis (24.2%), Echinolaelaps echidinus (21.6%), Glyciphagid sp. (2 %) and Euchoengastia sp. (0.2%). Moreover, 6 species of mites and one flea were isolated and identified on a study conducted concerning the infestation of house mouse (Mus musculus) collected from Diliman, Quezon City (Tongson and Lasam, 1980). Out of the 100 mice they collected, 69 were infested with the following ectoparasites: Radfordia affinis, Radfordia ensifera, Myocoptes musculinus, Echinolaelaps sp., Myobia musculi, Ornithonyssus bacoti and Xenopsilla cheopis.
In other parts of the globe, lice- Polyplax spp., and mites- Myobia musculi, Radfordia spp., and Myocoptes musculinus, are the common ectoparasites of rats and mice. A study conducted by Clark and Durden (2002), wherein they live trapped 12 species (292 individuals) of small mammals in 17 localities in Mississippi from June to November 1998 and examined for parasitic arthropods. Fifteen species of ectoparasites were collected: 2 species of sucking lice (Anoplura), 4 species of fleas (Siphonaptera), larvae of 2 species of bots (Cuterebridae), 4 species of mesostigmatid mites (Mesostigmata), and immature stages of 3 species of hard ticks (Ixodidae). The white-footed mouse (Peromyscus leucopus) harbored the most species of parasitic arthropods (8), followed by the cotton mouse (Peromyscus gossypinus-6), and the cotton rat (Sigmodon hispidus-5). Of all the specimens collected, there was only one Rattus norvegicus. R. norvegicus was parasitized by the mesostigmatid mite Laelaps echidnina, an attributable ectoparasite of domestic rats (Pratt and Good 1954; Whitaker and Wilson 1974). There was a previous documentation from the Mississippi records made by Smith (1955a, 1955b) for L. echidnina from the house mouse, Mus musculus.
The first cases of zoonotic parasite infections were documented by Tubangui (1931) and Nishimura and Yogore (1960) from rats collected in Manila. The said rats were found to be infected with Reillietina garrisoni and Angiostrongylus cantonensis. Infection with Babesia sp. of Rattus mindanensis mindanensis collected from 3 barangays in Bulacan showed an 8.0% prevalence and a range of 0.3% to 25.2% parasitemia (Dionisio, 1995).
The general rodent endoparasites are the helminthes—the parasitic roundworms, which include the classes of nematodes, and cestodes. Some are also acanthocephalans, and protozoans (single-celled organisms).
Nematodes are the roundworms. There are thousands of species of nematodes, but only a small percentage of those are parasitic to animals. The nematodes that infect mice and rats are the Oxyurids, commonly called pinworms. Syphacia obvelata, Aspiculuris tetraptera, and Syphacia muris are the species that infect them both, with the latter being the main pinworm of rats. Another pathogenic nematode of rats is Trichosomoides crassicauda, a threadworm found in the bladder. It produces few signs of disease in an affected rodent, and none of these mentioned so far are considered a threat to humans (Koski and Scott, 2001).
Cestodes are the tapeworms. Mice, rats, gerbils, and hamsters are the definitive hosts for the tapeworms Hymenolepis nana, and Hymenolepis diminuta. Mice and rats are the intermediate hosts for the feline tapeworms, Taenia taenaeformis. H. nana is the most important of the tapeworms because it does not require an intermediate host to complete its life cycle. The worm can live its entire life in one host so as to cause disease, even in humans. H. diminuta can also be infective to humans, but it requires an intermediate host such as a flea, cockroach, or grain beetle to complete its life cycle.
The thorny headed worm, Moniliformis moniliformis, may live in the small intestine of rats, mice, and other rodents. Although not a common parasite in rodents, it can cause serious problems such as enteritis, ulceration, and intestinal perforation leading to peritonitis in rodents (McArthur,1999). Tapeworms and pinworms are the most common intestinal parasites of mice and rats. Pinworms are especially difficult and sometimes even possible to not be present in mice and rats. The risk occurs when the transmission of these parasites are led to people. This is possible, but is rather unlikely (Woerpel et al., 1998).
Transmission of Rodent Parasites and Rodent Diseases to Humans
In a study made by Suntsov et al. (1997), the authors stated that the sources of human plague outbreaks in Southeast Asia, like Vietnam, have yet to be completely clarified. Vietnam lies in the tropical forest zone, and it is generally held that plague in this ecological area is imported through ports into urban areas and towns, thereafter establishing itself in the local commensal rodent population. In Vietnam plague-specific antibodies have previously been found in the treeshrew, Tupaia glis, and the black rat, Rattus rattus, in a boundary area between tropical forest and a coffee plantation in the village of Cu-Zut in Dak Lak Province, this has been taken by some workers as confirmation of the existence of natural foci of plague in tropical forests in the region. Still to be clarified are the identity of the species of fleas that are vectors of plague to the above-mentioned mammals and whether small species of wild mammals maintain plague in natural foci.
Ostfeld et al. (1996) found that white-footed mice are the principal hosts responsible for infecting ticks with the spirochete that causes Lyme disease in humans. Lyme disease includes symptoms like fever, headache, fatigue, and a characteristic skin rash called erythema migrans. The infection can spread to the joints, the heart and the nervous system if left untreated (Shiel Jr., 2005). A female of the sand-flea species, Tunga penetrans, can cause tungiasis (Herkelbach, 2004). This ectoparasite is widely distributed in the tropics but human infestation occurs mainly in poor neighborhoods. Peri-domestic rodents, including dogs, cats and pigs are affected by this ectoparasite. Sand-fleas are not taken out soon after penetration and could lead to ulceration. Tetanus also follows.
“Animal diseases that can be transmitted to humans are known as zoonotic diseases, or zoonoses. Some people are more likely than others to get zoonoses: the elderly, pregnant women, infants and children less than 5 years old, people undergoing treatments for cancer, people who have received organ transplants, and people with suppressed immune systems, such as those with HIV/AIDS.
Two diseases of emerging concern, especially in young children, may be spread by rodents, including pet hamsters, mice and rats. Lymphocytic choriomeningitis (LCM) is a viral disease that people can get from inhaling infectious airborne particles of rodent urine, feces, or saliva, or by ingesting food contaminated with the virus. Rat-bite fever is a bacterial illness that can be transmitted through the bite or scratch of a rodent or by ingesting food or water contaminated with rodent feces.
As a precautionary initiative, owners of pet rodents should avoid exposure to their droppings and should periodically disinfect rodent habitats while wearing gloves and washing hands afterward. There should also be an effort to trap and keep wild mice and rats away from your house and property. Make sure to tell your doctor if you or your child has flu-like symptoms and has had recent contact with rodents (Bren, 2004).
Armitage D. 2004. Rattus norvegicus (On-line). Animal Diversity Web. At
Ballenger L. 1999. Mus musculus (On-line). Animal Diversity Web. At http://animaldiversity.ummz.umich.edu.
Bren L. Keeping pets (and people) healthy. FDA Consumer [serial online] 2004; 28(1): 30. Available from EBSCOhost Online via the De La Salle University Library Portal (http://search.epnet.com/login.aspx?direct=true &db=buh&an=11945970)
Burnie, D. 2000. The kingfisher illustrated animal encyclopedia. London:
Calhoun J. 1962. The ecology and sociology of the Norway rat. Bethesda, MD: U.S. Department of Health, Education and Welfare.
Clark, K., Durden, L. 2002. Parasitic arthropods of small mammals in Mississippi. Journal of Mammalogy 83(4): 1039-1048.
Dionisio, A. 1995. A Survey on the Prevalence of Babesia sp. in Rattus mindanensis mindanensis Collected from Calumpit, Bulacan. De La Salle University Taft Avenue, Manila. Thesis 1-27.
Eduardo, S., Mercado, B. Jr. 1981. Notes on Ectoparasites of Rats (Rattus norvegicus) inhabiting marketplaces in the City of Manila. Philippine Journal of Veterinary Medicine. 20:67-75.
Herkelbach, J., Feldmeier, H. Ectoparasites-the underestimated realm. The Lancet 363(9412):889-891.
Jueco, N. 1983. Rodent diseases transmissible to man. Acta Medica Philippina. 19:164-169.
Koski K., Scott M. Gastrointestinal nematodes, nutrition and immunity: breaking the negative spiral. Annual Review of Nutrition [serial online] 2001; 21: 297. Available from Proquest Online via the De La Salle University Library Portal (http://proquest.umi.com/pqdweb?did= 78191748&Fmt=4&clientId=47883&RQT=309&VName=PQD).
McArthur J. 1999. Medical corner: the worms crawl in, the worms crawl out. Rat and Mouse Gazette. 9(10): 1-4.
Ostfeld, R., Miller, M., Hazler, K. (1996). Causes and consequences of tick (Ixodes scapularis) burdens on white-footed mice (Peromyscus leucopus). Journal of Mammalogy 77:1.
Pratt, H., Good N. 1954. Distribution of some common domestic rat ectoparasites in the United States. Journal of Parasitology 40:113-129.
Shiel Jr. W., 2005. Lyme Disease (On-line). MedicineNet.com. At http://www.medicinenet.com/lyme_disease/article.htm.
Silver, J. 1927. The introduction and spread of house rats in the United States. Journal of Mammalogy 8(1): 58-60.
Smith, W. 1955a. The abundance and distribution of the ectoparasites of the house mouse in Mississippi. Journal of Parasitology 41:58-62.
Smith, W. 1955b. Relation of certain environmental factors to the abundance and distribution of house mouse ectoparasites in Mississippi. Transactions of the American Microscopical Society 74:170-175.
Suntsov, V., Huong L., Suntsova N., Gratz, N. Plague foci in Viet Nam: Zoological and parasitological aspects. Bulletin of the World Health Organization75(2):117.
Tongson, M., Lasam, D. 1980. A study on the prevalence of ectoparasites of house mouse (Mus musculus) in Diliman, Quezon City. Philippine Journal of Veterinary Medicine 19:15-21.
Tubangui (1931) and Nishimura and Yogore (1960)
Whitaker, J., Wilson, N. 1974. Host and distribution lists of mites (Atari), parasitic and phoretic, the hair of wild mammals of North America, north of Mexico. American Midlands Naturalist 91: 1-67.
Woerpel R., Rosskopf W. 1998. Avian exotic animal care guides. New York: American Veterinary. 12 p.
the spell was cast: 7:12 PM
RESULTS AND DISCUSSION
Of the 15 samples of Rattus norvegicus, 8 were infested with Polyplax sp. and mesostigmatids, each having a 26.7% rate of infestation. On the other hand, 12 of 15 individuals of Mus musculus were infested mainly with Polyplax sp. accounting for an 80.0% rate of infestation. No mesostigmatids like those found in R. norvegicus were isolated from M. musculus (Table 1).
Table 1. Identification and % infestation rate of the ectoparasites isolated from the rodent species.
No. of infested samples
% infestation rate
No. of infested samples
% infestation rate
Eight of fifteen R. norvegicus samples examined were infected with Hymenolepis sp. and Rictularia sp. accounting for 46.7% and 6.7% rate of infection, respectively. On the contrary, 5 of 15 M. musculus samples were infected mainly with Hymenolepis sp. with 33.3% rate of infection. No Rictularia sp. was isolated from M. musculus (Table 2).
Table 2. Identification and % infection rate of the endoparasites isolated from the rodent species.
No. of infested samples
% infestation rate
No. of infested samples
% infestation rate
M. musculus has a higher infestation rate of 80.0% compared to R. norvegicus which is 53.3%. Polyplax sp. Was the only ectoparasite isolated from M. musculus. In contrast, R. norvegicus are highly infected with endoparasites having 53.3% rate of infection compared to M. musculus with an infection rate of 33.3%. Hymenolepis sp. accounts for the high infection rate for both rodent species. The over-all percent prevalence of parasites for both rodent species is 76.7%. 11 of 15 R. norvegicus were positive for ectoparasites and/or endoparasites. Comparatively, 12 of 15 M. musculus, are infested and/or infected.
Polyplax sp., a sucking louse isolated from both rodents, was observed to have blunt heads, which are narrow than the body. Their bodies are slender with scales. The have segmented antennaes and 3 pairs of legs (Fig. 1).
The mesostigmatids isolated from Rattus norvegicus was observed to have round bodies, bearing 4 pairs of legs without pincers. A pair of pointed structures could also be seen projecting from the anterior part (Fig 2). The mesostigmatids could not be identified up to the genus level because other distinguishing structures are not clear as seen in the prepared slides. The specimens are resistant to clearing with potassium hydroxide solution due to the preservative solution used.
Tapeworms from the genus Hymenolepis sp. isolated from both rodents were identified based on the number and arrangement of the testes—3 lobes forming a straight line — and also on the appearance of the scolex and rostellum Fig 3). Two species were identified: Hymenolepis nana, with unarmed suckers and armed but small rostellum, and Hymenolepis diminuta, with small suckers and small, unarmed rostellum.
The nematode isolated from Rattus norvegicus was observed to be mature females of the genus Rictularia sp. The worms have two longitudinal rows of backward projecting hook-like spines that extend from the anterior down to some distance posteriorly. The buccal capsule is well-sclerotized while the esophagus’ opening is surrounded by three serrated lancets (Fig 4).
Ewing (1929) documented that Polyplax spinulosa, also called the common sucking louse of rats, occurs on all of the domestic rats and is almost worldwide in distribution. Another species, Polyplax serrata, has been documented as a common parasite of the house mouse in Europe. This species of Polyplax has also been found on the house mouse in the United States only on laboratory animals. Polyplax species belong to the family Haematopinidae and members of this sucking lice family are confined largely to rodents, insectivores and ungulates. In a study conducted by Eduardo and Mercado (1982), Polyplax spinulosa accounted for 27% infection rate and ranked third among the seven ectoparasites they isolated from R. norvegicus. This study and the previous studies suggest that Polyplax sp. may be among the common ectoparasites of rodents.
One species from the Order Mesostigmata that commonly infest rats is the tropical rat mite, Ornithonyssus bacoti, family Dermanyssidae. O. bacoti is found worldwide, in both temperate and tropical climates. This species can retard growth and eventually kill young mice. These mites do not transmit any pathogens to humans but it was found experimentally that they can transmit plague, ricketssialpox, Q fever and murine typhus (Schmidt 1992).
The results obtained in this study for parasite infection on rodents agree with previous literatures describing parasite species such as Polyplax and Hymenolepis as common parasites of rodents. Tapeworms such as Hymenolepis sp., for example, have already been established in rodent host species (McArthur, 1999). Studies by Morozov (1960) showed Rictularia species such as R. cristata isolated from rodents in Eastern Europe. Another species, R. proni was also found in the intestine of the rodent Apodemus sylvaticus by Quentin (1970), and Quentin et al. (1973) in France (Anderson, 2000).
The greater variety of parasite species isolated from R. norvegicus can be attributed to their preferred habitats such as garbage dumps, sewers, open fields, and basements (Armitage, 2004). In these settings, they are more prone in making contact with various ectoparasites such as fleas and mites, and also to intermediate hosts of endoparasites such as fleas, cockroaches and the like (McArthur, 1999).
the spell was cast: 7:11 PM
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