Rat race

Living in poorly maintained accommodation, students may find themselves playing host to hundreds of unwelcome visitors--rats. Ellen Welch and Geoff Gill give you the lowdown on these common pests

Student houses in the United Kingdom are renowned for being pretty disgusting. Stereotypically owned by a dodgy landlord, juggling to keep a dozen properties within the legal health and safety requirements, they are often overrun with a host of nasties--mould, damp, carbon monoxide poisoning, and rats.

Some 16% of UK students live in vermin infested flats and up to 950'000 UK homes have been found to be afflicted with the same problem.^{1 2} A recent report by the National Pest Technicians Association claims that brown rat infestations in Britain have risen 32% in 5 years.³ But, contrary to popular political viewpoint, it is not just the United Kingdom that is home to lots of rats; they can be found scurrying around every country in the world.

Disease

Rats have gnawed their way into the lives of humans for centuries, gaining recognition as one of the most destructive pests on earth. The great bubonic plagues of the middle ages swept through Europe causing mass hysteria and the death of one third of the population of Europe.⁴ Responsibility for the disaster rested on the backs of the black rats and the diseased fleas they carried (Xenopsylla cheopis). Outbreaks of plague do still occur throughout the world, most commonly in the Americas, Central Africa, and the Far East but they are more effectively controlled nowadays.

Yersinia pestis, the causative gram negative bacillus has two main clinical presentations. Pneumonic plague is fatal in almost all affected patients without treatment and is characterised by sudden onset fever and pneumonia which can progress to severe illness with haemoptysis within 15 hours. It is spread by infected droplets from the respiratory tract. The bubonic type is more common and transmitted via the pus of infected buboes. After an incubation period of 1-6 days, patients develop high fever, headache, nausea, and tender buboes (lymphadenopathy) often in the inguinal region. Petechial or purpuric haemorrhages may also occur, and if toxaemia develops patients often become delirious. Infection is controlled using intramuscular streptomycin (1 g twice daily) or in less severe cases, oral tetracycline (500 mg four times daily). It is highly infective, so patients should be isolated and contacts monitored for fever. Plague vaccine is a killed bacterial vaccine available for travellers venturing to plague endemic regions, but its efficacy has been poorly documented, and prophylactic tetracycline is a favourable alternative.⁵

Plague, food poisoning, and leptospirosis (box) are carried by rats universally, although rats from different parts of the world have been found to carry a whole host of other diseases specific to their locality. A study of wild brown rats on a farm in Britain showed that rats there carried a plethora of organisms, responsible for diseases such as toxoplasmosis, listeriosis, Q fever, and Hantaan fever among others.⁶ These diseases can be passed on to humans through contact with rat droppings or urine, or bites from the rats or their fleas (table 1).

A gnawing problem

Rats eat a fifth of the world's crops every year. Since rats have been known to feast on everything from grain and meat to strips of cloth and old soap, they can make their home anywhere--from sewers, ships, and farms to student flats, where they will nest in wall cavities and beneath floorboards.

The name rat comes from the Latin "rodere" meaning "to gnaw"--which they need to do to wear down their ever growing incisors. Millions of pounds worth of flood and fire damage are caused each year by rats chomping their way through gas pipelines, power cables, and lead water pipes.

Rat catching

The lifespan of a rat--brown or black--is a mere 18 months, but in this time, a single pair of rats can produce up to 11 pups a month. Litters show remarkable resilience to environmental difficulties, showing a flair for swimming through the S bend in toilets and staying afloat in sewage for 72 hours before tiring. Attempts made by humans to control them are often in vain. You will need professional help to control colonies of rats in your house, so contact your local council if you suspect a problem. It is common for rat infestations to build up without being detected, since their nocturnal habits keep them away from human contact. Their presence can usually be detected by the damage they cause or their distinctive faeces, which can vary in colour and smell, measure about 1 cm by 0.5 cm, and are pointed at one end. Gnaw marks, footprints, and smear marks produced by their fur rubbing against surfaces are other clues that you have an unwelcome visitor. Usual methods of rodent eradication include the setting of traps and laying poison bait along rat runs and in the drainage system.

Disease focus: leptospirosis

Leptospirosis occurs in every country in the world (excluding the Polar regions), making it the most common zoonosis globally. Human infection is particularly rife in the warm moist climate of the subtropical regions such as Hawaii. Here, the annual incidence of the disease is about 130 per 100 000 population, and more temperate countries such as the UK see only about 20-30 cases each year. It remains largely an occupational disease of farmers, sewage workers, and vets, but it is notably associated with recreational activities around canals and docklands that bring people into closer contact with rodents, such as swimming, canoeing, fishing, and gardening.⁷

More than 200 serotypes of the spirochaete Leptospira interrogans can cause leptospirosis in humans, the commonest being Leptospira icterohaemorrhagiae. Rats, mice, dogs, and cattle can all act as hosts to the leptospires, which multiply in the kidneys, often causing no harm to the infected animals. Once excreted in the urine, the organism can survive for days in fresh water, damp soil, and mud. Humans exposed to contaminated urine pick up the infection through damaged skin or intact mucous membranes. Occassionally animal bites can transmit the infection.

Typical cases present after an incubation period of 7-14 days with fever, intense headache, and myalgia. Dilation of the conjunctival vessels without inflammation (conjunctival suffusion) is pathognomonic of leptospirosis. This symptomatic phase lasts 3-7 days and during this time, leptospires can be cultured from the blood. An immunological phase follows, lasting for a month coinciding with the formation of circulating IgM antibodies. Most patients are asymptomatic during this stage, but some develop meningism or uveitis.

More than 90% of cases are mild and self limiting, however, the severe cases (referred to as Weil’s disease) can be life threatening. The onset of severe illness is indistinguishable from the milder form in the initial stages. Progression to Weil’s disease is characterised by jaundice and hepatosplenomegaly. Lymphadenopathy and skin rashes are sometimes seen and patients can go on to develop renal impairment and cardiopulmonary failure. In severe leptospirosis mortality rate is 5-10%, but overall mortality is less than 1%.

Early antibiotic therapy will limit progression of the disease. Oral doxycycline can be given for the milder cases, replaced with intravenous penicillin or erythromycin in severe disease together with intensive supportive care. Prevention is possible by avoiding contaminated areas or wearing protective clothing while at risk.

Prevention

Students can make it difficult for rats to gain access to their premises by removing any sources of food, water, and rubbish and by clearing areas which may offer shelter or nesting materials, such as piles of timber or overgrown areas of the garden. Repairing damaged drain pipes and sealing structural defects to a house can also prevent rodent infestation.

Ellen Welch, preregistration house officer, Royal Liverpool University Hospital
Email: welchellen@yahoo.co.uk

Geoff Gill, reader in tropical medicine, Liverpool School of Tropical Medicine
Email: g.gill@liverpool.ac.uk


studentBMJ 2005;13:45-88 February ISSN 0966-6494

1. Knight S. NUS says students' living conditions are "second class." studentBMJ 2001;9:447.
2. Meyer AN, Shankster A, Langton SD, Jukes G. National commensal rodent survey 1993. Environ Health J 1995;103:127-35.
3. National Pest Technicians Association. National rodent survey report 2003. Kinoulton: NPTA, 2002. www.npta.org.uk/rodent-report%20htm.htm
4. Cartwright FF. Disease and history. New York: Dorset, 1991
5. Jong EC, McMullen R. The travel and tropical medicine manual. London: Saunders, 2003
6. Webster JP, Macdonald DW. Parasites of wild brown rats (Rattus norvegicus) on UK farms. Parasitology 1995;111:247-53.
7. Mumford CJ. Leptospirosis and water sports. Br J Hosp Med 1989;41:519.

       

           

Responses published this month Articles Responses LIFE Rat race       Ellen Welch, Geoff Gill (February 2005) Dr Shobha K.L (February 01, 2005) Read this response LIFE Rate race       Ellen Welch, Geoff Gill (February 2005) Dr Shobha K.L (February 01, 2005)       Department of Microbiology, Melaka Manipal Medical College(Manipal campus)shobhamicro@yahoo.com Editor-Last months article , Rat race 1 Included all the diseases transmitted by rats to humans. Route of transmission included rats urine or excreta contamination in the food and water, also vectors infested on the rats transmitting the disease. Another mode of transmission which was not included is through rat bite causing rat bite fever, though uncommon but seen worldwide. This is specially important where students are living in rat infested flats or carrying out research experiments with rats in the laboratory. Rat bite fever is caused by one of the two species Spirillum minor ( or minus),a Gram negative spiral-shaped organism (Spirillar fever,occurs mainly in Asia). Streptobacillus moniliformis, a Gram negative filamentous bacillus (Streptobacillary fever).These bacteria are found in the oropharyngeal flora of 50% of healthy wild and laboratory rats. Transmission to humans is through rat bite. Man to man transmission has not been documented. After an incubation period of 7-10 days , patients develop fever , headache and myalgia. In case of Streptobacillary fever it causes inflamed local lesion ,lymphadenopathy,rash and myalgia. Fever may be recurrent if untreated .Complications include endocarditis and pneumonia. Mortality upto 10% in untreated cases.2 Treatment with Penicillin or Doxycycline is the drug of choice. Ellen Welch,Geoff Gill;Rat race ,StudentBMJ, Feb 2005,13;45-88 Cediac Mims,Hazel M Dockrell,Richard V Georing, Ivan Roitt ; Medical Microbiology;3rd Edition ;Elsevier;2004