Leptospirosis

Related Topics:
Leptospirosis

Leptospirosis (also known as Weil's disease, canicola fever, canefield fever, nanukayami fever or 7-day fever) is a bacterial zoonotic disease caused by spirochaetes of the genus Leptospira that affects humans and a wide range of animals, including mammals, birds, amphibians, and reptiles. It was first described by Adolf Weil in 1886 when he reported an "acute infectious disease with enlargement of spleen, jaundice and nephritis". The pathogen, Leptospira-genus bacteria was isolated in 1907 from post mortem renal tissue slice.

Though being recognised among the world's most common zoonosis, leptospirosis is a relatively rare bacterial infection in humans. The infection is commonly transmitted to humans by allowing fresh water that has been contaminated by animal urine to come in contact with unhealed breaks in the skin, eyes or with the mucous membranes.

Except for tropic areas, leptospirosis cases have a relatively distinct seasonality with most of them occurring August through September (in the Northern Hemisphere).

Causes

Leptospirosis is caused by a spirochaete bacterium called Leptospira interrogans that has at least 5 different serovars of importance in the United States causing disease (icterohaemorrhagiae, canicola, pomona, grippotyphosa, and bratislava). There are other (less common) infectious strains. It should however be noted that genetically different leptospira organisms may be identical serologically and vice versa. Hence, an argument exists on the basis of strain identification. The traditional serologic system is seemingfully more useful from diagnostic and epidemiologic standpoint at the moment (which may change with further development and spread of technologies like PCR).

Leptospirosis is transmitted by the urine of an infected animal, and is contagious as long as it is still moist. Deer, rats, raccoons, possums, voles, skunks, mice, specific marine mammals and even infected dogs may serve as hosts. Dogs may lick the urine of an infected animal off the grass, or drink from an infected puddle. There have even been reports of "house dogs" getting leptospirosis apparently from licking the urine of infected mice that entered the house. There is a direct correlation between the amount of rainfall and the incidence of leptospirosis, making it seasonal in temperate climates and year-round in tropical climates.

Humans become infected through contact with water, food, or soil containing urine from these infected animals. This may happen by swallowing contaminated food or water or through skin contact. The disease is not known to be spread from person to person and cases of bacterial dissemination in convalescence are extremely rare in humans. Leptospirosis is common among watersport enthusiasts in specific areas as prolonged immersion in water is known to promote the entry of the bacteria. Occupational risk factors include veterinarians, slaughter house workers, farmers, and sewer workers. An outbreak in an inner city environment has been linked to contact with rat urine.

Symptoms

In animals, the incubation period (time of exposure to first symptoms) is anywhere from 2 to 20 days. In dogs, the liver and kidney are most commonly damaged by leptospirosis. Vasculitis can occur, causing edema and potentially disseminated intravascular coagulation (DIC). Myocarditis, pericarditis, meningitis, and uveitis are also possible sequelae. One should strongly suspect leptospirosis and include it as part of a differential diagnosis if the whites of the dog's eyes appear jaundiced (even slightly yellow), though the absence of jaundice does not eliminate the possibility of leptospirosis, and its presence could indicate hepatitis or other liver pathology rather than leptospirosis. Vomiting, fever, failure to eat, reduced urine output, unusually dark or brown urine, and lethargy are also indications of the disease.

In humans, leptospiral infection causes a wide range of symptoms, and some infected persons may have no symptoms at all. Because of the wide range of symptoms the infection is often wrongly diagnosed. This leads to a lower registered number of cases than there really are. Symptoms of leptospirosis include high fever, severe headache, chills, muscle aches, and vomiting, and may include jaundice, red eyes, abdominal pain, diarrhea, and/or a rash. The symptoms in humans appear after 4-14 day incubation period.

Complications

Complications include meningitis, respiratory distress and renal interstitial tubular necrosis, which results in renal failure and often liver failure (this severe form of the disease is known as Weil's disease). Cardiovascular problems are also possible. Approximately 5-50% of severe leptospirosis cases are fatal, however, such cases only constitute about 10% of all registered incidents.

Diagnostics

On infection the microorganism can be found in blood for the first 7 to 10 days (invoking serologically identifiable reactions) and then moving to the kidneys. After 7 to 10 days the microorganism can be found in fresh urine. Hence, early diagnostic efforts include testing a serum or blood sample serologically with a panel of different strains. It is also possible to culture the microorganism from blood, serum, fresh urine and possibly fresh kidney biopsy. Kidney function tests (Blood Urea Nitrogen and creatinine) as well as blood tests for liver ferments are performed. The later reveal a moderate elevation of transaminases. Diagnosis of leptospirosis is confirmed with tests such as Enzyme-Linked Immunosorbent Assay (ELISA) and PCR. Serological testing is laborious and expensive, thus underused in developing countries.

Differential diagnosis list for leptospirosis is very large due to diverse symptomatics. For forms with middle to high severity, the list includes dengue fever and other hemorrhagic fevers, hepatitis of various etiologies, viral meningitis, malaria and typhoid fever. Light forms should be distinguished from influenza and other related viral diseases. Specific tests are a must for proper diagnosis of leptospirosis. Under circumstances of limited access (e.g., developing countries) to specific diagnostic means, close attention must be paid to anamnesis of the patient. Factors like certain dwelling areas, seasonality, contact with stagnant water (swimming, working on flooded meadows, etc) and/or rodents in the medical history support the leptospirosis hypothesis and serve as indications for specific tests (if available).

Treatment

Leptospirosis treatment is a relatively complicated process comprising two main components - suppressing the causative agent and fighting possible complications. Aetiotropic drugs are antibiotics, such as doxycycline, penicillin, ampicillin, and amoxicillin (doxycycline can also be used as a prophylaxis). There are no human vaccines; animal vaccines are only for a few strains, and are only effective for a few months. Human therapeutic dosage of drugs is as follows: doxycycline 100 mg orally every 12 hours for 1 week or penicillin 1-1.5 MU every 4 hours for 1 week. Doxycycline 200-250 mg once a week is administered as a prophylaxis. In dogs, penicillin is most commonly used to end the leptospiremic phase (infection of the blood), and doxycycline is used to eliminate the carrier state.

Supportive therapy measures (esp. in severe cases) include detoxication and normalization of the hydro-electrolytic balance. Glucose and salt solution infusions may be administered; dialysis is used in serious cases. Elevations of serum potassium are common and if the potassium level gets too high special measures must be taken. Serum phosphorus levels may likewise increase to unacceptable levels due to renal failure. Treatment for hyperphosphatemia consists of treating the underlying disease, dialysis where appropriate, or oral administration of calcium carbonate, but not without first checking the serum calcium levels (these two levels are related). Corticosteroids administration in gradually reduced doses (e.g., prednisolone starting from 30-60 mg) during 7-10 days is recommended by some specialists in cases of severe haemorrhagic effects.

Improper treatment greatly reduces the survival rate. A patient with leptospirosis SHOULD be treated at a specialized medical institution and MUST remain hospitalized until proper resolution of organ(s) failure and clinical infection.

Research

In a study of 38 dogs diagnosed and properly treated for leptospirosis published in the February 2000 issue of the Journal of the American Veterinary Association, the survival rate for the dialysis patients was slightly higher than the ones not put on dialysis, but both were in the 85% range (plus or minus). Of the dogs in this study that did not die, most recovered adequate kidney function, although one had chronic renal problems.

References

External links

Infectious diseases | Zoonoses | Dog health

Gourt Home::Gourt :: Leptospirosis