Etiology and Epidemiology

Leptospires are obligate aerobes and classified serologically as a bacterium, subdivided into two species. One is Leptospira biflexa, which includes the various water spirochetes, whereas the other, Leptospira interrogans, embraces the parasitic strains. The species interrogans (so named because of an appearance like a question mark) is now subdivided by the main antigen into 187 serotypes or serovars. Human leptospirosis generally results from direct or indirect exposure to the urine of infected animals, although it can also be transmitted by handling infected animal tissue, by animal bites, and by the ingestion of contaminated food and water. The leptospires can enter the body through breaks in the skin, as well as through the lining of the mouth, nose, and eyes.

Persons of all ages are susceptible to the infection, and although the disease may occur at any time, it is most often seen during warmer weather and periods of heavy rainfall. Its presence in mud and swamps has often placed soldiers at special risk. As a rule, it appears as isolated cases, but it can also manifest itself in small clusters and even in large outbreaks, depending on the type and the circumstances of its transmission.

Figure VIII.81.1. Leptospires on dark field. (From O. Gsell. 1978. Leptospires and relapsing fever. In Handbook of Clinical Neurology, Part III, Chapter 18, 395-418, by permission of Elsevier Science Publishing.)

In most of the world, leptospirosis is an occupational disease. Field workers and those who work around farm animals are at risk, as are employees of slaughter houses and poultry and fish production plants, and persons employed in sewers, mines, and in other wet places infested with rodents. Infected wild animals such as rats and mice are the source of infection for domesticated animals, especially dogs (Leptospira canicola), pigs (Leptospira pomona), and cattle (Leptospira hardjo), who may in turn infect humans.

As Table VIII.81.1 indicates, localized leptospirosis infections produced by one or another strain of the pathogen occur across the globe. The pig-raising areas of the European alpine region, northern Australia, and parts of Argentina see one form of the disease caused by L. pomona and Leptospira hyos or tarassovi and called swineherd's disease. Similarly, the sugarcane plantation regions of East Asia and rice-growing regions of Spain and Italy harbor other forms, which are the result of infection by field mice. Local names for the various forms of leptospirosis often reflect the circumstances under which it is contracted. Thus there is "harvest" or "swamp" fever, caused by Leptospira grippotyphosa. In Germany, agricultural workers contracted "field fever"; in Silesia, there was "mud fever"; in Russia, "water fever"; and in Germany and Switzerland, "pea pickers disease." On the other hand, leptospirosis can also be an urban disease carried by the ubiquitous Rattus norwegicus, as well as by dogs.

Table VIII.81.1. Serologic classification of leptospires

Important serogroups

Principal human diseases

Rare serogroups

1. L. icterohaemorrhagiae

Morbus Weil

10. L. pyrogenes

2. L. bataviae

Indonesian Weil,

11. L.javanica

rice field fever

3. L. canicola

canicola fever

12. L. ballum

4. L. grippotyphosa

field or swamp fever

13. L. celledoni

5. L.pomona

swineherd's disease

14. L. cynopteri

6. L. hyos = tarassovi

swineherd's disease

15. L. panama

7. L. australis

cane fever

16. L. shermani

8. L. autumnalis

Japanese autumnal fever

17. L. semeranga

9. L. hebdomadis

7-day fever

18. L. andamana

19. L. sejroe, including serovarL.

hardjo

Source: O. Gsell. 1978. Leptospiroses and relapsing fever. In Handbook of Clinical Neurology, Part III, Chapter 18, 397. New York: Elsevier Science Publishing, by permission of publisher.

Source: O. Gsell. 1978. Leptospiroses and relapsing fever. In Handbook of Clinical Neurology, Part III, Chapter 18, 397. New York: Elsevier Science Publishing, by permission of publisher.

Your Heart and Nutrition

Your Heart and Nutrition

Prevention is better than a cure. Learn how to cherish your heart by taking the necessary means to keep it pumping healthily and steadily through your life.

Get My Free Ebook


Post a comment