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Leptospira and Dengue Fever

Dr. Sushil Shah and Dr. Nilesh Shah from Metropolis Health Services Pvt. Ltd., Mumbai, on page 284, report a very exciting finding of cross reactivity when testing blood samples of fever patients for dengue viral fever and leptospirosis.
In the last issue of Bombay Hospital Journal, I drew the attention of the Family Physicians to start asking for indirect blood tests to diagnose the above two illnesses.1 Now that Sushil Shah and Nilesh Shah have drawn our attention to the above finding, which is reported perhaps for the first time in world literature, it will be advisable for our readers to read my article in detail.

1 First of all, a clinical diagnosis is very important. These illnesses should be suspected in any patient, who suddenly becomes very sick and ill with very high fever in first 24 hours only. Complaints of skeletal pains specially in the back, all the bones and joints and even eye balls (in the past, dengue fever was known as break bone fever), appearance of rash or lymphadenopathy, will help in the diagnosis of dengue fever. Severe muscle pains especially in calf muscles and injected bulbar conjunctiva of the eyes (though this finding and pain on rotating the eyeballs could also be present in dengue) would favour the diagnosis of leptospirosis.

Talking about the investigations, a simple leucocyte count will, more or less in all cases, differentiate between these two illnesses. In dengue viral fever, leucocyte count is markedly low, while in leptospirosis, it is not only high but markedly high and may go upto 50,000. A routine urine examination of dengue is normal, while in leptospirosis, it is always abnormal and may show presence of albumin, casts, RBC and bile pigments.

Instead of asking for a CBC test, it is always better to send the blood to the laboratory which is doing haemograms where the platelet count is always reported (and as in falciparum malaria, so in case of dengue fever, the platelet count is very low). In fact, repeating the platelet count in dengue fever can predict the haemorrhagic variety of dengue fever, and the patient can be sent to ICU and the life of the patient can be saved. Similarly asking for a battery of tests like the SMA 12 is often very helpful because the combination of abnormality in the liver function tests and the kidney function tests like increased SGPT, bilirubin, blood urea and creatinine is diagnostic of leptospirosis and any antibiotic, from penicillin or tetracycline group or doxycycline can cure the patient.

Yes, the Elisa tests for IgM antibodies for both are extremely useful, but more for excluding the illnesses. Now that the cross reactivity has been shown, the family physicians will have to diagnose the two illnesses by history taking and clinical examination (red eyes and marked tenderness of calves). A routine haemogram rather than CBC, urine examination and SMA 12, should be asked for, instead of asking for only Elisa test for IgM antibodies, which could be misguiding.

1. Kapoor OP. Why not to start indirect blood testing to diagnose malaria, typhoid, dengue and leptospirosis. Bombay Hospital Journal 2003; 1 : 134.

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