Leishmaniasis, Biology


Leishmaniasis is a group of disease caused by protozoa of the group Leishmania, and are transmitted to man by the bite of female sandfly (Phlebotomus). Three types of leishmaniasis are recognized, viz. visceral leishmaniasis ( kala-azar), cutaneous leishmaniasis (oriental sore) and mucocutaneous leishmaniasis (espundia).

Three specific agents, viz., Leishmania donovani, the causative agent of Kala-azar,L. tropica, the causative agent of oriental sore and L. braziliensis, the causative agent of mucocutaneous leishmaniasis, are responsible for different forms of leishmaniasis. But this distinction is not absolute, visceral forms of may produce cutaneous lesions and cutaneous form may produce visceral lesions.

Epidemiology: Kala-azar is widely distributed throughout the world including India. Oriental sore occurs in dry, semi-dry rural areas of the Central Asia, the Middle East, the North and West Africa. Mucocutaneous form is native to Brazil only. Kala-azar was a public problem in India in 1940s and was endemic in Assam, West Bengal, Bihar, Uttar Pradesh and to a lesser extent in Tamil Nadu and Orissa. As a result of the massive insecticide spraying for malaria eradication, kala-azar has almost disappeared.

The majority of the leishmaniases are zoonoses involving wild or domestic mammals (rodents, dogs, foxes and marsupials). Indian kala-azar is a non-zoonotic infection with man as the sole reservoir of the disease (anthroponosis).
Leishmaniases are transmitted by the bite of the female sandfly (Phlebotomus). After an infective blood meal, the sandfly becomes infective in 6 to 9 days (extrinsic period). Kala-azar occurs in all age groups including infants. Kala-azar is mostly confined to the plains; it does not occur in altitude over 2,000 feet. There is high prevalence of the disease during and after rains with a humidity above 70 %.

Clinical features:

The incubation period in man is usually 1 to 4 months.
Kala-azar: Onset of the disease is sudden or insidious. Irregular malaise, headache, and fever with progressive enlargement of spleen (spleenomegaly), and liver (hepatomegaly) are the classical clinical signs. The double rise of temperature in 24 hours is a characteristic feature. The disease is generally fatal if it is not treated.

Cutaneous leishmaniasis: The disease may be mistaken for leprosy. The agent is restricted to skin. The disease is characterized by ulcers in the legs, arms or face – the parts exposed to the sandfly.
Mucocutaneous leishmaniasis: The agent involves the skin and mucosa. Ulcers appear around the margins of the mouth and nose.
Laboratory diagnosis: Following diagnostic methods are used for diagnosis of the disease.
Demonstration of parasite: Demonstration by microscopical examination of bone
marrow, spleen or liver biopsy for the presence of Leishmania bodies. Culture of bone morrow is more sensitive a test than examination by smear.

Demonstration   of   antibodies: 
  Complement   fixation   test ,indirect immunofluorescence test and enzyme-linked immunosorbent assay are used for diagnosis of leishmaniasis antibodies. Leishmania or Montenegro skin test (allergic test) indicates delayed hypersensitivity to leishmanial antigens. The test is less specific than the serological tests.

Control and prevention: The basic control measures include:
1.  Control of dogs and rodents.
2.  Application of suitable insecticides to kill the sandfly.
3.  Immunoprophylaxis with attenuated strains would be an alternative approach to control the infection.

Posted Date: 9/20/2012 3:19:40 AM | Location : United States

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