Epidemiology

Leishmaniasis is a zoonotic infection affecting 12 million people worldwide in 88 countries. The annual incidence is 2 million, with 1.5 million having the cutaneous form and 0.5 million the visceral form.

In visceral leishmaniasis, human-sandfly-human cycles occur in some areas (India), whereas in other areas rodents or canines serve as reservoir hosts. Visceral leishmaniasis is found in the Mediterranean basin, tropical Africa, Indian subcontinent, Southeast Asia, China, South and Central America.

Probably visceral leishmaniasis is not due to a single organism and there are biological differences in distinct geographic regions. Visceral leishmaniasis occurs in >80 countries in Africa, Asia, southern Europe (L. infantum) and S. America (L. chagasi). About 90% of the 500,000 new cases each year occur in 5 countries: Bangladesh, India, Sudan, Nepal, Brazil. India alone contributes to ~50% of all cases in the world. Males are usually infected more than females. Under unusual circumstances the disease can be transmitted by sexual intercourse. In one case in 1955, a female who never left England developed vaginal lesions containing amastigotes. Her husband had contracted leishmaniasis in 1941 and was obviously treated insufficiently.

Recently, there has been an increase in visceral leishmaniasis due to the AIDS pandemic. Leishmania/HIV co-infection is considered to be a real “emerging disease”, especially in southern Europe, where 25-70% of adult VL cases are related to HIV infection, and 1.5-9.5% of AIDS cases suffer from newly acquired or reactivated VL. Epidemics of visceral leishmaniasis still occur in southern and eastern Sudan, and at the junction of Eritrea, Ethiopia and Sudan.

Recently there has also been a resurgence of visceral leishmaniasis in Brazil. Click here to see an article on this.

Old World cutaneous leishmaniasis due to L. tropica occurs in urban areas of the Mediterranean basin, the Middle East, Pakistan and parts of India. Cutaneous leishmanisis due to L. major occurs in rural areas, usually dry desert regions of Central Asia, Southern Russia, Middle East and Africa. New World cutaneous leishmaniasis due to L. braziliensis and L. mexicana occurs in Mexico and central and South America.

Like many other tropical diseases, leishmaniasis is related to economic development and man-made environmental changes, which increase exposure to the sandfly vector.

An Outbreak of Leishmaniasis in Hunting Dogs in the US

In 1999 foxhounds at a hunt club in Millbrook, New York, came down with a mysterious illness. They showed bleeding, wasting, hair loss and kidney failure. More than 24 dogs died. Examination of joint fluid from the sick dogs led to the discovery of Leishmania parasites. Since then all of the 12,000 foxhounds in the US have been tested and 12% have antibodies to Leishmania. But no antibodies were found in stray dogs from the Millbrook area nor from any other area in the US.

For those of you who thought that fox hunting was limited to England, look at these drawings from Harpers magazine in 1878, and the cigarettes advertisement from 1922:

1878: Long Island Fox Hunting. Original Harper's Weekly (1878).
Seven views of A Queen's County, Long Island, Fox-Hunt.
(from http://www.printsoldandrare.com/foxhunting/)

1922 Fox Hunting Cigarette Ad. Colorful advertisement for Murad cigarettes, featuring a man and woman on horseback, following their hounds on a hunt.
(from http://www.printsoldandrare.com/foxhunting/)

The transmission of this disease is a mystery. There are four sandfly species in the US but none can live further north than New Jersey. A scientist at Walter Reed theorizes that the dogs could infect each other by sexual contact or by wounds, but experts in the Leishmania field do not agree. They theorize that the dogs were bitten by sandflies while touring in the South. Another possibility is that an unknown sandfly species exists or even that there are other vectors. The Leishmania species is L. infantum and it is possible that there has been a low level epidemic in people in the US and it was missed.

Outbreak of cutaneous leishmaniasis in American soldiers in Iraq war:

Following are two news stories about this problem

Troops Being Treated For Leishmaniasis
By Lisa Burgess
Stars and Stripes
European Edition
March 20, 2004,

ARLINGTON, Va. — About 500 soldiers who have served in Iraq have been diagnosed with a skin disease caused by sand flies in the largest outbreak of leishmaniasis faced by the U.S. military since World War II, according to Defense Department doctors.

The disease is caused by parasites transmitted via sand fly saliva, and comes in three forms: cutaneous, affecting the skin; mucosal, affecting the mouth, nose and throat; and visceral, affecting internal organs, which can be fatal if untreated. All but two of the cases diagnosed so far have been the cutaneous form and all but three of those were contracted in Iraq, according to Dr. Alan Magill, a specialist in infectious diseases at Walter Reed Army Institute of Research in Maryland. The remaining three cases of cutaneous "leish" were contracted by U.S. service members deployed to Afghanistan, Magill said in a Thursday interview, as were the two cases of visceral leishmaniasis. The last time the Pentagon doctors had to cope with a leishmaniasis outbreak was 1943, when about 1,000 U.S. soldiers stationed in what is now Iran came down with the cutaneous version.

FORT DETRICK, Md. (Army News Service, March 4, 2004) -- A little-known parasite that causes chronic, festering sores will be returning home with some of Operation Iraqi Freedom's warfighters.
Cutaneous leishmaniasis, which affects the skin, is caused by a sand fly bite that deposits the parasite that eventually causes weeping sores that don't heal as quickly as regular sores.
"The majority of these are lesions on the face or on the hands over joints. So in the short term, it's just not pleasant to have a lesion that won't heal potentially for up to a year - -and some of these get quite large," said Lt. Col. Peter Weina, a "leish" expert at the Walter Reed Army Institute of Research. "In the long term, the problem is the scarring, which can be disfiguring if it's on the face and can limit movement of the hands if it's over a joint."
Iraq's sand flies are most active during warm nights from March to October, so troops on the move during Operation Iraqi Freedom were right in the middle of "Sand fly Central."

Study questions:

1. Why is Leishmaniasis considered a "zoonosis"?

2. Why is Leishmaniasis considered an "opportunistic disease"?