Humid weather conditions in the country have brought in their wake, several skin related diseases. One of these is the Sandflies disease ( Leishmaniasis), now on the increase in various parts of the country. According to the Epidemiology Unit around 3,000 cases of Leishmaniasis islandwide were reported in 2018. This vector borne disease transmitted by sandflies is still little understood by most people living in high risk areas. Health officials have repeatedly warned that if prompt medical advice from a qualified doctor was not sought, this skin disease could leave ugly disfiguring scars difficult to heal and serious complications if treatment is delayed.
Consultant Epidemiologist, Epidemiology Unit, Ministry of Health, Dr Nirupa Pallewatte shares her expertise with the Sunday Observer on this highly contagious disease and why it is important to get prompt treatment.
Excerpts …
Q. Several cases of Leishmaniasis have been recently reported in different parts of the island. Although Leishmanaisis was first reported in the 1990s not many people seem to know much about the disease that leaves ugly sores on the skin and if neglected could lead to more complications. What is Leishmaniasis?
A. Leishmaniasis is a vector borne disease caused by a parasite called ‘Leishmania’. There are over 20 species of Leishmania that can cause leishmaniasis in humans. The causative organism of leishmaniasis prevailing in Sri Lanka is identified as Leishmania donovani
Q. It is also called sandflies disease .Why?
A. Leishmaniasis is transmitted through an infected female sandfly.
Q. How is it transmitted, from human to human or from insect to human?
A. The parasite ‘Leishmania’ has two developmental stages, part of which undergoes in the body of the sandfly and the other part in the body of the mammalian host (rats, dogs, humans).
When an infected female sandfly takes a blood meal from an animal or a human host, promastigotes (the infective stage of leishmanial parasite) are injected into the site of the bite. Promastigotes are usually phagocytized by the macrophages at the site of the bite. Inside the macrophage, promastigotes transform into the amastigote (tissue type) which multiply by simple division. Sandflies become infected by ingesting infected cells during blood meals. In the gut of the sandfly, amastigotes transform into promastigotes.
Q. I understand that it has been included in the list of notifiable diseases in 2009. Does that mean it is an infectious disease?
A. Surveillance data of the Epidemiology Unit have shown that 2,000- 3,000 cases have been reported in the last decade from different regions of the county.
Q. Where have you found the highest number of cases and why? Does it mean that the climate and weather condition has anything to do with it?
A. The first case of locally acquired cutaneous Leismaniasis was reported in 1992 in southern Sri Lanka. From 2002 onwards, a large number of suspected leishmania cases were identified and made notifiable in 2009.
There were over 3,000 cases of leishmaniasis notified to the epidemiology unit in 2018. More than 90% of this is reported from five districts: Anuradhapura, Hambantota, Polonnaruwa, Kurunegala and Matara. People in these areas mainly engage in agricultural activities which expose them to environments with high density of sandflies, making them more vulnerable to sandfly bites. A higher number of cases were reported from Matale, Moneragala and Gampaha as well.
Q. What about environmental surroundings? Are villages close to forests more vulnerable?
A. Environmental conditions such as rainfall and temperature have an impact on the distribution of sandflies. They predominantly habitat in warm, humid and tropical climates. Sandflies need an environment with high humidity to develop their eggs and moist soil with decaying organic matter for the development of larvae. The common breeding places include bark and buttress roots in old trees, animal shelters, cracks and holes in floors and walls, household garbage dumps rich in moisture and humus.
It takes 20 - 30 days to become an adult sandfly in favourable environmental conditions.
Forests having thick vegetation, moist and dark gloomy environment too provide a favourable condition for breeding of sandflies. Deforestation and other human activities in forests may disturb the normal behaviour of sandflies exposing humans to sandfly bites.
Q. Is it vector borne? Does the vector belong to the same family of mosquitoes that cause dengue and malaria ? Or is it some other kind of insect?
A. The vector of Leishmania is a sandfly of subfamily Phlebotominae. Of over 800 Phlebotominae species only 98 species are proven or suspected vectors of Leishmaniasis.
Phlebotomus argentipes is the likely vector of L. donovani in Sri Lanka.
Sandflies are locally known as hohaputuwa weli massa in different parts of the country.
Sandflies are small in size (1.5 to 3.5 mm) and hard to see. They are only one fourth the size of the typical mosquito, have a hairy appearance, large black eyes and long, stilt-like legs. They are weak flyers and have characteristic hopping movements. They do not make a sound when they move, and tend to remain close to the breeding sites. Most species of sandflies fly horizontally, not too high from ground level.
Sandflies are most active from dusk to dawn and less active during the hottest times of the day. Both female and male sandflies feed on plant juices and sugary secretions. But the female sandfly needs a blood meal to mature eggs. Their feeding activity is influenced by temperature, humidity and air flow.
Q. Can other animals like rats, bandicoots, monkeys, dogs, pigs transmit the disease to humans?
A. Humans have been identified as the main reservoir for L. donavani. But there is evidence suggestive of possible reservoir status of domestic dogs.
Q. Are there specific types of Leishmanais. What are the common types we see in Sri Lanka?
A. There are three main clinical forms of leishmaniasis in humans. i.e cutaneous leishmaniasis, mucosal Leishmaniasis and visceral leishmaniasis. Cutaneous Leishmaniasis is predominantly seen in Sri Lanka. Very few cases of visceral and mucosal leishmaniosis were reported in the past.
Q. What are the early signs/symptoms of this disease?
A. The clinical picture varies according to the causative species and host factors.
Cutaneous leishmaniasis is the commonest form. It starts with the appearance of a small papule on the skin which then develops into a nodular lesion that may enlarge and become a chronic ulcer.
The incubation period is usually two weeks to several months following a sandfly bite
The lesions develop in exposed areas of the body such as face, neck, arms and legs though it can appear in any part of the body where the sandfly bite occurred. Lesions can be multiple or single, are usually painless and may take 3 -18 months to heal.
Mucosal leishmaniasis – is less common. Some types of the parasite might spread to the mucosal tissues following initial sandfly bite and cause sores in the mucous membranes of the nose, mouth or throat.
Visceral leishmaniasis - is also known as Kala- azar.
The incubation period is usually 3-8 months, but can be prolonged to several years.
The clinical features include fever, weight loss, excessive tiredness, anemia and enlargement of spleen. This condition is potentially fatal if untreated.
Q. Who are more vulnerable to get infected with Leishmaniasis
A. People living in endemic areas, with a history of recent travel to endemic areas, who engage in outdoor work such as, agricultural workers are at high risk
Malnourished people with impaired immunological status, are also prone to get the disease.
Q. Is it treatable?
A. Prompt treatment of cutaneous Leishmaniosis will reduce the size of the scar and disfiguration. It would prevent the secondary infections and spread of the disease in the community.
Patients with suspected lesions should seek advice from the nearest health institution/ dermatology clinic. Following a complete evaluation by a dermatologist decisions regarding treatment are taken. There are several treatment options. The commonly used methods are cryotheraphy, injection of Sodium stiboglucanate or application of hypertonic sodium chloride solution to the lesion. .
The procedure of cryotherapy is painful and treatment include several sessions up to four months. Treatment with Sodium stiboglucanate or with hypertonic sodium chloride solution also require several sessions.
Q. Some basic hygienic rules and your message to those living in high risk areas?
A. Apapule, nodule or a non-healing ulcer on the skin following a sandfly bite may be a sign of Leishmaniasis. It is important to get examined at the nearest hospital
Timely and complete treatment is important for cure and to prevent disfiguration
Regular cleaning of houses, opening of windows to allow sunlight and air circulation would limit the resting places of sandflies
Old buildings, animal shelters and mud huts may have cracks and holes. Plastering of the cracks and holes on walls would help reduce breeding sites of the sandfly
The outdoor environment should be kept clean, and the compound cleared of unnecessary vegetation
Avoid collection of garbage and decaying items near houses and control of rodent habitats
Clean animal shelters regularly and keep them dry
Avoid outdoor activities as much as possible, especially from dusk to dawn. Try to avoid outdoor sleeping
Wear protective clothing ( long sleeved shirts, ankle length pants) that cover the whole body when working outdoors, in animal shelters
Apply insect repellent to uncovered skin and under the sleeves and pant legs. Re application of repellants need to be done as they are effective only for 4-6 hours
Use bed nets impregnated with pyrethroid - containing insecticides if available. Normal bed nets do not prevent sandfly entry as they are tiny insects.