Jacobs Journal of Gastroenterology and Hepatology

Visceral Leishmaniasis; An Autobiography of the most important Vector-borne Disease

*Alaka Hassan Olayemi
Department Of Microbiology, Obafemi Awolowo University, IleIfe Osun State, Nigeria

*Corresponding Author:
Alaka Hassan Olayemi
Department Of Microbiology, Obafemi Awolowo University, IleIfe Osun State, Nigeria
Email:alakahassan41359@gmail.com

Published on: 2019-04-30

Abstract

Visceral leishmaniasis, also known as kala-azar is undoubtedly one of the most important vector-borne diseases in the world. Visceral leishmaniasis (VL) affects the liver, spleen and the bone marrow of the human host. It is characterised by anemia (deficiency in the number or quality of red blood cells), fever, enlarged liver, enlarged spleen and significant weight loss. The disease is often fatal if left untreated. The disease, kala-azar, was first described in the mid18th century in Africa and India. William Leishman, a British Army doctor, identified ovoid bodies in a spleen sample from a British soldier who had been experiencing bouts of fever, anemia, muscle wasting and an enlarged spleen. He published his findings in 1903. Charles Donovan recognized these symptoms in other patients and also identified these same bodies. They were subsequently called Leishman-Donovan bodies after the two men [1].

Keywords

Introduction

Visceral leishmaniasis, also known as kala-azar is undoubtedly one of the most important vector-borne diseases in the world. Visceral leishmaniasis (VL) affects the liver, spleen and the bone marrow of the human host. It is characterised by anemia (deficiency in the number or quality of red blood cells), fever, enlarged liver, enlarged spleen and significant weight loss. The disease is often fatal if left untreated. The disease, kala-azar, was first described in the mid18th century in Africa and India. William Leishman, a British Army doctor, identified ovoid bodies in a spleen sample from a British soldier who had been experiencing bouts of fever, anemia, muscle wasting and an enlarged spleen. He published his findings in 1903. Charles Donovan recognized these symptoms in other patients and also identified these same bodies. They were subsequently called Leishman-Donovan bodies after the two men [1].

Visceral leishmaniasis is caused by two species of the Leishmania parasite - Leishmania donovani and Leishmania infantum. They are not usually found in the same areas. Leishmania is a digenetic single-celled organism i.e., it exists in two forms. In the human host, it is an obligate intracellular amastigote and in the sand fly vector, it is a flagellated promastigote. Transmission is via the bite of a female phlebotomine sand fly. Amastigotes can be transmitted between humans by the sharing of hypodermic needles and syringes or by contaminated blood transfusion. These are avoidable accidents. Less easily avoided is the natural transmission of Leishmania species by sand flies which are the only proven transmitter or vectors of the disease-causing parasites. Specifically, the vectors are phlebotomine sand flies (Phlebotomus duboscqi), which are small insects (up to 4mm long) recognisable by their hopping flight and half-closed pair of wings when resting. Male sand flies are not vectors. Only the adult female has the proboscis that permits blood feeding, during which the amastigote parasites are taken up from the infected skin or blood of a mammalian host and then passed on to another host during a later blood meal. Not all sand flies have females that are competent vectors [2]. Visceral Leishmaniasis is broadly distributed throughout the tropics, along with the presence of sand flies that are competent for transmitting Leishmanis donovani and Leishmania infantum. In 2014, the vast majority, 90% of the new cases reported to WHO occurred in just six countries - Brazil, Ethiopia, Somalia, Sudan, South Sudan and India. There are a number of online resources that collate data from specific regions. This makes it possible to look at changes to VL cases numbers through time. For example, in 2008, 1090 VL cases were reported in the Middle East. In 2012, the WHO conducted a large scale review of the worldwide incidence of VL, where the data was available - there was a reported 9936 new VL cases in the Eastern Mediterranean region alone, with most of these found in Sudan and South Sudan. More recently, in 2015, there were 3456 cases of VL reported in the WHO America’s region, most of them in Brazil [1]. 

Status of endemicity of visceral leishmaniasis worldwide (WHO, 2016)

In 2017, 20792 out of 22145 (94%) new cases reported to WHO occurred in seven countries: Brazil, Ethiopia, India, Kenya, Somalia, South Sudan and Sudan. In the WHO South-East Asia Region, the kala-azar elimination programme is progressing satisfactorily and countries such as Bangladesh that reported more than 9000 cases in 2006 reported 253 and 192 new cases in 2016 and 2017 respectively. Diagnosis of visceral leishmaniasis is carried out by combining clinical signs with parasitological or serological tests (mainly rapid diagnostic tests). A robust surveillance is an essential component in control or elimination programmes. Two forms of surveillance - passive and active case detection or searches - are mainly applied in disease control programmes. Routine surveillance is usually too insensitive to accurately access any changes in the prevalence of VL, with most case detection being passive. Also, it is not always possible to estimate human inoculation rate of parasites by the sand fly vectors because most sand fly surveys use light and sticky trap but do not target hostseeking female flies and the reports often mention only the relative abundance of species without distinguishing males from females[4].

Socioeconomic conditions, malnutrition, population mobility, environmental changes and poverty have been highlighted as major risk factors of visceral leishmaniasis. Poverty increases the risk for VL. Poor housing and domestic sanitary conditions (such as lack of waste management or open sewerage) may increase sand fly breeding and resting sites, as well as their access to humans. Sand flies are attracted to crowded housing as this provides a good source of blood-meals. Human behaviors such as sleeping outside or on the ground may increase the risk. As per a survey which was done across various patients in four countries including India and Bangladesh, it was found that 40-50% of communities or the patients interviewed said that they have expended more than 20% of their household income on a single episode of VL.

Figure 1: Status of endemicity of visceral leishmaniasis worldwide (WHO, 2016) [3].

In conclusion, more awareness on visceral leishmaniasis should be created and health workers should be trained more on VL. It is essential to know the specific sets of symptoms, treatment, and interventions in each endemic region. It is surely more important to understand what determines the distribution of parasite of importance for treatment and control within each region.

References

1. WHO, 2014; https://www.who.int/en/news-room/ fact-sheets/detail/leishmaniasis.

2. Ready PD. Biology of Phlebotomine sand flies as vectors of disease agents. Annual Review of Entomology 2013; 58: 227-250.

3. WHO, 2016; https://www.who.int/leishmaniasis/ burden/en/.

4. Ready PD. Epidemiology of Visceral leishmaniasis. Clinical Epidemiology 2014; 6: 147-154.