A Review on Biology, Epidemiology and Public Health Significance of Leishmaniasis

Leishmaniasis is a major vector-borne disease caused by obligate intramacrophage protozoa of the genus Leishmania and transmitted by the bite of phlebotomine female sand flies of the genera Phlebotomus and Lutzomyia in the old and new worlds, respectively. Among 20 well-recognized Leishmania species known to infect humans, 18 have zoonotic nature, which include agents of visceral, cutaneous and mucocutaneous forms of the disease in both the old and new worlds. Currently, leishmaniases show a wider geographic distribution and increased global incidence. Environmental, demographic and human behaviors contribute to the changing landscape for zoonotic cutaneous and visceral leishmaniasis. The primary reservoir hosts of Leishmania are sylvatic mammals, such as forest rodents, hyraxes and wild canids and dogs are the most important species among domesticated animals in the epidemiology of this disease. These parasites have two basic life cycle stages: one extracellular stage with in the invertebrate host (female phlebotomine sand fly) and one intracellular stage with in a vertebrate host. Co-infection with HIV intensifies the burden of visceral and cutaneous leishmaniasis by causing severe forms and more difficult to manage. The disease is endemic to Ethiopia and the clinical signs are not pathognomic. The visceral form (kala-azar) may be confused with other similar conditions such as malaria, tropical splenomegaly, schistosomiasis, milliary tuberculosis and brucellosis. Similarly, cutaneous leishmaniasis should be differentiated from disease like tropical ulcers, impetigo and leprosy. There are several methods of laboratory diagnosis of leishmaniasis including parasitological, immunological and molecular. Methods of control are largely limited to destruction of animal reservoirs, treatment of infected humans and management of sand fly populations. Development of an effective vaccine against leishmaniasis has been largely unsuccessful and hinders its prevention.


INTRODUCTION
million people are considered at risk of contracting Leishmaniasis is a major vector-borne metazoonosis in 88 countries [2, 6,7] and the visceral form of the disease disease caused by obligate intramacrophage protozoa is the most severe and is lethal if not treated [7]. of the genus Leishmania [1, 2]. The parasite is of great The primary reservoir hosts of Leishmania species medical and veterinary public health significance for it are sylvatic mammals, such as forest rodents, hyraxes, infects numerous mammal species, including humans.
wild canids and among domesticated animals; dogs are Leishmaniasis is transmitted by the bite of phlebotomine the most important species in the epidemiology of this female sand flies of the genera Phlebotomus and disease. In addition to becoming ill, dogs are reservoir Lutzomyia in the old and new worlds, respectively [3,4].
hosts for L. infantum, one of the two most important The species are widespread on all continents except organisms in human visceral leishmaniasis [8][9][10]. Antarctica [5]. Leishmaniasis is still one of the world's Currently, leishmaniasis has a wider geographical most neglected tropical diseases, affecting largely the distribution pattern than before and it is considered to be poorest of the poor, mainly in developing countries; 350 a growing public health concern for several countries.
leishmaniasis and some 2 million new cases occur yearly The increase in leishmaniasis worldwide incidence is mainly attributed to the increase of several risk factors that are clearly man made and include massive migration, deforestation, urbanization, immunosuppression, malnutrition and treatment failure [11]. Man made changes to the environment, as well as the population movements, may lead to alterations in the range and density of the vectors and reservoirs and consequently may increase human exposure to infected sand flies [1].
In Ethiopia, the disease affects people living in a significant portion of the country. Recurrent epidemics of visceral leishmaniasis (V L) have occurred in Metema and Humera. Following agricultural development in the region a large number of labor migrants from the highlands were moved to the endemic areas in the late 1970 for crop harvesting. This led to out breaks of VL, which resulted in high morbidity and mortality [12]. A recent study investigating risk factors associated with the outbreak in Libo Kemkem identified dog ownership and habitual outdoor-sleeping to be risk factors for infection [13]. The cutaneous form was first described in Ethiopia in 1913 and is common in highland areas of altitude ranging from 1,700 to 2,700 meter above sea level. The majority of cutaneous Leishmaniasis (CL) cases in Ethiopia are caused by L. aethiopica [14].
Leishmaniasis is one of the opportunistic infections that attack HIV-infected individuals. Recently more notice has been taken of Leishmania/HIV co-infection. V L has a mortality rate as high as 100% if left untreated and is spreading in several areas of the world due to increase number of AIDS victims [9]. Leishmania and HIV coinfections have been reported in 35 out of 88 countries in which leishmaniasis are endemic, emerging disease and as  Morphology: The amastigote are small, round to oval, may also act as mechanical vectors [20]. These parasites bodies which measure about 3-5ìm without flagellum but have also been transmitted via blood transfusions in a short flagellum may be seen arising from the kinetosome people and dogs [26] and by trans-placental transmission [2, 4,8,22] and found only in the macrophages of infected in dogs, mice and humans [12]. Rare cases of horizontal vertebrate hosts. They are colorless, have a homogenous transmission have been reported between dogs in the cytoplasm and are surrounded by a pellicle [7,22]. The same household or kennel. In canine leishmaniasis caused promastigote forms are seen in the gut of the sand fly that by L. infantum, the parasites can sometimes be found in the parasite reaches the buccal cavity which becomes the saliva, urine, semen and conjunctival secretions, as well insect vector of the parasite. They are motile, slender as in blood. Venereal transmission has been proven to organisms measuring 10-15ìm in length with a single occur in dogs and other routes of spread might be anterior flagellum [17].
possible [20].  [11]. The burden of VL wild animals or captive wild species including non-human remains unknown worldwide, since several cases are not primates, bush dogs and wolves. Mountain hyraxes are diagnosed [27][28][29]. It has been estimated that there are the most reservoir host in Ethiopia for L. aethiopica approximately half a million new cases of VL annually [12,24]. worldwide, with more than 50,000 associated deaths. More These parasites have two basic life cycle stages: than 90% of VL cases occur in just six countries, namely one extracellular stage with in the invertebrate host India, Nepal, Bangladesh, Sudan, Ethiopia and Brazil [30]. (phlebotomine sand fly) and one intracellular stage within However, it is also an important disease in several other a vertebrate host. The parasites exist in two main East African countries, with an incidence rate of 30,000 morphological forms the amastigotes and promastigotes, cases per year and a mortality rate of 4,000 deaths per year which are found in vertebrate and invertebrate hosts, [31]. Leishmania infantum and L. chagasi cause VL respectively [2, 25]. The promastigotes are then almost exclusively in infants, young children and phagocytosed by the host's macrophages and immunosuppressed. In contrast, L. donovani infects both consequently the parasite evolves into amastigote forms children and adults [32]. During the last two decades, which they reproduce by binary fission. The emergence of resistance to pentavalent antimonial had a multiplication of the parasites occurs inside the huge impact on the epidemiology of leishmaniasis [33][34][35]. macrophages, which are their main targets. The Epidemiology of new world C L is found in Mexico, macrophage lyses and the cycle continue when other Central America and South America-from Northern hosts' phagocytes are being infected [2, 5,26]. In cases of Argentina to Southern Texas and southern Europe. Many VL, all organs, containing macrophages and phagocytes, such patients develop unusual cutaneous manifestations can be infected, especially the lymph nodes, spleen, liver [36]. and bone marrow [17].
Old world C L occurs in Asia, Middle East and Africa. The disease is transmitted indirectly to vertebrate Zoonotic cutaneous leishmaniasis (rural, wet type) is host by the female infected sand fly of the genera caused by L. aethiopica and L. major in most part of the Phlebotomus and Lutzomyia, which are biological vectors Central Asia, Middle East and North Africa and [2, 7, 17]. The female needs a blood meal for egg transmission of infection is maintained in wild production. Hence, like mosquitoes, only the female sand rodent/gerbil colonies. The estimated annual incidence is fly is haematophagous [25]. Some ticks and canine fleas 1-1.5 million cases of C L in the old world over 90% of 0 0 annual cases occur in Afghanistan, Algeria, Iran, Iraq, Environmental Changes: In most endemic regions, Saudi Arabia and Syria [1,27]. The risk of C L may be increased when agricultural projects are launched and irrigation systems extended. These man made ecological changes are accompanied by the intrusion of large numbers of non-immune immigrants into an existing sylvatic cycle of leishmaniasis [12,24]. In foci of cutaneous leishmaniasis caused by L. aethiopica in the highlands of Ethiopia and other places in East Africa, increased human fly contact occurs in villages built on rock hills or river banks, which are the natural habitat of hyraxes (reservoir hosts). Cases have also been reported in and near urban centers, including Addis Ababa [6]. Malnutrition: Poor protein, energy, iron, vitamin A and zinc nutritional status increase the risk that an infection will progress to clinically manifests visceral leishmaniasis. Recent experiments in protein, energy, zinc and iron deficient mice suggest that this effect is mediated primarily through functional failure of the lymph node barrier and increased early visceralization of the parasite. Protein-energy malnutrition has also been associated with an increased risk for mucocutaneous leishmaniasis (M CL), [24,30].

Factors Affecting the Occurrence of Leishmaniasis
Population Movements: Epidemics of both visceral and cutaneous leishmaniasis in both the old and the new world are often associated with migration and the introduction of non-immune people into areas with existing endemic or enzootic transmission cycles. Prediction of such outbreaks depends on the availability of ecological information and on evaluation of development areas before implementation of projects or population movements [4,12]. Seasonal labor movements may also spread the disease, with the return of migrants to non-endemic areas, as appears to have occurred in the highlands of Ethiopia in the 2000s. Behaviour such as sleeping outside under acacia trees and living in houses constructed of grassy material appears to increase risk for the disease [6]. leishmaniasis is characterized by a patchy distribution with discrete transmission foci. This focal distribution of leishmaniasis transmission sites is due to micro ecological conditions that affect the vector, the parasite and the reservoir host [4,6]. Environmental changes that can affect the incidence of leishmaniasis include urbanization, domestication of the transmission cycle and the incursion of agricultural farms and settlements into forested areas [6,37,38] Climate Change: Leishmaniasis is a climate-sensitive disease, occupying a characteristic climate space that is strongly affected by changes in rainfall, atmospheric temperature and humidity [24]. Global warming and land degradation together are expected to affect the epidemiology of leishmaniasis by a number of mechanisms. First, changes in temperature, rainfall and humidity can have strong effects on the ecology of vectors and reservoir hosts by altering their distribution and influencing their survival and population sizes [32]. Secondly, drought, famine and flood resulting from changes in climate conditions could lead to massive displacement and migration of people to areas with transmission of leishmaniasis and poor nutrition could compromise their immunity [6,11,30].
HIV co-Infection: It is the fifth opportunistic diseases. The human immunodeficiency virus (HIV) /acquired immunodeficiency syndrome-pandemic had also an impact on the epidemiology of VL [16,39]. Due to deficient diagnostic capacities and surveillance, the burden of VL-HIV-co-infection in Africa remains grossly unknown; however HIV-co-infection is emerging in this continent. In North West Ethiopia up to 30% of VL cases are HIV/co-infected [32].
Vector Distribution: The Vector of Leishmania is transmitted by phlebotomine female sand flies. These sand flies are widely distributed in the tropics and other warm mainland areas and extend northwards to latitudes in the region of 50 N. o Species in three genera, Phlebotomus, Lutzomyia and Sergentomyia, suck blood from vertebrates, only the former two transmit disease to man [27]. There are over 50 species of genus Phlebotomus in the old world and genus Lutzomyia in the new world that transmit disease to man [19].

Clinical Signs in Humans and Animals: The incubation
(pinnae), eyelids or lips. Systemic cases in cats have period is difficult to evaluate precisely. It is generally involved the liver, spleen, lymph nodes and kidney [20]. 2-6 months, but can range from 10 days to many years.
Horses, mules and donkeys may develop skin lesions, The onset of disease may be sudden or gradual; the particularly on the head, ears, neck, legs and scrotum. The overall condition of the patient is usually good in the most common lesions are solitary or multiple papules or early stages [30]. Leishmaniases are characterized by a nodules, which are often ulcerated, disseminated skin spectrum of clinical manifestations: ulcerative skin lesions disease has been [42]. Skin lesions were the only clinical which they develop at the site of the sand fly bite signs reported in a sheep, goat and calf in Africa. The localized cutaneous leishmaniasis, diffuse cutaneous goat also had enlarged lymph nodes. Captive wild species leishmaniasis, mucosal leishmaniasis and disseminated and wild animals: Infections seem to be inapparent in visceral leishmaniasis [4,12,27]. The most common many infected wild animals. In rodents, may cause symptoms of visceral leishmaniasis are a prolonged swellings with hair loss or ulcers. This animal later undulant fever, weight loss, decreased appetite, signs of developed ascites and cervical edema and eventually died anemia and abdominal distension with splenomegaly and [20]. hepatomegaly [1]. Other symptoms may include coughing, chronic diarrhea, darkening of the skin, lymphadenopathy Diagnostic Techniques and in many cases, signs of chronic kidney disease. Post-Conventional Parasite Detection Techniques: kala azar dermal leishmaniasis (PKDL) occurs after The confirmatory diagnosis of leishmaniasis relies on recovery in some cases of visceral leishmaniasis [20,40].
either the microscopical demonstration of Leishmania The first sign of an infection is a small erythema. The amastigotes in the relevant tissues aspirates or biopsies erythema develops into a papule then into a nodule and such as bone marrow, spleen, lymph nodes, liver and skin the nodule ulcerates over a period of two weeks to six slit smears. The amastigotes are readily seen in smears or months to become a lesion that is characteristic of the CL touch preparations of infected tissue stained with [20, 41]. Mucocutaneous leishmaniasis tends to occur 1 to Giemsa's stain [22,40]. Animal inoculation and Culture: 5 years after cutaneous leishmaniasis caused by these Leishmania spp. can also be cultured. However, each organisms has healed, but it can also be seen while skin species will grow only in certain media and some species lesions are still present. The initial signs are erythema and can be difficult to isolate. Novy-MacNeil-Nicole medium, ulcerations at the nares, followed by destructive Grace's medium and Schneider's Drosophila medium inflammation that can spread to involve the nasal septum might be used initially. Animal inoculation into hamsters and in some cases, the pharynx or larynx. Frequent nose may also be valuable, especially with contaminated bleeds can be an early sign. The inflammation may material [43,44]. perforate the nasal septum, cause severe disfigurement of the face and block the pharynx or larynx. In some cases, Immunological Methods of Diagnosis: The indirect the genitalia may also be involved. Mucocutaneous fluorescent antibody (IFA) test is one of the commonly leishmaniasis does not heal spontaneously [20].
used tests for anti leishmanial antibody detection using Both visceral and cutaneous manifestations may be fixed promastigotes. The test is based on detecting found simultaneously in dogs; unlike humans, separate antibodies, which are demonstrated in the very early cutaneous and visceral syndromes are not seen. In stages of infection and are undetectable six to nine symptomatic cases, common visceral signs include months after cure. The lower sensitivity of the tests can lethargy, weight loss, a decreased appetite, anemia, be overcome by using Leishmania amastigotes as the splenomegaly and local or generalized lymphadenopathy.
antigen instead of the promastigotes. The direct Bleeding disorders including epistaxis and hematuria can fluorescence test is more useful in the diagnosis of CL, also be seen [42]. Chronic renal disease is common in MCL  It is cheap and simple to perform making it ideal for both Localized nodules, papules and chronic crusted or field and laboratory use. DAT in various studies has been ulcerated lesions are most often found on the nose, ears found to be 91-100 per cent sensitive and 72-100 per cent specific [1, 12,43,[45][46][47]. Study was conducted in 2006-Differential Diagnosis: The differential diagnosis of V L 2007 in Humera investigating the accuracy of the rK39 includes other tropical and infectious diseases that cause rapid diagnostic test. Sensitivity of the rK39 RDT was fever or organomegaly (e.g., typhoid fever, miliary found to be 84%, which was lower than that found for tuberculosis, brucellosis, histoplasmosis, malaria, tropical DAT (94%). However, specificity of the rK39 rapid splenomegaly syndrome and schistosomiasis) as well as diagnostic test was higher than that of DAT, at 99%, diseases such as leukemia and lymphoma. PKDL should compared to 92%, respectively. Sensitivity was also be differentiated from syphilis and leprosy [6]. CL is disaggregated by HIV-positive and HIV-negative frequently confused with tropical, traumatic and patients [48]. Enzyme Linked Immunosorbent Assay venousstasis ulcers, foreign-body reactions, (ELISA): ELISA is a valuable tool and one of the most superinfected insect bites, myiasis, impetigo, fungal sensitive tests for the serodiagnosis of V L. The test is infections [46]. useful for laboratory analysis or field applications and to screen a large number of samples at a rapid pace. Research into new antileishmanial drugs such as molecular techniques such as PCR have been developed miltefosine, paromycin and sitamaquine may expand for the detection of Leishmania parasites in clinical treatment options in the future [30]. Data on miltefosine samples [40,49]. Amongst the molecular methods used for use in East Africa are restricted to one study that was clinical diagnosis, PCR has been proved to be most conducted in northern Ethiopia, in which it was found to sensitive and specific technique. The specificity of the be as safe and effective as sodium stibogluconate in HIV-PCR can be adapted to specific needs by targeting negative patients and safer, but less effective, in HIV coconserved region of the gene. Gene amplification through infected patients [16,51]. Oral sitamaquine, an 8the PCR has several advantages compared to traditional aminoquinoline derivative, has been shown to have techniques, because of its extremely high sensitivity, clinically significant antileishmanial activity. This effective rapidity and the ability to be performed with a broad range oral anti leishmanial compound has been tested in Kenya, of clinical specimens [43,47]. Several studies have Brazil and India [17]. Patients should be properly hydrated reported that PCR assay could detect parasitaemia a and given nutritional supplements. Severe anemia should few weeks before the appearance of any clinical be corrected with blood transfusions and concomitant signs [22]. Also a modified form of PCR such as nested infections should be treated with appropriate anti-PCR has proved its predictive values in diagnosis of infective agents. Successful therapy improves the general PKDL. In a study, nested PCR was positive in 27 of 29 condition, resolves fever and causes regression of (93%) samples while only 20 of 29 (69%) samples were splenomegaly and recovery of blood counts towards positive in the primary PCR assay [22,40,50]. The real-normal [6]. time PCR is used qualitatively and quantitatively, as the Treatment can produce clinical improvement, fluorescence is directly proportional to the number of although it may not eliminate the parasite in animals. amplicons, or in other words, the parasite load in the Pentavalent antimonials are often used for treatment given specimen. The multiplex PCR can be used where they are available. Other drugs used, such whenever, double or mixed infections are suspected as in allpurinol, amphotericin B, or second line drugs may also AIDS patients [6,22]. be employed, either alone or in combination. Allopurinol leishmaniasis depending upon the form of the disease.
the 1940's but are complicated by adverse side effects, has been used as a maintenance drug to prevent relapses. transmission habitats. A number of control methods are The prognosis is poorer in dogs that are severely ill and available, including chemicals, environmental management animals with kidney disease [20]. and personal protection [6,26]. Health education is a core Since antileishmanial vaccines are still being element in implementation of any disease prevention and developed, the current control strategies for control programme. Multidisciplinary working groups leishmaniasis rely on case management (case detection should be established [6,12]. and treatment), vector and reservoir control. Attention has been mainly focused on prevention strategies of Disease Status in Ethiopia: Economic impact of the VL, the form with the highest fatality rate. disease in Ethiopia is not only limited to high cost of Nevertheless, prevention strategies should be also treatment, but also time lost during hospitalization. The considered for CL, which is also a major burden for disease affects the rural poor community and usually certain areas, with serious psychosocial effects [25].
outbreak occurs during harvesting seasons [13]. Its The integrated analysis of parasite genetics, parasite prevalence is steadily rising in northern Ethiopia posing virulence factors, host immune responses, host genetics, a public health challenge in the region [53]. The MoH as well as socioeconomic and environmental risk factors estimates the annual burden of VL to be between 4,500 will provide a better understanding of the interplay and 5,000 cases. While there is currently no reliable between these different factors and the risk of developing estimate of the prevalence of CL, it has been estimated the disease [ Gelana (Sidamo) and Genale (Bale) river basins. Recently Active case detection, surveillance and effective a devastating epidemic occurred in Humera with an treatment, accompanied by measures for preventing estimated annual incidence of 1,500-2,000 cases. Due to reinfection, depending on the coverage achieved, should high mortality, occurrence of epidemics and high reduce or eliminate the parasite load and reduce incidence of the disease in 15-45 age group leishmaniasis transmission. The use of insecticide-treated bed nets and has become one of the leading health problems in Ethiopia other materials by patients with kala-azar and PKDL or [12,24]. with chronic L. tropica skin lesions may also decrease the The north-western VL focus in Ethiopia covers the likelihood that sandflies will feed on infected individuals Semi-arid Metema and Humera plains in Tigray and [6].The elimination of stray and feral dogs is justified for Amhara regional states bordering Sudan. A marked many reasons connected with health, the environment increase occurred during the 1970s when migrants from and conservation. Before control activities begin, the the non-endemic highlands began to arrive in the area to distribution and frequency of the infection in dogs should harvest crops on the large-scale agricultural schemes be determined. Mass screening of domestic dogs is introduced at the time. In 2005, an outbreak of VL in Libo usually done by serological examination (ELISA, IFAT).
Kemkem woreda, a highland area of Amihara regional All symptomatic or seropositive dogs should be state, was identified. By 2007, around 2,450 primary cases eliminated [6,52]. Control of hyraxes around villages may and 120 deaths had been reported since the outbreak reduce the transmission of East African cutaneous began in 2003 [13]. The north-western VL focus in leishmaniasis caused by L. aethiopica. Elimination of Ethiopia has the highest known VL/HIV co-infection rate hyraxes within 1 km of settlements is thought to be in the world. Approximately 30% of VL patients are effective in reducing transmission [26]. estimated to have HIV [16]. The south west foci include The aim of a vector control program is to reduce or the Omo plains, Aba Roba plains and Weyto River Valley interrupt transmission of disease. An effective strategy in Southern Nations and Nationalities People's Region-all for reducing human leishmaniasis is to control sandfly areas of lowland savannah with low rainfall. The lower vectors, especially in domestic and peridomestic Omo plains are the oldest known VL focus in Ethiopia. The other main focus in the southwest occurs in the lower a growing public health concern for several countries course of the Rift Valley, most notably the Segen (Aba including Ethiopia and this is mainly due to risk factors Roba focus) and Weyto valleys in the drainage basin of such as environmental, demographic and human behavior the Chew Bahir Lake, near Konso woreda. The Aba Roba contribute to the changing landscape of leishmaniasis for focus has a particularly high VL endemicity and high zoonotic cutaneous and visceral leishmaniasis. The population immunity, with 36.4% testing positive with the disease is public health significance in Ethiopia and both leishmanin skin test [24].
VL and CL are endemic. HIV/AIDS co-infection VL focus CL occurs in highlands of Ethiopia. Transmission in Ethiopia has the highest known VL/HIV co-infection occurs in Cuttaber (Dessie), Aleku (Wellega) and Ochollo rate in the world. Taking into consideration the lack of a (Gemu Gofa). In Ochollo the overall prevalence of commercially available vaccine, the lack of access to localized CL was 3.6-4.0%, with a peak value of 8.55 in the efficient drug therapy mainly in the developing countries, 0-10 years old age group. Sporadic cases of CL have been the limited local resources of the affected countries, it is diagnosed from many localities in the northern, central concluded that elimination of the disease is still a and southern high lands of Ethiopia. CL transmission in challenge for the international health community. Priority Ethiopia is zoonotic, with the rock hyrax acting as the should be given to the establishment of control programs main reservoir [12]. Cutaneous form has been extensively and governments should take the lion share to empower studied in the western highlands and lake areas of the Rift and support concerned institutions to address control Valley. The main areas of transmission include the programs. Destroy the breeding and resting sites of the Ochollo focus in the Rift Valley escarpment above Lake vector, control of hyraxes and rodents in the proximity of Abaya, the Kutaber area in the eastern Ethiopian plateau human dwellings should also be implemented. Policy near Dessie, the Aleku area of Wollega zone, the south-should be formulated to control leishmaniasis in the west highlands of Bale and Sidamo and the Sebeta area direction of to eliminate stray and feral dogs. Extensive near Addis Ababa [55].
research in epidemiology of leishmaniasis should also be

CONCLUSION AND RECOMMENDATIONS
Leishmaniasis is caused by a protozoan parasite. The parasite is transmitted from one host to another through 1. Zavitsanou, A., C. Koutis and F. Babatsikou, 2008. the bites of female sandfly and with some exceptions, the Leishmaniasis: an overlooked public health concern. leishmaniases are zoonoses and the human infection is