The use of DNA hybridization for the detection of Leishmania aethiopica in naturally infected sandfly vectors

Prevalence and environmental determinants of cutaneous leishmaniasis in rural communities in Tigray, northern Ethiopia

Background

In Ethiopia guidelines for diagnoses and treatment of leishmaniases are available, but only a few hundred people are diagnosed and receive treatment. A field study has been carried out to determine the status and environmental determinants of cutaneous leishmaniasis (CL) and assess the degree of awareness of the rural communities in affected areas in Tigray, northern Ethiopia.

Methodology / Principal findings

Following a reconnaissance survey that identified endemic foci, a cross sectional door-to-door survey was conducted in 2009 in five rural communities around the towns of Adigrat and Hagereselam in Tigray. In total 9,622 residents of 1,721 households were clinically screened and household heads interviewed regarding the determinants of infection. The χ² test and logistic regression were used to determine differences in prevalence between localities, age and sex, and to identify environmental determinants of infection.

The overall prevalence of localized CL was 2.3% (highest 4.7%), with marked inter-village differences. Another 20.9% had scars from previous infections. While risk was sex-independent, prevalence was significantly higher in the 0–9 (4.5%) and 10–19 (2.5%) age groups and predominantly involved the face (82.1%) and upper limbs (13.1%). Nearly 11% of the households had one or more cases of CL and this was associated with proximity to hyrax habitats. All interviewees were knowledgeable about the lesions but ignorant of the disease’s mode of transmission and its association with hyraxes.

Conclusions

The study established that CL is an important public health problem in the study communities, and has been so for a while, as demonstrated by the widespread presence of scars. CL in Tigray appeared to be predominantly of zoonotic nature, mainly transmitted in peri-domestic habitats in proximity to hyrax habitats. Integrated interventions, including awareness creation, are highly recommended.

Cutaneous leishmaniasis (CL) is a skin infection, transmitted by sandflies. It is most common in Ethiopia, but so far only a few hundred people have received treatment. Five rural villages in Tigray Region, in the north of Ethiopia, were visited to assess the status and determinants of CL. In a door-to-door survey 9,622 residents of 1,721 households were examined and interviewed. A total of 222 had active lesions, an average prevalence of 2.3% CL. Children (up to 9 years old) and teenagers (age 10–19) were more affected than other groups. Most active lesions were found in the face and on arms. Almost 11% of the households had one or more cases of CL and this was associated with proximity to habitats of hyrax, intermediate hosts of the disease. A total of 2009 people (20.9%) showed scars from earlier infections. The findings show how widespread the disease is in the north of Ethiopia and provide some first insights into the environmental factors that influence transmission.

Detection and quantification of Leishmania infantum in naturally and experimentally infected animal samples

Leishmania infantum is one of the causative agents of visceral leishmaniasis (VL). VL is the most severe form of leishmaniasis and can be fatal if it is not properly treated. Although several PCR works are intended to detect L. infantum, in silico analysis of available primers and/or primer-probes reveals potential cross species amplification. Here, a TaqMan-based quantitative real time PCR (qPCR) assay was developed for specific detection and quantitation of L. infantum in tissue samples from experimentally or naturally infected animals, mice or dogs, respectively. For this assay, primers and probes were designed for the kinetoplast minicircle DNA of L. infantum. The qPCR assay achieved a detection limit of 0.01pg of parasite DNA, and allowed specific amplification of L. infantum in both asymptomatic and symptomatic naturally infected dogs with inter-assay variation coefficients between 0.05-0.11. There was no cross amplification with dog DNA or with L. braziliensis, L. donovani, L. major, L. tropica or Trypanosoma cruzi. In addition, our assay detected a significantly higher parasite load in symptomatic than in the asymptomatic animals (p<0.0001). We believe this approach will be a valuable tool for the specific detection of L. infantum in regions of sympatric transmission of VL-causing parasites.

Serial quantitative PCR assay for detection, species discrimination, and quantification of Leishmania spp. in human samples

The Leishmania species cause a variety of human disease syndromes. Methods for diagnosis and species differentiation are insensitive and many require invasive sampling. Although quantitative PCR (qPCR) methods are reported for leishmania detection, no systematic method to quantify parasites and determine the species in clinical specimens is established. We developed a serial qPCR strategy to identify and rapidly differentiate Leishmania species and quantify parasites in clinical or environmental specimens. SYBR green qPCR is mainly employed, with corresponding TaqMan assays for validation. The screening primers recognize kinetoplast minicircle DNA of all Leishmania species. Species identification employs further qPCR set(s) individualized for geographic regions, combining species-discriminating probes with melt curve analysis. The assay was sufficient to detect Leishmania parasites, make species determinations, and quantify Leishmania spp. in sera, cutaneous biopsy specimens, or cultured isolates from subjects from Bangladesh or Brazil with different forms of leishmaniasis. The multicopy kinetoplast DNA (kDNA) probes were the most sensitive and useful for quantification based on promastigote standard curves. To test their validity for quantification, kDNA copy numbers were compared between Leishmania species, isolates, and life stages using qPCR. Maxicircle and minicircle copy numbers differed up to 6-fold between Leishmania species, but the differences were smaller between strains of the same species. Amastigote and promastigote leishmania life stages retained similar numbers of kDNA maxi- or minicircles. Thus, serial qPCR is useful for leishmania detection and species determination and for absolute quantification when compared to a standard curve from the same Leishmania species.

A zoonotic focus of cutaneous leishmaniasis in Addis Ababa, Ethiopia

BACKGROUND

Cutaneous leishmaniasis (CL) is endemic in the highlands of Ethiopia, and almost always caused by Leishmania aethiopica. Hitherto, Addis Ababa (the capital city of Ethiopia) was not considered endemic for CL, mainly due to absence of epidemiological and field ecological studies. This report summarizes the preliminary epidemiological investigation that proved the existence of active transmission in southeastern Addis Ababa.

RESULTS

Active case finding surveys were conducted in 3 localities, Saris, Kality, and Akaki, which are found in and around Bulbula-Akaki river gorges. During the surveys conducted in January 2005 - May 2006, a total of 35 cases with 9 active and 26 healed skin lesions were identified. Eighteen of the cases (51.4%) were found in Saris; while 10 (28.6%) and 7 (20%) cases were from Kality and Akaki respectively.Ten colonies of rock hyraxes (Heterohyrax brucei) were identified in the vicinities of the 3 localities. Three of the 48 hyraxes (6.3%) trapped from the surroundings harbored natural infections of Leishmania aethiopica. Confirmation of the Leishmania species of the 3 isolates was achieved by PCR amplification and RFLP analysis of the ribosomal DNA internal transcribed spacer (ITS) sequences. Based on sandfly species composition and proximity of resting sites to human settlements, Phlebotomus longipes is circumstantially proven to be the vector of CL in south east Addis Ababa.

CONCLUSION

The study proves the existence of isolated zoonotic foci of CL in south eastern Addis Ababa, with P. longipes as the likely vector and H. brucei as the natural reservoir host.

Use of enzyme-linked immunosorbent assay for detection of natural leishmania infections in phlebotomine sand flies from southeastern Turkey

In total, 320 phelebotomine sand flies from Alibozlu (Osmaniye), Kizyusuflu (Osmaniye), and Sanliurfa in southeastern Turkey were tested for the detection and identification of Leishmania in vector sand flies by enzyme-linked immunosorbent assay with species-specific monoclonal antibodies. We used monoclonal antibodies that recognize both Leishmania tropica and Leishmania major, and a monoclonal antibody specific only to L. tropica. Phosphate-buffered saline and monoclonal antibody M2 recognizing Leishmania amazonensis were used as controls. Infection rates of sand flies were 0.9% in Alibozlu, 0% Kizyusuflu, and 3.6% in Sanliurfa. Positive sand flies were identified as Phlebotomus sergenti Parrot and Phlebotomus major syriacus Adler & Theodor.

The isolation of Leishmania tropica and L. aethiopica from Phlebotomus (Paraphlebotomus) species (Diptera: Psychodidae) in the Awash Valley, northeastern Ethiopia

In a survey of Leishmania infections in phlebotomine sandflies in a highly suspected focus of leishmaniasis in the Awash Valley (northeastern Ethiopia) between January 1994 and August 1997, a total of 3307 females of 11 Phlebotomus species (P. orientalis, P. fantalensis, P. saevus, P. sergenti, P. gemetchi, P. alexandri, P. bergeroti, P. duboscqi, P. arabicus, P. martini, and P. rodhaini) were dissected. Promastigotes were detected in 17 females of three species (11 P. saevus, 4 P. sergenti and 2 P. arabicus). Of these, only two P. saevus (one from Upper Awash and one from Middle Awash) and three P. sergenti (from Upper Awash) positives were successfully isolated in culture and were typed by isoenzyme analysis. Four isolates (two each from P. saevus and P. sergenti) were identified as new zymodemes (Z) of L. tropica and one isolate from P. sergenti was typed as a new zymodeme of L. aethiopica. This is the first finding of natural infections of P. saevus and P. arabicus and the first evidence for the former to be a vector of L. tropica. This is also the first time P. sergenti has been implicated in L. tropica transmission in Ethiopia; the isolation of L. aethiopica from a Paraphlebotomus species (P. sergenti) is also a new record. The possible presence of human cutaneous leishmaniasis (L. tropica and L. aethiopica), and wild reservoir host(s) of the parasites, especially rock hyrax (Procavia capensis) in the Upper and Middle Awash Valley remain to be determined.

Species-specific detection of Leishmania in sandflies using an enzyme-linked immunosorbent assay

A direct enzyme-linked immunosorbent assay (ELISA) using species-specific monoclonal antibodies was developed for the detection and identification of Leishmania in sandflies. A titration of mock-infected Phlebotomus papatasi showed that fewer than 2000 L. major promastigotes could be detected. The percentage of infected P. papatasi collected in the field, as determined by dissection, was compared to that revealed by the ELISA. Both methods gave similar results, irrespective of whether the flies were caught by sticky papers or light-traps. The percentage of infected flies determined by either method was also similar in experimentally infected colony reared sandflies. The ELISA can be carried out using multiple species-specific antibodies, and is as accurate as identification of infected sandflies by microscopical examination. The technique should be useful for identifying sandfly species involved in transmitting different species of Leishmania, and for rapid assessment of leishmanial infection rates in endemic regions.

A new sandfly species, Phlebotomus (Larroussius) ashfordi (Diptera, Psychodidae) from Ethiopia, previously confused with P. (L.). aculeatus

The sandfly subgenus Phlebotomus (Larroussius) contains species which transmit parasites causing cutaneous and visceral leishmaniasis in East Africa, including Ethiopia. The Gewasha caves in central Ethiopia harbour a new species (Phlebotomus ashfordi) belonging to the subgenus Larroussius and previously identified as P. (L.) aculeatus Lewis, Minter and Ashford. Although generally similar to P. (L.) aculeatus and P. (L.) elgonensis Ngoka, Madel and Mutinga, the species is distinct in eight male characters and in the female spermatheca. Given its taxonomic affinity to known vectors of cutaneous leishmaniasis and the presence of disease in the Gewasha caves area, the medical importance of this species needs to be assessed.

Detection of cutaneous Leishmania infection in paraffin-embedded skin biopsies using the polymerase chain reaction

In this study the polymerase chain reaction (PCR) with previously developed oligonucleotide primers was used to detect Leishmania aethiopica in paraffin-embedded skin biopsy specimens. The Leishmania-specific 120 base pair fragment of the kinetoplast deoxyribonucleic acid (kDNA) minicircles has been amplified from all parasitologically or histologically confirmed cases of cutaneous leishmaniasis (CL), as demonstrated by gel electrophoresis and hybridization with L. aethiopica kDNA. Control specimens from patients with skin diseases other than CL were all negative. Using PCR, Leishmania were demonstrated in the skin lesions of 7 cases in a group of 40 patients in whom the parasites could not be demonstrated by histopathology or culture in vitro although lesions were clinically suggestive of CL. These data indicate that PCR, carried out on DNA extracted from formalin-fixed and paraffin-embedded tissue specimens, is a valuable method for the diagnosis of CL, especially in chronic cases where the parasite load in the lesion is low.

Vectors of cutaneous leishmaniasis in north-central Venezuela

An entomological survey was undertaken from January 1991 to February 1992 in El Ingenio, Miranda State, Venezuela, an endemic area of cutaneous leishmaniasis: prevalence of 10.7 cases per 100,000 inhabitants. A total of 4863 female sandflies (Phlebotominae) of fourteen species were collected in Shannon traps, then dissected and examined for leishmanial infections. Lutzomyia ovallesi (85.4%) and Lu. gomezi (11.2%) were the predominant anthropophilic species of sandfly. Fifty-one (1.19%) Lu.ovallesi and two (0.47%) Lu.gomezi had natural infection with Leishmania promastigotes. Identification of the parasites was done by using the polymerase chain reaction (PCR) and DNA hybridization. Two isolates from Lu.gomezi and forty-nine from Lu.ovallesi were typed as Leishmania braziliensis and three of the latter reacted with Le.mexicana also. This is the first report of Lu.gomezi with parasites typed as Le.braziliensis. We concluded that Lu.ovallesi is the primary vector of cutaneous leishmaniasis in the north-central area of Venezuela and Lu.gomezi should be regarded as an additional vector.

Leishmaniases of the New World: current concepts and implications for future research

Recent epidemiologic studies indicate that leishmaniasis in the Americas is far more abundant and of greater public health importance than was previously recognized. The disease in the New World is caused by a number of different parasite species that are capable of producing a wide variety of clinical manifestations. The outcome of leishmanial infection in humans is largely dependent on the immune responsiveness of the host and the virulence of the infecting parasite strain. This article reviews current concepts of the clinical forms, immunology, pathology, laboratory diagnosis, and treatment of the disease as well as aspects of its epidemiology and control. Recommendations for future research on the disease and its control are made.

Cutaneous leishmaniasis in south-western Ethiopia: Ocholo revisited

The borough of Ocholo, on the western side of the Ethiopian Rift Valley, is an endemic focus for Leishmania aethiopica infection and has been surveyed thrice between 1987 and 1990. In 1989, 3022 inhabitants (> 95% of the population) were interviewed and examined. The overall prevalence of localized cutaneous leishmaniasis (LCL) was 3.6-4.0%, with a peak value of 8.5% in the 0-10 years old age group. In half of the patients the active disease was estimated to last for 9.6 +/- 6 months; in 10%, it exceeded 3 years. Scars of LCL were present in 34.3% of the residents. Leishmanin skin tests were positive in 54% of 120 school-children without signs of the disease. Therefore, in Ocholo a minimum of 71.6% of the population has been exposed to L. aethiopica infection. Two cases of the diffuse form of cutaneous leishmaniasis were observed. In this highland biotope, Phlebotomus pedifer was found to be the major, and possibly the only, vector for L. aethiopica.