Post Kala-azar Dermal Leishmaniasis

Post kala-azar dermal leishmaniasis (PKDL) is a neglected tropical disease, which has got the attention in recent times after the London Declaration on “Neglected Tropical Diseases” in 2012 set a target of 2020 to eliminate visceral leishmaniasis (VL) as a public health problem.[1,2] Understanding the fact that PKDL is the interepidemic reservoir of VL, this is needless to say that all efforts of elimination of VL would go in vain if PKDL is not simultaneously eliminated.[3] The symposium on PKDL is planned at a time when we are approaching the deadline for the target.

It has happened in the past that similar deadlines with respect to target, were missed. Government of India, Bangladesh, and Nepal had worked towards the elimination of kala-azar by 2015,[4] but unfortunately it had not culminated in success. Understandably, the success of any public health program not only depends on the management of the particular disease but to a holistic approach to the understanding of the disease involving all the stakeholders, including governmental and nongovernmental agencies, public health personnel, clinicians, microbiologists, and basic scientists.

Keeping these aspects in perspective, the symposium is planned in two sections comprising of “Understanding and Diagnosing Post Kala-azar Dermal Leishmaniasis” and “Epidemiology, Clinical features, and Management of PKDL”.

PKDL is an enigmatic disease with lots of lacunae in our knowledge as to why it develops only in 5%–10% of cured VL patients in the Indian subcontinent and over 60% of those in eastern Africa; how the viscerotropic agent Leishmania donovani evades the immunity and finds shelter in the dermis; why the Sudanese variant resolves spontaneously, whereas the Indian variant requires treatment.[5] Whether this is contributed by the differential uptake of the parasite by the monocyte/macrophage, processing and presentation of the opsonized parasite to the T-cells, the response of T-cells towards Th1 or Th2 cytokines, which can favor the survival of the parasite in the host, or any other factor(s) playing role are the focus of research. Basic scientists are working relentlessly to come up with facts and figures and it is like joining the jig-saw puzzle to get a complete picture. Chatterjee et al. have delved into the topic to give a comprehensive overview of the immunopathogenesis of PKDL.

Just like pathogenesis, the pathology of PKDL is also full of unknown domains. Diagnosing PKDL is a task that is challenging and with the understanding of the pathogenesis, newer diagnostic tools are evolving. Nevertheless, histopathology of the lesion remains the backbone for any dermatologist, and dermatopathologists have researched overtime to gain insight of the cellular composition and the pattern of infiltrate that can serve as tell-tale signs of PKDL. Ramesh et al. have elaborated the histology and immunohistochemistry of PKDL with important clues to differentiate it from leprosy and highlighting the differences among the macular and nodular lesions, and Indian and Sudanese PKDL.

In spite of all the efforts, histology has its own set of unavoidable limitations and confirmation of diagnosis cannot always be relied on histological features. The demonstration of anti-leishmanial antibodies (serology) and the detection of parasite DNA (molecular diagnoses) are the cornerstones of newer diagnostic tools.[6] The sensitivity and specificity of the newer tools are much higher than histology, but the search for better diagnostic methods are continuing keeping in mind the affordability and accessibility of these newer tools in the field-setting. Salotra et al. have reviewed the pros and cons of these newer tools, and they have provided an insight on the applicability of each of these tools in the diagnosis of PKDL.

Knowledge of PKDL would be incomplete without the understanding of the spread and magnitude of the PKDL as well as VL. Though VL has a widespread distribution in 47 countries (predominantly China, India, central Asia, East Africa, the Mediterranean basin, and Brazil); PKDL is limited to two major geographical pockets (Indian subcontinent and eastern Africa).[6] The role of the environment, agent (L. donovani), and vector (sandfly) are to be explored, and this has been elucidated by Ghosh et al. in the chapter on the epidemiology of the disease.

PKDL has got diverse clinical manifestations, which range from hypopigmented lesions to papulo-plaques and even nodules. PKDL is also a great mimicker of another neglected disease, leprosy, which incidentally has got similar geographic distribution. The high index of suspicion aided by some subtle clinical clues helps in reaching a clinical diagnosis. Involvement of muzzle-areas of mouth, sparing of vault of axillae and groin, and photosensitivity are few of such tell-tale signs.[6] The article on clinical features by Kumar et al. elaborates on the typical and atypical clinical features and discusses the differential diagnosis along with it.

The ultimate aim of knowing everything about PKDL is to treat the patients. The treatment has evolved over time and the search for better agents continues. There are many hurdles in the management of PKDL, namely the absence of end-point of therapy, lack of standard therapeutic regime, the emergence of resistance to the drugs, side-effects and the cost of the therapy, and most importantly the reluctance of the patients to seek treatment. The article by Datta et al. is a systematic review of the effectiveness and side-effects of all the drugs in use along with the future prospect of treatment.

We are looking forward towards the success of the elimination of kala-azar and its reservoir, PKDL and at the same time, we have to keep in mind that elimination is a public health goal of having an annual incidence of VL to less than one per 10,000 population at district or sub-district level.[3,7] Even after elimination, the fight against VL and PKDL would continue, and it is required that there should be no complacency, which can cause resurgence. This neglected disease should not be neglected anymore.