Organism
Leishmania (protozoa)
Transmission
Via sandflies
Leishmania anastigotes infect sandflies when they take them up with their blood meal.
Pathogenesis
- The adult female sand ingests the pathogen in the form as amastigotes when feeding on host blood
- Amastigotes transform into promastigotes in the stomach of the sandfly
- These live in the GI tract, reproducing asexually, then migrate to be regurgutated back into a mammal host, when the fly injects its saliva into prey as it bitesàinside the new host they invade macrophages
- Here they change back into the smaller amastigote form and replicateàeventually burst out into bloodstream and repeat the cycle infecting target tissuesàresponse to infection varies according to the type of immune reaction mounted.
Comparison of types of infection
| CUTANEOUS | MUCOCUTANEOUS | VISCERAL (Kala-azar) | |
| Epidemiology | Most common form Carries 5% rsik of going onto develop mucutaneous disease | Majority of cases are in South america | 3:1 F:M 90% cases found in India, Bangladesh, Nepal, Sudan, and Brazil |
| Site | Skin | Oral and nasal musoca | Systemic disease vital organs |
| Clinical features | Lesion develops at bite site, beginning as itchy papule, becomes nodule then forms ulcer. Occasionally sore develop on mucous membranes. Diffuse cutaneous disease: Leishmaniasis recividans: | Onset a few years after resolution of cutaneous lesion Can begin with symptoms of chronic nasal congestion but results in longterm cartilaginous destruction and ulceration. | fever (twice daily peak), weight loss, mucosal ulcers, fatigue, anaemia and substantial hepatosplenomegaly and lymphadenopathy |
| Complications | Can enlarge to several cm and persist for years before eventually healing to atrophic scar. | Can lead to very destructive and disfiguring lesions of the face | Untreated all patients die within approx. 2 years |
| Diagnosis | Microscopy and culture of aspiration from base of ulcer. | Clinical diagnosis + PCR (gold standard) | Serology (may be negative in HIV positive patients) |
| Treatment | Only needed if not healed by 6 months | long courses (e.g. 30 days) sodium stiboglucanate in a high dose (20 mg/kg) –high failure rate Amphoteracin B is also used. | |
| Prevention | Preventing sandfly bites: Mosquito nets, protective clothing and insect repellent Public health measures to reduce the sandfly There are no vaccine currently availiable | ||
| Other | Important cause of chronic ulcerating skin lesions Recently seen in soliers retuirning from afganistan | substantial part of the disfigurement is possibly due to immunological mechanisms | Even following successful treatment, a secondary form of the disease can develop= post kala-azar dermal leishmaniasis. Manifests small, skin lesions on the face, which gradually spread over the body forming disfiguring, swollen structures resembling leprosy, |
