Immunosuppression is the major individual risk factor facilitating the development of disease from infection, particularly that caused by HIV infection. The spread of HIV to rural areas where VL is endemic, and the spread of VL to suburban areas, has resulted in a progressively increasing overlap between the two diseases, initially in the Mediterranean basin, and, more recently, in other historical foci of VL, such as East Africa, India, and Brazil. In southern Europe, between 1990 and 1998, 1616 cases were reported, 87% of which occurred in the Mediterranean area: Spain, southern France, Italy, and Portugal (Desjeux, 1999). In Spain, the prevalence of VL during HIV infection was around 2% (Alvar, 1994).
A potential health problem is the increase of organ transplantations in endemic VL countries. So far, according to a recent literature review (Basset et al., 2005), the number of reported VL cases related to organ transplantation is limited to about 50, but this is a gross underestimate and will increase with multiplication of organ transplantation programs, principally renal transplants.
Control Strategies
Intervention strategies for prevention or control are hampered by the diversity of the structure of leishmaniasis foci, with many different reservoir hosts of zoonotic forms and a multiplicity of sand fly vectors, each with a different pattern of behavior. In 1990, a WHO Expert Committee described 11 distinct eco-epidemiological entities and defined control and etoparasiticides strategies for each one (WHO, 1990).
Prevention
The aim of prevention is to avoid host infection (human or canine) and subsequent disease. It includes means to prevent intrusion of people into natural zoonotic foci and protection against infective bites of sand flies. Prevention can be at an individual or collective level. It includes the use of repellents, pyrethroid-impregnated bed nets, self-protection insecticides, indoor residual spraying, and forest clearance around human settlements. For dog protection, insecticide collars and etoparasiticides have been available for a few years.
Control
Control programs are intended to interrupt the life cycle of the parasite, to limit or, ideally, eradicate the disease. The structure and dynamics of natural foci of leishmaniasis are so diverse that a standard control program cannot be defined and control measures must be adapted to local situations. The strategy depends on the ecology and behavior of the two main targets, the reservoir hosts and the vectors, which are not mutually exclusive.
Control measures will be very different depending on whether the disease is anthroponotic or zoonotic. In the New World, almost all the leishmaniases are sylvatic, and control is not usually feasible. Even removal of the forest itself may not be effective, as various Leishmania species have proved to be remarkably adaptable to environmental degradation.
Case detection and treatment are recommended when the reservoir host is human or dog, while destruction may be the chosen intervention if the reservoir host is a wild animal. The reduced efficacy of the current antileishmanial drugs and their toxicity limit their use for systematic treatment of cases. The high level of asymptomatic infection both in human and canine hosts affects the efficiency and the feasibility of systematic case detection and treatment programs.
As far as vectors are concerned, control of breeding sites is limited to the few instances where they are known (rodent burrows for P. papatasi and P. duboscqi). Antiadult measures consist of insecticide spraying. Malaria control programs, based on indoor residual insecticide spraying, have had a side benefit for leishmaniasis incidence in several countries where a resurgence of leishmaniasis was observed after the ending of these campaigns: India, Italy, Greece, the Middle East, and Peru.
In practice, control programs include several integrated measures targeted not only at the reservoir host and/or vector but also at associated environmental changes. Health education campaigns can considerably improve the efficiency of control programs. National leishmaniasis control programs have been developed in various countries to face endemics or epidemics (India, China, and Brazil for VL; Central Asian republics of the former USSR and Tunisia for CL).
In conclusion, the leishmaniases are widely distributed and are an important public health problem in various countries. Despite progress in understanding of most facets of their epidemiology, control of leishmaniasis remains unsatisfactory. There is much still to be done.
Bibliography:
- Alvar J (1994) Leishmaniasis and AIDS co-infection: The Spanish example. Parasitology Today 10: 160–163.
- Alvar J and Jimenez M (1994) Could infected drug users be potential Leishmania infantum reservoirs? AIDS 8: 854.