The fall and rise of Andean cutaneous leishmaniasis: transient impact of the DDT campaign in Peru

Rickettsioses in Colombia during the 20th century: A historical review

Rickettsioses are vector-borne zoonotic diseases whose etiological agents are bacteria of the genera Rickettsia and Orientia. In Colombia, literature published on rickettsioses during the 20th century is limited and disperse; to date, there are no detailed publications that compile the affected regions or the involved Rickettsia species in each outbreak. Since early works of Luis Patiño-Camargo, the study of rickettsioses gained major importance with the subsequent description of significant outbreaks in some departments of the country. During the 1940s, many articles were published reporting outbreaks probably caused by Rickettsia rickettsii, Rickettsia typhi, and Rickettsia prowazekii, as well as studies on their diagnosis, vaccination, and prophylaxis. One of the most notorious works was published by Patiño-Camargo where he named the R. rickettsii rickettsiosis as "Tobia fever". However, in the subsequent decades, these entities entered a prolonged period of neglected research and surveillance, and just gained importance until the 21st century, when new fatal cases began to be reported in the country; thus, many questions remained unanswered during this overlooked period. The present work reviewed online databases, repositories, and libraries to compile literature related to rickettsioses in Colombia published during the 20th century. Gathered data show that typhus group rickettsioses (including infections by R. typhi and R. prowazekii) were broadly distributed in departments from the Andean and Caribbean regions, and that spotted fever group rickettsioses cases (including infections by R. rickettsii) were registered in other locations different from Tobia (Cundinamarca), like Atlántico, Bolivar, and Santander departments. These findings contribute to the knowledge of these diseases, their historical distribution, public health burden, and set new horizons for rickettsioses research in different Colombian locations.

The importance of vector control for the control and elimination of vector-borne diseases

Vector-borne diseases (VBDs) such as malaria, dengue, and leishmaniasis exert a huge burden of morbidity and mortality worldwide, particularly affecting the poorest of the poor. The principal method by which these diseases are controlled is through vector control, which has a long and distinguished history. Vector control, to a greater extent than drugs or vaccines, has been responsible for shrinking the map of many VBDs. Here, we describe the history of vector control programmes worldwide from the late 1800s to date. Pre 1940, vector control relied on a thorough understanding of vector ecology and epidemiology, and implementation of environmental management tailored to the ecology and behaviour of local vector species. This complex understanding was replaced by a simplified dependency on a handful of insecticide-based tools, particularly for malaria control, without an adequate understanding of entomology and epidemiology and without proper monitoring and evaluation. With the rising threat from insecticide-resistant vectors, global environmental change, and the need to incorporate more vector control interventions to eliminate these diseases, we advocate for continued investment in evidence-based vector control. There is a need to return to vector control approaches based on a thorough knowledge of the determinants of pathogen transmission, which utilise a range of insecticide and non-insecticide-based approaches in a locally tailored manner for more effective and sustainable vector control.

EA, Cáceres AG, Velez LN, Villegas NV, Hashiguchi K, Mimori T, Uezato H, Kato H. Andean cutaneous leishmaniasis (Andean-CL, uta) in Peru and Ecuador: the vector Lutzomyia sand flies and reservoir mammals

The vector Lutzomyia sand flies and reservoir host mammals of the Leishmania parasites, causing the Andean cutaneous leishmaniasis (Andean-CL, uta) in Peru and Ecuador were thoroughly reviewed, performing a survey of literatures including our unpublished data. The Peruvian L. (V.) peruviana, a principal Leishmania species causing Andean-CL in Peru, possessed three Lutzomyia species, Lu. peruensis, Lu. verrucarum and Lu. ayacuchensis as vectors, while the Ecuadorian L. (L.) mexicana parasite possessed only one species Lu. ayacuchensis as the vector. Among these, the Ecuadorian showed a markedly higher rate of natural Leishmania infections. However, the monthly and diurnal biting activities were mostly similar among these vector species was in both countries, and the higher rates of infection (transmission) reported, corresponded to sand fly's higher monthly-activity season (rainy season). The Lu. tejadai sand fly participated as a vector of a hybrid parasite of L. (V.) braziliensis/L. (V.) peruviana in the Peruvian Andes. Dogs were considered to be principal reservoir hosts of the L. (V.) peruviana and L. (L.) mexicana parasites in both countries, followed by other sylvatic mammals such as Phyllotis andium, Didelphis albiventris and Akodon sp. in Peru, and Rattus rattus in Ecuador, but information on the reservoir hosts/mammals was extremely poor in both countries. Thus, the Peruvian disease form demonstrated more complicated transmission dynamics than the Ecuadorian. A brief review was also given to the control of vector and reservoirs in the Andes areas. Such information is crucial for future development of the control strategies of the disease.

Leishmaniasis sand fly vector density reduction is less marked in destitute housing after insecticide thermal fogging

BACKGROUND

Insecticide thermal fogging (ITF) is a tool to control vector borne diseases. Insecticide application success for vector control has been associated with housing materials and architecture. Vector abundance is correlated with weather changes. Nevertheless, housing quality and weather impacts on vector abundance have been unaccounted for in most New World insecticide control trials for leishmaniasis vectors.

METHODS

We conducted a 15 month insecticide control trial that included two deltamethrin [6 mg a.i.m-2] based ITF interventions in 12 of 24 monitored houses at Trinidad de Las Minas, a hyperendemic cutaneous leishmaniasis transmission village in western Panamá. During the study we followed sand fly (SF) abundance, keeping track of rainfall and quantified housing quality using an index based on architecture and construction materials.

RESULTS

We found a 50 to 80% reduction in SF density in the fogged houses when compared with control houses, while controlling for seasonal changes in SF abundance associated with rainfall. We found heterogeneities in the reductions, as abundance changed according to SF species: Lutzomyia gomezi, Lu. panamensis, Lu. dysponeta and Lu. triramula reduced in density between 40% and 90% after ITF. In contrast, Lu. trapidoi density increased 5% after ITF. Differences in the impact of ITF were associated with housing quality, the most destitute houses, i.e., those with features that ease insect entrance, had a disproportionally larger SF abundance, in some cases with increased domiciliary SF density following the ITF.

CONCLUSION

Our results suggest the potential of insecticide application to control SF density and leishmaniasis transmission could depend on housing quality beyond insecticide efficiency.

Reconstructing historical changes in the force of infection of dengue fever in Singapore: implications for surveillance and control

OBJECTIVE

To reconstruct the historical changes in force of dengue infection in Singapore, and to better understand the relationship between control of Aedes mosquitoes and incidence of classic dengue fever.

METHODS

Seroprevalence data were abstracted from surveys performed in Singapore from 1982 to 2002. These data were used to develop two mathematical models of age seroprevalence. In the first model, force of infection was allowed to vary independently each year, while in the second it was described by a polynomial function. Model-predicted temporal trends were analysed using linear regression. Time series techniques were employed to investigate periodicity in predicted forces of infection, dengue fever incidence and mosquito breeding.

FINDINGS

Force of infection estimates showed a significant downward trend from 1966, when vector control was instigated. Force of infection estimates from both models reproduced significant increases in the percentage and average age of the population susceptible to dengue infections. Importantly, the year-on-year model independently predicted a five to six year periodicity that was also displayed by clinical incidence but absent from the Aedes household index.

CONCLUSION

We propose that the rise in disease incidence was due in part to a vector-control-driven reduction in herd immunity in older age groups that are more susceptible to developing clinical dengue.

Avaliação de medidas de controle de flebotomíneos no norte do Estado do Paraná, Brasil

Comparam-se os resultados de coletas de flebotomíneos de abril de 2001 a setembro de 2002 com os resultados de coletas de outubro de 1996 a setembro de 1997 e de outubro de 1998 a abril de 2000, para avaliar as medidas empregadas para diminuir a densidade destes insetos, no Recanto Marista, Município de Doutor Camargo, Estado do Paraná, Brasil. As coletas de flebotomíneos foram feitas com armadilhas do tipo Falcão, em domicílios e galinheiros, das 22 às 2 horas, duas vezes ao mês. Em 2001/2002 coletaram-se 199.821 flebotomíneos, com média horária de 1.625,5 insetos; em 1996/1997 e 1997/1998, estas médias foram 1.641,9 e 806,7, respectivamente. Nyssomyia neivai predominou (90,4%) em todos os ecótopos. Esta espécie, juntamente com N. whitmani, Migonemyia migonei e Pintomyia fischeri representaram 99,9% do total coletado. A média horária do total de flebotomíneos aumentou, contudo, 85% destes insetos foram coletados nos galinheiros construídos com a finalidade de atraí-los, diminuindo a densidade dos mesmos nos demais ambientes, especialmente no domicílio.

[Prevalence of infection by Leishmania chagasi using ELISA (rK39 and CRUDE) and the Montenegro skin test in an endemic leishmaniasis area of Maranhão, Brazil]

A prospective study was undertaken in 1,520 children less than 15 years of age in São José de Ribamar, Maranhão, Brazil, from June 1994 to January 1995, to evaluate the prevalence and characteristics (socioeconomic, environmental, and behavioral) associated with infection by Leishmania chagasi. Montenegro skin test (MST) and enzyme-linked immunosorbent assay (ELISA-rK39 and CRUDE) test were used to detect infection. The statistical analysis used the chi2 test with Yates correction and a p value less than 0.05 was considered statistically significant. Prevalence of infection was 61.7% as measured by MST, 19.4% according to ELISA (rK39), and 19.7% by ELISA (CRUDE). Association was detected between leishmaniasis in the family, water supply, application of insecticide, and infection by L. chagasi using MST. No association with infection by L. chagasi was detected using ELISA rK39 or CRUDE. More effective control measures are needed to reduce prevalence and to detect asymptomatic cases in this high percentage of infected children.

Control of phlebotomine sandflies

Phlebotomine sandflies (Diptera: Psychodidae) transmit many zoonotic diseases (arboviruses, bartonelloses and especially leishmaniases) of importance to human health in at least 80 countries. Measures used to control adult sandflies (Lutzomyia and Phlebotomus) include the use of insecticides (mostly pyrethroids) for residual spraying of dwellings and animal shelters, space-spraying, insecticide-treated nets, impregnated dog-collars and personal protection through application of repellents/insecticides to skin or fabrics. Because the breeding-sites of sandflies are generally unknown, control measures that act specifically against immatures are not feasible, although the effectiveness of a few biological and chemical agents has been demonstrated in laboratory evaluations. Reports of insecticide-resistance refer to only three sandfly species (P. papatasi, P. argentipes and S. shorttii) against DDT in one country (India), although there are reports of DDT-tolerance in several countries. Current knowledge of sandfly susceptibility to various insecticides is summarized. Constraints and advantages of different compounds, formulations and delivery methods for sandfly control under different environmental conditions are discussed.

The prolonged epidemic of anthroponotic cutaneous leishmaniasis in Kabul, Afghanistan: ‘bringing down the neighbourhood’

In order to investigate the distribution and causes of the spread of anthroponotic cutaneous leishmaniasis (ACL) in Kabul, Afghanistan, a cross-sectional study was conducted during 1997-98 amongst 75,787 residents in the 13 central districts of the city. Using data on active lesions and scars with their times of onset, migration patterns and age of subjects, 2 independent methods were used to estimate, retrospectively, the annual incidence of ACL in recent years. Results indicated a rapid increase in incidence from 1987, peaking in 1996 when an estimated 12% of the population had active disease. Active prevalence was lowest in infants (aged < 2 years), and while risk was gender-independent in children and adolescents, active prevalence in those aged > 20 years was significantly higher amongst females than males (odds ratio [OR] = 1.51, 95% CI 1.34-1.70). About 44% of lesions were located on the head, 38% on upper limbs, 16% on lower limbs and 2% elsewhere. The relative frequency of head lesions dropped with age (P < 0.001), and amongst adults was lowest amongst males (P < 0.001), possibly due to the protective effect of a beard. Within the study population, 32% reported that they had immigrated from outside Kabul, 34% that they had been born in Kabul but had since migrated to another district of the city, and 34% that they had been born in the district of their present residence. Active prevalence amongst those born in their current district of residence was positively associated with the percentage of immigrants in their district (P = 0.027), indicating that a 1% increase in the percentage of immigrants increased the odds of an active lesion by 12% (OR = 1.12, 95% CI 1.01-1.24), but there was no association with the percentage of migrants from other districts in Kabul (P = 0.65) or with war damage (P = 0.33). As active prevalence was not significantly greater in immigrants than local Kabulis, these results support the hypothesis that the epidemic in Kabul has been maintained by a steady influx of susceptible immigrants. It is important that the new opportunities for social development that now exist in Kabul are not hampered by this unpleasant and stigmatizing disease. As population movement is clearly a contributing factor to its transmission, this threat is very real.

[Cutaneous leishmaniasis in Northern Argentina: identification of risk factors in a case-cohort study of three municipalities in Salta]

The objective of this work was evaluate risk factors for acquiring cutaneous leishmaniasis in Salta, the region with the greatest indices of transmission in Argentina. A Case-cohort study was realized from June 1989 to December 1992. The procedures performed on cases and controls included: a) socio-demographic questionnaire; b) domestic and peridomestic environment description; c) physical exam of skin and nasal and oral mucosal; d) Montenegro Skin Test. Multivariate analysis showed a significant risk for factors outside the home (cattle management, hunting, sleeping at the work place) and while at home (sleeping outside of the bedroom, presence of three or more pigs in the yard and windows that cannot be locked in the closed position). This association allowed the identification of risk factors linked to the transmission of leishmaniasis in the home for the first time in Salta (Argentina).

Spraying houses in the Peruvian Andes with lambda-cyhalothrin protects residents against cutaneous leishmaniasis

A household vector control trial was carried out in the Peruvian Andes to measure the effect of spraying inside walls and ceilings with lambda-cyhalothrin on the risk for residents of cutaneous leishmaniasis caused by Leishmania peruviana. The mortality rates of Lutzomyia verrucarum measured with WHO contact bioassay cones set on adobe walls characteristic of the endemic region indicated an LD95 for lambda-cyhalothrin of about 20 mg/m2, and no reduction in effectiveness for at least 6 months on indoor adobe walls sprayed with 25 mg/m2. A random selection of 112 houses were sprayed (starting in 1992/93) at 6-monthly intervals with a mean dose of 34 mg/m2, leaving 154 control houses (with closely matched pre-intervention measurements of incidence and sandfly abundance). Comparisons of pre- and post-intervention sandfly indoor abundance, measured at regular intervals for up to 2 years using CDC light traps, in 22 sprayed and 21 control houses demonstrated that spraying significantly reduced the indoor abundance of Lu. verrucarum by an average of 78% and of Lu. (Helcocyrtomyia) peruensis by 83%. Spraying was also associated with a significant reduction of 77% in the proportion of bloodfed sandflies collected in light traps. The proportion of susceptible householders acquiring leishmaniasis during the trial was significantly reduced by 54% as a result of spraying. The observed impact of spraying was greatest, 81% (95% confidence intervals 20-95%), when the cases detected during the first 6 months after the intervention were excluded from the analysis, suggesting a significant pre-patent period.

A randomized controlled trial of insecticide-treated bednets and chaddars or top sheets, and residual spraying of interior rooms for the prevention of cutaneous leishmaniasis in Kabul, Afghanistan

Anthroponotic cutaneous leishmaniasis (ACL) is a significant public health problem in many towns and cities of south central Asia and the Middle East, resulting in disfigurement and disability which warrants preventive action. A randomized controlled trial was conducted in 1997/98 amongst a non-immune study population of 3666 people in Kabul, Afghanistan, to compare the efficacy of insecticide-treated nets (ITNs), insecticide-treated Islamic cloth wraps (chaddars) used to sleep in, and residual pyrethroid spraying of individual houses for the prevention of ACL. Dosages of insecticide were: ITNs with permethrin, 0.5 g/m2; chaddars with permethrin, 1 g/m2; rooms with lambdacyhalothrin, 30 mg/m2. Cases of ACL were diagnosed on clinical criteria. At the end of the trial period (15 months) the incidence of ACL amongst controls was 7.2%, amongst ITN users 2.4% (OR 0.31, 95% CI 0.2-0.5), amongst impregnated chaddar users 2.5% (OR 0.33, 95% CI 0.2-0.6) and amongst residents of sprayed houses 4.4% (OR 0.60, 95% CI 0.3-0.95). ITNs and impregnated chaddars were equally effective, providing about 65% protective efficacy, with approximately 40% protective efficacy attributable to individual house spraying. No significant differences for age or sex were found between new cases in the intervention and control groups. No serious side-effects were reported and interventions were generally popular; ITNs were the most popular, followed by residual spraying and then impregnated chaddars.

Epidemiological surveys confirm an increasing burden of cutaneous leishmaniasis in north-east Brazil

Health service records for north-east Brazil suggest a consistent rise in numbers of cases of cutaneous leishmaniasis due to Leishmania (Viannia) braziliensis over the past decade. In a study site in Pernambuco, prospective, cross-sectional and retrospective epidemiological surveys of infection (a positive Montenegro skin test response) and/or clinical symptoms confirmed a high current force of infection (0.092/year), and an approximately 10-fold increase in transmission during the last 10 years. Cross-sectional analysis indicated that the incidence rate among children (aged < or = 15 years) was lower than that among adult immigrants exposed for similar time periods, but there was no apparent difference in transmission rate according to gender. Coupled with the known behaviour of the local sandfly vector, Lutzomyia whitmani, this suggests that most people are infected outside their houses, rather than either indoors or while visiting remnant rainforest. The estimated proportion of infections which lead to cutaneous lesions (0.81-0.87) is relatively high for L. braziliensis areas. However, an unusually low proportion of clinical infections (0.0042) apparently leads to metastasis.

Emerging and resurging vector-borne diseases

Over the last four decades, a number of arthropod-borne infections have been recognized for the first time. Some have become of considerable public health importance, such as dengue hemorrhagic fever (DHF), and others are spreading geographically and their incidence is increasing. There has been an important recrudescence of several long-known vector-borne diseases. Malaria, leishmaniasis, dengue, and plague have resurged in numerous foci, in some cases where they were thought to be under effective control. In most instances, the appearance of new diseases and syndromes and the resurgence of old can be associated with ecological changes that have favored increased vector densities. Dam construction, irrigation and other development projects, urbanization, and deforestation have all resulted in changes in vector population densities that appear to have enabled the emergence of new diseases and the resurgence of old diseases. Greatly increased human travel has spread infectious agents, introducing them into areas in which they had been hitherto absent. It is essential to understand the factors that caused increased vector densities and hence the transmission of disease to prevent the emergence and resurgence of more diseases, as well as to serve as a basis for effective control.

Differential application of lambda-cyhalothrin to control the sandfly Lutzomyia longipalpis

To study the impact of residual pyrethroid insecticide on the abundance and distribution of peridomestic Lutzomyia longipalpis, the sandfly vector of visceral leishmaniasis in Brazil, lambda-cyhalothrin was applied at 20 mg a.i.m-2 in the following interventions: (i) spraying of all animal pens in a village (blanket coverage); (ii) treatment of a subset of animal pens, either by spraying, or by installation of insecticide-impregnated 1 m2 cotton sheets as 'targets' (focal coverage). By sampling with CDC light traps, and using a novel analytical approach, we detected a 90% reduction in Lu.longipalpis abundance in sprayed sheds of the focal intervention. However, there was no discernible effect on the abundance of other phlebotomines trapped in sheds, or on the abundance of Lu.longipalpis in untreated dining-huts and houses. This differential impact on Lu.longipalpis abundance is explained in terms of the disruption of male pheromone production. Treated targets were approximately half as effective as residual spraying in reducing the abundance of Lu.longipalpis in sheds. Following blanket intervention, the abundance of Lu.longipalpis in traps fell by only 45% (not significant): catches at untreated dining-huts actually increased, possibly because the blanket coverage diverted Lu.longipalpis away from major aggregation sites at animal pens. It is recommended that care be taken during vector control programmes to ensure that all potential aggregation sites are treated. The possible consequences of leaving some sites untreated include poor control of peridomestic sandfly abundance and an increase in the biting rate on dogs and humans.

The relationship between CDC light-trap and human-bait catches of endophagic sandflies (Diptera: Psychodidae) in the Peruvian Andes

A study was carried out in the Peruvian Andes to test the suitability of CDC light traps for monitoring changes in the human-landing rate of endophagic phlebotomine sandflies, following house-spraying with pyrethroid insecticide. On four pairs of consecutive nights, sandflies were caught inside eight sprayed and eight unsprayed houses, either by human bait or by CDC light traps. The sandflies collected were Lutzomyia verrucarum (97%) and Lu.peruensis (3%), both probable vectors of Leishmania peruviana, and the species composition was unaffected by house-spraying. A non-linear relationship was detected between light-trap and human-bait catches, but the relationship did not diverge significantly from linearity within the range of sandfly abundance found in most houses in the endemic area (i.e. between 3 and 200 sandflies/house-night), and did not differ significantly between sprayed and unsprayed houses. However, light trap catches had a significantly lower proportion of blood-fed females in sprayed than in unsprayed houses, probably due to an insecticidal effect on post-blood-feeding behaviour. The proportion of Lu. verrucarum was significantly higher in light trap than in human bait catches, indicating that Lu.peruensis is either more anthropophilic or less phototropic than Lu.verrucarum.

Cutaneous leishmaniasis in the Peruvian Andes: an epidemiological study of infection and immunity

A prospective longitudinal survey of cutaneous leishmaniasis (Leishmania peruviana) was carried out in Peru on a study population of 4716 persons living in 38 villages (Departments of Lima, Ancash and Piura). Demographic and clinical data were collected from all individuals, and a Montenegro skin test (MST) was carried out on 72% (3418) of the study population. Each household was revisited at 3-monthly intervals for up to 2 years to detect new leishmaniasis cases; 497 people received a second MST at the end of the study. Analysis of the epidemiological data indicated that (i) 17% (16/94) of all infections were subclinical, (ii) this percentage increased significantly with age, (iii) clinical infections led to 73.9% protective immunity (95% C.I. 53.0-85.5%) and relatively permanent MST responsiveness (recovery rate = 0.0098/year; 95% C.I. 0.000-0.020/year), (iv) sub-clinical infections led to protective immunity, which was positively correlated with their MST induration size (increasing by 17.9% per mm; P < 0.0001), and a mean MST recovery rate of 0.114/year (4/421 man-months), and (v) recurrent leishmaniasis was dominated by reactivations, not by reinfections.