Disease Burden of Spinal Muscular Atrophy: A Comparative Cohort Study Using Insurance Claims Data in the USA

BACKGROUND

Spinal muscular atrophy (SMA) is a neuromuscular disease caused by homozygous deletion or loss-of-function mutations of the survival of motor neuron 1 (SMN1) gene, resulting in reduced levels of SMN protein throughout the body. Patients with SMA may have multiple tissue defects, which could present prior to neuromuscular symptoms.

OBJECTIVE

To assess the signs, comorbidities and potential extraneural manifestations associated with SMA in treatment-naïve patients.

METHODS

This observational, retrospective and matched-cohort study used secondary insurance claims data from the US IBM® MarketScan® Commercial, Medicaid and Medicare Supplemental databases between 01/01/2000 and 12/31/2013. Treatment-naïve individuals aged≤65 years with≥2 International Classification of Diseases, Ninth Revision (ICD-9) SMA codes were stratified into four groups (A-D), according to age at index (date of first SMA code recorded) and type of ICD-9 code used, and matched with non-SMA controls. The occurrence of ICD-9 codes, which were converted to various classifications (phecodes and system classes), were compared between groups in pre- and post-index periods.

RESULTS

A total of 1,457 individuals with SMA were included and matched to 13,362 controls. Increasing numbers of SMA-associated phecodes and system classes were generally observed from pre- to post-index across all groups. The strongest associations were observed in the post-index period for the youngest age groups. Endocrine/metabolic disorders were associated with SMA in almost all groups and across time periods.

CONCLUSIONS

This exploratory study confirmed the considerable disease burden in patients with SMA and identified 305 unique phecodes associated with SMA, providing a rationale for further research into the natural history and progression of SMA, including extraneural manifestations of the disease.

Evaluating the Economic Burden of Relapses in Neuromyelitis Optica Spectrum Disorder: A Real-World Analysis Using German Claims Data

Introduction

Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune disease of the central nervous system which causes recurrent relapses, resulting in blindness, paralysis, and spinal cord damage. This study sought to explore the real-world burden, treatment, and cost of NMOSD in Germany using claims data.

Methods

Our study consisted of a retrospective analysis of two anonymized health insurance datasets covering around 9 million patients in Germany from 01/01/2013 to 31/12/2019. NMOSD patients were identified using inpatient and outpatient International Classification of Diseases, Tenth Revision (ICD-10) diagnoses of neuromyelitis optica (NMO; G36.0) and relevant symptom codes. Active periods of disease were identified based on relapse events (including hospitalizations and acute treatment); healthcare resource utilization (HCRU) and direct costs were allocated to active and inactive periods based on treatment dates. Propensity score matching was used to compare HCRU and cost outcomes among patients with and without NMOSD.

Results

Overall, 130 patients were identified as having NMOSD (mean age: 46.84 years; 58% female). NMOSD patients recorded 16.52 active and 348.48 inactive days per patient year (PPY). HCRU and associated costs were approximately tenfold higher during active periods than during inactive periods, with the largest share of the cost difference driven by hospitalizations (€6424.09/€259.10 per active/inactive month) and outpatient drug prescriptions (€412.83/€271.58). Direct healthcare costs incurred by patients with NMOSD (€12,913.28 PPY) were approximately threefold higher than those incurred by patients without NMOSD (€4667.66 PPY). Costs of hospitalization (€6448.32/€1937.64 PPY) and outpatient prescriptions (€3335.67/€1037.64 PPY) contributed most strongly to the difference.

Conclusion

Patients with NMOSD consume substantial healthcare resources and incur heavy costs during active disease phases. This study captured direct measurable healthcare costs and likely underestimates the real societal/emotional burden on patients and their families. Nevertheless, prevention of acute relapses represents one compelling strategy to minimize the economic burden of NMOSD in Germany.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40120-021-00311-x.

Classification, Prediction, and Concordance of Cognitive and Functional Progression in Patients with Mild Cognitive Impairment in the United States: A Latent Class Analysis

Background:

Progression trajectories of patients with mild cognitive impairment (MCI) are currently not well understood.

Objective:

To classify patients with incident MCI into different latent classes of progression and identify predictors of progression class.

Methods:

Participants with incident MCI were identified from the US National Alzheimer’s Coordinating Center Uniform Data Set (09/2005-02/2019). Clinical Dementia Rating (CDR^®) Dementia Staging Instrument-Sum of Boxes (CDR-SB), Functional Activities Questionnaire (FAQ), and Mini-Mental State Examination (MMSE) score longitudinal trajectories from MCI diagnosis were fitted using growth mixture models. Predictors of progression class were identified using multivariate multinomial logistic regression models; odds ratios (ORs) and 95% confidence intervals (CIs) were reported.

Results:

In total, 21%, 22%, and 57% of participants (N = 830) experienced fast, slow, and no progression on CDR-SB, respectively; for FAQ, these figures were 14%, 23%, and 64%, respectively. CDR-SB and FAQ class membership was concordant for most participants (77%). Older age (≥86 versus≤70 years, OR [95% CI] = 5.26 [1.78–15.54]), one copy of APOE ɛ4 (1.94 [1.08–3.47]), higher baseline CDR-SB (2.46 [1.56–3.88]), lower baseline MMSE (0.85 [0.75–0.97]), and higher baseline FAQ (1.13 [1.02–1.26]) scores were significant predictors of fast progression versus no progression based on CDR-SB (all p < 0.05). Predictors of FAQ class membership were largely similar.

Conclusion:

Approximately a third of participants experienced progression based on CDR-SB or FAQ during the  4-year follow-up period. CDR-SB and FAQ class assignment were concordant for the vast majority of participants. Identified predictors may help the selection of patients at higher risk of progression in future trials.

Central Demyelinating Diseases after Vaccination Against Hepatitis B Virus: A Disproportionality Analysis within the VAERS Database

INTRODUCTION

Hepatitis B (HB) vaccination programs were set up worldwide in the early 1990s. Despite their major focus on reducing the burden of HB infection, they have seldom achieved the targeted population coverage in most countries, including the USA, with around 24.5% of adults being vaccinated against HB. Among proposed reasons for this is the persisting doubt about a possible link between HB vaccination and the occurrence of cases of multiple sclerosis (MS).

OBJECTIVE

Our objective was to evaluate a potential safety signal between MS and HB vaccination. We conducted a disproportionality analysis (DPA) using the cases reported to the Vaccine Adverse Event Reporting System (VAERS).

METHODS

We calculated the proportional reporting rate (PRR) and reporting odds ratio (ROR) of MS having occurred within the 120 days following HB immunization in adults aged 19-49 years when compared with other vaccines using the reports recorded in the VAERS database. Both ratios were estimated globally and then according to the origin of reports (USA vs. non-USA). We then performed a sensitivity analysis using a broader category of demyelinating events.

FINDINGS

MS cases following HB vaccination were more likely to originate from outside the USA and to be reported before 2000 than those associated with other immunizations. All computed ratios were found to be statistically significant, with PRRs ranging from 3.48 to 5.56 and RORs ranging from 3.48 to 5.62. When considering the geographical origin, similar RORs were obtained for both US and non-US cases.

CONCLUSION

In VAERS, MS cases were up to five times more likely to be reported after an HB vaccination than after any other vaccination. Since DPA is mainly suited for hypothesis generation, further studies evaluating the nature of the link between MS and HB vaccination would be of considerable importance.

Human papillomavirus vaccine and demyelinating diseases-A systematic review and meta-analysis

Approved in 2006, human papillomavirus (HPV) vaccines were initially targeted for girls aged 9-14 years. Although the safety of these vaccines has been monitored through post-licensure surveillance programmes, cases of neurological events have been reported worldwide. The present study aimed to assess the risk of developing demyelination after HPV immunization by meta-analysing risk estimates from pharmacoepidemiologic studies. A systematic review was conducted in Medline, Embase, ISI Web of Science and the Cochrane Library from inception to 10 May 2017, without language restriction. Only observational studies including a control group were retained. Study selection was performed by two independent reviewers with disagreements solved through discussion. This meta-analysis was performed using a generic inverse variance random-effect model. Outcomes of interest included a broad category of central demyelination, multiple sclerosis (MS), optic neuritis (ON), and Guillain-Barré syndrome (GBS), each being considered independently. Heterogeneity was investigated; sensitivity and subgroup analyses were performed when necessary. In parallel, post-licensure safety studies were considered for a qualitative review. This study followed the PRISMA statement and the MOOSE reporting guideline. Of the 2,863 references identified, 11 articles were selected for meta-analysis. No significant association emerged between HPV vaccination and central demyelination, the pooled odds ratio being 0.96 [95% CI 0.77-1.20], with a moderate but non-significant heterogeneity (I² = 29%). Similar results were found for MS and ON. Sensitivity analyses did not alter our conclusions. Findings from qualitative review of 14 safety studies concluded in an absence of a relevant signal. Owing to limited data on GBS, no meta-analysis was performed for this outcome. This study strongly supports the absence of association between HPV vaccines and central demyelination.

A double-blind placebo-controlled randomised trial of omega-3 supplementation in children with moderate ADHD symptoms

OBJECTIVE

Clinical trials and inconclusive meta-analyses have investigated the effects of omega-3 supplements in children with Attention-Deficit Hyperactivity Disorder (ADHD). We performed a randomised placebo-controlled trial to evaluate the efficacy of omega-3 fatty acids.

METHODS

Children aged 6-15 years with established diagnosis of ADHD were randomised 1:1 to receive either supplements containing docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) or a placebo for 3 months. Psychotropic or omega-3-containing treatments were not authorised during the study. The primary outcome was the change in the Attention-Deficit Hyperactivity Disorder Rating Scale version 4 (ADHD-RS-IV). Other outcomes included safety, lexical level (Alouette test), attention (Test of Attentional Performance for Children-KiTAP), anxiety (48-item Conners Parent Rating Scale-Revised-CPRS-R), and depression (Children's Depression Inventory-CDI).

RESULTS

Between 2009 and 2011, 162 children were included in five French child psychiatry centres. The mean age was 9.90 (SD 2.62) years and 78.4% were boys. The inclusion ADHD-RS-IV at was 37.31 (SD 8.40). The total ADHD-RS-IV score reduction was greater in the placebo group than in the DHA-EPA group: -19 (-26, -12)  % and -9.7 (-16.6, -2.9) %, respectively, p = 0.039. The other components of the Conners score had a similar variation but the differences between groups were not significant. Two patients in the DHA-EPA group and none in the placebo group experienced a severe adverse event (hospitalisation for worsening ADHD symptoms).

CONCLUSION

This study did not show any beneficial effect of omega-3 supplement in children with mild ADHD symptoms.

Effects of Three‐Hour Restricted Food Access during the Light Period on Circadian Rhythms of Temperature, Locomotor Activity, and Heart Rate in Rats

The effects of food on biological rhythms may influence the findings of chronopharmacological studies. The present study evaluated the influence of a restricted food access during the rest (light) span of nocturnally active Wistar rats on the 24 h time organization of biological functions in terms of the circadian rhythms of temperature (T), heart rate (HR), and locomotor activity (LA) in preparation for subsequent studies aimed at evaluating the influence of timed food access on the pharmacokinetics and pharmacodynamics of medications. Ten-wk-old male Wistar rats were housed under controlled 12:12 h light:dark (LD) environmental conditions. Food and water were available ad libitum, excepted during a 3 wk period of restriction. Radiotelemetry transmitters were implanted to record daily rhythms in T, HR, and LA. The study lasted 7 wk and began after a 21-d recovery span following surgery. Control baseline data were collected during the first wk (W1). The second span of 3 wk duration (W2 to W4) consisted of the restricted feeding regimen (only 3 h access to food between 11:00 and 14:00 h daily) during the L (rest span) under 12:12 h LD conditions. The third period of 3 wk duration (W5 to W7) consisted of the recovery span with ad libitium normal feeding. Weight loss in the amount of 5% of baseline was observed during W1 with stabilization of body weight thereafter during the remaining 2 wk of food restriction. The 3 h restricted food access during the L rest span induced a partial loss of circadian rhythmicity and the emergence of 12 h rhythms in T, HR, and LA. Return to ad libitum feeding conditions restored circadian rhythmicity in the manner evidenced during the baseline control span. Moreover, the MESORS and amplitudes of the T, HR, and LA 24 h patterns were significantly attenuated during food restriction (p < 0.001) and then returned to initial values during recovery. These changes may be interpreted as a masking effect, since T, HR, and LA are known to directly react to food intake. The consequences of such findings on the methods used to conduct chronokinetic studies, such as the fasting of animals the day before testing, are important since they may alter the temporal structure of the organism receiving the drug and thereby compromise findings.

Malaria transmission in Southern Madagascar: influence of the environment and hydro-agricultural works in sub-arid and humid regions. Part 1. Entomological investigations

A 4-year entomological study was carried out in Southern Madagascar to identify malaria vectors, evaluate the transmission and compare the influence of irrigation in the sub-arid and adjacent humid regions. Three villages were involved in this entomological survey: Androvasoa (located in the natural sub-arid ecosystem), Pépiniére (sited at the centre of an irrigated rice scheme in the sub-arid region) and Esana (bordered with rice fields in the humid region). Mosquitoes were collected inside and outside dwellings when landing on human beings, with light traps and with knockdown indoor sprays. Anopheles arabiensis, Anopheles merus and Anopheles funestus were found in every village while Anopheles gambiae s.s. was only found in the village bordering the rice-fields (Pépiniére) and Anopheles mascarensis, a mosquito native to Madagascar, was only found in the humid region (Esana). In Pépiniére, the annual entomological inoculation rate (EIR) was low (EIR=0.4 infective bites/man/year (IBM)). In the irrigated scheme of the sub-arid region, malaria transmission was 150 times higher (mean EIR=63 IBM) than in the natural ecosystem and A. funestus was the main vector, responsible for 90% of infective bites. In Esana, the level of malaria transmission was high (EIR=41 IBM) and 2/3 of the infective bites were due to A. mascarensis, despite the presence of A. gambiae s.s. and A. funestus. These results are discussed with reference to the impact of irrigation on malaria in Africa ("the paddies paradox").

Lack of daily rhythms major modifications despite continuous infusion of melatonin in the rat

The present study was conducted to evaluate the effect of melatonin on the daily rhythms of temperature, heart rate and locomotor activity in rats that received subcutaneously a continuous infusion of two different doses e.g. 1 and 5 mg/kg per day for seven days. Our results indicate that melatonin does not induce a loss of the daily rhythmicity of temperature, heart rate and locomotor activity. Whatever the dose, melatonin slightly modifies the main parameters of these rhythms e.g. a decrease of the amplitude of the daily rhythms of temperature and heart rate and an increase of the mesor of temperature. Taking into account these results obtained after constant rate delivery in normal rats, we plan now to investigate the effects of melatonin on our experimental model of Parkinson's disease (double bilateral intrastriatal 6-hydroxydopamine injection).

[Molecular identification of sibling Anopheles species: example of the Anopheles minimus and Anopheles dirus complexes, major malarial vectors in Southeast Asia]

Effective control of malaria vectors requires precise identification of species. This is especially important within complexes of species that cannot be distinguished based on morphological features. Two methods based on polymerase chain reaction (PCR) analysis have been developed to identify 2 species in the Anopheles minimus complex and 5 species of the Minimums group as well as 4 species of the Anopheles dirus complex. Association of oligonucleotide couples in the form of multiplex PCR has allowed development of two simple, reliable PCR techniques adapted to each one of these species complexes that comprise the major vectors of malaria in Southeast Asia. Specifically designed to meet the needs of entomologist working in the field for reliable, cost-effective tests, these techniques will facilitate assessment of the geographical distribution of each vector. These data will help to better target vector control measures.

[Malaria vector control in Cameroon: past, present, future. Reflections]

During the fifties, large scale malaria vector control projects based upon house spraying were implemented in Southern and Northern parts of Cameroon in line of malaria eradication concept. In the South, the pilot zone of Yaounde gathered about 150,000 inhabitants, in the forest area. First operations started in 1953 but the programme became actually operational in 1956. It was divided in two parts: the western part was treated with DDT, while the eastern one was treated with dieldrin. At the same time, the whole forested area was also treated with dieldrin until 1960. Yaounde itself was not treated because it was free of anopheles and malaria. House spraying in the pilot area of Yaounde was a complete success and plasmodic index dropped below 1%. The same success was observed in most of the southern treated areas. Unfortunatly dieldrin resistance of An. gambiae hampered this programme which stopped in 1960. The northem pilot project dealt with some 250,000 inhabitants around Maroua, in a savanna area. To avoid dieldrin resistance observed in 1956, DDT was selected and house spraying started in 1959. From a strictly operational point of view, the campaign was considered as a success. But after two years, it was noticed that plasmodic index remained still around the same value of 35% and the programme stopped. It was thus stated that according to available techniques it was not possible to reach the ultimate goal of eradication even when chemoprophylaxis (chloroquin + pyrimethamin) was added. The comparison between south (= success) and north (= failure) was very interesting as it underlined the big differences between epidemiological faces, an unaccepted concept at that time. Now ecological and epidemiological diversity is the well acknowledged. It also underlined the need of diversity of strategies according to the epidemiology of the disease and the ecology of its vector Vector control was then stopped for a while. In the eighties, Primary Health Care was promoted and malaria control shifted from vector to parasite control, vector control remaining as a prevention method. But chemioresistance of Plasmodium falciparum appeared and. quickly spread, at different levels, across the country. A new emphasis was therefore given to vector control thank to the newly developed technique of insecticide impregnated mosquito nets. Two kinds of studies were undertaken: - what people were actually doing in term of mosquito control at family level, the main reason and the costs as well as current use of mosquito nets - the efficacy of pyrethroid treated mosquito nets (IMN) in different areas of southern forested area against different malaria vectors: An. gambiae, An. nili, An. moucheti. It thus clearly appeared that IMN were very successful in sharply reducing malaria transmission aAd morbidity. But its promotion is limited by the current poor use of mosquito nets in Yaoundé (1 mosquito net for 27 "beds") while in Douala, where IMN are largely used against the bite of the huge population of Culex. quinquefasciatus, the implementation of the first riational centre for impregnation of mosquito net was a great success, as long as it was headed by a motivated and skill manager Impregnated mosquito nets appear thus as a tool of great efficacy but their sustainability is still matter of concern and promotional campaigns must be developed involving private and public, political and scientific spheres as well as the general population who should be encouraged to become partners and even actors of vector and malaria control at their household level.

Effects of a seven-day continuous infusion of L-DOPA on daily rhythms in the rat

The present study was conducted to evaluate the effect of L-3, 4-dihydroxyphenylalanine (L-DOPA) on the daily rhythms of temperature, heart rate and locomotor activity in rats that received a 7-day continuous infusion. Our results indicate that L-DOPA does not induce a loss of the daily rhythmicity of temperature, heart rate and locomotor activity but modifies the main parameters of these rhythms, e.g. it increased the MESOR (midline estimating statistic of rhythm) of temperature and heart rate and increased the amplitude of temperature but decreased the amplitude of heart rate. Taking into account these results obtained after constant rate delivery, we now plan to investigate the effects of DOPA therapy by changing the time of its administration.

Airport malaria : a rare disease still poorly understood

The article by Daniel Lusina and colleagues in this issue of Eurosurveillance is a timely reminder of the dangers of airport malaria. Since 1977, when the disease was first documented, 75 cases of airport malaria have been observed in western Europe, 28 o

Diversity of malaria in rice growing areas of the Afrotropical region

It is well known that 'in many instances the rice agrosystem perfectly fits the ecological requirements of pathogens or vectors' and in fact 'malaria, schistosomiasis and Japanese encephalitis are important vector-borne diseases associated with rice production in developing countries' (IRRI, 1987). In spite of these fears, rice cultivation has been on the increase in the African region in response to demographic and economic pressures. However, although rice fields provide suitable breeding places for Anopheles mosquitoes and rice cultivation leads to an increase in the biting rates, the species which are adapted to these sites are not the same in all parts of Africa. Several examples illustrate this phenomenon: An. funestus in the rice fields of Madagascar, An. pharoensis in saline water rice fields in the delta of the Senegal river, An. arabiensis in northern Cameroon and Burundi, An. gambiae Mopti form in the Kou Valley (Burkina Faso) and An. gambiae Savanna form in the rice fields of Kafine near Bouaké (Côte d'Ivoire). The vectorial capacities of these species are not the same and malaria inoculation rates are not necessarily increased in the riceland agroecosystem. The consequences for malaria of introducing rice cultivation depend on the situation before its introduction: it could be worsened in unstable malaria areas but not in stable malaria areas. Therefore, sound epidemiological and entomological knowledge are needed before causing any environmental modifications for agricultural purposes and there should be regular monitoring to avoid any outbreak.

[Anopheline population genetics]

Population genetic studies of vectors are essential for (i) the determination of their taxonomic status and consequently the definition of their vectorial role in the transmission of pathogenic agents; (ii) the evaluation of the species genetic variability and the estimation of their capacities of adaptation to selection pressure; (iii) an estimation of gene flow among populations in order to evaluate their degree of isolation and gene circulation, especially resistance genes. Among the malaria vectors taken as examples on three continents, Africa, South-East Asia and Latin America, the large majority of the species showed an important polymorphism. The Gambiae Complex, which is by far the most studied one, includes at present 7 species with the recent description of An. quadriannulatus A and B from Ethiopia. An. gambiae s.s. includes itself 5 chromosomal forms. One of them, the Mopti form, should be considered as a species unto itself. For An. arabiensis, a strong differentiation has been observed among the populations from Senegal and the Indian Ocean Islands. The kdr mutation, which confers resistance to pyrethroid knockdown effect, has never been found either in the Mopti form, or An. arabiensis, indicating a restricted gene flow between these latter two and An. gambiae s.s. The speciation process of the Gambiae Complex seems to be a recent phenomenon due to environmental selection pressure. Species of the Funestus Group are distinguishable by morphological characters. The genetic study of An. funestus s.s. did not show the presence of a complex, in spite of high polymorphism and population structure. Anophelines from eastern areas present an important biodiversity. The Minimus Complex includes two species, A and C, which are widely distributed in South-East Asia. Species A is strongly endophilic, on the contrary species C is at once more exophilic and zoophilic. The latter species might have been selected by DDT indoor house spraying. After numerous taxonomic investigations, the Dirus Complex includes now 7 species. In Latin America, An. pseudopunctipennis clustered into three geographic populations which are under a speciation process. One covers North America and Guatemala, the other South America and Belize, whilst the last one is restricted to Grenada Island. On the contrary, An. darlingi showed little morphologic and genetic variability throughout the species geographic range suggesting the existence of a single species. The main objective of these studies is to implement a more selective approach of vector control programs in relation to the incriminated species, their bioecology and their role in malaria transmission. The improvement of efficiency and selectivity of vector control is becoming a major goal in order to make the best out of the available tools and control the impact of interventions on the environment.

[Epidemiological stratification of malaria in the Comoro archipelago]

In the Comoros Islands, the level of malarial endemicity varies greatly from one island to the other, even though the total area (4 islands) covers less than 2,300 km2 and has a population of some 600,000 people only. The epidemiological stratification is based on the diversity of human and physical characterisation. They both determine the presence and the behaviour as well as the size of the vector's populations. Vectorial dynamics can explain varying levels of endemicity given parasitological indicators and specific morbidity. Analyzing these criteria shows up different epidemiological features and serves as a basic guideline for malaria control. The efficiency of this control depends on the relationships between the intensity and the length of the transmission, in the framework of protection mechanisms; it is of crucial importance for clinical treatment. Further elements are the age of the patient, the season and the geographic situation of the area. Stratification provides explanations for these relationships and helps to define antimalarial programmes adapting to each situation a range of therapeutic and antivectorial methods. The availability and accessibility of anti-malarial medicine is the minimum requirement for reducing mortality: domestic spray insecticides for reducing transmission are effective for several years and should be followed by the use of mosquito nets or curtains impregnated with pyrethrinoids, and in the particular case of Grande Comore, the use of larvivorous fish. As anywhere else, the economic development, which is dependent on political stability, is the essential basis for malaria control.

[Vectors and environmental factors in malaria]

Malaria is a major risk for more than two billion human beings on Earth, and is the cause of 700,000 to 2.5 million deaths per year. The causative factor, Plasmodium (four species), involves an asexual cycle in man and a sexual one in anopheline mosquitoes. The four species of Plasmodium are pathogenic for man but P. falciparum accounts for more than 90% of deaths. Only black Africans are refractory to P. vivax, a characteristic linked to the lack of Duffy antigen. Among the 400 species of anophelines so far recorded, less than 50 are recognized malaria vectors. Every one has its own geographic and ecological characteristics, which locally induce the epidemiological trends and its biodiversity. In a given site transmission depends on competent anopheline species, their infective rate and their biting rate. Inhabitants of endemic areas develop during infancy immunity which protect them during the rest of their lives. This immunity (premunition) between parasite and its host is acquired at an heavy price of infant mortality. It can decrease rapidly when people leave endemic areas. Because inhabitants of endemic areas continue to harbor asymptomatic parasites they become good parasite reservoirs. The diversity of epidemiological situations needs a diversification of malaria control measures. The prognosis of the evolution of malaria depends on control measures, applied or not, and on the evolution of climatic and anthropic environment, which are very hard to predict for the time being.

Status of pyrethroid resistance in Anopheles gambiae sensu lato

The present study confirms the presence of pyrethroid resistance among Anopheles gambiae s.l mosquitos in Côte d'Ivoire and reports the observation of such resistance in two other countries in West Africa (Benin and Burkina Faso). Malaria vector populations from Cameroon (Central Africa), Senegal (West Africa) and Botswana (southern Africa) were found to be susceptible to pyrethroids. In the most resistant mosquito populations, resistance to permethrin was associated with reduced mortality, not only with respect to this compound but also towards deltamethrin. Moreover, a significant increase in knockdown time was observed in some mosquito populations before any decrease in mortality, suggesting that knockdown time could be a good indicator for the early detection of pyrethroid resistance. In view of the current extension of such resistance, there is an urgent need to set up a network in Africa to evaluate its development. It is also vital that the impact of this resistance on pyrethroid-impregnated bednets be assessed.

[Comparison of the transmission of malaria in 2 epidemiological patterns in Senegal: the Sahel border and the Sudan-type savanna]

From September 1992 to October 1993 a longitudinal entomological study was carried out in two villages located in different ecological conditions of Senegal, a sahelian area and a sudan-type savanna. Mosquitoes were sampled by night-bites catches and by daytime pyrethrum spray collections. In both villages Anopheles gambiae s.l. is the main vector with An. gambiae in the savanna area of Wassadou and An. arabiensis in the sahelian area of Thiaye. Malaria transmission is mainly seasonal with a man biting rate (ma) and an entomological inoculation rate (h) higher in Wassadou than in Thiaye. In this last one (sahelian area), a high variation of An. gambiae s.l. density was observed, females disappear in the dry season. In the rainy season the main biting rate increases but no infected bite was recorded. In Wassadou (sudan-type savanna), a great difference in An. gambiae s.l. specific composition was observed with An. gambiae predominant in the rainy season and An. arabiensis generally more abundant in the dry season. The biting and inoculation rates were minimum during the dry season (ma = 4 bites/man/night; h = 0.07 infected bites/man/night-, they increase during the rainy season (ma: 52 bites/man/night; h = 1.6 infected bites/man/night). An inhabitant of this village gets annually some 63, bites and 220 infected bites of An. gambiae s.l., mainly during the six months of the rainy season and the early dry season.

Origin and prevention of airport malaria in France

Since 1969, 63 cases of airport malaria have been reported in Western Europe, 24 of which occurred in France. Most were due to Plasmodium falciparum. In 1994, 7 cases occurred in and around Roissy Charles de Gaulle airport (CDG), showing 4 types of contamination: among employees working on airstrips or opening containers, among residents living near the airport, among people living at some distance from the airport after a secondary transport of vectors, and by vectors transported in luggage. In-flight or stop-over infection is not considered as airport malaria. The infective anophelines originated from airports where malaria transmission occurs, mostly in subsaharan Africa. A tentative list is given taking into account aerial traffic with France. Surveys in the airports of Dakar (Senegal), Cotonou (Benin), Abidjan (Cote d'Ivoire) and Yaoundé (Cameroun) found potential vectors in all of these from July to September. After 1994, the Contrôle Sanitaire aux Frontières (CSF) in charge at CDG concentrated its efforts on the flights at risk, as well as information and sensitization of airline companies, which resulted in 73% and 87% of the flights at risk being properly disinsected in 1995 and 1996. Despite pyrethroid resistance in Anopheles gambiae s.s. in West Africa, the efficacy of aircraft spraying with permethrin aerosols is still acceptable. However, surveillance of resistance should be improved and search for nonpyrethroid insecticides suitable for aircraft strongly encouraged.

[Chloroquine resistance and malaria control in Ivory Coast]

We present here data from the Ivory Coast on the susceptibility of Plasmodium falciparum to chloroquine, obtained since the first chloroquine-resistant strains were discovered in 1987. Susceptibility was assessed using the WHO 7-day field test. Almost all the tests were carried out in the capital, Adidjan, and in the southern forest zone. The frequency of chloroquine resistance was below 30% in most cases, the actual frequency differing between regions. The frequency of R3 chloroquine-resistant P. falciparum was very low. Such resistant parasites were found only on an oil-palm plantation and in the south west of the country, probably due to the free medical care available at both locations. In general, access to health care is limited. Fevers attributed to malaria are generally treated at home using plants or incomplete courses of chloroquine. Our data suggest that R3 chloroquine-resistant P. falciparum strains are selected by repeated high doses of chloroquine, rather than by low doses. Thus, symptomatic treatment of uncomplicated malaria and treatment at home with the "correct" medication may be more effective than systematic medication, for limiting the level of chloroquine resistance in the parasite. Pyrethroid-resistant Anopheles gambiae s.l. is present in West Africa and this may reduce the short-term effectiveness of impregnated mosquito nets. In the absence of R3 chloroquine-resistant P. falciparum, self-medication at home may be a practical and realistic way to treat malaria. However, more knowledge about the effectiveness of anti-malaria drugs, their use in various social, cultural and economic environments and the geographical distribution of insecticide-resistant vectors is required before effective strategies can be designed. However, it would certainly be of value to consistently check the quality of anti-malaria drugs and to try to improve the effectiveness of self-medication at home.

[Individual protection against insect vectors]

Many diseases for which no vaccine is available are transmitted by insect and arthropod vectors, the main exceptions being yellow fever and Japanese encephalitis B. Treatment is less and less effective due to the development of chemoresistance to therapeutic and prophylactic drugs as is well-illustrated by malaria. One of the best methods of preventing these diseases is personal protection against insect bites. Personal protection measures can be divided into three categories which can be used separately or in combination : application of repellents to the skin, wearing clothes impregnated with insecticides, and use of bed nets and other barriers impregnated with insecticides. The choice of method depends on the type of insect vector involved. For insects that are active during the day or at dusk, application of repellents to the skin gives good short-term protection and wearing impregnated clothes is useful. Bed nets that have been properly impregnated with pyrethroids are highly effective for night-time protection. Since personal protection methods are not 100% effective, they must be used in association with chemoprophylaxis according to medical guidelines. Medical advice should be sought if fever should occur especially after returning from a trip in the tropics.

Evolution of malaria in Africa for the past 40 years: impact of climatic and human factors

Different malarial situations in Africa within the past 40 years are discussed in order to evaluate the impact of climatic and human factors on the disease. North of the equator, more droughts and lower rainfall have been recorded since 1972; and in eastern and southern Africa, there have been alternating dry and wet periods in relation to El Niño. Since 1955, the increase in human population from 125 to 450 million has resulted in both expansion of land cultivation and urbanization. In stable malaria areas of West and Central Africa and on the Madagascar coasts, the endemic situation has not changed since 1955. However, in unstable malaria areas such as the highlands and Sahel significant changes have occurred. In Madagascar, cessation of malaria control programs resulted in the deadly epidemic of 1987-88. The same situation was observed in Swaziland in 1984-85. In Uganda, malaria incidence has increased more than 30 times in the highlands (1,500-1,800 m), but its altitudinal limit has not overcome that of the beginning of the century. Cultivation of valley bottoms and extension of settlements are in large part responsible for this increase, along with abnormally heavy rainfall that favored the severe epidemic of 1994. A similar increase in malaria was observed in neighboring highlands of Rwanda and Burundi, and epidemics have been recorded in Ethiopia since 1958. In contrast, in the Sahel (Niayes region, Senegal), stricken by droughts since 1972, endemic malaria decreased drastically after the disappearance of the main vector, Anopheles funestus, due to the destruction of its larval sites by cultivation. Even during the very wet year of 1995. An funestus did not reinvade the region and malaria did not increase. The same situation was observed in the Sahelian zone of Niger. Therefore, the temperature increase of 0.5 degree C during the last 2 decades cannot be incriminated as a major cause for these malaria changes, which are mainly due to the combination of climatic, human, and operational factors.

[Human diseases transmitted by Culicidae in southwest Indian Ocean islands]

South-West Indian Ocean islands were inhabited at the beginning and free from all kind of vector. In Madagascar, Mayotte, Moheli and Anjouan, malaria vectors were carried by the first settlements. According to epidemics, the anopheles arrived in 1867 in Mauritius, 1869 in La Reunion and 1920 in Grande Comore. Rodrigues, Saint-Brandon and the Seychelles are still free from malaria vectors in the coastal part of Madagascarcar and in Comores archipelago, malaria is stable with a permanent transmission. Unstable malaria is seasonaly transmitted in the high territories of Madagascar; it was the same in Mauritius and Reunion island before the eradication campaign. Lymphatic filariasis is quoted in Madagascar, but Comores archipelago is an area with high transmission. The incidence of the disease is moderate in La Reunion and Mauritius and very low in Chagos and Seychelles archipelagos. There is no transmission in Rodrigues and St Brandon. Epidemics of dengue were described during the second part of the XIXth century in Mauritius and La Reunion, then in 1943 in Mayotte. But the disease was controlled in the fifties by the antimalaria campaign. A new epidemy appeared in Seychelles by the end of 1976 and then in Reunion and Mauritius next year. An isolated outbreak was described in Grande Comore only in 1994.

[Impact of antivectorial control on malarial morbidity and mortality in a health district of the Madagascar highlands]

After the dramatic increase of malaria infections from 1985 to 1988 in the Highlands of Madagascar, the vector control programme was reactivated. In order to evaluate the impact of this strategy in the district of Arivonimamo, we have analysed the morbidity and the mortality data collected in all the health care centers of this district. Since 1988, extensive residual house spraying has been carried out on a yearly basis in the eastern part of this district whereas the western part was not included in this spraying programme. Data from each area were compared. In the eastern part, a dramatic decrease of morbitity and mortality related to malaria was observed, the benefit was 69% of expected simple cases, 87% of expected serious cases and 40% of expected deaths due to malaria. It has to be noted that only presumptive cases have been reported since no laboratory facilities are available in these health centers. Nevertheless such findings provide strong support to the continuation of the spraying programme, maybe in a less intensive way, together with an accurate epidemiological surveillance.

[Origin of malaria epidemics on the plateaus of Madagascar and the mountains of east and south Africa]

The Highlands of Madagascar were malaria free until 1878, when a severe epidemic occurred, following the development of irrigated rice farming. Then, the disease became endemic. Between 1949 and 1962, malaria was "eradicated" on the Highlands by joint house spraying and chemoprophylaxis measures. The main vector An. funestus disappeared. In 1986-1988, a very severe epidemic with high lethality rate devastated the Highlands. It is now under control. Thanks to the data of a religious dispensary, we could follow the evolution of malaria on the Highlands from 1971 to 1995. The number of cases begin to grow in 1975 when the surveillance was neglected. A second step was observed in 1979, when chemoprophylaxis/chemotherapy centres were closed. Then, the increase of malaria became exponential up to 1988. At the time, the prevalence had became similar to that of 1948, before the eradication. The epidemic is not due to global warming because the temperature has been stable for the last 30 years. The malaria rise was due the cancellation of control measures. When control was reactivated, the epidemic ceased. In Swaziland, Zimbabwe and South Africa, malaria epidemics were also due to control failure. In Uganda Highlands, above 1500 m, malaria rise seems linked to the environmental changes, e.g. the cultures which replace papyrus swamp in the valley. But malaria did not overcame the altitude of 1900 which it had already reached in 1960. Rainfall should also be considered as a key factor in the epidemics. In the Sahel West Africa, temperature increased from 0.5 degree C to 01 degree C degree in the last 25 years, but rainfall decreased from 30%. As a result, one of the vector, Anopheles funestus disappeared and malaria prevalence dropped by 60 to 80%. It is not acceptable to predict the future evolution of malaria in taking in account only one parameter: the temperature. The whole factors involved in the epidemiology should be taken into account. The predictions based only on the temperature increase (global warming) can be totally wrong if the rainfall, for example, decreases.

[The anopheles of Niger]

Nineteen species of Anopheles have been observed in the Republic of Niger but only Anopheles gambiae, An. arabiensis and An. funestus are of epidemiological importance as malaria vectors. The two species of the An. gambiae complex have the same breeding sites. But in a large part of the country they disappear all during the dry season because of the lack of adequate pools of water. Their survival is as yet an unexplained phenomenon. The most northern wet season distribution of An. gambiae complex, depending on the latitude of the intertropical front. An. funestus was no longer found after 1970 because its breeding places were destroyed both by dryness and human activity. The Republic of Niger is a border area between the palearctic Mediterranean biogeographical region and the Afrotropical one. Two different vectorial systems of malaria transmission are separated by the Sahara desert. The risk of importation of an African vector such as An. gambiae and a parasite such as Plasmodium falciparum must be considered. For the time being, the low volume of road traffic limits the risk but the construction of a paved Transsaharian highway with new human settlements and developing cultivated areas with irrigation increases the dangers of epidemic outbreaks in these oases.

[The reconquest of the Madagascar highlands by malaria]

A strong malaria epidemic with a high mortality rate occurred on the Madagascar Highlands in 1986-88. Vector control and free access to antimalaria drugs controlled the disease. The authors have searched for the causes of the epidemic to propose a strategy avoiding such events. The Highlands on Madagascar were known as malaria free. In 1878 a very severe epidemic flooded all the country. Development of irrigated ricefields which house both An. arabiensis and An. funestus had created a new anthropic environment. Moreover manpower imported from malarious coastal areas for rice cultivation and also for building large temples, could have brought P. falciparum. After several outbreaks the disease became endemic up to 1949. In 1949 a malaria eradication programme based on DDT spraying and drug chemoprophylaxis and chemotherapy was launched. By 1960 malaria was eliminated and DDT spraying cancelled. Only 3 foci were kept under surveillance with irregular spraying until 1975. The prophylaxis and treatment centres ("centres de nivaquinisation") were kept open up to 1979. The catholic dispensary of Analaroa, 100 km N.E. of Tananarive, opened in 1971 and worked without interruption up to now. The malaria diagnosis has always been controlled by microscopy. Its registers are probably the more reliable source of information on malaria in the area. They show that malaria was already present on the Highlands in 1971 but at a low prevalence; in 1980 when the "centres de nivaquinisation" were closed the number of cases increased by three times the progressive increase of the number of cases became exponential from 1986 to 1988 which was the peak of the epidemic; malaria remained at a high level until the end of 1993; yearly DDT spraying since 1993 have decreased the number of malaria cases among the dispensary attendants by 90%. The epidemic peak of 1988 was well documented by the Pasteur Institute of Madagascar around Tananarive. Before the epidemic started it was observed a come back of An. funestus which had been previously eliminated of most of the villages by DDT spraying. More than an epidemic the malaria increase in 1988 was a reconquest by malaria of the land from which it had been eliminated in the years 1950. This episode became dramatic because the lack of immunity of the population and the shortage of medicaments. The global warming which was advocated to explain the epidemic has no responsibility because the temperature on the Madagascar Highlands has not changed during the last 30 years. Also the cyclones do not seem to have played any role. It is very likely that the gradual decline of control measures, first DDT spraying, later drug distributions, had the main responsibility in the Highlands drama. Everywhere An. funestus reached a high level during the time where the parasite reservoir was rebuilding. They synergised each other. These findings should be taken in account in drawing the strategy planning for the next years.

Pitfalls in the diagnosis of airport malaria. Seven cases observed in the Paris area in 1994

Clinical and biological pitfalls that lead to incorrect or delayed diagnoses of airport malaria are described based on 7 cases reported from the Paris region in the summer of 1994. We also report the outcome and the epidemiological features of these patients.

[Impact of changes in the environment on vector-transmitted diseases]

We have defined the relationship between infectious diseases and environmental conditions and considered the development of this relationship to its current situation, where human intervention is occurring more often and is becoming more aggressive. The increase in the transport of freight and passengers by air has allowed parasite vectors to spread quickly and easily over large distances. Every country can now be reached from any other country within a couple of days. Usually, foreign species are unable to establish themselves and to persist in the new environment; but the recent arrival of Aedes albopictus in Albania, Italy and the Americas is a cause for concern. Demographic pressure has increased the need for land and the exploitation of new areas leads to large changes in the vegetation. The classic example of this man-made damage is the destruction of tropical forest in Western Africa, but the destruction of herbaceous vegetation, such as papyrus, in East Africa, could also have serious epidemiological consequences. Streams and rivers have been managed for power production and irrigation. The use of dams, both large and small, and the culture of rice in paddy-fields produces large expanses of water which are suitable breeding grounds for mosquitoes and snails, the vectors of human diseases such as malaria and schistosomiasis in sub-Saharan Africa. They are, however, of lesser importance in Asia and the Americas. Urbanization imposes a set of very similar structures on a specific rural environment. The effect of these two factors on each other determines the pathologies associated with each town. The suburban area is a specific environment where both urban and rural diseases occur and are made worse by poor hygiene conditions (waste, sewage, etc.). However, not all man-made changes to the environment cause a deterioration in public health. Urban and agricultural development projects must consider these issues and should use medical and environmental studies to avoid causing epidemic-prone conditions or spreading endemic diseases. Currently, most studies are limited to listing the specific diseases in the target area and very few attempt to assess the possible consequences of changing the environment. Forecasting the consequences of changes in environmental management is of great importance, but it requires the development of multi-disciplinary teams in the field who must be involved in the planning and implementation of the projects.

Indoor resting by outdoor biting females of Anopheles gambiae complex (Diptera:Culicidae) in the Sahel of northern Senegal

Three villages in the Senegal River basin were selected to study the biting and resting behavior of Anopheles gambiae s.l. in relation to human habits, rainfalls, and rice culture irrigation. All inhabitants sleep outside throughout the year, mainly under poor quality bednets. Mosquitoes were collected host-seeking during the night on human bait outside and resting during the day inside and outside in pit shelters. An. gambiae s.s. and An. arabiensis fed mainly outside, the only place where hosts are available; fed and gravid females resting indoors fed outside. The proportions of An. gambiae s.s. and An. arabiensis in outdoor biting catches and in indoor spray catches were not significantly different, but they differed from year to year with the latter sampling method, An. gambiae s.s. predominated in 1990, a more wet and humid year, whereas An. arabiensis was more common in 1991, which was an arid year. Both species are highly endophilic in this arid area where outdoor-resting places are limited.

[Eco-epidemiology of malaria in Niamey and in the river valley, the Republic of Niger, 1992-1995]

The Niger valley is an original ecosystem in the Sahelian belt. For more than 25 years it has been affected by dryness and rainfall decreased by more than 30% as compared to the period 1950-1960. Moreover the demography has sharply increased and the capital town Niamey grew by 10% a year. The Niger valley including Niamey has about 1 million inhabitants. Three sites have been selected to study the status of malaria and its evolution for the last 30 years: Niamey, Karma 40 km on the N.W. on the river and the nearby fossil valley of Fatay-Karma. In the sixties the malaria vectors were An. gambiae, An. arabiensis et An. funestus. The last species was no more harvested after 1970 because its breeding places have been destroyed on the combined action of dryness and human activities. In Niamey, parasite index was very low in the dry season but grew by 5 to 10 times during the rainy season to reach 50% in certain corners. The highest plasmodic index (PI) were recorded along the river banks where vectors are found all the year long. It decreases in the central part of the city and becomes very low in some peripheral suburban settlements. This situation is quite different of most of the cities of the area where prevalence decrease from outskirts to city centre. The serology confirms these points. In Karma, along the Niger and despite a perennial transmission, the PI removes low as well as the malaria antibodies, probably because of the self use of antimalarial drugs by the population. In Fatay-Karma the PI of 23.9% after the rainy season drops to 6% in the dry one. In data prior to 1970 the PI was over 60%, reaching 89% in young children of Niamey suburbs. Obviously it has strongly decreased. It is very likely that this is due partly to the disappearance of An. funestus after the drought.

[The progress of malaria in sahelian eastern Niger. An ecological disaster zone]

The south eastern part of the Republic of Niger was ecologically damaged by the dryness since 1971. Rainfall decreased by 30 to 40% as compared to 1961-70 and lake Chad retreated 100 km to the south. Now it does not reach any more the Republic of Niger. Malaria studies have been carried out in urban and suburban places in Zinder and in the Diffa area at the extreme east. In Zinder parasitic indexes (PI) after the rainy season were around 30% to 10% according to the situation of the corner in respect with surface waters during the rains. In dry season the index fell to 3%. In Diffa in a part of the city at high risk because lining the Komadougou river, PI was only 6.7% in October after the rains. Before 1970 PI recorded in Niamey were up to 50%. In Diffa area they were of 49% in N'Guigmi and 32% in Bosso, ecologically similar to Diffa. Obviously there was a sharp decrease of malaria which could be due to the disappearance of An. funestus after 1970. It was one of the main malaria vectors. Its larvae were developing in pools remaining after the rains with heavy standing vegetation. These breeding sites have been destroyed by both dryness and human activities. Now the area has became hypoendemic and is suitable for epidemic because population has not much immunity. A surveillance system for epidemic control should be settle.

[Rice: source of life and death on the plateaux of Madagascar]

Since the 17th century, Europeans travelling in Madagascar described the contrast between the fever-free Plateau and the fever-ridden coasts. The former were inhabited by people of Asiatic origins and the latter by African migrants. At the end of the 18th century, "Merina" kings developed land irrigation and rice cultivation, using manpower from the coasts. Since then, rice has become a monoculture covering most of the arable lands of the Highlands. The first malaria epidemic occurred in the Tananarive area in 1878, and rapidly spread throughout the Plateau. The mortality rate was high. A second epidemic in 1895 may have been a resurgence of the previous one. Subsequently, malaria became meso-epidemic despite control measures, mainly consisting of larvivorous fishes, quinine treatment and prophylaxis. In 1949, an eradication program was launched based on DDT house-spraying and chloroquine prophylaxis in children. It was very successful on the Highlands where malaria disappeared, in 1962. Spraying was cancelled and only three small foci remained under surveillance. In 1987 and 1988, a malaria outbreak devastated the plateau. Subsequently, intensive spraying operations brought the situation under control by 1993. The main malaria vector on the Madagascar Highlands is An. funestus. More than 95% of its breeding sites are in the rice fields just before the harvest and afterwards in the fallow lands. The vector peak and the corresponding peak of malaria cases occur between February and May, depending on the farming calender. The second but less important vector, An. arabiensis, breeds in the rice fields just after seeding when the surface water is sunlit. Although rice fields remain the main source of this vector, it also breeds in rainwater pods and borow-pits. Malaria vectors on the plateau are products of human activities of rice cultivation, which is the basis of the economy. The epidemiological importance of rice fields varies greatly from one country to another. In Southeast Asia, the rice fields harbor several anopheline species most of which are only vectors of P. vivax. In West Africa where malaria is holoendemic, they produce large populations of An. gambiae; however, the malaria pattern is unaltered and remains at peak levels. In the dry areas of southern Madagascar, the vector An. funestus and meso-hyperendemic malaria are restricted to areas of cultivated rice. In West and Central Africa, An. funestus is never found in rice fields even though it is common in marshes. In Madagascar, this vector breeds in irrigated rice fields. Because it is practically impossible to control anophelines in rice fields by chemical, biological and ecological methods on the Highlands of Madagascar, house-spraying remains the best method for mass malaria control. Bed-nets impregnated with pesticides may offer an alternative, but their use is resisted by the local population.

[Malaria: research perspectives in medical entomology in Madagascar]

The entomological studies on malaria in Madagascar had especially concerned the behavior of vectors in relation to insecticides. The cessation of spraying within the homes and the absence of chloroquine allowed a re-emergence of malaria on the Plateau in the 1980's. This phenomenon pointed out the heterogeneity of the transmission on the island. It was necessary to define the entomological characteristics of the four principal facies of transmission in Madagascar. These studies provided the services of public health with the epidemiological basis to organize the measures of the battle and prevention of malaria. In the very populated countryside of the Plateau, the nature of the vectors, their density and their vectorial competence present large local variations. The entomological studies search to define the different human and environmental factors which modulate the transmission and constitute the risk factors of epidemy. This micro-epidemiological approach will facilitate the analysis and comparison of the clinical and biological results obtained in the different residences. The research on medical entomology will equally enable the proposal of plans for the fight against malaria adapted to the different situations.

[Particularities and stratification of malaria in Madagascar]

The first factor is the malaria parasite, for which the species P. falciparum and P. vivax are important. Secondly, the transmission determines the disease stability and challenges the host's immunity. The third factor is the human host, consisting of people of both African and Asiatic origin, the latter of whom are more susceptible to P. vivax. Human activities such as cultivating rice fields are of paramount importance for the proliferation of the vectors. The vectors A. gambiae, A. arabiensis and A. funestus are very similar to those of the African continent. These vectors are not endemic on Madagascar, suggesting that they were recently introduced to the island where 95% of the fauna species are endemic. On the Plateau and in the South, the rice fields provide most of the breeding places for A. gambiae s.l. and A. funestus. Five epidemiological belts are found in Madagascar which are very similar to their analogs on continental Africa (fig. 1). These facies include the equatorial belt on the east coast and the tropical belt on the west coast north of Morondava, the Plateau belt analogous to the southern African continent, the southern Madagascar belt which is similar to the Sahelian areas, and finally the zones above 1,500m, which are essentially free of malaria. The first two facies have a stable type of malaria, and in the following two, malaria is unstable. These areas include the Plateau, the area of the severe epidemics which occurred between 1985 and 1988 with more than 50,00 deaths. Malaria control is based on a variety of strategies to respond to the epidemiological heterogeneity of the disease. Spraying within the homes with DDT, used on the Plateau after 1988, was and still is very successful.

[Human diffusion of arthropod disease vectors throughout the world]

The present distribution of animals and plants throughout the world is the result of an evolutionary process involving tectonic, climatic and biotic factors. Humans, since their appearance, have contributed to the spreading of many species including disease vectors and pests. When humans left their native African home, they brought with them ectoparasites such as lice and acarids. During the neolithic era, humans were leading domesticated animals which carried their own parasites into new areas. Dwelling commensals, flea, bugs, triatomids, flies, and cockroaches followed human migrations. In the second millennium, sailboats transported mosquito species which were resistant and reproduced on board, including Culex quinquefasciatus, Aedes aegypti, and Ae. albopictus. Steamers further shortened the length of trips and allowed the transport of anophelines. The opening of the Tamatave-Port-Louis line was immediately followed by the transport of An. gambiae from Madagascar to Mauritius and Reunion, and epidemics of malaria occurred on the two islands which had been free of the disease. Also, An. gambiae was transported from Senegal to Brazil. Old tires destined for recycling carried Ae. albopictus to the USA, Brazil, and then Italy. The pandemic of the plague at the end of the nineteenth century was propagated from harbour to harbour by steamers carrying both infected rats and their fleas Xenopsylla cheopsis. Aircrafts have reduced the travel time so much that in less than two days an insect could reach every point of the world. As soon as the airports had been built on the islands of French Polynesia, they were all colonized by Ae. aegypti. The same phenomenon occurred with midges (Fig. 2). Also, the construction of the airport on a Galapagos Island coincided with the importation of the blackfly Simulium bipunctatum from the continent. In addition, infected malaria mosquitos imported from tropical countries reached Europe and contaminated airport employees and local inhabitants. Six cases of malaria were recorded during the summer of 1994 around the Charles de Gaulle Airport, north of Paris, suggesting that the anophelines could have been imported from West and Central African countries which are served by this airport. The serious threat of vector importation is moderated by the vector's difficulty in adapting to new conditions. However any prediction is questionable.

Impact of deltamethrin-impregnated bednets on biting rates of mosquitoes in Zaire

In a rural area of Zaire, the whole population of a village was protected by deltamethrin-impregnated mosquitoes bednets. A similar village was observed as a control. Biting rates for mosquitoes were recorded in both villages. The principal man-biting species were Mansonia africana, Mansonia uniformis, and Aedes aegypti. In the village protected by the impregnated mosquito bednets, the number of Mansonia bites was reduced 96% indoors and at a lesser rate outdoors. Biting rates of Ae. aegypti dropped to 0 indoors, but the outdoor biting rate remained unchanged. It is concluded that the reduction in mosquito bites is not only caused by the repellent action of the deltamethrin but also by a reduction in mosquito numbers.

[The recycling of waste water and mosquitoes]

Recycling waste water in the Achères complex (North-West Paris) is based on both sophisticated industrial techniques and simple agricultural methods. The sewage farms and settling pools provide suitable breeding sites for more than ten mosquito species. Aedes caspius is the major pest for the local population. Moreover Culex pipiens (anthropophilic form) breeds in the sewers of the neighbouring towns. Mosquito control is based early ground treatment of breeding sites. Temephos and fenotrothion are used against A. caspius. Spherimos (Bacillus sphaericus) is used to control C. pipiens. The two insecticides have no adverse effect on humans or the environment and Spherimos is harmless. Aedes pest have been virtually eliminated. Urban Culex control is generally good despite being performed by less well trained municipal employees. In the areas treated by the specialized team of the SIAAP, pest mosquitoes have disappeared. The techniques used in the Achères complex do not require sophisticated equipment. Thus, if adapted to local ecological, epidemiological and financial conditions they could be transferred to developing countries.

[Study of 6 cases of malaria acquired near Roissy-Charles-de-Gaulle in 1994. Necessary prevention measures in airports]

During the very hot 1994 summer, six new cases of airport malaria have been observed in and around Roissy-Charles-de-Gaulle airport. Four patients were regular or occasional airport employees. The two other cases were inhabitants of a city at 7 km. Entomological investigations suggest that cars of airport employees served to disseminate anophelines outside the airport areas. The six cases were very severe. One patient died. Apparently, W.H.O. recommendations on aircraft disinsecting procedures have not been fully followed. There is obviously a threat for areas near the airports.