Persistent respiratory effort after adenotonsillectomy in children with sleep-disordered breathing.

OBJECTIVES: Adenotonsillectomy (AT) markedly improves but does not necessarily normalize polysomnographic findings in children with adenotonsillar hypertrophy and related sleep-disordered breathing (SDB). Adenotonsillectomy efficacy should be evaluated by follow-up polysomnography (PSG), but this method may underestimate persistent respiratory effort (RE). Mandibular movement (MMas) monitoring is an innovative measurement that readily identifies RE during upper airway obstruction. We hypothesized that MMas indices would decrease in parallel of PSG indices and that children with persistent RE more reliably could be identified with MMas. METHODS: Twenty-five children (3-12 years of age) with SDB were enrolled in this individual prospective-cohort study. Polysomnography was supplemented with a midsagittal movement magnetic sensor that measured MMas during each respiratory cycle before and > 3 months after AT. RESULTS: Adenotonsillectomy significantly improved PSG indices, except for RE-related arousals (RERA). Mandibular movement index changes after AT significantly were correlated with corresponding decreases in sleep apnea-hypopnea index (AHI) and O2 desaturation index (ODI) (Spearman's rho = 0.978 and 0.922, respectively), whereas changes in MMas duration significantly were associated with both RERA duration (rho = 0.475, P = 0.017) and index (rho = 0.564, P = 0.003). Conditional multivariate analysis showed that both AHI and RERA significantly contributed to the variance of MMas index after AT (P = 0.0003 and 0.0005, respectively), whereas MMas duration consistently was related to the duration of RERA regardless of AT. CONCLUSION: Adenotonsillectomy significantly reduced AHI. However, persistent RERA were apparent in a significant proportion of children, and this was reflected by the remaining abnormal MMas pattern. Follow-up of children after AT can be recommended and readily achieved by monitoring MMas to identify persistent RE. LEVEL OF EVIDENCE: 4. Laryngoscope, 128:1230-1237, 2018.

Monitoring mandibular movements to detect Cheyne-Stokes Breathing.

BACKGROUND: The patterns of mandibular movements (MM) during sleep can be used to identify increased respiratory effort periodic large-amplitude MM (LPM), and cortical arousals associated with "sharp" large-amplitude MM (SPM). We hypothesized that Cheyne Stokes breathing (CSB) may be identified by periodic abnormal MM patterns. The present study aims to evaluate prospectively the concordance between CSB detected by periodic MM and polysomnography (PSG) as gold-standard. The present study aims to evaluate prospectively the concordance between CSB detected by periodic MM and polysomnography (PSG) as gold-standard. METHODS: In 573 consecutive patients attending an in-laboratory PSG for suspected sleep disordered breathing (SDB), MM signals were acquired using magnetometry and scored manually while blinded from the PSG signal. Data analysis aimed to verify the concordance between the CSB identified by PSG and the presence of LPM or SPM. The data were randomly divided into training and validation sets (985 5-min segments/set) and concordance was evaluated using 2 classification models. RESULTS: In PSG, 22 patients (mean age ± SD: 65.9 ± 15.0 with a sex ratio M/F of 17/5) had CSB (mean central apnea hourly indice ± SD: 17.5 ± 6.2) from a total of 573 patients with suspected SDB. When tested on independent subset, the classification of CSB based on LPM and SPM is highly accurate (Balanced-accuracy = 0.922, sensitivity = 0.922, specificity = 0.921 and error-rate = 0.078). Logistic models based odds-ratios for CSB in presence of SPM or LPM were 172.43 (95% CI: 88.23-365.04; p < 0.001) and 186.79 (95% CI: 100.48-379.93; p < 0.001), respectively. CONCLUSION: CSB in patients with sleep disordered breathing could be accurately identified by a simple magnetometer device recording mandibular movements.

Mandibular position and movements: Suitability for diagnosis of sleep apnoea.

BACKGROUND AND OBJECTIVE: Mandibular movements (MMs) and position during sleep reflect respiratory efforts related to increases in upper airway resistance and micro-arousals. The study objective was to assess whether MM identifies sleep-disordered breathing (SDB) in patients with moderate to high pre-test probability. METHODS: This was a prospective study of 87 consecutive patients referred for an in-laboratory sleep test. Magnetometer-derived MM signals were incorporated into standard polysomnography (PSG). Respiratory events detected with MM analysis were compared with PSG for respiratory disturbance index (RDI) with a blinded scoring. All records were scored manually according to American Academy of Sleep Medicine rules. Primary outcome was to rule-in obstructive sleep apnoea syndrome (OSAS) defined as RDI cut-off value ≥5 or 15/h total sleep time (TST). RESULTS: High concordance emerged between MM and PSG-derived RDI with high temporal coincidence between events (R2 = 0.906; P < 0.001). The mean diagnostic accuracy of MM for OSAS using RDI MM cut-off values of 5.9 and 13.5 was 0.935 (0.86-0.97) and 0.913 (0.84-0.95), with a mean positive likelihood ratio (LLR+) of 3.73 (2.7-20.4) and 8.46 (2.3-31.5), respectively. Receiver operating characteristic (ROC) curves at PSG cut-off values of 5 and 15/h TST had areas under the curve (AUC) of 0.96 (95% CI: 0.89-0.99) and 0.97 (95% CI: 0.91-0.99) (P < 0.001), respectively. MM analysis accurately identified SDB at different levels of severity. CONCLUSION: RDI assessed by MM is highly concordant with PSG, suggesting a role of ambulatory MM recordings to screen for SDB in patients with moderate to high pre-test probability.

In vivo estimates of NO and CO conductance for haemoglobin and for lung transfer in humans.

Membrane conductance (Dm) and capillary lung volume (Vc) derived from NO and CO lung transfer measurements in humans depend on the blood conductance (θ) values of both gases. Many θ values have been proposed in the literature. In the present study, measurements of CO and NO transfer while breathing 15% or 21% O2 allowed the estimation of θNO and the calculation of the optimal equation relating 1/θCO to pulmonary capillary oxygen pressure (PcapO2). In 10 healthy subjects, the mean calculated θNO value was similar to the θNO value previously reported in the literature (4.5mmHgmin(-1)) provided that one among three θCO equations from the literature was chosen. Setting 1/θCO=a·PcapO2+b, optimal values of a and b could be chosen using two methods: 1) by minimizing the difference between Dm/Vc ratios for any PcapO2, 2) by establishing a linear equation relating a and b. Using these methods, we are proposing the equation 1/θCO=0.0062·PcapO2+1.16, which is similar to two equations previously reported in the literature. With this set of θ values, DmCO reached the morphometric range.

Evidence of dengue virus transmission and factors associated with the presence of anti-dengue virus antibodies in humans in three major towns in Cameroon.

BACKGROUND: Dengue is not well documented in Africa. In Cameroon, data are scarce, but dengue infection has been confirmed in humans. We conducted a study to document risk factors associated with anti-dengue virus Immunoglobulin G seropositivity in humans in three major towns in Cameroon. METHODOLOGY/PRINCIPAL FINDINGS: A cross sectional survey was conducted in Douala, Garoua and Yaounde, using a random cluster sampling design. Participants underwent a standardized interview and were blood sampled. Environmental and housing characteristics were recorded. Randomized houses were prospected to record all water containers, and immature stages of Aedes mosquitoes were collected. Sera were screened for anti-dengue virus IgG and IgM antibodies. Risk factors of seropositivity were tested using logistic regression methods with random effects. Anti-dengue IgG were found from 61.4% of sera in Douala (n = 699), 24.2% in Garoua (n = 728) and 9.8% in Yaounde (n = 603). IgM were found from 0.3% of Douala samples, 0.1% of Garoua samples and 0.0% of Yaounde samples. Seroneutralization on randomly selected IgG positive sera showed that 72% (n = 100) in Douala, 80% (n = 94) in Garoua and 77% (n = 66) in Yaounde had antibodies specific for dengue virus serotype 2 (DENV-2). Age, temporary house walls materials, having water-storage containers, old tires or toilets in the yard, having no TV, having no air conditioning and having travelled at least once outside the city were independently associated with anti-dengue IgG positivity in Douala. Age, having uncovered water containers, having no TV, not being born in Garoua and not breeding pigs were significant risk factors in Garoua. Recent history of malaria, having banana trees and stagnant water in the yard were independent risk factors in Yaounde. CONCLUSION/SIGNIFICANCE: In this survey, most identified risk factors of dengue were related to housing conditions. Poverty and underdevelopment are central to the dengue epidemiology in Cameroon.

Human antibody response to Aedes aegypti saliva in an urban population in Bolivia: a new biomarker of exposure to Dengue vector bites.

Aedes mosquitoes are important vectors of re-emerging diseases in developing countries, and increasing exposure to Aedes in the developed world is currently a source of concern. Given the limitations of current entomologic methods, there is a need for a new effective way for evaluating Aedes exposure. Our objective was to evaluate specific antibody responses to Aedes aegypti saliva as a biomarker for vector exposure in a dengue-endemic urban area. IgG responses to saliva were strong in young children and steadily waned with age. Specific IgG levels were significantly higher in persons living in sites with higher Ae. aegypti density, as measured by using entomologic parameters. Logistic regression showed a significant correlation between IgG to saliva and exposure level, independently of either age or sex. These results suggest that antibody responses to saliva could be used to monitor human exposure to Aedes bites.

Genetic structure and phylogeography of Aedes aegypti, the dengue and yellow-fever mosquito vector in Bolivia.

Between the 16th and 18th centuries, Aedes aegypti (Diptera: Culicidae), a mosquito native to Africa, invaded the Americas, where it was successively responsible for the emergence of yellow fever (YF) and dengue (DEN). The species was eradicated from numerous American countries in the mid-20th century, but re-invaded them in the 1970s and 1980s. Little is known about the precise identities of Ae. aegypti populations which successively thrived in South America, or their relation with the epidemiological changes in patterns of YF and DEN. We examined these questions in Bolivia, where Ae. aegypti, eradicated in 1943, re-appeared in the 1980s. We assessed the genetic variability and population genetics of Ae. aegypti samples in order to deduce their genetic structure and likely geographic origin. Using a 21-population set covering Bolivia, we analyzed the polymorphism at nine microsatellite loci and in two mitochondrial DNA regions (COI and ND4). Microsatellite markers revealed a significant genetic structure among geographic populations (F(ST)=0.0627, P<0.0001) in relation with the recent re-expansion of Ae. aegypti in Bolivia. Analysis of mtDNA sequences revealed the existence of two genetic lineages, one dominant lineage recovered throughout Bolivia, and the second restricted to rural localities in South Bolivia. Phylogenic analysis indicated that this minority lineage was related to West African Ae. aegypti specimens. In conclusion, our results suggested a temporal succession of Ae. aegypti populations in Bolivia, that potentially impacted the epidemiology of dengue and yellow fever.

Evaluation of the human IgG antibody response to Aedes albopictus saliva as a new specific biomarker of exposure to vector bites.

BACKGROUND: The spread of Aedes albopictus, a vector for re-emergent arbovirus diseases like chikungunya and dengue, points up the need for better control strategies and new tools to evaluate transmission risk. Human antibody (Ab) responses to mosquito salivary proteins could represent a reliable biomarker for evaluating human-vector contact and the efficacy of control programs. METHODOLOGY/PRINCIPAL FINDINGS: We used ELISA tests to evaluate specific immunoglobulin G (IgG) responses to salivary gland extracts (SGE) in adults exposed to Aedes albopictus in Reunion Island. The percentage of immune responders (88%) and levels of anti-SGE IgG Abs were high in exposed individuals. At an individual level, our results indicate heterogeneity of the exposure to Aedes albopictus bites. In addition, low-level immune cross-reactivity between Aedes albopictus and Aedes aegypti SGEs was observed, mainly in the highest responders. CONCLUSION/SIGNIFICANCE: Ab responses to saliva could be used as an immuno-epidemiological tool for evaluating exposure to Aedes albopictus bites. Combined with entomological and epidemiological methods, a "salivary" biomarker of exposure to Aedes albopictus could enhance surveillance of its spread and the risk of arbovirus transmission, and could be used as a direct tool for the evaluation of Aedes albopictus control strategies.

Morphological and genetic variability within Aedes aegypti in Niakhar, Senegal.

Aedes aegypti (Linné, 1762) is a major vector of arboviruses such as Yellow Fever, Dengue and Chikungunya. In Africa, where the species exhibits major variations in morphology, ecology, behavior and vector competence, two subspecies have been described: a light form, named Ae. aegypti aegypti (Aaa) with highly domestic and anthropophilic habits and a cosmotropical distribution; and a dark form, referred to as Ae. aegypti formosus (Aaf), which is endemic to Africa and thrives in sylvan environments. In East Africa, both forms were described to occur in sympatry whereas only Aaf was reported from Central/West Africa. However, recent findings suggest Aaa was also common in Senegal. Here, we report on a longitudinal survey of morphological and genetic variability of Ae. aegypti sampled in the rural environment of Niakhar, Senegal. In agreement with recent findings, most of specimens we analyzed were classified as Aaa suggesting typical Aaf was scarce in the studied area. Among Aaa, significant temporal variations in abdominal pale scales pattern were detected. Depending on the season and the nature of larval breeding places, the specimens (particularly females) tend to segregate in two main morphological groups. Microsatellite-based estimates of genetic differentiation did not provide any clear evidence that the two groups were genetically distinct. Overall, these results improve our understanding of the diversity of Ae. aegypti in West Africa, where data are crucially lacking.

Comparative role of Aedes albopictus and Aedes aegypti in the emergence of Dengue and Chikungunya in central Africa.

Since its discovery in Nigeria in 1991, Aedes albopictus has invaded much of Central Africa, a region where Ae. aegypti also occurs. To assess the relationship between the invasion by Ae. albopictus and the recent emergence of dengue virus (DENV) and chikungunya virus (CHIKV), we undertook vector competence experiments on populations collected from Cameroon and conducted field investigations during concurrent epidemics of DENV and CHIKV in Gabon. Overall, infection and dissemination rates were not significantly different between Ae. albopictus and Ae. aegypti when exposed to titers of 10(8.1) mosquito infectious dose 50/mL and 10(7.5) plaque forming units/mL of DENV type 2 and CHIKV, respectively. Field investigations showed that Ae. albopictus readily bit man, was abundant, and outnumbered Ae. aegypti to a large extent in Gabon, particularly in suburban environments. Nevertheless, Ae. aegypti was predominant in the more urbanized central parts of Libreville. In this city, CHIKV and DENV were detected only in Ae. albopictus. These data strongly suggest that Ae. albopictus acted as the major vector of both viruses in Libreville in 2007, impacting on the epidemiology of DENV and CHIKV in this area.

Molecular epidemiological analysis of dengue fever in Bolivia from 1998 to 2008.

Dengue fever was first recognized in Bolivia in 1931. However, very limited information was available to date regarding the genetic characterization and epidemiology of Bolivian dengue virus strains. Here, we performed genetic characterization of the full-length envelope gene of 64 Bolivian isolates from 1998 to 2008 and investigated their origin and evolution to determine whether strains circulated simultaneously or alternatively, and whether or not multiple introductions of distinct viral variants had occurred during the period studied. We determined that, during the last decade, closely related viruses circulated during several consecutive years (5, 6, and 6 years for DENV-1, DENV-2, and DENV-3, respectively) and the co-circulation of two or even three serotypes was observed. Emergence of new variants (distinct from those identified during the previous episodes) was identified in the case of DENV-1 (2007 outbreak) and DENV-2 (2001 outbreak). In all cases, it is likely that the viruses originated from neighboring countries.

Gene flow between domestic and sylvan populations of Aedes aegypti (Diptera: Culicidae) in North Cameroon.

Polymorphisms at eight microsatellite loci and a fragment of the mitochondrial DNA (mtDNA)-ND4 gene were surveyed in Aedes aegypti (L.) (Diptera: Culicidae) populations collected from six localities in North Cameroon, with emphasis on comparing domestic versus sylvan populations. The microsatellites revealed significant genetic differentiation among sylvan populations, with mean F(ST) = 0.066. Domestic collections were genetically homogeneous (mean F(ST) = 0.012). No pattern of isolation by distance was detected, and one of highest levels of genetic differentiation was estimated between populations sampled a few kilometers apart, each in a distinctly different ecological environment (F(ST) = 0.076). Analyses of mtDNA-ND4 polymorphisms and divergence between the two neighboring populations revealed increased genetic diversity within the domestic population, with molecular signatures suggesting recent demographic expansion, whereas a single haplotype was observed in the sylvan sample. These data suggest reduced gene flow between sylvan and domestic Ae. aegypti populations in North Cameroon, reminiscent of the situation for Ae. aegypti in Kenya in East Africa.

Levocetirizine for treatment of immediate and delayed mosquito bite reactions.

People frequently experience whealing and delayed papules from mosquito bites. Various antihistamines have previously been tried for the treatment of this condition. We performed a double-blind, placebo-controlled, cross-over study with levocetirizine 5 mg and matched placebo in 30 adults who were sensitive to mosquito bites. On the third treatment day the subjects received two Aedes aegypti bites on the forearm. The size of the bite lesions and the intensity of pruritus (visual analogue scale) were measured. Bite symptoms could be analysed in 28 subjects at 15 min and in 8 subjects at 24 h. Levocetirizine decreased the size of wheals by 60% (p < 0.001) and accompanying pruritus by 62% (p < 0.001) compared with placebo. The effect of levocetirizine increased in a linear fashion with the size of wheals and was most significant in the subjects with largest bite lesions. Levocetirizine also decreased the size of 24-h bite lesions by 71% (p=0.008) and accompanying pruritus by 56% (p=0.016). These results show that prophylactic levocetirizine 5 mg is an effective treatment for both immediate and delayed mosquito bite symptoms and is especially effective in subjects with large wheals.

Evaluation of the antibody response to Anopheles salivary antigens as a potential marker of risk of malaria.

The evaluation of human immune responses to arthropod bites may be a useful marker of exposure to vector-borne diseases, with applications to malaria, the most serious parasitic infection in humans. The specific antibody (Ab) IgG response to saliva obtained from Anopheles gambiae mosquitoes was evaluated in young children from an area of seasonal malaria transmission in Senegal. Specific IgG was higher in children who developed clinical Plasmodium falciparum malaria within the 3 months that followed than in those who did not (P<0.05), and it increased significantly (P<0.0001) with the level of Anopheles exposure, as evaluated by conventional entomological methods. These results suggest that evaluation of antisalivary Ab responses could be a useful approach for identifying a marker for the risk of malaria transmission.

Assessment of laboratory and field assays of sunlight-induced killing of mosquito larvae by photosensitizers.

The effectiveness of light-induced killing of mosquito larvae in the presence of photosensitizers was studied with larvae of Aedes aegypti (L.), Anopheles stephensi (Liston), and Culex quinquefasciatus Say grown in the laboratory and of Cx. quinquefasciatus grown under field conditions. Tested photosensitizers included xanthene, chlorin, and porphyrin derivatives. All the larvae were treated at the fourth instar. Preliminary laboratory experiments showed a light-induced lethal effect of Rose Bengal (RB) on three species of mosquito larvae. Compared with other photosensitizers, RB seemed to be more efficient at even lower concentration than chlorin (e6) and chlorophyllin on Ae. aegypti larvae. Among the four porphyrin derivatives, i.e., chloroquinoline tetraphenyl propioamidoporphine, tetraphenyl porphine tetrasulfonate, hematoporphyrin (HP), and tetraphenylporphinepropionic acid porphine, HP was the only effective photosensitizer on Ae. aegypti larvae. The best conditions for field tests using RB were conducted on Cx. quinquefasciatus in Bobo-Dioulasso, Burkina Faso. The mortality induced by RB varied from 80 to 96% obtained with unfiltered cesspit water to 0.4 to 6.7% in cesspits with a heavy load of organic materials, thus providing the basis for further developments of this technique under field conditions.

The frist laboratory confirmed cases of dengue fever in Brazil: virus isolation and sorological results

Investigation of an extensive outbreak of febrile illness in the city of Boa Vista, Roraima State, Brazil, that began in late 1981 lasted until August 1982, established that dengue virus was incriminated in the etiology. Virological studies were madeon 31 selected patients, dengue virus (types 1 and 4) was isolated in 12 of them. The virus (both types) was also isolated from three of 51 pools (1,478 mosquitoes) of Aedes aegypti captured especially downtown. To isolate the virus, allthe material was inoculatedin Aedes albopictus cells (C6/36) and in suckling mice, and virus isolates were identified by the indirect immunofluorescence usingthe monoclonal antibodies. The results of hemagglutination inhibition and complement fixationtest with 27 paired acute convalescent phase sera and 359 single convalescent or contacts sera were highly suggestive of dengue etiology.The clinical features were those os classical dengue fever. Later, afterthe outbreak, serological survey involving899 sera was conducted in order to determine the extent of the epidemic. The results indicated that at 11,000 dengue cases ocurred. These are the first laboratory confirmed cases of dengue fever in Brazil

Entomological studies on Dengue fever vectors in Brazil: the epidemics of Boa Vista, Roraima, 1982, Niteroi, Rio de Janeiro, 1986, and Ceara State, 1986, 1994

No Brasil, o virus deo dengue é transmitido pelo mosquito urbano Aedes Aegypti. Foi na ocasiäo dos primeiros isolamentos realizados a partir de casos humanos em Boa Vstas (RR) que o virus foi também isolado - sorotipos DEN 1 (1 amostra) e DEN 4 (2 amostras) - a partir de mosquitos naturalmente infectados. Durante o segundo episódio epidêmico, em Niterói (RJ) , foram isoladas 3 amostras de DEN 1 a partir de mosquitosfêmeas coletadas com isca humana ou em repouso. Durante essa epidemia, nos locais nâo tratados por inseticidas, o índice de Breteau era de 102. A dissecaçäo de uma amostragen dos mosquitos mostrou que (1) as fêmeas agressivas eram mais velhas que as coletadas em repouso, (2) a proporçäo de repastos interrompidos ou múltiplos era elevada. Inquéritos entomológicos foram realizados durante as epidemias de 1986 e 1994 no Ceará. Tres amostras de DEN 1 e 16 amostras de DEN 2 foram isoladas a partir de AE. aegypti coletados em Cascavel e Caucaia, respectivamente. A suscetibilidade à infecçäo oral dos mosquitos sobre os pacientes com viremia pelo virus DEN 2 foi testada. Positividade dos mosquitos apareceu a partir do terceiro dia após repasto. 44 por cento dos mosquitos form infectados após ter sido alimentados com sangue contendo um título de virus ( Log TCD 50) igual a 3,5 . Tentativas de isolamento a partir de mosquitos machos, imaturos ou outras espécies foram negativas

Modifications of arbovirus transmission in relation to construction of dams in Brazilian Amazonia

The Amazonian region of Brazil seems to be the world's richest reservoir of arboviruses. To date, 183 different types of arboviruses have been detected in the Amazonian region, accounting for more than one third of the 535 arboviruses reported in the world. Of these, 136 (74.3 per cent) are endemic. The main objective of this paper was to evaluate what the effects of the construction and flooding of dams would be on the transmission and epidemiology of sylvatic arboviruses, in order to define the potential health hazards to which the human population would be subjected. Five areas were surveyed but only one could be thoroughly studied. Comparisons were made between surveys: i) inside the dam region, before, during and after the flooding period; ii) outside the dam region, in an area with a similar climate, landscape and vegetation, during the total time of the studies. The two chosen areas, namely Altamira and Tucuruí, were studied since 1974, and since September, 1982, respectively. The former, and the latter before the outset of flooding (September 6, 1984) were considered as a control or reference for comparisons with data obtained in Tucuruí during flooding and thereafter. The surveys consisted of sampling as many wild vertebrates and haematophagous Diptera as possible. Human sera were collected from febrile cases and random serological surveys. Very few variations seem to have occurred among the three phases of the study, with a maximum of positive serologies during the flooding period, but the differences were not statistically significant. Similarly, in the reference region, the prevalence of antibodies against the four more important arbovirus groups did not vary significantly. The arboviruses were classified under two categories: i) those which showed enhanced transmission and ii) those which showed no apparent modifications in their transmission patterns (referring to the control area). Three new and three already known types in the Anopheles A group of Bunyavirus were favoured by the great proliferation of Anopheles nuneztovari and An. triannulatus which accompanied the flooding of the dam. An epizootic of the Gamboa virus (Bunyavirus, Gamboa serogroup), newly reported in Brazil, was observed one year after the outset of flooding, when the mosquito Aedeomyia squamipennis showed very large populations. Guaroa (Bunyavirus, California group), an endemic arbovirus, showed an epizootic probably as a consequence of the proliferation of anopheline mosquitoes. A temporary proliferation of Culex spp. mosquitoes and the presence of a rich avifauna in the dam area during flooding are probable causes of the enhanced circulation of Turlock (Bunyavirus, Turlock group) and Kwatta-like (Rhabdoviridae, Kwatta group) viruses...

A comparative study of yellow fever in Africa and South America

In order to look for an ecoepidemiological model of sylvatic yellow fever (YF) transmission in South America, differences from and similarities to available African YF data are considered. Strains from both areas, representing various topotypes, are distinct serologically, genetically and biochemically. In Africa, all vector mosquitoes are Aedes species, some related to the forest cycle and others responsible for the transmission in dryer areas. In South America, and particularly in Brazil, the main vector is Haemagogus janthinomys. Hg. albomaculatus has been incriminated in human peridomestic transmission in Central Amazonia. In the two continents, monkeys are the only regular vertebrate hosts of YF but the indigenous neotropical monkeys, show higher mortality rates. The South American and African vectors are diurnal and crespuscular/nocturnal in habit, respectively. The urban vector (Ae. aegypti) has the same habits in both continents, but its competence in transmitting the virus is very variable, and no urban epidemic has been notified in South America since the 4Os. A general ecoepidemiological model was elaborated to explain the maintenance and circulation of YF virus in West and Central Africa, which are related to the phytoclimatical regions. Because no such hypothesis has yet been presented in the case of YF in South America, we tested this with the available data from Brazil. All occurrences (of which 386 were lab-confirmed) were distributed in five phytogeographical zones: dense rain forest (l89), open rain forest (30), savannah with gallery forest (l47), ecotones (lO) and decidual seasonal forest (7). For each of these zones mean intervals between years with occurrences of YF were estimated. They were all found to be lower than 3 years, and lower than 5 years when standard deviation was added. Despite the close values obtained for the means, the distribution of the years as a function of number of occurrences of YF showed two groups: a) gallery forest and dense forest and b) open forest and ecotones. However, more data are necessary to enable the study of such variations which are thought to be related to ecological differences in YF transmission.