The nematode Anisakis simplex in American shad (Alosa sapidissima) in two Oregon rivers.

This paper represents the first report of the nematode Anisakis simplex in the American shad (Alosa sapidissima) in its introduced range in the American Pacific Northwest. All the adult shad sampled from spawning populations in the Willamette (n = 9) and Umpqua (n = 12) rivers were infected with A. simplex with intensities ranging from 6 to 89 worms per fish. This preliminary investigation contrasts sharply with previous studies in the native range of American shad and confirms that this fish may be an important intermediate host for A. simplex in the Pacific Northwest. It is suggested that this new parasite-host relationship has led to an ecological expansion into rivers and Anisakis may present an emerging health risk for wildlife and some human consumers.

An olfactometer for discriminating between attraction, inhibition, and repellency in mosquitoes (Diptera: Culicidae).

We constructed an olfactometer that differentiates and quantifies attraction, inhibition, and repellency to mosquitoes. Using this device, 22 formulations of various chemicals on gauze pads and 8 dilutions of DEET on skin were tested. Four novel formulations were discovered acting as true repellents, whereas DEET did not act as a true repellent but as an inhibitor.

Recovery of a second instar Gasterophilus larva in a human infant: a case report.

We report a case in an infant of horse bot fly myiasis that was unusual because the maggot had developed to the second instar (of three potential instars). This represents the first report of such late development in a human. The case occurred in a rural area of the Pacific northwest (Washington) in late summer.

Behavioural mode of action of deet: inhibition of lactic acid attraction.

Using the mosquito Aedes aegypti in a novel olfactometer that measures movement towards and away from a stimulus, we could not confirm that 'deet' is a repellent of mosquitoes. In the absence of a host, deet was an attractant and in the presence of a host, it was an inhibitor of attraction. This inhibition occurred in the gaseous phase and was therefore not the result of the physical properties of deet. We determined that L-lactic acid, a component of human sweat that is an attractant to mosquitoes, is the target of this inhibition, implying that lactic acid may be a bottleneck in the behavioural cascade preceding blood-sucking.

Probability model on the use of sentinel animal monitoring for arbovirus.

We specify the relations among the major parameters involved in using sentinel animals to monitor arbovirus transmission. By using probability models, first we demonstrate that vector density, infection rate, incubation period of sentinel animals, the number of sentinel animals used, and blood sampling frequency could directly affect the observed seroconversion rates and the comparison of these rates. Second, we evaluate the reliability of using sentinel animals to monitor arbovirus transmission under various conditions. On the basis of the model, we propose some measures for enhancing the reliability of using sentinel animals to monitor arbovirus. Third, we present a formula for estimating the number of sentinel animals used for a study designed to compare seroconversion rates. Fourth, we derive a necessary condition for deciding the blood sample frequency of sentinel animals. Fifth, we develop a formula that could be used to obtain the vector infection rate by using seroconversion data. Finally, we evaluate the epidemiology consequences of heterogeneous exposure of human hosts to vectors by theoretical modeling.

Evaluation of commercial insect repellents on human skin against Aedes aegypti (Diptera: Culicidae).

An olfactometer was used to evaluate the efficacy of selected commercial insect repellent products against Aedes aegypti (L.). A comparison of 12 commercial repellent products was made on human skin. The products tested included 2 natural oil insect repellent formulations (Buzz Away and Green Ban) containing plant extracts, 2 proprietary products (Skin-So-Soft lotion and bath oil), and 8 commercial deet preparations in various concentrations and forms of spray, aerosol, stick, cream, and lotion. Behavioral responses and time to probe were determined in triplicate using 10 female mosquito challenges per replicate for each product. Generally, products with higher concentrations of deet were found to have longer repellence times. OFF spray and Muskol lotion offered the longest repellence times. However, there was no significant difference in time for mosquitoes to probe among the formulations. Skin-So-Soft lotion and bath oil were not as effective as deet in repelling Ae. aegypti. Natural oil insect repellent formulations offered essentially no repellency against Ae. aegypti. This is a simple and reproducible method to evaluate the efficacy of insect repellents and is recommended for preliminary screening of new insect repellents or formulations.

Malaria in central Haiti: a hospital-based retrospective study, 1982-1986 and 1988-1991.

A retrospective study conducted at central Haiti's Albert Schweitzer Hospital in the June 1991-January 1992 period sought to assess the numbers of malaria cases seen at the hospital in 1982-1991, the distribution of cases by age and sex in 1988-1991, and the validity of official reports indicating an overall decline in malaria cases. Review of the hospital's laboratory records (1982-1986, 1988-1991), patient medical records (1989-1991), and patient discharge summary cards (1989-1991) revealed a total of 5,251 malaria cases identified through examination of approximately 65,000 blood smears. The largest numbers of cases were diagnosed in 1982 (1,150) and 1988 (980); the smallest numbers in 1990 (120) and 1991 (317). Peak case incidences occurred yearly in the November-January period, a few months after the rainy season. Of the 838 cases found in the 1989-1991 period, 53% occurred in females and 47% in males. Relatively high numbers of cases (averaging 41.1 cases per year of age) were found among children 0-6 years old, with the largest number of cases in any 1-year age group (54 cases) occurring among children 1 year old. (In general, the numbers of cases declined with increasing age.) Eight cases among hospital in-patients ended in malaria-related death, five of these deaths occurring among children 0-6 years old and six involving cerebral malaria (a common complication of P. falciparum infection). Overall, the results of this study support official reports showing a general decline in the number of malaria cases in this region of Haiti between 1982 and 1991.

PIP: Official reports indicate that the incidence of malaria is declining in Haiti. This paper reports findings from a retrospective study conducted at central Haiti's Albert Schweitzer Hospital June 1991-January 1992 to confirm the validity of these reports. Review of hospital laboratory records, patient medical records, and patient discharge summary cards for the period 1982-91 found 5251 malaria cases identified through examination of approximately 65,000 blood smears. The largest numbers of cases were diagnosed in 1982 and 1988; 1150 and 980 cases, respectively. The fewest cases were diagnosed in 1990 and 1991; 120 and 317, respectively. Peak case incidences occurred yearly during November-January, a few months after the rainy season. 53% of the 838 cases identified during 1989-91 were among females. Relatively high numbers of cases were found among children aged 0-6 years, with the largest number of cases in any one-year age group (54) occurring among children aged one year. Eight cases among hospital inpatients resulted in malaria-related death, with five deaths occurring among children aged 0-6 years and six cases involving cerebral malaria. These results support official reports indicating a general decline in the number of malaria cases in central Haiti between 1982 and 1991.

Extracts of mosquito salivary gland inhibit tumour necrosis factor alpha release from mast cells.

Extracts of salivary glands of the yellow fever mosquito Aedes aegypti inhibit tumour cell-stimulated release of tumour necrosis factor alpha (TNF alpha) from rat mast cells, but do not inhibit antigen-induced histamine secretion. This inhibitory activity for TNF alpha is found in salivary glands of female but not in male mosquitoes. This inhibition is not mediated by bacterial contamination (LPS), by calcitonin gene related peptide (CGRP), nerve growth factor (NGF), epidermal growth factor (EGF) or transforming growth factor beta (TGF beta). The factor(s) has a molecular weight > 10 kDa and is neutralized by boiling for 10 min or heating at 56 degrees C for 30 min. The modulation of this proinflammatory mediator, TNF alpha, produced by mast cells in sites of blood feeding may facilitate completion of the blood meal, and as reported for certain vector-transmitted parasites, may enhance infectivity.

Blood vessel location time by Anopheles stephensi (Diptera: Culicidae).

Probing behavior of Anopheles stephensi Liston is characterized by the following: the first probe is longer than subsequent ones, the probability of blood location rises initially and then falls, and blood vessel location is deterministic. The overall probing behavior of An. stephensi, therefore, is similar to that of Aedes aegypti (L.); i.e., differences between them were quantitative and may be accounted for by different levels of salivary apyrase and different experimental vertebrate hosts.

Probing behaviour and sporozoite delivery by Anopheles stephensi infected with Plasmodium berghei.

We observed that Plasmodium berghei sporozoite-infected Anopheles stephensi was not impaired in its ability to locate blood on a host. When probing rats, infected mosquitoes took as long as non-infected mosquitoes to locate blood. Contrary to previous suggestions, infective mosquitoes delivered sporozoites into mineral oil even after extensively probing a vertebrate host. We observed that, in mosquitoes having probed a host, both the mean number of sporozoites ejected over 3 min into oil (35.9 v. 31.7 sporozoites) and the proportion of mosquitoes delivering sporozoites (60% v. 50%) were similar to mosquitoes not having probed. We then developed a model of sporozoite delivery, taking into account observations that sporozoites are clumped in the lumen of the glands as well as upon delivery, and that output is uneven and inconsistent. We conclude that clumping optimizes transmission, if a threshold of infection exists and the mean number of sporozoites per clump is greater than the threshold.

Reduction of tracheal mite parasitism of honey bees by swarming.

Based on population dynamics, tracheal mite (Acarapis woodi) parasitism of colonies of honey bees (Apis mellifera) appears to be, potentially at least, regulatory and stable. Empirical and theoretical considerations suggest, however, that intracolony population dynamics of mite-honey bee worker seem to be unstable in managed situations where honey bee worker population is allowed to grow unchecked. Experimental studies showed that tracheal mite population levels increased in a managed honey bee colony but were impaired in one in which brood rearing was interrupted by loss of the queen. Mite densities but not prevalence were lowered in experimental swarms kept from rearing brood. We propose that swarming reduces mite density within a colony, therefore implicating modern techniques of hive management in the sudden historical appearance of the mite on the Isle of Wight.

Mosquito salivary glands: Parasitological and molecular aspects.

The salivary glands of mosquitoes serve in sugar feeding and blood vessel location. Components have been recently identified that may function in sugar feeding and digestion and platelet anti-aggregation. These factors correlate with salivary gland structure and appear to be controlled differentially in female mosquitoes. Analysis of gene expression has led to the discovery of three novel moieties in saliva: two involved in sugar feeding and one, specific to female mosquitoes, which is probably involved in blood feeding. Studies of parasite involvement in the salivary glands and host haemostasts have shown that parasites target specific interactions and modify them to enhance transmission. Here, Anthony James and Philippe Rossignol present an overview of mosquito salivary gland morphology and function, discuss recent advances in salivary gland molecular biology that have led to the discovery of new components and describe how parasites may modify salivary function to enhance transmission,.

Honey bee mortality due to tracheal mite parasitism.

We demonstrate, by truncating the expected negative binomial distribution, that the tracheal mite parasite, Acarapis woodi, causes mortality in the European honey bee, Apis mellifera, but, that this mortality can be documented only during periods of low mite densities (mites per bee). At high mite densities, this technique no longer reveals mite-induced mortality. We suggest that this paradox results from a reduction in the mortality threshold at high mite densities, concealing mortality from our truncation procedures. Longitudinal comparisons of hive and forager bee cohorts, nevertheless, suggests mortality at all levels of infestation. We propose that persistent parasitism overcomes a colony's ability to compensate for losses, leading to its sudden decline and death.

Age dependence of salivary bacteriolytic activity in adult mosquitoes.

1. Bacteriolytic activity in the salivary glands of adult Aedes aegypti female mosquitoes starts from a low level upon emergence, increases 6-fold over the first 3 days, then levels off. 2. Mosquitoes start sugar-feeding after 2 days, when lytic activity is one-half of the peak level. 3. Bacteriolytic activity in salivary gland extracts is not influenced by removal of corpora allata.

Epidemiology of honey bee parasites.

The epidemiology of honey bee parasites has been somewhat neglected, but Lynn Royce and Philippe Rossignol describe their unique characteristics. Indeed, it appears that a parasite of social insects has in essence to adapt to two hosts: first, the individual worker within a colony, the numbers of which grow linearly and second, to the colony itself, the actual reproductive 'organism'. Transmission also has vertical and horizontal components. Analysis of tracheal mite populations in particular suggests that intracolony parasite levels are regulated by the swarming behavior of their hosts. Ironically, current and highly productive methods of honey bee management with movable hives curb swarming and may contribute to increasing the spread and the impact of some parasites. This insight may result in changing management practices to reduce the detrimental effects of bee parasites.

Simulations of enhanced malaria transmission and host bias induced by modified vector blood location behaviour.

Monte Carlo simulations were developed to assess the potential impact of parasite pathology on vector salivary function as well as of host haemostasis on transmission. Assuming that a proportion of desisting vectors switch host following failure to locate blood, we demonstrate three possible consequences: (1) infected vectors contact more hosts than non-infected host, (2) non-infected vectors are biased to infected hosts, independently of attraction, and (3) an exponential relationship exists between parasite load and transmission. We discuss possible epidemiological implications.

Increased biting rate and reduced fertility in sporozoite-infected mosquitoes.

Because salivary function and blood location are impaired in sporozoite-infected mosquitoes, we determined whether such pathology also could lead to an increased biting rate. For 5 days, we compared relative daily biting rates of Plasmodium gallinaceum sporozoite-infected mosquitoes (Aedes aegypti) and noninfected mosquitoes with an olfactometer. Mosquitoes then were exposed for 5 min to an anesthetized guinea pig. Infected mosquitoes exhibited a significant increase in olfactometer response which was also reflected in a decreased egg output. We conclude that if duration of contact with a host is limited, then infected mosquitoes may make more attempts at probing before being successful, and thus enhance transmission.

Bacteriolytic factor in the salivary glands of Aedes aegypti.

Salivary gland homogenates from adult Aedes aegypti lyse Micrococcus lysodeikticus cells. The bacteriolytic factor is present in a cell type common to both male and female mosquitoes, as well as in the crop of sugar-feeding mosquitoes. The bacteriolytic factor releases digestion products from sacculi of Escherichia coli that are different from those of hen egg white lysozyme.