The Influence of Insecticide Resistance, Age, Sex, and Blood Feeding Frequency on Thermal Tolerance of Wild and Laboratory Phenotypes of Anopheles funestus (Diptera: Culicidae)

Resistance to insecticides is a global phenomenon and is increasing at an unprecedented rate. How resistant and susceptible strains of malaria vectors might differ in terms of life history and basic biology is often overlooked, despite the potential importance of such information in light of changing climates. Here, we investigated the upper thermal limits (ULT50) of wild and laboratory strains of Anopheles funestus Giles mosquitoes, including resistance status, sex, age, and blood feeding status as potential factors influencing ULT50. No significant differences in ULT50 were observed between strains displaying different resistance patterns, nor was there a significant difference between wild and laboratory strains. In some instances, strains showed a senescence response, displaying decreased ULT50 with an increase in age, and differences between males and females (females displaying higher ULT50 than males). Blood feeding did not seem to influence ULT50 in any way. For An. funestus, it seems evident that there is no cost to resistance despite what is displayed in other anopheline species. This could have significant impacts for vector control, with resistant populations of An. funestus performing just as well, if not better, than susceptible strains, especially under changing environmental conditions such as those expected to occur with climate change.

The stomach in health and disease

The stomach is traditionally regarded as a hollow muscular sac that initiates the second phase of digestion. Yet this simple view ignores the fact that it is the most sophisticated endocrine organ with unique physiology, biochemistry, immunology and microbiology. All ingested materials, including our nutrition, have to negotiate this organ first, and as such, the stomach is arguably the most important segment within the GI tract. The unique biological function of gastric acid secretion not only initiates the digestive process but also acts as a first line of defence against food-borne microbes. Normal gastric physiology and morphology may be disrupted by Helicobacter pylori infection, the most common chronic bacterial infection in the world and the aetiological agent for most peptic ulcers and gastric cancer. In this state-of-the-art review, the most relevant new aspects of the stomach in health and disease are addressed. Topics include gastric physiology and the role of gastric dysmotility in dyspepsia and gastroparesis; the stomach in appetite control and obesity; there is an update on the immunology of the stomach and the emerging field of the gastric microbiome. H. pylori-induced gastritis and its associated diseases including peptic ulcers and gastric cancer are addressed together with advances in diagnosis. The conclusions provide a future approach to gastric diseases underpinned by the concept that a healthy stomach is the gateway to a healthy and balanced host. This philosophy should reinforce any public health efforts designed to eradicate major gastric diseases, including stomach cancer.

Altered physiology of acid secretion in depression-prone Flinders rats results in exacerbated NSAID and stress-induced gastric damage

BACKGROUND

Flinders Sensitive Line (FSL) rats are characterized by hypersensitivity to cholinergic stimuli and have been extensively used for studying depressive disorders. A link between depression and peptic ulcers has long been established; however, there is a lack of data from animal models.

METHODS

We studied the physiology of acid secretion in FSL and Flinders Resistant Line (FRL) rats in vivo and in vitro. We also examined the susceptibility of Flinders rats to water immersion restraint stress (WIRS) or NSAID-induced gastric damage and explored the effect of an anticholinergic agent, atropine, in reversing this effect.

KEY RESULTS

Basal acid output was more than twofold greater in FSL compared with FRL rats in vivo, 213.5 and 92.8 μEq/3 h/100 g (P = 0.02), respectively. Carbachol was a more potent secretagog in vitro, and somatostatin was a less potent inhibitory agent, while paradoxically stimulating acid secretion over and above the carbachol response in gastric glands from FSL rats. The FSL rats were more susceptible to indomethacin and WIRS-induced gastric mucosal damage compared with FRL rats. Atropine reduced acid output, which resulted in a reduction in indomethacin and stress-induced gastric damage in FSL rats.

CONCLUSIONS & INFERENCES

Our study, for the first time, demonstrates that the altered vagally mediated physiology of acid secretion in depression-prone FSL rats contributes to gastric hypersecretion and, consequently, results in exacerbated stress and NSAID-induced gastric damage. Flinders rats may be a useful animal model for studying acid-related and also gastrointestinal functional disorders in depression.

Spontaneous autoimmune gastritis and hypochlorhydria are manifest in the ileitis-prone SAMP1/YitFcs mice

SAMP1/YitFcs mice serve as a model of Crohn's disease, and we have used them to assess gastritis. Gastritis was compared in SAMP1/YitFcs, AKR, and C57BL/6 mice by histology, immunohistochemistry, and flow cytometry. Gastric acid secretion was measured in ligated stomachs, while anti-parietal cell antibodies were assayed by immunofluorescence and enzyme-linked immunosorbent spot assay. SAMP1/YitFcs mice display a corpus-dominant, chronic gastritis with multifocal aggregates of mononuclear cells consisting of T and B lymphocytes. Relatively few aggregates were observed elsewhere in the stomach. The infiltrates in the oxyntic mucosa were associated with the loss of parietal cell mass. AKR mice, the founder strain of the SAMP1/YitFcs, also have gastritis, although they do not develop ileitis. Genetic studies using SAMP1/YitFcs-C57BL/6 congenic mice showed that the genetic regions regulating ileitis had comparable effects on gastritis. The majority of the cells in the aggregates expressed the T cell marker CD3 or the B cell marker B220. Adoptive transfer of SAMP1/YitFcs CD4(+) T helper cells, with or without B cells, into immunodeficient recipients induced a pangastritis and duodenitis. SAMP1/YitFcs and AKR mice manifest hypochlorhydria and anti-parietal cell antibodies. These data suggest that common genetic factors controlling gastroenteric disease in SAMP1/YitFcs mice regulate distinct pathogenic mechanisms causing inflammation in separate sites within the digestive tract.

The pharmacodynamics and pharmacokinetics of S-tenatoprazole-Na 30 mg, 60 mg and 90 mg vs. esomeprazole 40 mg in healthy male subjects

BACKGROUND

Racemic tenatoprazole 40 mg/day provides more prolonged acid suppression than esomeprazole 40 mg/day.

AIM

To compare pharmacodynamic and pharmacokinetic profiles of tenatoprazole and esomeprazole.

METHODS

A single-centre, double-blind, double-dummy, randomized, 4-way, cross-over study was conducted in 32 healthy male subjects. S-tenatoprazole-Na 30, 60 or 90 mg, or esomeprazole 40 mg was administered once daily for 5 days with 10-day washout intervals. The 24-h intragastric pH was recorded at baseline and on day 5 of each period.

RESULTS

On day 5, median pH (5.34 +/- 0.45 and 5.19 +/- 0.52 vs. 4.76 +/- 0.82, respectively, P < 0.002) and percentage time with pH > 4 (80 +/- 11 and 77 +/- 12, vs. 63 +/- 11 respectively, P < 0.0001) for 24-h were higher with S-tenatoprazole-Na 90 mg and 60 mg than esomeprazole. In nocturnal periods, S-tenatoprazole-Na 90 mg, 60 mg and 30 mg were superior to esomeprazole with regard to median pH (5.14 +/- 0.64, 4.94 +/- 0.65, 4.65 +/- 0.86 and 3.69 +/- 1.18 respectively, P < 0.0001) and percentage time with pH > 4 (77 +/- 12, 73 +/- 17, 64 +/- 17 and 46 +/- 17 respectively, P < 0.0001). Proportion of subjects with nocturnal acid breakthrough with S-tenatoprazole-Na 90 mg, 60 mg and 30 mg was significantly less than with esomeprazole (54.8, 43.3, 56.7 and 90.3 respectively, P < 0.04). The proportion of subjects with >16 hrs with pH >4 was significantly higher with S-tenatoprazole-Na 90 mg and 60 mg than with esomeprazole (87.1%, 83.3% and 41.9% respectively, P < 0.02).

CONCLUSIONS

S-tenatoprazole-Na produced significantly greater and more prolonged dose-dependent 24-h and nocturnal acid suppression than esomeprazole. S-tenatoprazole-Na may provide greater clinical efficacy compared with current PPIs for patients with ineffective once-daily therapy.

Malaria vector composition and insecticide susceptibility status in Guinea Conakry, West Africa

This study provides data on malaria vector species composition and insecticide susceptibility status from three localities in Guinea Conakry. A total of 497 mosquitoes were collected resting indoors and morphologically identified as belonging to the Anopheles gambiae complex. The majority of these were An. gambiae s.s. (99.6%), but a small percentage (0.4%) were identified as Anopheles arabiensis. Thirty-four Anopheles funestus s.s. were also collected. The molecular S form of An. gambiae s.s. was predominant over the M form in Siguiri (95%) and Boffa (97.4%), whereas at Mt Nimba the M form was more abundant (61.4%) than the S form (38.1%). One hybrid M/S specimen was recorded from Mt Nimba. Siguiri populations showed high levels of resistance to DDT, dieldrin and bendiocarb. Anopheles gambiae from Boffa were largely susceptible to the insecticides tested. At Mt Nimba, resistance to DDT and bendicocarb was detected. Biochemical enzyme analysis showed that an altered acetylcholinesterase is operating in the field at low levels. The frequency of the 1014F kdr allele in the An. gambiae S form was 0.24 at Siguiri and 0.14 at Mt Nimba. A single RR specimen was found in the M form. The heterogeneity in species composition and resistance profiles between sites requires vector control interventions to be tailored to each site based on the data collected from ongoing monitoring and surveillance.

Meta-analysis: incidence of endoscopic gastric and duodenal ulcers in placebo arms of randomized placebo-controlled NSAID trials

BACKGROUND

The safety of NSAIDs is often evaluated by comparison with placebo in clinical trials.

AIM

To investigate the incidence of gastric and duodenal ulcers (GDU) in placebo arms in NSAID trials over the last three decades.

METHODS

Randomized placebo-controlled trials of oral NSAIDs from 1975 to 2006 were systematically reviewed. The pooled incidence of GDU in placebo arms was calculated and compared. Meta-regression was used to identify risk factors related to the incidence of the placebo ulcer at the study level.

RESULTS

Thirty-six studies met inclusion criteria (duration of 6.5 days to 24 weeks). In total, 3.29% GDUs were reported in 36 placebo arms. The incidence of GDU in placebo arms was 0, 4.20% and 3.03% in the studies from 1975-1989, 1990-1999 and 2000-2006 respectively (P > 0.05). Eligible subjects with previous GI events and eligible subjects on co-therapy with low-lose aspirin/corticosteroids were associated with the increase in placebo ulcer incidence after adjusting for other factors.

CONCLUSIONS

The incidence of GDU in placebo arms has not changed significantly over the last three decades, although has decreased in the past 10 years. Studies show that previous GI events and co-therapy with low-dose aspirin/corticosteroids were associated with increasing GDU in placebo arms.

Diagnosis and management of non-erosive reflux disease--the Vevey NERD Consensus Group

BACKGROUND/AIMS

Although considerable information exists regarding gastroesophageal reflux disease with erosions, much less is known of non-erosive reflux disease (NERD), the dominant form of reflux disease in the developed world.

METHODS

An expert international group using the modified Delphi technique examined the quality of evidence and established levels of agreement relating to different aspects of NERD. Discussion focused on clinical presentation, assessment of clinical outcome, pathobiological mechanisms, and clinical strategies for diagnosis and management.

RESULTS

Consensus was reached on 85 specific statements. NERD was defined as a condition with reflux symptoms in the absence of mucosal lesions or breaks detected by conventional endoscopy, and without prior effective acid-suppressive therapy. Evidence supporting this diagnosis included: responsiveness to acid suppression therapy, abnormal reflux monitoring or the identification of specific novel endoscopic and histological findings. Functional heartburn was considered a separate entity not related to acid reflux. Proton pump inhibitors are the definitive therapy for NERD, with efficacy best evaluated by validated quality-of-life instruments. Adjunctive antacids or H(2) receptor antagonists are ineffective, surgery seldom indicated.

CONCLUSIONS

Little is known of the pathobiology of NERD. Further elucidation of the mechanisms of mucosal and visceral hypersensitivity is required to improve NERD management.

Cryptic species within Anopheles longipalpis from southern Africa and phylogenetic comparison with members of the An. funestus group

House-resting Anopheles mosquitoes are targeted for vector control interventions; however, without proper species identification, the importance of these Anopheles to malaria transmission is unknown. Anopheles longipalpis, a non-vector species, has been found in significant numbers resting indoors in houses in southern Zambia, potentially impacting on the utilization of scarce resources for vector control. The identification of An. longipalpis is currently based on classical morphology using minor characteristics in the adult stage and major ones in the larval stage. The close similarity to the major malaria vector An. funestus led to investigations into the development of a molecular assay for identification of An. longipalpis. Molecular analysis of An. longipalpis from South Africa and Zambia revealed marked differences in size and nucleotide sequence in the second internal transcribed spacer (ITS2) region of ribosomal DNA between these two populations, leading to the conclusion that more than one species was being analysed. Phylogenetic analysis showed the Zambian samples aligned with An. funestus, An. vaneedeni and An. parensis, whereas the South African sample aligned with An. leesoni, a species that is considered to be more closely related to the Asian An. minimus subgroup than to the African An. funestus subgroup. Species-specific primers were designed to be used in a multiplex PCR assay to distinguish between these two cryptic species and members of the An. funestus subgroup for which there is already a multiplex PCR assay.

The relationship between the control of pH and healing and symptom relief in gastro-oesophageal reflux disease

Gastro-oesophageal reflux disease (GERD) is generally considered to be the result of a motility disorder which permits the abnormal and prolonged exposure of the lumen of the oesophagus to the acidic gastric contents. This view is supported by experimental data, intra-oesophageal pH measurement, and the dramatic results of symptom relief and healing seen with effective antisecretory treatment. Oesophageal mucosal injury is determined by the pH of the refluxate and duration of acid exposure. Most patients experience meal-stimulated reflux during the day and the more severe cases experience 24-h acid exposure. In contrast to the H2-receptor antagonists (H2RAs), the proton pump inhibitors (PPIs) are more effective at controlling meal-stimulated acid secretion when each is given in standard doses. Therefore, the degree and duration of acid suppression throughout 24 h is greater. Treatments which maintain intra-oesophageal pH > 4 for 96% or more of the 24 h normalize acid exposure and are associated with the highest healing rates. Peptic activity is minimized at or above pH 4. The time above pH 4 is significantly longer with the PPIs than with the H2RAs. Thus, the healing-time curves for GERD (grades II-IV) are shifted to the left for the PPIs which heal a significantly greater proportion of patients earlier than the H2RAs or sucralfate. Symptoms in GERD are related to the degree and duration of oesophageal acid exposure. Symptom relief is more rapid and complete with the PPIs than with the H2RAs or other treatments in standard doses.

Access to specialist gastroenterology care in Canada: comparison of wait times and consensus targets

BACKGROUND

Monitoring wait times and defining targets for care have been advocated to improve health care delivery related to cancer, heart, diagnostic imaging, joint replacements and sight restoration. There are few data on access to care for digestive diseases, although they pose a greater economic burden than cancer or heart disease in Canada. The present study compared wait times for specialist gastroenterology care with recent, evidence-based, consensus-defined benchmark wait times for a range of digestive diseases.

METHODS

Total wait times from primary care referral to investigation were measured for seven digestive disease indications by using the Practice Audit in Gastroenterology program, and were benchmarked against consensus recommendations.

RESULTS

Total wait times for 1903 patients who were undergoing investigation exceeded targets for those with probable cancer (median 26 days [25th to 75th percentiles eight to 56 days] versus target of two weeks); probable inflammatory bowel disease (101 days [35 to 209 days] versus two weeks); documented iron deficiency anemia (71 days [19 to 142 days] versus two months); positive fecal occult blood test (73 days [36 to 148 days] versus two months); dyspepsia with alarm symptoms (60 days [23 to 140 days] versus two months); refractory dyspepsia without alarm symptoms (126 days [42 to 225 days] versus two months); and chronic constipation and diarrhea (141 days [68 to 264 days] versus two months). A minority of patients were seen within target times: probable cancer (33% [95% CI 20% to 47%]); probable inflammatory bowel disease (12% [95% CI 1% to 23%]); iron deficiency anemia (46% [95% CI 37% to 55%]); positive occult blood test (41% [95% CI 28% to 54%]); dyspepsia with alarm symptoms (51% [95% CI 41% to 60%]); refractory dyspepsia without alarm symptoms (33% [95% CI 19% to 47%]); and chronic constipation and diarrhea (21% [95% CI 14% to 29%]).

DISCUSSION

Total wait times for the seven indications exceeded the consensus targets; 51% to 88% of patients were not seen within the target wait time. Multiple interventions, including adoption of evidence-based management guidelines and provision of economic and human resources, are needed to ensure appropriate access to digestive health care in Canada. Outcomes can be evaluated by the 'point-of-care', practice audit methodology used for the present study.

New algorithm for the treatment of gastro-oesophageal reflux disease

BACKGROUND

Gastro-oesophageal reflux disease (GERD) is associated with a variety of typical and atypical symptoms. Patients often present in the first instance to a pharmacist or primary care physician and are subsequently referred to secondary care if initial management fails. Guidelines usually do not provide a clear guidance for all healthcare professionals with whom the patient may consult.

AIM

To update a 2002-treatment algorithm for GERD, making it more applicable to pharmacists as well as doctors.

METHODS

A panel of international experts met to discuss the principles and practice of treating GERD.

RESULTS

The updated algorithm for the management of GERD can be followed by pharmacists, for over-the-counter medications, primary care physicians, or secondary care gastroenterologists. The algorithm emphasizes the importance of life style changes to help control the triggers for heartburn and adjuvant therapies for rapid and adequate symptom relief. Proton pump inhibitors will remain a prominent treatment for GERD; however, the use of antacids and alginate-antacids (either alone or in combination with acid suppressants) is likely to increase.

CONCLUSION

The newly developed algorithm takes into account latest clinical practice experience, offering healthcare professionals clear and effective treatment options for the management of GERD.

Insecticide susceptibility and vector status of natural populations of Anopheles arabiensis from Sudan

Species composition, blood meal source, sporozoite infection rate, insecticide resistance and the kdr mutations were investigated in the Anopheles gambiae complex from 13 sentinel sites in central Sudan. Species identification revealed that 89.5% of 960 specimens were A. arabiensis. Of 310 indoor resting females, 88.1% were found to have fed on humans, while 10.6% had fed on bovines. The overall sporozoite infection rate from the five localities tested was 2.3%, ranging from 0 to 5.5%. Insecticide susceptibility bioassay results showed 100% mortality on bendiocarb, 54.6-94.2% on permethrin, 55.4-99.1% on DDT and 76.8-100% on malathion. The kdr analysis by PCR and sequencing revealed the presence of the Leu-Phe mutation in both permethrin and DDT bioassays. There was no significant difference in the frequency of kdr (P>0.05) between dead and surviving specimens. These findings have serious implications for the malaria control programmes in Gezira and Sennar states.

Relative developmental and reproductive fitness associated with pyrethroid resistance in the major southern African malaria vector, Anopheles funestus

The effect of pyrethroid resistance on the fitness of a laboratory strain of Anopheles funestus originating from southern Mozambique was evaluated by comparing the developmental and reproductive characteristics of a pyrethroid resistant strain with an insecticide susceptible strain. Fitness was evaluated in terms of fecundity, fertility, egg production, developmental time and life stage progression and survival. Of the eggs laid by females of the resistant strain, 81.5% hatched while only 66.9% were recorded in the susceptible strain. The time from egg hatch to adult emergence was longer for the resistant strain (15.9 days) than the susceptible strain (15.2 days). A significantly higher proportion of eggs from the resistant strain (61.6%) survived to adulthood compared with those of the susceptible strain (49%). Fecundity and larval and pupal survival did not differ significantly between strains. Of spermathecae dissected from females of the resistant strain, 56.8% were fertilized compared to 52.6% from the susceptible strain. The proportion of females that successfully produced eggs was 43.3% and 23.3% for the resistant and susceptible strains respectively. Complete failure of larval hatch was recorded in 28.6% of susceptible strain families compared to 7.7% of resistant families. Our results show that pyrethroid resistance in southern African An. funestus does not incur any loss of fitness under laboratory conditions. These results suggest that the removal of pyrethroid insecticide selection pressure may not lead to a regression of resistance alleles in pyrethroid resistant An. funestus populations in southern Africa.