Liver Damage and Exposure to Toxic Concentrations of Endogenous Retinoids in the Pathogenesis of COVID-19 Disease: Hypothesis.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has a marked tropism for the biliary tract; it damages the bile ducts and hepatocytes and can lead to liver decompensation, cirrhosis, and sepsis. The pathogenesis of liver damage and its association with damage to the lung, heart, and brain and to the other protean manifestations of COVID-19 disease are not fully understood. In particular, tissue damage from thinning and leaky blood vessels appears to result from an inflammatory response to the virus rather than the virus itself. This article outlines a new hypothesis of the nature of the inflammatory factor responsible for tissue damage in COVID-19. Review of the literature reveals that COVID-19 disease closely resembles an endogenous form of hypervitaminosis A. We propose that SARS-CoV-2 virus-induced liver damage causes retinoic acid and stored retinyl esters to be released into the circulation in toxic concentrations, unbound to protein, with resulting damage to organs including the lungs, heart, blood vessels, and skin. Several lines of evidence support this model of disease causation. Subject to testing, strategies for the effective treatment and prevention of COVID-19 could include targeting the action and accumulation of retinoids.

Multiple Vaccinations and the Enigma of Vaccine Injury.

A growing number of vaccines are administered at the same time or in close succession, increasing the complexity of assessing vaccine safety. Individual vaccines are assumed to have no other effect than protection against the targeted pathogen, but vaccines also have nonspecific and interactive effects, the outcomes of which can be beneficial or harmful. To date, no controlled trials and very few observational studies have determined the impact of vaccination schedules on overall health. The balance of the risks and benefits from mass vaccination therefore remains uncertain. Recent studies worryingly suggest links between multiple vaccinations and increased risks of diverse multisystem health problems, including allergies, infections, and neuropsychiatric or neurodevelopmental disorders. Here, we propose that, in susceptible persons, multiple vaccinations activate the retinoid cascade and trigger apoptotic hepatitis, leading to cholestatic liver dysfunction, in which stored vitamin A compounds (retinyl esters and retinoic acid) enter the circulation in toxic concentrations; this induces endogenous forms of hypervitaminosis A, with the severity of adverse outcomes being directly proportional to the concentration of circulating retinoids. In very low concentrations, vitamin A and its major metabolite retinoic acid contribute to immune function and to the process of immunization, whereas excess vitamin A increases the risk of adverse events, including common "side-effects" as well as chronic adverse outcomes. The increasing rates of allergy, ear infections, and neurodevelopmental disorders (NDDs) in countries with high rates of vaccination could be related to mass vaccination and to its impact on liver function and vitamin A metabolism, collectively representing endogenous manifestations of hypervitaminosis A. Further studies of health outcomes in vaccinated and unvaccinated groups are urgently needed, to increase understanding of the pathophysiology and treatment of vaccine injury, to identify the risk factors and screen for vaccine injury, to inform public health policy on potential hazards related to vaccination schedules, and to optimize the safety and benefits of vaccines.

Rubella Virus Infection, the Congenital Rubella Syndrome, and the Link to Autism.

Rubella is a systemic virus infection that is usually mild. It can, however, cause severe birth defects known as the congenital rubella syndrome (CRS) when infection occurs early in pregnancy. As many as 8%-13% of children with CRS developed autism during the rubella epidemic of the 1960s compared to the background rate of about 1 new case per 5000 children. Rubella infection and CRS are now rare in the U.S. and in Europe due to widespread vaccination. However, autism rates have risen dramatically in recent decades to about 3% of children today, with many cases appearing after a period of normal development ('regressive autism'). Evidence is reviewed here suggesting that the signs and symptoms of rubella may be due to alterations in the hepatic metabolism of vitamin A (retinoids), precipitated by the acute phase of the infection. The infection causes mild liver dysfunction and the spillage of stored vitamin A compounds into the circulation, resulting in an endogenous form of hypervitaminosis A. Given that vitamin A is a known teratogen, it is suggested that rubella infection occurring in the early weeks of pregnancy causes CRS through maternal liver dysfunction and exposure of the developing fetus to excessive vitamin A. On this view, the multiple manifestations of CRS and associated autism represent endogenous forms of hypervitaminosis A. It is further proposed that regressive autism results primarily from post-natal influences of a liver-damaging nature and exposure to excess vitamin A, inducing CRS-like features as a function of vitamin A toxicity, but without the associated dysmorphogenesis. A number of environmental factors are discussed that may plausibly be candidates for this role, and suggestions are offered for testing the model. The model also suggests a number of measures that may be effective both in reducing the risk of fetal CRS in women who acquire rubella in their first trimester and in reversing or minimizing regressive autism among children in whom the diagnosis is suspected or confirmed.

Gulf War Illness: Unifying Hypothesis for a Continuing Health Problem.

An estimated 25%⁻32% of veterans of the 1991 Gulf War continue to experience multiple unexplained health problems known as Gulf War Illness (GWI). GWI encompasses chronic pain, musculoskeletal weakness, headache, fatigue, cognitive deficits, alterations in mood, and numerous multi-system complaints. Most potential exposures implicated in GWI were not well documented but included varying levels of several neurotoxicants as well as the anticholinergic drug pyridostigmine bromide (PB), which was routinely taken as prophylaxis against the nerve agent soman. While some veterans also took chloroquine as an antimalarial agent, the literature suggests an association between receipt of multiple vaccinations prior to or during the conflict (perhaps combined with other exposures), and GWI. In-theater exposures may account for any single individual veteran's ill health but many veterans of the same era who were not deployed overseas also suffer the same or similar symptoms. The features of GWI also overlap with those of fibromyalgia, chronic fatigue syndrome and multiple chemical sensitivity, in all of which liver dysfunction has been documented, suggesting a unifying hypothesis. It is proposed that multiple vaccinations, with concurrent or subsequent exposure to PB or additional chemical insults of a liver-damaging nature, plausibly explain the pathogenesis and the observed chronicity of GWI. The suggested mechanism for GWI is thus a chemically-induced impaired liver function, with the spillage of stored vitamin A compounds ("retinoids") into the circulation in toxic concentrations, resulting in an endogenous chronic form of hypervitaminosis A. Implications of the hypothesis are briefly reviewed.

Psychiatric effects of malaria and anti-malarial drugs: historical and modern perspectives.

The modern medical literature implicates malaria, and particularly the potentially fatal form of cerebral malaria, with a risk of neurocognitive impairment. Yet historically, even milder forms of malaria were associated in the literature with a broad range of psychiatric effects, including disorders of personality, mood, memory, attention, thought, and behaviour. In this article, the history of psychiatric effects attributed to malaria and post-malaria syndromes is reviewed, and insights from the historical practice of malariotherapy in contributing to understanding of these effects are considered. This review concludes with a discussion of the potentially confounding role of the adverse effects of anti-malarial drugs, particularly of the quinoline class, in the unique attribution of certain psychiatric effects to malaria, and of the need for a critical reevaluation of the literature in light of emerging evidence of the chronic nature of these adverse drug effects.

Malaria: prevention in travellers (non-drug interventions).

INTRODUCTION: Malaria transmission occurs most frequently in environments with humidity greater than 60% and ambient temperature of 25°C to 30°C. Risks increase with longer visits and depend on activity. Infection can follow a single mosquito bite. Incubation is usually 10 to 14 days but can be up to 18 months, depending on the strain of parasite. METHODS AND OUTCOMES: We conducted a systematic review and aimed to answer the following clinical questions: What are the effects of non-drug interventions to prevent malaria in non-pregnant adult travellers? What are the effects of non-drug interventions to prevent malaria in child travellers and in pregnant travellers? We searched: Medline, Embase, The Cochrane Library, and other important databases up to November 2013 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations, such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA). RESULTS: We found five studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions. CONCLUSIONS: In this systematic review we present information relating to the effectiveness and safety of the following interventions: aerosol insecticides, air conditioning and electric fans, bath or chemical-base oils, biological control measures, dietary supplementation, electronic mosquito repellents, insecticide-treated clothing/nets, lifestyle changes (full-length and light-coloured clothing, behaviour modification), mosquito coils and vapourising mats, skin-applied chemical repellents (containing diethyltoluamide [DEET] or picaridin), skin-applied plant-based repellents, and smoke.

Helminth therapy (worms) for induction of remission in inflammatory bowel disease.

BACKGROUND: Inflammatory bowel disease (IBD) is a chronic, globally-occurring gastrointestinal disorder and a major cause of illness and disability. It is conventionally classified into Crohn's disease (CD) and ulcerative colitis (UC). Helminths are parasitic worms with complex life cycles involving tissue- or lumen-dwelling stages in their hosts, and causing long-lasting or chronic infections that are frequently asymptomatic. Helminths modulate immune responses of their hosts, and many observational and experimental studies support the hypothesis that helminths suppress immune-mediated chronic inflammation that occurs in asthma, allergy and IBD. OBJECTIVES: The objective was to evaluate the efficacy and safety of helminth treatment for induction of remission in IBD. SEARCH METHODS: We searched the following databases from inception to 13 July 2013: MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials, and the Cochrane Inflammatory Bowel Disease Group Specialized Trials Register. We also searched four online trials registries, and abstracts from major meetings. There were no language restrictions. SELECTION CRITERIA: Randomised controlled trials (RCTs) where the intervention was any helminth species or combination of helminth species, administered in any dose and by any route and for any duration of exposure to people with active CD or UC, confirmed through any combination of clinical, endoscopic and histological criteria were eligible for inclusion. DATA COLLECTION AND ANALYSIS: Two authors independently extracted data and assessed eligibility using a standardized data collection form. We used the RevMan software for analyses. The primary outcome was induction of remission as defined by the included studies. Secondary outcomes included clinical, histologic, or endoscopic improvement as defined by the authors, endoscopic mucosal healing, change in disease activity index score, change in quality of life score, hospital admissions, requirement for intravenous corticosteroids, surgery, study withdrawal and the incidence of adverse events. We calculated the risk ratio (RR) and corresponding 95% confidence interval (CI) for dichotomous outcomes. We calculated the mean difference (MD) and 95% CI for continuous outcomes. We assessed the methodological quality of included studies using the Cochrane risk of bias tool. The overall quality of the evidence supporting each outcome was assessed using the GRADE criteria. MAIN RESULTS: Two RCTs (90 participants) were included. One trial assessed the efficacy and safety of Trichuris suis (T. suis) ova in patients with UC (n = 54). The other RCT was a phase one that assessed the safety and tolerability of T. suis ova in patients with CD (n = 36). The risk of bias in both studies was judged to be low. In the UC study, during the 12-week study period, participants in the active arm received 2-weekly aliquots of 2500 T. suis eggs, added to 0.8 mL of saline; those in the placebo arm received 0.8 mL saline only. There were sparse data available for the outcomes clinical remission and clinical improvement. Ten per cent (3/30) of patients in the T. suis arm entered remission compared to 4% (1/24) of patients in the placebo arm (RR 2.40, 95% CI 0.27 to 21.63). Forty-three per cent (13/30) of patients in the T. suis group achieved clinical improvement compared to 17% (4/24) of placebo patients (RR 2.60, 95% CI 0.97 to 6.95). The mean ulcerative colitis disease activity index (UCDAI) score was lower in the T. suis group (6.1 +/- 0.61) compared to the placebo group (7.5 +/- 0.66) after 12 weeks of treatment (MD -1.40, 95% CI -1.75 to -1.05). There was only limited evidence relating to the proportion of patients who experienced an adverse event. Three per cent (1/30) of patients in the T. suis group experienced at least one adverse event compared to 12% (3/24) of placebo patients (RR 0.27, 95% CI 0.03 to 2.40). None of the adverse events reported in this study were judged to be related to the study treatment. GRADE analyses rated the overall quality of the evidence for the primary and secondary outcomes (i.e. clinical remission and improvement) as low due to serious imprecision. In the CD study, participants received a single treatment of T. suis ova at a dosage of 500 (n = 9), 2500 (n = 9), or 7500 (n = 9) embryonated eggs or matching placebo (n = 9). The CD study did not assess clinical remission or improvement as outcomes. There were sparse data on adverse events at two weeks. Thirty-seven per cent (10/27) of patients in the T. suis group experienced at least one adverse event compared to 44% (4/9) of placebo patients (RR 0.83, 95% CI 0.35 to 2.01). Only one adverse event (dysgeusia) was judged to be possibly related to treatment in this study. Dysgeusia was reported in one patient in the T. suis group and in one patient in the placebo group. AUTHORS' CONCLUSIONS: Currently, there is insufficient evidence to allow any firm conclusions regarding the efficacy and safety of helminths used to treat patients with IBD. The evidence for our primary efficacy outcomes in this review comes from one small study and is of low quality due to serious imprecision. We do not have enough evidence to determine whether helminths are safe when used in patients with UC and CD. Further RCTs are required to assess the efficacy and safety of helminth therapy in IBD.

Helminth therapy (worms) for allergic rhinitis.

BACKGROUND: Allergic rhinitis is a disorder of the nasal membranes and surrounding tissues, and a worldwide cause of illness and disability. Helminths are complex tissue-dwelling or lumen-dwelling organisms that inhabit larger organisms and are frequently asymptomatic. Helminths modulate the natural immune responses of their human hosts, and may prevent or cure immune-mediated or allergic diseases (e.g. allergic rhinitis) in the host. Non-randomised studies support this hypothesis. OBJECTIVES: To assess the safety and effectiveness of helminth therapy in people with allergic rhinitis. SEARCH METHODS: We searched the Cochrane Ear, Nose and Throat Disorders Group Trials Register; the Cochrane Central Register of Controlled Trials (CENTRAL); PubMed; EMBASE; CINAHL; Web of Science; BIOSIS Previews; Cambridge Scientific Abstracts; ICTRP and additional sources for published and unpublished trials. The date of the search was 24 June 2011. SELECTION CRITERIA: All randomised controlled trials where the intervention was any helminth species or combination of helminth species, administered to people with allergic rhinitis in any dose, by any route and for any duration of exposure. We accepted both intermittent and persistent allergic rhinitis patients. DATA COLLECTION AND ANALYSIS: We independently extracted data and assessed eligibility and risk of bias using a standardised data collection form. We resolved any disagreement through discussion. We combined dichotomous data using risk ratio (RR) and continuous data using mean difference (MD), presenting both with 95% confidence intervals (CI). MAIN RESULTS: We found five reports of two single-centre, placebo-controlled, double-blinded studies (130 participants). Participants in both studies were a mix of adults with either intermittent or persistent allergic rhinitis. Both studies had a low risk of bias. One study, with 12 weeks' follow-up, used a single percutaneous application of 10 Necator americanus (i.e. human hookworm) larvae. The other study, with 24 weeks' follow-up, used three-weekly oral dosing with 2500 Trichuris suis (i.e. pig whipworm) eggs in aqueous suspension. Of 17 outcomes evaluated in this review, eight were positive (i.e. favoured helminths). Participants taking helminths had no reduction in allergic rhinitis symptoms, percentage of well days (i.e. days with minimal symptoms and no use of medication for allergic rhinitis), lung function measures and quality of life scores. Total use of medication for allergic rhinitis (eye drops, nasal sprays, tablets) did not change; however, in the helminth group there was a statistically significant reduction in the percentage of days during the grass pollen season when participants needed to take tablets as rescue medication for their allergic rhinitis symptoms (MD -14.0%, 95% CI -26.6 to -1.40); in a typical 60-day pollen season this 14% reduction translates into 19 days when tablets would be needed in the helminth group versus 27 days when tablets would be needed in the placebo group. Participants taking helminths percutaneously (i.e. as hookworm larvae) had local skin itching and redness in the first few days after administration. Participants taking helminths were more likely to report any gastrointestinal adverse event (RR 1.79, 95% CI 1.31 to 2.45), moderate or severe abdominal pain (RR 7.67, 95% CI 1.87 to 31.57), moderate or severe flatulence (RR 2.01, 95% CI 1.06 to 3.81) and moderate or severe diarrhoea (RR 1.99, 95% CI 1.18 to 3.37). There was no difference between the helminth and placebo groups in the incidence of serious adverse events, and in study withdrawals. AUTHORS' CONCLUSIONS: There is currently insufficient evidence on the efficacy, tolerability and likely costs of helminth therapy to support its use in the routine management of allergic rhinitis. Administered to humans in carefully measured doses, helminths appear to be safe. More preclinical studies should be performed, before larger and extended duration trials of helminths for allergic rhinitis are carried out. Future studies should collect and report comparative data on the costs of helminth therapy versus conventional pharmacotherapy.

Malaria: prevention in travellers.

INTRODUCTION: Malaria transmission occurs most frequently in environments with humidity greater than 60% and ambient temperature of 25 °C to 30 °C. Risks increase with longer visits and depend on activity. Infection can follow a single mosquito bite. Incubation is usually 10 to 14 days but can be up to 18 months depending on the strain of parasite. METHODS AND OUTCOMES: We conducted a systematic review and aimed to answer the following clinical questions: What are the effects of non-drug preventive interventions in non-pregnant adult travellers? What are the effects of drug prophylaxis in non-pregnant adult travellers? What are the effects of antimalaria vaccines in adult and child travellers? What are the effects of antimalaria interventions in child travellers, pregnant travellers, and in airline pilots? We searched: Medline, Embase, The Cochrane Library, and other important databases up to November 2009 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA). RESULTS: We found 79 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions. CONCLUSIONS: In this systematic review we present information relating to the effectiveness and safety of the following interventions: aerosol insecticides, amodiaquine, air conditioning and electric fans, atovaquone-proguanil, biological control measures, chloroquine (alone or with proguanil), diethyltoluamide (DEET), dietary supplementation, doxycycline, electronic mosquito repellents, full-length and light-coloured clothing, insecticide-treated clothing/nets, mefloquine, mosquito coils and vapourising mats, primaquine, pyrimethamine-dapsone, pyrimethamine-sulfadoxine, smoke, topical (skin-applied) insect repellents, and vaccines.

Drugs for preventing malaria in travellers.

BACKGROUND: Malaria infects 10,000 to 30,000 international travellers each year. It can be prevented through anti-mosquito measures and drug prophylaxis. However, antimalaria drugs have adverse effects which are sometimes serious. OBJECTIVES: To compare the effects of currently used antimalaria drugs when given as prophylaxis to non-immune adult and child travellers who are travelling to regions with Plasmodium falciparum resistance to chloroquine. Specifically, to assess the efficacy, safety, and tolerability of atovaquone-proguanil, doxycycline, and mefloquine compared to each other, and also when compared to chloroquine-proguanil and to primaquine. SEARCH STRATEGY: In August 2009 we searched the Cochrane Infectious Diseases Group Specialized Register, CENTRAL (The Cochrane Library 2008, Issue 4), MEDLINE, EMBASE, LILACS, BIOSIS, mRCT, and reference lists. We handsearched conference proceedings and one specialist journal, and contacted researchers and drug companies. We searched PubMed for drug-related deaths. SELECTION CRITERIA: Randomized and quasi-randomized controlled trials of any antimalaria drug regimen currently used by non-immune international travellers. DATA COLLECTION AND ANALYSIS: We independently extracted data and assessed eligibility and risk of bias using a standardized data collection form. We resolved any disagreement through discussion. We combined dichotomous outcomes using risk ratio (RR) and continuous data using mean difference (MD), presenting both with 95% confidence intervals (CI). MAIN RESULTS: Eight trials (4240 participants) met the inclusion criteria. Evidence on comparative efficacy from head-to-head comparisons was limited. Atovaquone-proguanil compared to doxycycline had similar adverse events reported. Compared to mefloquine, atovaquone-proguanil users had fewer reports of any adverse effect (RR 0.72, 95% CI 0.6 to 0.85), gastrointestinal adverse effects (RR 0.54, 95% CI 0.42 to 0.7), neuropsychiatric adverse events (RR 0.86, 95% CI 0.75 to 0.99), and neuropsychiatric adverse effects (RR 0.49, 95% CI 0.38 to 0.63), besides a better total mood disturbance score (MD -7.20, 95% CI -10.79 to -3.61). Similarly, doxycycline users had fewer reported neuropsychiatric events than mefloquine users (RR 0.84, 95% CI 0.73 to 0.96). We also examined these three regimens against chloroquine-proguanil; this latter regimen had more reports of any adverse effect (RR 0.84, 95% CI 0.73 to 0.96) and of gastrointestinal adverse effects (RR 0.71, 95% CI 0.6 to 0.85). AUTHORS' CONCLUSIONS: Atovaquone-proguanil and doxycycline are the best tolerated regimens, and mefloquine is associated with adverse neuropsychiatric outcomes.

Cysticercosis in a female Nicaraguan traveler.

Cysticercosis is a tissue infestation with Taenia solium (pork tapeworm) larvae and should feature in the differential diagnosis of all soft tissue swellings arising after travel to Central and South America, Eastern Europe, China, and India. We describe a patient who presented 8 months after travel to Nicaragua with pea-sized, intermittently tingling nodules in limbs and trunk and a lump in her mouth, which moved constantly. Various British practitioners misdiagnosed the patient's complaint as sebaceous cysts, diffuse lipomata, neurosis, and gnathostomiasis. The diagnosis was finally made by immunoblot assay testing for cysticercosis immunoglobulin (Ig)G, and the patient was cured with a course of albendazole 400 mg, taken twice daily for 30 days. This case illustrates the importance of careful history taking and appropriate investigations.

African trypanosomiasis in a British soldier.

BACKGROUND: Sleeping sickness (human African trypanosomiasis) is a parasitic infection transmitted by day-biting tsetse flies. The diagnostic standard is microscopy of blood, lymph node aspirates, or cerebrospinal fluid. The disease is invariably fatal if not treated. There are >300,000 new cases of sleeping sickness each year and approximately 100,000 deaths. CASE PRESENTATION: We describe a British soldier who acquired sleeping sickness in Malawi. He gave no history of a painful insect bite but presented with classic early signs of sleeping sickness (a primary chancre, regional lymphadenopathy, circinate erythema, and a cyclical fever pattern). His condition worsened in the next week, and trypanosomes were observed in a blood sample. The patient was aeromedically evacuated to Johannesburg, where stage 1 Trypanosoma brucei rhodesiense infection was confirmed; he also had renal and liver failure, pancytopenia, and heart block. He was treated with intravenously administered suramin, and he recovered fully over the next 5 months. RECOMMENDATIONS: Medical officers deploying to eastern and southeastern Africa must be familiar with the common presenting signs and symptoms of T. b. rhodesiense sleeping sickness and should have 24-hour access to a reliable, local, clinical microscopy service. Confirmed sleeping sickness requires immediate transfer to a tertiary diagnostic and treatment center, where suramin (for T. b. rhodesiense infection), pentamidine (for Trypanosoma brucei gambiense infection), and melarsoprol (for stage 2 disease) must be immediately available.

Acute knee injuries in military personnel: A case-control study of the effectiveness of direct-access magnetic resonance imaging in a primary care setting.

AIM: To evaluate magnetic resonance (MR) imaging as a direct-access diagnostic tool for primary care physicians. METHOD: Prospective, case-control study in a Royal Air Force setting. We obtained institutional review board approval and informed consent. Cases consisted of patients with acute knee injury and a physician-ordered MR scan. Controls were matched for gender, age, and knee injury and had MR investigation ordered by an orthopedic specialist. RESULTS: MR imaging cost $341 U.S. dollars per scan. Sixteen patients were enrolled, ages 17 to 44 years, and there were 48 controls. There was a significant intergroup difference for time to MR scan (p < 0.001), and no difference in time to specialist orthopedic assessment (p = 0.39). There was a significant intergroup difference (p < 0.001) in time to return to full fitness. CONCLUSIONS: Used as a primary care diagnostic tool and in settings where times to surgery are unacceptably long, direct-access MR imaging significantly decreases the amount of time to definitive treatment for military personnel with acute knee injuries. It may also improve clinical outcomes. MR imaging technology should be made more widely available in military primary care, including during mature combat missions.

Malaria: prevention in travellers.

INTRODUCTION: Malaria transmission occurs most frequently in environments with humidity over 60% and ambient temperature of 25-30 degrees C. Risks increase with longer visits and depend on activity. Infection can follow a single mosquito bite. Incubation is usually 10-14 days but can be up to 18 months depending on the strain of parasite. METHODS AND OUTCOMES: We conducted a systematic review and aimed to answer the following clinical questions: What are the effects of non-drug preventive interventions in adult travellers? What are the effects of drug prophylaxis in adult travellers? What are the effects of antimalaria vaccines in travellers? What are the effects of antimalaria interventions in child travellers, pregnant travellers, and in airline pilots? We searched: Medline, Embase, The Cochrane Library and other important databases up to February 2006 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA). RESULTS: We found 69 systematic reviews, RCTs, or observational studies that met our inclusion criteria. CONCLUSIONS: In this systematic review we present information relating to the effectiveness and safety of the following interventions: acoustic buzzers, aerosol insecticides, amodiaquine, air conditioning and electric fans, atovaquone-proguanil, biological control measures, chloroquine (alone or with proguanil), diethyltoluamide (DEET), doxycycline, full-length and light-coloured clothing, insecticide-treated clothing/nets, mefloquine, mosquito coils and vaporising mats, primaquine, pyrimethamine-dapsone, pyrimethamine-sulfadoxine, smoke, topical (skin-applied) insect repellents, and vaccines.