Vector-borne Disease and HealthENVR 890-2Mark D. SobseySpring, 2009

Vectors and Vector-borne Diseases

Mosquitoes and Key VBDsResponsible for a great VBD burdenMalaria parasiteYellow fever virusDengue fever/hemorrhagic fever virusOther viral feversWest Nile, Rift Valley, BunyamweraFiliariasis helminthEncephalitis virusesWestern Equine, Eastern Equine, St. Louis, etc.

Flies and VBDsAfrican sleeping sickness african trypanosome parasite tsetse fly biteEnteric bacteria diseases houseflies food contaminationVibrio cholerae (cholera), typhoid fever (Salmonella typhi), Shigella spp. (bacterial dysentery)Onchoceriasis (river blindness) helminth black fly bite

Lice and VBDs Typhus FeverAgent: Rickettsia prowazeckiiVector: body licePediculus humanus corporisAssociated with poor sanitation and lice infestation (ectoparasite carriage)Transmitted by louse feces penetrating skin or inhaled in dustControlled with incecticidal body powder and improved sanitationOther louse-borne diseasesTrench fever Bartonella quintana (bacterium)Relapsing fever Borrellia recurrentensis (spirochete bacterium)

Fleas and VBDs - PlaguePlague: Pasteurella (now Yersinia) pestis (Gram-negative bacterium)Fleas carried on rats & other rodentsZoonosisRats bitten by fleas become infected and dieRats then hop onto humans, biting (taking a blood meal) and infecting with P. pestisBubonic plague: flea biteinfection lymph nodes swelling called buboes septicemia fever bubonic plague dark patches on skincalled Black DeathPneumonic plague: secondary spread to lungs can result in pneumonia and ability to spread via respiratory secretions and droplets, resulting in person-to-person spread as Pneumonic PlagueHistorically, a cause of major epidemics and pandemicsNow readily controllable with antibioticsConcern as a bioterrorism agent

Ticks and VBDsRocky Mountain Spotted Fever Rickettsia rickettsi tick bite Causes systemic infection with fever, nausea, vomiting, muscle pain, lack of appetite, severe headache; later: rash, abdominal pain, joint pain, diarrhea Lyme disease spirochete bacterium Borrelia burgdorferi tick bite leads systemic disease with fever, headache, fatigue, and a characteristic skin rash called erythema migrans. Untreated, infection can spread to joints, the heart, and the nervous system; neurological sequelaeErlichiosis - Ehrlichia chaffeensis a bacteriumInfection causes systemic illness with fever, headache, fatigue, and muscle aches. Also, nausea, vomiting, diarrhea, cough, joint pains, confusion, and occasionally rashQ fever: Coxiella burnetti ricketsia - zoonoticTularemia Francisella tularensis - zoonoticOthers

Malaria - Biology

Malaria Disease Burden and Economic Costs>1.2 million people, mostly children, die of malaria yearlyBurden of disease: 46 486 000 Disability Adjusted Life Years (DALYs) lostcombined toll of death, illness, and disability.>85% of malaria deaths, disease, and disability occur in the African RegionSouth-East Asia Region, 2ndEastern Mediterranean Region, 3rd Experts suggest even higher incidence than that reported by countries

Impact of Malaria-related IllnessReduced Economic ProductivityEx.: In Cte d'Ivoire, farmers diagnosed as sick from malaria for more than two days out of a growing season had 47% lower yields and 53% lower revenues than farmers who missed no more than two days of work. families highly affected by disease of various kinds may turn from growing higher value crops to less labour demanding and yield-sensitive productsConsequences: reduced household income and nutrition. Countries with intense malaria had rates of GDP growth that were 1.3% lower than those in comparable countries with less intense malaria. Countries with more than 50% of the population living at risk of infection from malaria parasites had average income levels that were one third of those in countries with less intense rates of disease, even when other confounding factors were removed.

Malaria Control in Endemic CountriesMalaria Control Conventional ApproachReduce as much as possible the health impact of malaria on a populationUse available resourcestake into account other health priorities.Does not aim to eliminate malaria totallyComplete elimination of the malaria parasite (and thus the disease) is eradication. Eradication is desirable butis not currently a realistic goal for most of the countries where malaria is endemic.

Interventions for Malaria ControlThese are often combinedCase management (diagnosis and treatment) of patients suffering from malaria Prevention of infection through vector control Prevention of disease by administration of antimalarial drugs to particularly vulnerable population groups such as pregnant women and infants.

Case ManagementTreat sick persons promptly and correctly. Malaria is often a debilitating disease Treatment eliminates an essential component of the cycle (the parasite)interrupts the transmission cycle.World Health Organization recommends suspected malaria cases receive diagnosis and treatment with an effective drug within 24 hours of the onset of symptomsWhen the patient cannot have access to a health care provider within that time period (as is the case for most patients in malaria-endemic areas), home treatment is acceptable.

Prevent InfectionPrevent infection by preventing the malaria-carrying Anopheles mosquitoes from biting humans. Vector control:To reduce contacts between mosquitoes and humans. Vector control measures:Destruction of larval breeding sitesinsecticide spraying inside houses Requires organized teamse.g., Ministry of HealthResources are not always available.Alternate approach: insecticide-treated bed nets (ITNs)combines vector control and personal protection Can often be conducted by the communities themselvesHas now become a major intervention in malaria control.

Preventing DiseaseAdministering antimalarial drugs to vulnerable population groups does not prevent infectionInfection happens through mosquito bites. Drugs can prevent disease by eliminating the parasites that are in the bloodThese are the forms that cause disease Pregnant women are the vulnerable group most frequently targeted. Intermittent preventive treatment" (IPT) Antimalarial drugs given at antenatal consultations during the second and third trimesters of pregnancy.

Partnerships for Malaria ControlSuccessful malaria control activities require coordinated actions by:National authoritiesespecially the Ministry of HealthInternational organizations: World Health Organization and UNICEF GovernmentsNongovernmental organizations (NGOs) Private sector Communities

Activities for Malaria Control InterventionsHealth education (also called Information-Education-Communication, IEC)Communities are informed of what they can do to prevent and treat malaria. Training and supervision of health workersTo ensure that they carry out their tasks correctly. Provision of equipment and supplies:Diagnosis (microscopes)Drugs (treatment and prevention)Bed nets (prevention)Other resources for health workers and the communities to carry out the interventions

Current Barriers to Malaria ControlDrug-resistant malaria parasitesHinders case managementDecreases the efficacy of antimalarial drugsRequires the use of alternate drugsOften more costly, less safe and less easy to administerInsecticide resistanceDecreases the efficacy of interventions relying on insecticidesinsecticide-treated bed netsinsecticide spraying.Inadequate health infrastructures in developing countriesunable to conduct the recommended interventions.Povery and lack of educationPeople most exposed are often poor and lack education. Do not know how to prevent or treat malariaEhen they do know, they lack financial means to respondCant purchase the necessary products, such as drugs or bed nets

Integrated Vector Management - IVMNew strategy for prevention and control of vector-borne diseasesAn approach that reinforces linkages between health and environment, optimizing benefits to both.Key vector-borne diseases:Malaria: the most deadly vector borne diseaseKills >1.2 million people/yr, mostly African children under the age of five. Dengue fever and associated dengue haemorrhagic fever (DHF)World's fastest growing vector borne disease.Environmental factors contributing to vector-borne diseases:Poorly designed irrigation and water systemsinadequate housingpoor waste disposal and water storagedeforestation and loss of biodiversityThese factors contribute factors to the most common vector-borne diseases including malaria, dengue and leishmaniasis.

IVM StrategiesDesigned to achieve the greatest disease control benefit in the most cost-effective mannerMinimizing negative impacts on ecosystems (e.g. depletion of biodiversity)Minimize adverse side-effects on public health from the excessive use of chemicals in vector control.Does not rely on a single method of vector controlStresses the importance of:first understanding the local vector ecology and local patterns of disease transmissionthen choosing the appropriate vector control tools, from the range of options available.

OptionsEnvironmental management strategies that educe or eliminate vector breeding grounds altogether through improved design or operation of water resources development projectsBiological controls (e.g. bacterial larvicides and larvivorous fish) that target and kill vector larvae without generating the ecological impacts of chemical useChemical methods:Use judiciously if other measures are ineffective or not cost-effective to indoor residual spraysspace sprayinguse of chemical larvicides and adulticidesThese reduce disease transmission by shortening or interrupting the lifespan of vectors

IVM: A Framework for Improved Personal Protection and Preventive StrategiesCombines environmental management & chemical tools for new synergies e.g. insecticide-treated bed nets (ITNs). Reduced child and infant mortalityIn trials using ITNs in some malaria-endemic African countriesSupports effective, accessible and affordable disease diagnosis and treatment within the framework of a multi-disease control approach. Requires a multi-sectoral approach to vector-borne disease control. E.g., Health Impact Assessments of new water resource infrastructure development to identify potential impacts on vector-borne disease prior to major policy decisions so effective action may be taken.In some cases has been shown to be: cost-effective in terms of disease controla potential generator of economic co-benefits in terms of development and growth

The Power of Integrated Action in Malaria ControlDesigned to achieve the greatest disease-control benefitDo so in the most cost-effective mannerMinimize negative impacts on ecosystemse.g. depletion of biodiversityMinimize adverse side-effects on public health of:Acute exposures to pesticidesPesticide residue bio-accumulation of toxic chemicals Development of vector resistance to widely-used pesticides and drugs.

WHO Global Strategic Framework for Integrated Vector Management Defines IVM as a strategy toImprove the efficacy, cost-effectiveness, ecological soundness and sustainability of disease vector control. Encourage a multi-disease control approach,Integrate with other disease control measuresUse considered and systematic application of a range of interventionsoften in combination and synergistically.No reliance on a single method of vector control (e.g. chemical spraying), Stresses the importance of first understanding the local vector ecology and local patterns of disease transmissionThen choosing the appropriate vector control tools from the range of options available.

Elements of IVMEnvironmental management strategiesReduce or eliminate vector breeding grounds altogetherImprove design or operation of water resources development projectsBiological controlsuse bacterial larvicides and larvivorous fish that target and kill vector larvae without generating the ecological impacts of chemicalsChemical methodsWhen other measures are ineffective or not cost effective make judicious use of vector control chemicalsindoor residual spraysspace sprayingchemical larvicides and adulticidesreduce disease transmission by shortening or interrupting vector lifespans

IVM:Personal protection/preventionCombines the use of environmental management toolsphysical barrierschemical tools for new synergiese.g. insecticide-treated nets (ITNs). Supports more accessible and affordable disease diagnosis and treatment with effective anti-malarial drugs, within the framework of a multi-disease control approach.

Adaptive Management in IVMPeriodic evaluation and reassessment of the ecological settingMonitoring of disease incidence and transmissionHealth impact assessments of new developments to be undertaken by other sectors