Vector-borne Disease and Health

ENVR 890-2

Mark D. Sobsey

Spring, 2009

Vectors and Vector-borne Diseases

Mosquitoes and Key VBDs

• Responsible for a great VBD burden– Malaria – parasite– Yellow fever – virus– Dengue fever/hemorrhagic fever – virus– Other viral fevers

• West Nile, Rift Valley, Bunyamwera

– Filiariasis – helminth– Encephalitis – viruses

• Western Equine, Eastern Equine, St. Louis, etc.

Flies and VBDs

• African sleeping sickness – african trypanosome parasite – tsetse fly bite

• Enteric bacteria diseases – houseflies – food contamination– Vibrio cholerae (cholera), typhoid fever

(Salmonella typhi), Shigella spp. (bacterial dysentery)

• Onchoceriasis (river blindness) – helminth – black fly bite

Lice and VBDs – Typhus Fever

• Agent: Rickettsia prowazeckii• Vector: body lice

– Pediculus humanus corporis• Associated with poor sanitation and lice infestation

(ectoparasite carriage)– Transmitted by louse feces penetrating skin or inhaled in

dust• Controlled with incecticidal body powder and improved

sanitation• Other louse-borne diseases

– Trench fever – Bartonella quintana (bacterium)– Relapsing fever – Borrellia recurrentensis (spirochete

bacterium)

Fleas and VBDs - Plague• Plague: Pasteurella (now Yersinia) pestis (Gram-negative

bacterium)• Fleas carried on rats & other rodents

– Zoonosis– Rats bitten by fleas become infected and die– Rats then hop onto humans, biting (taking a blood meal)

and infecting with P. pestis• Bubonic plague: flea bite→infection →lymph nodes →swelling

called buboes →septicemia →fever bubonic plague →dark patches on skin– called “Black Death”

• Pneumonic 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 Plague– Historically, a cause of major epidemics and pandemics

• Now readily controllable with antibiotics• Concern as a bioterrorism agent

Ticks and VBDs• Rocky 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 sequelae

• Erlichiosis - Ehrlichia chaffeensis – a bacterium– Infection causes systemic illness with fever, headache,

fatigue, and muscle aches. – Also, nausea, vomiting, diarrhea, cough, joint pains,

confusion, and occasionally rash• Q fever: Coxiella burnetti – ricketsia - zoonotic• Tularemia – Francisella tularensis - zoonotic• Others

Malaria - Biology

Malaria Disease Burden and Economic Costs

>1.2 million people, mostly children, die of malaria yearly

• Burden of disease: 46 486 000 Disability Adjusted Life Years (DALYs) lost– combined toll of death, illness, and disability.

• >85% of malaria deaths, disease, and disability occur in the African Region

• South-East Asia Region, 2nd

• Eastern Mediterranean Region, 3rd • Experts suggest even higher incidence than that

reported by countries

Impact of Malaria-related Illness• Reduced Economic Productivity

– Ex.: In Côte 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 products

• Consequences: 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 Countries

• Malaria Control – Conventional Approach• Reduce as much as possible the health impact

of malaria on a population– Use available resources– take into account other health priorities.

• Does not aim to eliminate malaria totally• Complete 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 Control

• These are often combined• Case 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 Management

• Treat 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 symptoms

• When 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 Infection• Prevent 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 sites• insecticide spraying inside houses

– Requires organized teams• e.g., Ministry of Health• Resources are not always available.

• Alternate approach: insecticide-treated bed nets (ITNs)– combines vector control and personal protection – Can often be conducted by the communities themselves– Has now become a major intervention in malaria control.

Preventing Disease• Administering antimalarial drugs to

vulnerable population groups does not prevent infection

• Infection happens through mosquito bites. • Drugs can prevent disease by eliminating the

parasites that are in the blood– These 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 Control

Successful malaria control activities require coordinated actions by:– National authorities

• especially the Ministry of Health

– International organizations: • World Health Organization and UNICEF

– Governments– Nongovernmental organizations (NGOs) – Private sector – Communities

Activities for Malaria Control Interventions

• Health 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 workers– To 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 Control• Drug-resistant malaria parasites

– Hinders case management– Decreases the efficacy of antimalarial drugs– Requires the use of alternate drugs

• Often more costly, less safe and less easy to administer• Insecticide resistance

– Decreases the efficacy of interventions relying on insecticides• insecticide-treated bed nets• insecticide spraying.

• Inadequate health infrastructures in developing countries– unable to conduct the recommended interventions.

• Povery and lack of education– People most exposed are often poor and lack education. – Do not know how to prevent or treat malaria– Ehen they do know, they lack financial means to respond

• Can’t purchase the necessary products, such as drugs or bed nets

Integrated Vector Management - IVM• New strategy for prevention and control of vector-borne diseases• An approach that reinforces linkages between health and

environment, optimizing benefits to both.• Key vector-borne diseases:• Malaria: the most deadly vector borne disease

– Kills >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 systems– inadequate housing– poor waste disposal and water storage– deforestation and loss of biodiversity

• These factors contribute factors to the most common vector-borne diseases including malaria, dengue and leishmaniasis.

IVM Strategies• Designed to achieve the greatest disease control

benefit in the most cost-effective manner• Minimizing 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 control• Stresses the importance of:

– first understanding the local vector ecology and local patterns of disease transmission

– then choosing the appropriate vector control tools, from the range of options available.

Options• Environmental management strategies that educe or

eliminate vector breeding grounds altogether through improved design or operation of water resources development projects

• Biological controls (e.g. bacterial larvicides and larvivorous fish) that target and kill vector larvae without generating the ecological impacts of chemical use

• Chemical methods:– Use judiciously if other measures are ineffective or not cost-

effective to • indoor residual sprays• space spraying• use of chemical larvicides and adulticides

– These reduce disease transmission by shortening or interrupting the lifespan of vectors

IVM: A Framework for Improved Personal Protection and Preventive Strategies

• Combines environmental management & chemical tools for new synergies– e.g. insecticide-treated bed nets (ITNs).

• Reduced child and infant mortality– In trials using ITNs in some malaria-endemic African countries

• Supports 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 control– a potential generator of economic co-benefits in terms of development

and growth

The Power of Integrated Action in Malaria Control

• Designed to achieve the greatest disease-control benefit

• Do so in the most cost-effective manner

• Minimize negative impacts on ecosystems

– e.g. depletion of biodiversity

• Minimize adverse side-effects on public health of:– Acute exposures to pesticides– Pesticide 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 to• Improve the efficacy, cost-effectiveness, ecological

soundness and sustainability of disease vector control. • Encourage a multi-disease control approach,• Integrate with other disease control measures• Use considered and systematic application of a range of

interventions– often 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 transmission

• Then choosing the appropriate vector control tools from the range of options available.

Elements of IVM• Environmental management strategies

– Reduce or eliminate vector breeding grounds altogether– Improve design or operation of water resources

development projects• Biological controls

– use bacterial larvicides and larvivorous fish that target and kill vector larvae without generating the ecological impacts of chemicals

• Chemical methods• When other measures are ineffective or not cost

effective make judicious use of vector control chemicals– indoor residual sprays– space spraying– chemical larvicides and adulticides– reduce disease transmission by shortening or interrupting

vector lifespans

IVM:Personal protection/prevention

Combines the use of • environmental management tools• physical barriers• chemical tools for new synergies

– e.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 IVM

• Periodic evaluation and reassessment of the ecological setting

• Monitoring of disease incidence and transmission

• Health impact assessments of new developments to be undertaken by other sectors