Class 9- Vector Borne Diseases

Question 1

Factors linked w/ Emergence of VBDs

Answer 1

• Increased ease and frequency of global travel
• Rapid urbanization resulting in slums with high density populations
• Profusion of nonbiodegradable containers
• Public health infrastructure has degraded
  
  • Less emphasis on vector control
• Environmental influences
  
  • Building of large dams
  • Deforestation and changes in land use
  • Introduction of new virus amplifying hosts
  • Climate change

Question 2

Influence of climate change on VBD

Answer 2

• Warmer temperatures allow
  
  • vector to survive in areas that were previously too cold
  • Speeds up virus replication in mosquito gut
    
    • Mosquito becomes infectious faster
  • Increases speed of pupae development and adult maturation
    
    • Faster the adult matures – sooner it will take a blood meal
  • Can cause changes in migratory pathways of viremic hosts

Question 3

Dengue Epidemiology

Answer 3

• 4 dengue subtype viruses
  
  • Life long immunity to exposed subtype
  • Risk of Dengue Hemorrhagic fever increases with subsequent exposures!
• Originated in monkeys and independently jumped to humans in Africa or South East Asia 100-800 years ago
• Transmitted by the Aedes mosquito
• Estimates 50-100 million infections each year
  
  • 500,000 DHF cases
  • 22,000 deaths
    
    • mostly in children
• Vaccine would need to be a tetravalent vaccine
  
  • Means it prevents all four virus subtypes

Question 4

Dengue Fever Clinical Presentation

Answer 4

• Reservoir- Transmitted principally by the Aedes aegypti mosquito
  
  • Bites during daylight hours.
• Route- Monkeys act as a reservoir host in west Africa and south-east Asia.
  
  • There is no direct person-to-person transmission.
• Dengue Fever (aka break-bone fever)
  
  • High-grade fever, chills, headache, and pain behind the eyes
  • Severe body aches
• Dengue Hemorrhagic Fever (DHF)
  
  • Bleeding appears as tiny spots of blood on the skin, gums, larger patches of blood under the skin, low blood pressure, hepatomegaly, seizures, encephalopathy, and liver damage
  • Symptoms are followed by a shock-like state
• There is no cure!
  
  • Requires close monitoring and IV fluids

Question 5

Aedes albopictus- the Tiger Mosquito

Answer 5

• Secondary spreader for Dengue Fever
• Species spread to the Western Hemisphere as a result of the international trade in used tires.
  
  • The United States imports millions of tires from Asia, for remanufacturing purposes.
  • Tiger mosquitoes are closely associated with used tires, which are used as a preferable site for ovaposition
  • It is likely that tires imported to Houston, Texas from Japan in 1985 brought tiger mosquitoes to the United States.

Question 6

West Nile Virus background

Answer 6

• First isolated in 1937 in the West Nile district of Uganda
  
  • First major outbreak in the US 1999 – Queens, NY
    
    • Thought to have been imported from Israel
• Humans are incidental hosts
  
  • Play little to no role in maintain cycle of transmission
• Viremic reservoirs are key contributing factor to outbreaks
• Can be transmitted by multiple mosquito genuses
  
  • Culex mosquito is primary vector
  • Assisted in spread across the US

Question 7

West Nile Disease/Clincal Profile

Answer 7

• Reservoir – Birds (passerines, crows, and magpies)
• Route – mosquito bites, (reports of cases through blood transfusion and organ transplant)
• Incubation – 3-14 days
• Symptoms – fever, headache, body ache, fatigue, back pain,
• Communicability- not applicable (although someone can check communicable disease manual and double check)

Question 8

Neglected Tropical Diseases Overview

Answer 8

• Why are called “neglected” tropical diseases
  
  • They don’t receive the same attention as fatal infectious diseases
  • They disproportionately impact “neglected” populations
    
    • Infectious diseases that are disproportionately endemic in developing countries
    • Often restricted to poor, marginalized sections of the population.
  • Neglected financially…
    
    • Most have known inexpensive preventative measures or treatments
      
      • not always available to those at the highest risk.
      • Impact the lives of over a billion people worldwide and threaten the health of millions more.
        
        • Tend to have low mortality rates

Question 9

NTD at the Community Level

Answer 9

• Neglected tropical diseases such as leprosy, lymphatic filariasis and leishmaniasis are feared and the source of strong social stigma and prejudice.
  
  • As a result, these diseases are often hidden – out of sight, poorly documented and silent.

Question 10

NTD Neglected at a National Level

Answer 10

• Neglected tropical diseases tend to be hidden below the radar screens of health services and politicians because they afflict populations that are often marginalized, with little political voice.
• How do you prioritize NTDs when compared to HIV, Malaria, TB, and acute respiratory infections?

Question 11

NTD Neglected at an International Level

Answer 11

• Neglected tropical diseases do not travel easily and thus do not pose an immediate threat to western society.
• The development of new diagnostic tools has been under-funded largely because neglected tropical diseases do not represent a significant market.

Question 12

NTDs targeted for elimination Globally

Answer 12

• Group 1 Diseases
  
  • Chagas
  • Lymphatic filariasis
  • Onchocerciasis
  • Rabies transmitted by dogs
  • Neonatal tetanus
  • Trachoma
  • Leprosy
  • Malaria
  • Plague
• Group 2 Diseases
  
  • Schistosomiasis
  • Soil-transmitted helminthiasis

Question 13

Guinea Worm

Answer 13

• Causative agent- Dracunculus medinensis
• Transmission: ingestion of unfiltered water containing infected copepods
• Prevention: Drink filtered water
  
  • Intervention: Individual pipe like filters to drink from
• Guinea worm disease is in the process of being erradicated

Question 14

What are the risk factors NTDs?

Answer 14

• Living in endemic regions
• Insufficient access to clean drinking water
• Lack of sanitation infrastructure
• Poor housing quality/exposure to vectors
• Inadequate education
• Limited access to health services
• Poverty

Question 15

Epidemiology of LF

Answer 15

• An estimated 120 million people in tropical and subtropical areas have lymphatic filariasis
  
  • ~25 million men have genital form of disease (most commonly hydrocele)
  • ~15 million people, mostly women, have elephantiasis of the leg
• Lymphatic Filariasis (LF) and Onchocerciasis are responsible for the loss of an estimated 6.3 million Disability-adjusted life years (DALYs)
  
  • 1 DALY is thought of as one lost year of “Healthy Life”
• Over 400 million at risk for LF

Question 16

Lymphatic Filariasis cause and vector

Answer 16

• Lymphatic Filariasis
  
  • Caused by Nematode infection (roundworms)
  • Vector
    
    • the mosquito

Question 17

Clinical Manifestation of LF

Answer 17

• Tends to cause
  
  • Lymphodema (swollen limbs)
  • Hydrocoele (swollen testes)
    
    • Can limit the ability
      to walk
• Social stigma
• Albendazole
  
  • $.05-.10 per person per year

Question 18

Environmental control of NTD

Answer 18

• Reduce standing water
• Reduce vegetation or organic material in standing water
• Change the salinity of the water
• Lay polystyrene beads on top of the brackish water in the pit latrine
  
  • Inhibiting the vectors ability to lay eggs

Question 19

Biological control of NTD

Answer 19

• Bacterial insecticides
  
  • Bacillus thuringiensis israelensis (Bti)
    
    • Larva have trouble digesting food after exposure
  • Larvivarous fish
    
    • Used to control Anopheles mosquitoes
  • Juvenile Turtles, Trachemys scripta
    
    • Control Aedes aegypti in cement laundry tanks, Honduras

Question 20

Behavioral changes to limit mosquito exposure

Answer 20

• Avoid peak biting hours (varies by vector)
• Apply repellant (DEET)
• Sleep under insecticide treated bed nets (ITNs)
• Avoid wearing dark clothing
• Mosquitoes are attracted to body heat, carbon dioxide, and movement
  
  • Flailing your arms around to slap mosquitoes, might only make the situation worse…

Question 21

Onchocerciasis epidemiology

Answer 21

• Estimated 37 million individuals have onchocerciasis
  
  • 270,000 are blind (River Blindness)
  • 500,000 suffer some form of visual impairment
  • 100 million at risk of Onchocerciasis
• Transmitted by female black flies

Question 22

Where do black flies lay eggs?

Answer 22

• Fast moving rivers
  
  • The river transports food and oxygen to them constantly

Question 23

Clinical Manifestations of Onchocerciasis

Answer 23

• Mainly comes in the form of dermatitis
• Ocular onchocerciasis- leads to keratitis or hardening of the sclera (whites of eyes
  
  • (1 in 72 cases)
  • No reported cases of blindness in Latin America since 1995
• Social stigma associated with disease
• Pathologies caused mainly by microfilaria and inflammatory response of Wolbachia bacteria

Question 24

Schistosomiasis Epidemiology

Answer 24

• Schistosomiasis ranks second only to malaria as the most common parasitic disease.
• 240 million people in as many as 78 countries
• 700 million at risk
  
  • 85% of all cases are in Africa
  • Estimated 25 million people live at risk in the Americas
• ​​Cercariae (free-swimming larval stage in which a parasitic fluke) are released into water through human fecal matter and urine.
  
  • School aged children are at most risk due to time spent swimming and bathing in contaminated water

Question 25

Clinical Manifestation of Schistosomiasis

Answer 25

* Hepatitis, splenomegaly (enlarged spleen), pulmonary shistosomiasis * Chronic infection can damage the liver, intestine, spleen, lungs, and bladder. * Treated annually with a single dose of 2.5 tablets of praziquantel ($.08 per tablet)

Question 26

Rabies Epidemiology

Answer 26

* Over 50,000 death annually * Africa and asia most effected * Transmission through bite from infected mamal (virus is in saliva) * 99.99% fatality rate. * Interventions must focus on prevention * Human cases have been reduced by 90% over the past 20 years * 90% of rabies exposures globally come from dogs * "Hair of the dog" came from rabies * people used to rub the hair of the dog that bit them on the wound

Question 27

Trachoma Epidemiology

Answer 27

* Estimated 50 million people live in risk areas in Latin America and the Caribbean * 7,000 cases identified (mainly in Brazil) * Almost eliminated in Mexico * More prominent in areas of water shortage, numerous flies, & crowded living conditions

Question 28

Clinical Manifestation of Trachoma

Answer 28

* Leading infectious cause of blindness * Repeated infection leads to progressive scarring of the eyelid and mechanical damage to the cornea * Infection in children leads to blindness later in life. * Chlamydia trachomatis * Spreads through contact with eye discharge * Transmitted through eye seeking flies * If left untreated, the infection eventually causes the eyelid to turn inwards * Eyelashes rub on the eyeball causing intense pain and scarring of the front of the eye (ultimately leads to irreversible blindness) * Children at highest risk of exposure * Child to child transmission * Fly to child transmission * Malnourished children unable to swat flies away

Question 29

WHO SAFE strategy for Trachoma

Answer 29

* S- Surgical component * A- Antibiotics * F- Facial cleanliness * E- Environmental improvement * controlling fly population

Question 30

Soil-transmitted helminthes (STH) Epidemiology

Answer 30

* Commonly known as intestinal worms * Most common infection worldwide * Infects over 1 billion people * Caused by ingestion of eggs from contaminated soil or active penetration by larvae (hookworms) * Most common in Africa, Asia and South America

Question 31

Clinical Manifestation of STH

Answer 31

* Wide range of symptoms including intestinal blockage, anemia, protein deficiency, painful passage of stool * Treated with the anthelmintic albendazole * (Cost $0.02-.03 cents per dose) * Also reduces risk of LF

Question 32

Chagas Epidemiology

Answer 32

* 8 to 11 million people are infected. * Individuals living in rural areas are at greatest risk for acquiring infection. * Chronic Chagas * ​Infection may remain dormant for decades * Can kill you! * Average life time risk of developing chronic chagas complications is about 30%

Question 33

Chagas Transmission

Answer 33

* Transmitted by infected triatomines (kissing bugs) * Infection can also occur: * Vertically * Contaminated blood products * Infected organ transplant * Lab accident * Contaminated food or drink (rare) * The triatomine bug thrives under poor housing conditions * (mud walls, thatched roofs) * Falls from the ceiling and uses exhaled CO2 to track your mouth * Individuals living in rural areas are at greatest risk for acquiring infection. * Public health efforts aimed at preventing transmission have decreased the number of newly infected people and completely halted vectorborne transmission in some areas.

Question 34

Sleeping sickness epidemiology

Answer 34

* Over 95 % of cases of human infection occur in Tanzania, Uganda, Malawi, and Zambia * Disease has been better controlled recently * 7,000-10,000 CASES ANNUALLY. * Transmitted by the Tsetse fly * Both male and females take blood meals * However, females take blood meals more often before oviposition * Cattle are effected as well

Question 35

Sleeping Sickness Clinical Manifestation

Answer 35

* East African Sleeping Sickness * Fever, headache, muscle pain, enlarged lymph nodes, and rash. * After a few weeks parasite will invade the central nervous system. * Death usually occurs within months. * Most reported cases are East African * West African sleeping sickness * Milder symptoms * CNS damage usually occurs after 1-2 years * Most often kills in about 3 years if left untreated

Question 36

The Tsetse fly

Answer 36

* Opportunistic feeders * Gives birth to one egg at a time. * Can live up to 3 months and produce 31 generations * Principal control method- reduce vector population * Using traps * Flies attracted to the blue and black colors