Vector Borne Diseases
What is the tick-borne disease life cycle?
1. Adult tick bites and infects a dog, deer, or a raccoon 2. Adult tick lays eggs (typically in fall) 3. Egg hatches to larva 4. Larva feeds on small mammals in the summer, larva leaves host and molts to nymph in spring 5. Nymph feeds on dog and transfers infection 6. Nymph leaves host and molts to adult tick
What are other ways to control vector-borne diseases?
1. Control of wild-reservoir host (impractical) 2. Sometimes control of one vector can result in control of several diseases 3. Personal protective measures (clothing, mosquito nets, window screens, insect repellents) 4. Environmental controls 5. Reduction of reservoir hosts where practical (rodent/bird control) 6. Vaccination against the agent itself
What the is the summer cycle of EEEV?
1. EEEV circulates between bird biting mosquitoes and birds throughout the summer 2. Other mosquitoes become infected with EEEV after blood feeding on an infected bird 3. Infected mosquito feeds on a person or a horse
What are a few causes as to why there has been a resurgence of vector-borne diseases in the last 30 years?
1. Insecticide and drug resistance 2. Decreased resources for control of these diseases in some regions 3. Declining public health infrastructure in some regions 4. Population growth 5. Increased urbanization 6. Increased global travel 7. Agricultural practice changes 8. Deforestation 9. Climate change
What does transmission of vector-borne diseases depend on?
1. Properties and prevalence of the infectious agent, and their adaptation to the vectors and host 2. Properties and prevalence of the arthropod vector and reservoir host species 3. Local environmental conditions (dampness, warmth) 4. Properties (behavioral, immunological) of the final host species (human, domestic animal)- are they going to get the disease? Are they vaccinated? Is it species specific?
What is the virus cycle for the reservoir host?
1. Reservoir host typically has the infectious agent in their blood 2. Arthropod vectors suck blood from reservoir hosts, becoming infected with the agent 3. The infectious agent multiplies and/or develops in the vector 4. The vector sucks blood from the final host and secretes fluids (saliva, etc) containing the infectious agent into the final host, transmitting the infection
What is the life cycle of a mosquito?
5-7 days depending on the species.
What is the typical virus cycle for West Nile Virus, Eastern Equine Encephalitis, and Western Equine Encephalitis?
A mosquito bites an infected bird (reservoir host). The virus will then replicate/develop in the mosquito. When the mosquito bites either a human or a horse, the infectious agent is transmitted through the saliva of the mosquito. Person or horse then shows clinical signs of disease
What is a vertebrate host?
A reservoir host
What do most vector-born species have?
A reservoir host species in nature
What is the vector of leishmania?
A sandfly. Protozoal disease.
What does the reservoir host species serve as?
A source of infection for the arthropod vector
What is the vector of tularemia?
A tick
What vector transmits Colorado tick fever?
A tick
What is the vector of q-fever?
A tick. Rickettsial disease
What is the vector of Human Granulocytic Anaplasmosis?
A tick. This is a rickettsial disease
What is a fomite?
An inanimate object that may serve as a temporary surface "home" for the infectious agent enabling it to be transmitted between hosts. No growth or development occurs on the fomite, it is simply a vehicle for transmission of the infectious agent
What is the vector of river blindness?
Blackflies
What are examples of fomites?
Buckets, kleenex, grooming equipment, needles
What is a reservoir host?
Commonly infected with the agent, but rarely has clinical disease associated with this infection
How do human inducing climate change and environmental factors impact the vector population?
Death rate, density, breeding places, and insecticide resistance
What occurs in a biological vector?
Development or multiplication of the infectious agent. Development may or may not be a necessary part of the infectious agent life cycle
What environmental factors have impacted vectors and the diseases they carry?
Drought and desertification, sea level rising, changes in vegetation, and agricultural practives
What are environmental controls used to control vector-borne diseases?
Environmental modification to reduce vector breeding grounds and chemical/biological control of vector development
What is rickettsia?
Essentially like a "combo" or in between form of bacteria and protozoa
What does the arthropod vector then do?
Feeds on the final host, whether that's a human or another domestic animal, and transmits the infectious agent, with possible resulting disease
What is the vector of tapeworm?
Flea
What is the vector for the plague?
Fleas and lice. Which then rode in on the backs of mice and rats.
What are a few examples of parasitic diseases?
Heartworm, tapeworm, and onchocerciasis (river blindness)
How can we vaccinate against the agent itself?
In final host (human or domestic animal) and in the reservoir host (rabies vaccine in wildlife vectors)
How does the plague transfer to humans?
Infections among rodents increase dramatically, causing an outbreak. During plague epizootics, many rodents die, causing hungry fleas to seek other sources of blood. Cats may eat these dead rodents, or the fleas may jump on and feast on the cat. Disease so infectious that if the cat coughs, infectious droplets are let out into the air and can infect humans. Not as likely in dogs but still possible.
What are arthropods?
Insects. Most common are ticks, mosquitoes, flies, lice, and fleas
What does each arthropod vector have?
Its own lifecycle
What is the tick that transmits lyme disease?
Ixodes Scapularis
What is critical to control of vector-borne diseases?
Knowledge of the vector life cycle. May be more efficient method than direct control of the infectious agent in some cases
What is the vector of heartworm disease?
MOSQUITO
How does human inducing climate change and environmental factors affect the human population?
Migration, spread of drug resistance, change in immune status, and spread of pathogens into new areas
What is the vector that transmits Dengue?
Mosquito
What is the vector of malaria?
Mosquito. Malaria is a protozoal disease
What is a vector?
Most commonly an arthropod, but may be other animals
Is the lifecycle the same for all species?
No, it varies. Example: Different species of ticks have very different life cycles with different number of hosts and a different life span
Can any species carry any infectious agent?
No, only certain species or arthopod vectors can carry certain infectious agents. Example: Not all species of mosquitos can carry yellow fever or west nile virus
What kinds of infectious agents are commonly transmitted by vectors?
Pathogens of viruses, bacteria, protozoa, rickettsia, and parasites
What are mechanical vectors?
Serve as a temporary host for the infectious agent, and transmit the agent from animal to animal, but are not involved in growth or development of the infectious agent
What contributes to parasite developing rate?
Temperature and other environmental factors
What human inducing climate change factors have impacted vectors and the diseases they carry?
Temperature, precipitation, humidity, and wind patterns
What does lyme disease, the plague, and tularemia all have in common?
They are bacterial diseases
What does Malaria, Human granuloctic anaplasmosis, rocky mountain spotted fever, q-fever, and leishmania have in common?
They are protozoal and rickettsial diseases
What do WNV, EEE and WEE, dengue, and colorado tick fever all have in common?
They are viral diseases
What is the vector of rocky mountain spotted fever?
Tick
What types of arthropods most commonly serve as infectious disease vectors?
Ticks, mosquitoes, flies, lice, and fleas.
How is the plague transmitted in nature?
Transmitted by fleas and cycles naturally among wild rodents, including rock squirrels, prairie dogs, and wood rats.
What is REQUIRED for the life cycle of a mosquito?
WATER
If a human took an anti-malarial drug, how would that affect the onset of disease?
When the mosquito would go to bite the person, the sporozites that it ejects through the saliva would not be able to go through developmental stages. Therefore, person would not contract disease even though the mosquito carries it.
What is the plague bacterium?
Yersinia pestis
What is the vector for West Nile Virus?
Zoonotic disease transmitted by a mosquito
What is the vector of EEE and WEE?
Zoonotic disease transmitted by a mosquito
What are vector-borne diseases?
infectious diseases transmitted by a vector from one host to another
What is lyme disease transmitted by?
the Ixodes Scapularis tick
