Disease Background and Vectors of Transmission

A change in the climate affects more than whether you need an umbrella or a coat. Climate changes along with other factors such as urbanization, deforestation and desertification can have life or death consequences. Global climate changes have increased the number of vector-borne diseases. The transmission of vector-borne diseases to large populations, depend upon the attributes and requirements of at least three different living organisms. The pathogenic agents are either protozoa virus, bacteria or helminth (worm). The vector is usually an arthropod such as a tick or mosquito or can be a human host. Also intermediary host such as a domesticated and/or a wild animal often serve as reservoir for the pathogen until the susceptible human population is exposed. The vector receives the agent from an infected individual and transmits it either to an intermediary host or directly to a human host. The different stages of the agent's life cycle occurs during this process and are intimately dependent upon the availability of suitable vectors and host.

The three key components that determine the occurrence of vector-borne diseases are as follows:

1. the abundance of vectors and intermediary and reservoir host
2. the prevalence of disease-causing parasites and pathogens suitably adapted to the vectors, the human or animal host and environmental conditions (these conditions would include such things as temperature and humidity, as well as, global warming)
3. the resilience and behaviors of the human population, which must be in dynamic equilibrium with the vector-borne parasites and pathogens.

CASE STUDIES
Background Information:

Hantavirus Pulmonary Syndrome is an infectious air-borne disease caused by the hantavirus. It seemed to be exclusively an all-world problem until the 1970's when one of its relatives, the Seoul virus was found in rats. El Nino, a weather pattern that brought a warm, wet winter to the Southwest, allowed more plant growth than usual. These rains produced an abundance of nuts and grasshoppers, thus creating a large supply of food sources that are staples of the deer mouse diet which led them to produce bigger litters. These rodents spread the disease to humans through their droppings, which people usually inhale as dusty air or take in by touching dirty surfaces.

Why did scientists suspect rodents as the culprits?

Rearchers began testing rats for antibodies to the virus all around the world. Results were positive on every continent. New hantaviruses have been discovered in India, Thailand, and New York. More study is needed to determine which of these have spread lately from Asia or Europe. Suspicion is high that hantaviruses, old and new, cause many cases of kidney disease, hypertension, and stroke. In 1993, a mystery disease broke out among Navajos in the Four Corners- New Mexico, Arizona, Utah, and Colorado. The disease did not pass easily to victims' families or friends. It struck almost randomly over a huge geographical area. This finding suggested an animal source, perhaps with secondary person to person transmission.

What is known about hantavirus?

Humans don't usually contract hantavirus directly from rodents. Rodents shed hantavirus particles in their saliva, urine, and droppings. Humans contract hantavirus by inhaling particles that are infected with the disease. The virus becomes air-borne when particles dry out and get stirred into the air. After long-term exposure, untreated cases of hantavirus in humans are almost always fatal. Hantavirus is a rare disease, but it can affect anyone, therefore, education in this field needs to be increased. This case study can be used as a model for looking at what would happen after the most recent El Nino.