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Insects and related arthropods transmit many organisms
that cause diseases in humans and animals. The most
widespread of the human diseases - malaria - infects up
to 500 million people annually and is responsible for 2.7 million
deaths per year. Less widespread diseases, such as trypanosomiasis, account for over 20,000 human deaths annually in sub-Saharan Africa, while rendering a huge area in
Africa - roughly the size of Europe - unsuitable for raising
cattle. Added to these, leishmaniasis (12 million human
cases), Chagas disease (20 million cases), river blindness (18
million cases), and dengue (100 million cases and 2/3 of the
world population at risk from infection), and it is clear that
the impact of insects on human health is significant.
Persistent veterinary problems include infestations of ticks,
fleas, mites and lice; myiasis; economic losses due to biting
and filth flies that can transmit anaplasmosis, East Coast
fever, babesiosis, African swine fever and food-safety organisms such as Salmonella, Campylobacter and E. coli 01 57:H7.
Arthropods are not just
important in other parts of
the world. In the U.S.,
insects and other arthropods transmit human diseases such as Rocky
Mountain spotted fever,
typhus, encephalitis, plague,
Lyme disease, ehrlichiosis,
and West Nile virus. The
alarming increase in the
incidence of asthma is
linked to cockroaches and
house dust mites. And,
certain pest species that were considered to be of minor importance, such as head lice and bed bugs, appear to be
significantly resurging.
Vectors of organisms that cause human and animal diseases, including those that transmit food-borne
pathogens and even anthrax, are of particular importance from the perspective of homeland security. Intentional introduction of insects carrying pathogens that have been biologically modified or engineered is a serious potential threat, thus requiring a vigilant and knowledgeable sector of our scientific community being capable of detecting and containing such biotic agents.
Major insect-borne diseases are currently more
important in tropical
regions of the world.
However, globalization
makes the U.S. increasingly vulnerable to the
introduction of new disease vectors and/or
pathogens that can be
transmitted by native
species. For example,
the Asian tiger mosquito, a potential vector of
dengue, was introduced into the southern US on a shipment of recycled tires from Japan. West Nile virus entered
the US in New York City, presumably with an infected bird
or human. A suitable mosquito vector, Culex pipiens,
already present on this continent was capable of quickly
spreading the disease to humans, birds, and horses. These
cases are not isolated incidents. With rapid movement of
humans and commerce around the world, disease agents
and insect vectors can be introduced into new environments quickly. These concerns call for a scientific community trained to recognize such threats and to be capable of mobilizing a quick response. Tools for suppressing disease vectors are currently inadequate, especially due to increased pesticide resistance. This has resulted, for example, in the recent reintroduction of DDT - a pesticide with known harmful effects on the environment - into several African countries to help combat malaria.
The genomes of the malarial mosquito (Anopheles), the
malarial protozoan (Plasmodium) and humans have all
been sequenced, thus offering a rich potential to investigate all aspects of this three-species relationship. Although the sequencing has been completed, the task remains to understand the functions and interactions of the genes relevant to disease transmission.
Despite recent advances in mosquito molecular biology,
there is still a huge demand for scientists to understand the
ecology of mosquitoes and
other vector species. In
fact, if laboratory experiments with genetically
transformed mosquitoes
are to succeed in the field,
we need much more
knowledge about the basic
ecology of these vectors.
Many basic questions that
are critical links in the
biology of important vectors remain unknown. For example, we do not yet know
how the malaria mosquito survives the dry season or how West Nile virus overwinters in North America.
Entomological research offers yet another extremely important link to the health sciences. During the past century,
humans have relied primarily on plant-derived chemicals
for combating disease, and such sources have yielded
potent pharmacological agents capable of combating
malaria, cancer and numerous other maladies. The advent
of the molecular sciences and recombinant DNA technology, however, opens up an entirely new resource in the form
of genes from insects that encode potent defense agents.
Insects are well known to contain an enormous number of
immune responses that could be captured by the pharmacological industry to offer defense against viruses, bacteria,
fungi, and other microorganisms. The venoms of ants and
wasps are yet another rich source of pharmacological
agents. Blood-feeding arthropods use many chemicals
from vasodilators to anticoagulants to modulate the speed and content of the blood being acquired. Entomologists can be at the forefront of this type of pharmacological prospecting. As chemical control technology changes, scientists are recognizing increased opportunities to use host immune responses to control both the vectors of arthropod-borne diseases as well as pest species. Existing technology already provides the opportunity to develop vaccines against species-specific targets.
Many of the solutions to improving human and animal
health call for a multi-faceted approach involving entomologists, medical personnel, veterinarians, epidemiologists, public health officials, social workers, and governmental agencies working together. Thus, scientists with
team-building skills and the ability to communicate across
disciplines and cultures are urgently needed. To enhance these efforts, we need to expand investments in the entomological sciences, in areas such as:
- Generating new tools for genetically identifying and manipulating populations of pathogen vectors.
- Developing risk-assessment protocols and biocontainment
methods and strategies for using genetically transformed
insects to mitigate human and animal disease transmission.
- Explaining the molecular interactions between vector
hosts, pathogens, and human and animal hosts.
- Managing resistance to insecticides, thus, making it possible to prolong the use of current insecticides.
- Discovering new low-cost, low-impact, sustainable
methods for suppressing insect vectors, so that the use
of agents such as DDT can once again be eliminated.
- Better understanding vector behavior and ecology, to exploit their vulnerability and judiciously time control measures.
- Training students to be competent in recognizing vectors and disease pathogens from around the world so that we can respond to new introductions and possible bioterrorism threats quickly.
- Developing new methods of long-term vector surveillance, to anticipate outbreaks and interrupt pathogen cycles.
- Mining the pharmacological capabilities of secretions from blood-feeding arthropods, and developing vaccines to deter or kill arthropods to prevent disease transmission.
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