Arthropodborne Diseases

1. Historically, arthropodborne
   diseases have caused more casualties than combat
   injuries. Arthropodborne diseases alone were
   responsible for the loss of 15,576,000 man-days among
   US Armed Forces during World War II.
   1. Today, harmful arthropods
      represent one of the greatest environmental hazard
      to soldiers in the field. The chain of infection for
      arthropodborne diseases involves a pathogenic
      organism in an infected person or animal (the
      reservoir), an arthropod to transmit the disease
      (vector), and a susceptible person (the host).
   2. The significance of vector efficiency in disease
      transmission from reservoir to host is related to
      many factors. Some of the factors are
      species-related such as vector reproductive
      capacity, physiology, morphology, and genetics.
   3. Other factors that affect the vector�s ability
      to transmit disease are physical and related to
      environmental conditions, such as temperature,
      moisture, rainfall, pH, weather, geographical and
      topographical location, photoperiod, and wind.
   4. Soldiers in a field environment must break the
      chain of infection for arthropodborne disease or
      arthropod injury by limiting arthropod pest
      exposures.
2. Arthropods (insects, ticks, mites,
   spiders, scorpions, and the like) make up over 75
   percent of all animal species. Less than 1 percent of
   the 750,000 species of arthropods are potentially
   dangerous to humans. However, their impact is
   significant due to their high numbers and the negative
   results of their activities. The impact is direct
   injury and disease transmission to man and other
   animals; damage to crops; infestation of stored
   products; and destruction of wooden structures. Still,
   many species are beneficial as pollinators, predators
   of other pests, scavengers of waste, manufacturers of
   food, and a part of the natural balance of nature.
   However, the economic damage and medical disorders
   caused by a few arthropods make some pest management
   practices necessary to control the problem pests.
   Protection of the soldier from arthropods and
   arthropodborne diseases is essential to mission
   accomplishment.

Direct Arthropod
Affects on Human Health

In addition to disease
transmission, arthropods can cause direct injuries to
man. Bites, stings, and allergic reactions are three
major categories of injuries caused by arthropods.
Arthropods also affect man by annoying and disturbing
him. The sound of a single mosquito buzzing around your
head while your are trying to sleep is annoying.
Standing guard with gnats buzzing around your face can
be disturbing. Also, finding cockroaches or other
insects or parts of insects in your food is disturbing.
The problems of arthropod injury and the exaggerated
fear of arthropods can even result in psychiatric
problems.

1. Biting Arthropods. Arthropods bite
   to feed, probe (taste), or defend themselves. Most
   penetrations of human skin are made by mouthparts that
   are developed for ingesting blood, tissue, and tissue
   fluids of animals or plants. These bites usually
   result in the arthropod injecting salivary fluids or
   regurgitating its digestive tract products into the
   man or animal. Some biting arthropods can also produce
   skin injuries. Each individuals reaction to arthropod
   bites can be very different. Biting arthropods are
   grouped according to the duration of host contact as
   (short-term) or prolonged (long-term).
   1. Short-term host contact.
      Most arthropods that bite man have only short-term
      host contact. Bloodsucking arthropods are frequently
      winged or highly mobile. This accounts for their
      ability to quickly attack and escape capture or
      detection. Some arthropods hide in structures close
      to the host and only feed when the host is nearby.
      Others that bite may not have intended to attack,
      but did so in defense or by mistake. Arthropods can
      bite in several stages of their development; that
      is, adult, larvae, or nymph stages. The mouthparts
      are generally classified into chewing or sucking
      types. Chewing mouthparts are generally not used for
      skin penetration. Usually, injuries of this type are
      not reported, but secondary infections may occur due
      to bacterial contamination. Sucking mouthparts are
      structured for skin penetration.
      1. Bloodsucking (hematophagous)
         arthropods. Blood,
         normally from warmblooded animals (including man),
         is used both for life support and growth and/or
         egg development. The mouthparts of sucking
         arthropods vary greatly in structure from
         arthropod-to-arthropod. For example, adults of the
         order Diptera (two-winged insects) have the most
         diverse mouthparts. Only the females of the
         mosquitoes, black flies, biting midges,
         horseflies, and deer flies are bloodsuckers, while
         both males and females of tsetse flies and stable
         flies are bloodsuckers. The mouthparts are
         different within each of these families of Diptera,
         but the goal of a blood meal is the same. Other
         examples of arthropods that are short-term are
         fleas, true bugs (conenose bugs and bedbugs), and
         soft ticks.
      2. Nonbloodsucking (nonhematophagous)
         arthropods. Some plant-feeding arthropods and
         some arthropod predators have piercing/sucking
         mouthparts, which are capable of penetrating the
         human skin. Bites from these arthropods can be as
         painful as bloodsuckers, if not more so. Bites
         from these arthropods are usually an act of
         defense.
   2. Long-term host contact.
      Some biting arthropods require a considerable time
      on the host to complete a normal life cycle. Since a
      continuous food supply is available on one host, the
      search for another host is reduced. Most of these
      arthropods are categorized as parasites. They are
      classified as either ectoparasites or endoparasites.
      Ectoparasites (those living outside the host body)
      may be flat (fleas) or thin (lice) which allows them
      to travel easily through a hairy environment. Their
      feet are specialized for holding on to hair. The
      mouthparts of ticks and mites are designed to anchor
      their bodies to the host. Endoparasites (those
      living inside the host body) are usually soft-bodied
      (fly larvae, mites) without legs or with very short
      legs; their bodies usually have specially arranged
      spines or hairs.
2. Stinging Arthropods.
   Some arthropods affect man by injecting venom (insect
   toxins) through stingers, fangs, modified front legs,
   or spines. An arthropod�s injection of poison is in
   defense or to kill prey. Usually, man is envenomized
   by arthropods in defense of themselves and their nest
   or eggs.
   1. Venoms from bites.
      Spiders and centipedes are arthropods in the
      category that uses mouthparts for envenomization.
      Most spiders use venom to kill prey. Man is not part
      of a spider�s diet. The fangs of many spiders cannot
      penetrate the human skin. Some species have venom
      that is more poisonous than other venomous animals,
      including snakes. Fortunately, most spiders are not
      aggressive, but will defend themselves and their
      eggs and/or webs. Antivenom has been developed for
      the venom of some species of spiders, but they may
      not be immediately available for use. Some of the
      more toxic spiders are night hunters, and by day,
      they hide in clothing and boots that were left on
      the floor or in tents on the ground. Less common are
      the bites of centipedes that are also night hunters.
      In the tropics, some species of centipedes reach 25
      centimeters in length; a bite by such a large
      specimen could be serious.
   2. Venoms from stings. The number of soldiers
      seeking medical assistance because of arthropod
      bites is far fewer than those seeking aid because of
      bee, wasp, hornet, or ant stings. Stings from these
      arthropods are frequently the result of defensive
      action. A single sting to an allergic person can be
      fatal. Even to a person who is not strongly
      allergic, medical complications due to swelling can
      occur with stings to the face, neck, or throat.
      Stings usually occur during daylight hours. However,
      night maneuvers can result in individuals running
      into paper wasp nests and being stung by wasps
      trying to protect their nests; or an individual may
      stand on an anthill and receive numerous stings from
      the ants trying to protect their nest. Therefore,
      individuals who are highly sensitive or have severe
      reactions to stings should carry an emergency first
      aid kit for stings as prescribed by a physician.
      Obviously, high-risk persons should use extreme
      caution in tropical areas. Another venomous
      arthropod with a potent sting is the scorpion.
      Scorpions are active at night. During the day
      scorpions are usually well-hidden from the light;
      they hide under rocks or in piles of debris outside
      and in clothing, cabinets, boxes, and footwear
      indoors. Stings often are the result of individuals
      walking barefoot or in stocking feet, or because
      they use their hand to move the object where the
      scorpion is hiding. Also, stings occur when
      individuals put on clothing or footgear without
      first shaking the item to make sure that it is free
      of unwanted arthropods. Some scorpion venoms are
      very painful or they may be deadly, while others are
      not. The absence of initial pain is not always an
      indication of no problem. The lack of or the
      nonavailability of antivenom and the possible
      medical problems associated with the use of
      antivenoms, even if they were on hand, are
      additional reasons for avoiding scorpion stings.
3. Allergy. Allergic reactions are
   caused by both the bites and stings of arthropods.
   Additionally, arthropod parts (live or dead) and their
   body fluids can cause allergic reactions. Allergic
   reactions are extremely variable in different people
   ranging from very mild to severe reactions. Highly
   sensitive persons should be prepared to deal with
   their problems in case they are bitten, stung, or
   exposed to other arthropod allergens.

Arthropodborne
Diseases

Diseases transmitted to
man by arthropods are some of the most serious known to
man. Uncontrolled, these illnesses can cripple or
destroy military forces. The effect of these diseases on
man can range from a very mild illness to death. For
examples of arthropodborne diseases and their vectors
see Table 2-1. House flies and other flying insects that
are attracted to human wastes or other organic material
can spread disease organisms to food and water. The
disease organisms or parasites of humans are carried
from diseased humans or animals (reservoirs) by
arthropods (vectors) to other humans or animals (hosts).
By employing individual PMM, soldiers can stop
arthropodborne diseases from being a factor in their
lives and in their units mission accomplishment. The
most common arthropodborne diseases that affect combat
troops are discussed below.

1. Malaria. Malaria is a serious disease
   occurring most commonly in tropical and semitropical
   regions. It is caused by a microscopic parasite
   carried by the Anopheles mosquito. This parasite
   destroys blood cells and causes chills, fever,
   weakness, and anemia. If untreated, malaria can cause
   death.
2. Yellow Fever. Yellow fever is a viral
   disease transmitted by the Aedes mosquito. It occurs
   in tropical Africa, Central America, and tropical
   South America. Symptoms are fever, headache, backache,
   jaundice, and internal bleeding. If untreated, yellow
   fever can result in death.
3. Dengue Fever. Dengue viruses of multiple
   types are now endemic throughout most tropical areas
   of the world and are highly endemic in Southeast Asia,
   the Philippines, West Africa, and northern Australia.
   Like yellow fever, it is transmitted by the Aedes
   mosquito. Symptoms are fever (lasting about 5 days),
   intense headaches, skin rash, and muscle pain which
   can be severe; for this reason, another name for
   dengue fever is �breakbone� fever. The disease seldom
   results in death, but the recovery time is usually
   long and the victim may be fatigued and depressed.