Overview of Arthropods and Disease

Overview of Arthropods and Disease

INTRODUCTION: You may ask yourself why the Army, with all of its high-tech weapons systems, concerns itself with something as small as a mosquito or a spider. The reason is that history is full of examples of armies that were decimated by arthropod-borne disease. In fact, worldwide, one out of every seventeen people die from malaria – a disease passed on by mosquitoes. Think about that number for a minute. That means that if your unit deploys to a malaria-prone area, they will be at very high risk unless they take the necessary precautions. It’s up to you to make sure the soldiers in your unit are aware of and realize the medical threat and to train your soldiers in the proper precautionary measures to protect themselves both in peacetime and wartime operations.

Terms and Definitions

Arthropods

Animals, including ticks, spiders, mites and other insects as well as crustaceans such as shrimp, lobster and crabs

Vector

A carrier. In this lesson, this term is used to describe an arthropod that transports a disease-causing organism, or pathogen, from one host to another

Arthropods important to military operations

Mosquitoes

(1) The most important arthropod for a number of reasons

(a) Can find them practically everywhere

(b) Found in usually in high numbers

(i) Some of which are war-stoppers

(ii) During WWII, Korea, and Viet Nam entire units were rendered combat ineffective by malaria

(2) Life cycle

(a) Live short lives – about one month

(b) Four life stages

(3) Habitat

(a) Mosquito larvae inhabit areas with standing water such as ponds, puddles, and ditches

(b) Anything that can hold water provides a habitat for mosquito larvae

(d) Adult mosquitoes continue to inhabit their larval habitats without venturing too far away

Filth flies

(1) Filth fly transmits many diseases

(a) There have been situations in which filth flies have been allowed to breed unhampered

(b) Resulting fly-borne disease outbreaks made hundreds of soldiers sick within a few days

(2) Life cycle

(a) Live short lives – usually about six weeks

(b) Four life stages

(3) Habitat

(a) Live in or near animal or human waste, garbage, decomposing plants and animals, or in mud with high organic content

(b) A large population of flies is usually a good indicator of unsanitary conditions

Fleas

(1) Adult fleas are not only persistent and painful biters, but are efficient vectors of a number of diseases

(2) Life cycle

(a) Four life stages

(b) The flea matures in about one month and the adult flea can live for as long as one year

(3) Habitat

(a) Often associated with animals, although many humans are carriers

(b) Large populations of fleas can usually be found around animal beds, burrows, and nests

Lice

(1) Head and body lice are considered external parasites of man

(a) They live outside the human body and obtain nutrients from it

(b) Both species bite causing an itching inflammation of the skin

(2) Life cycle

(a) Life cycle has only three stages

(b) Matures from egg to adult in about sixteen days

(3) Habitat

(a) Normally inhabit the hairy parts of the body, along with clothing

(b) Often prevalent in crowded or unsanitary conditions

(c) Soldiers who do not practice good personal hygiene can become infested with lice and pass them on to other soldiers when they come in contact with their hair, clothing, sleeping bags, or other linens

Cockroaches

(1) Cockroaches can carry a variety of disease-causing pathogens

(2) Life cycle

(a) Life cycle has only three stages

(b) They mature in about three months and live for adults for up to two hundred days

(3) Habitat

(a) Cockroaches prefer habitats with three criteria:

(i) Water

(ii) Shelter- such as cracks or crevices

(iii) Food, such as garbage or spillage

(b) Anytime these three conditions exist, you should look for the existence of cockroaches

(c) These three criteria usually exist together in kitchens and bath areas, especially when conditions are less than sanitary

Ticks and mites

(1) These two arthropods are very similar in biology, so are considered together

(a) Ticks are the most efficient arthropod when it comes to disease transmission

(b) This is because the female tick can pass the pathogen to the egg so that when the larva hatches it is already able to pass on the disease upon eating its first meal

(2) Life cycle

(a) Four life stages

(b) They live as adults for anywhere from one month to two years

(3) Habitat

(a) Ticks and mites are generally found in areas of tall grass or underbrush in close proximity to mammal resting places and watering holes

Arthropods affect on human health

Direct injury - Results when the arthropod, itself, causes the disease or discomfort

(1) Bites

(a) Most obvious mechanism for direct injury

(b) Annoying, painful, and can decrease a soldier’s productivity level

(2) Envenomization

(a) Direct injection of venom into the body through a bite or sting

(b) The damaging results of a bite or sting can range from

(d) To actual tissue damage (the result of the bit of the brown recluse spider)

(3) Entomophobia - This condition is the irrational fear of real or imaginary insects

NOTE: While this condition is not usually prevalent among soldiers, it can occur so it needs to be mentioned.

Direct Injury - Accidental Injury to Sensory Organs

(1) Insects can cause accidental injury to our sensory organs

(2) Any insect that enters the ear, nose, or eye can cause severe irritation

(3) Myiasis

(a) A condition in which fly larvae invade a human host

(b) Occurs in one of two ways:

(i) A fly lays its eggs on an open wound, when the eggs hatch the larvae begin to feed on human tissue

(ii) A person may eat fly larvae on contaminated food. However, when this happens, the food is usually passed through the digestive tract without damage or illness. The process of myiasis may also be used as a medical treatment. In such cases, fly larvae are intentionally placed on wounds. The larvae feed on the dead tissue, which in turn promotes the growth of living tissue.

(4) Allergies

(a) Potent allergens

(i) Cockroach feces and the skins they shed when molting

(ii) Dust mites that are found in many buildings and in bedding materials such as mattresses and pillows

(iii) Allergies to the venom of some biting and stinging arthropods are also prevalent

(iv) While not often considered deadly, the nuisance caused by allergic reactions can, itself, be enough to reduce a soldier’s productivity and effectiveness

Spread of disease

Passive transmission (also called Mechanical Transmission)

(1) This method of transmission occurs when the arthropod carries the pathogen from one host to another

(2) During this transmission, the pathogen does nothing during the transfer except ‘go along for the ride’

(a) Filth flies carry bacteria or other disease-causing organisms on their mouthparts and feet from infected human feces. If soldiers eat food that has been contaminated by a fly landing on it and depositing these pathogens, dysentery or other diarrheal disease may occur.

(b) Cockroaches provide a similar ‘taxi service’ by carrying disease organisms on their legs, feet, and mouthparts. These pathogens can cause diarrheal diseases such as cholera.

Active transmission (also called biological transmission)

(1) In this method of transmission the disease-causing agent undergoes some change in the body of the arthropod

(2) The pathogen may multiply or simply develop into an infectious form

(3) There are several ways a pathogen can be passed to humans via active transmission

(a) Inoculation

(i) A vector injects the pathogen into the host with its saliva while it feeds on the host

(ii) Mosquitoes transmit malaria by inoculation.

(b) Regurgitation

(i) The vector vomits the pathogen into the host while it feeds on the host

(ii) Fleas transmit bubonic plague by regurgitation

NOTE: The bacteria that causes bubonic plague multiplies rapidly in the flea’s gut and blocks it like stopping up a drain. When the flea attempts to eat, it can not ingest the host’s blood due to the blockage. The flea ends up regurgitating the bacteria into the host.

(i) The vector defecates into a wound on the host

(ii) As the wound itches, scratching and rubbing by the host causes the pathogen to enter the host’s body

(iii) Chagas’ disease, also known as North American Sleeping Sickness, is transmitted in this way by the kissing bug

NOTE: The kissing bug bites the host causing a wound. It then takes a few steps forward and defecates into the wound.

(d) Crushing the vector

(i) The vector is smashed onto the skin of the host

(ii) When the host wipes off the dead bug, the pathogen is rubbed into the skin

(iii) The body louse transmits epidemic typhus in this manner

NOTE: The bacteria that cause epidemic typhus live and multiply in the body of the body louse.

Arthropod-borne diseases and their vectors

Several arthropod-borne illnesses that are significant to military operations

(1) Malaria

(a) Most important disease to the military

(b) The Anopheles mosquito transmits this disease

(2) Yellow fever

(a) The Aedes mosquito transmits this viral disease

(b) No longer considered a real threat to soldiers in the army since soldiers are now inoculated against this disease

(3) Dengue fever

(a) The Aedes mosquito transmits this disease

(b) It is most prevalent in the tropical and sub-tropical areas of Asia, Africa, and Central and South America

NOTE: This disease is characterized by fever, headache, extreme pain in the joints and muscles, and a rash.

(4) Encephalitis

(a) The Aedes and Culex mosquitoes carry several forms of this disease

(i) St. Louis encephalitis

(ii) Japanese B encephalitis

(iii) California encephalitis

(b) Ticks carry another form of this disease known as Russian spring/summer encephalitis

NOTE: Symptoms of this disease may include headache, fever, and extreme drowsiness. The disease may leave lasting effects such as deafness, epilepsy, or an altered mental capacity, known as dementia.

Diseases and Their Vectors – Others

(1) Sand fly fever

(a) Also known as phlebotomus fever

(b) This viral disease is carried by the phlebotomine sand fly

(2) Leishmaniasis

(a) The sand fly transmits this disease

(b) Transmitted to humans by the transfer of a single-celled animal known as a protozoa

(3) Epidemic typhus

(a) The body louse is the vector for this disease

(b) Has occurred in widespread epidemics during wartime or other periods when sanitation has not been strictly observed

(d) During WWI, one hundred fifty thousand soldiers died of this disease

(4) Bubonic plague

(a) Any one of the arthropods that are parasitic on rodents may transmit this disease

(b) Most important of these is the rat flea

(d) These pandemics were known to wipe out the entire population of many cities

Pesticide

Sanitation practices

(1) The best way to control bugs is to first follow proper sanitation practices, then augment with chemicals

(2) Improper sanitation practices: Consider a pile of opened garbage. You can spray and spray, but unless you eliminate this breeding ground for flies, you’re still going to have a problem

(3) Eliminate arthropod habitats

(a) The safest way to control most arthropods is to eliminate their living and breeding areas

(b) Control rodents in the unit area

(d) Avoid animal nesting areas

Chemical practices

(1) Even the best sanitation efforts fall short of controlling arthropods, when this is the case, augment efforts with the use of pesticides. (AUGMENT is the operative word here – chemicals are not meant to take the place of the individual or unit-level preventive medicine measures)

(2) Properties of pesticides

(a) Pesticides are toxic, or poisonous, substances designed to kill pests such as mosquitoes, ticks, and rodents

(b) Pesticides and solvents

(i) The toxic ingredients in pesticides are often mixed with solvents such as kerosene or fuel oil

(ii) The presence of these solvents makes them more hazardous to humans.

(i) The toxic chemicals in pesticides are often mixed with an oil-based solution

(ii) Human skin repels water but absorbs oil. Therefore, the pesticide is absorbed into the skin along with the oil.

(iii) protective clothing is required when working with pesticides

WARNING: Because of their toxic properties, all pesticides should be considered potentially hazardous. You can find the hazard and risk information on the pesticide label. Always refer to the label instructions for use, protective clothing requirements, and safety precautions prior to using a pesticide. In all cases, THE LABEL IS THE LAW.

(3) Estimating the hazard potential for any pesticide is important prior to using it

(a) Several factors to consider when determining the hazards associated with chemical use

(b) Determine the hazard posed by a particular chemical by asking yourself these questions:

(i) What are the toxic effects if the pesticide is accidentally inhaled or ingested?

(ii) What is the concentration of the toxic substance I will be handling while mixing the pesticide? While applying it?

(iii) How much pesticide needs to be applied in order to achieve the desired results?

(iv) How often do I need to apply the pesticide?

(v) What environmental conditions exist at the time of application?

(vi) Am I indoors or outdoors? Is there proper ventilation?

(vii) Is there a breeze?

(viii) What temperature is best and safest for the application of this chemical?

NOTE: It is important to remember that the hazard for any pesticide is negligible, as long as you use it correctly.

Safety precautions

(1) Consult the label instructions for additional safety precautions that are unique to the chemical that you plan to use

(2) Pesticides should not be stored or used near an open flame.

(3) Do not mix pesticides. Mixing pesticides can render them ineffective or, worse, can create an even more toxic substance.

(4) Dispose of any unused pesticide properly

5) When a pesticide can not be used for its intended purpose or when a pesticide is no longer authorized for use, any unused quantity should be returned to the manufacturer through the Defense Marketing and Utilization Office (DRMO)

(6) Dispose of the empty pesticide container properly

(a) Triple-rinse the container to ensure that the container is free of chemicals prior to disposal

(i) First, fill the pesticide container with water

(ii) Pour the rinse water into the 2-gallon sprayer along with the water used to dilute the pesticide being applied.

(iii) Repeat steps 1 and 2 two more times

(b) Then crush or puncture the container prior to disposal to render the container unusable

SUMMARY

As you have learned, arthropods can affect a soldier’s health in many ways. Many people have the tendency to overlook the impact that arthropods can have on military operations, even though history is full of examples in which their impact can be devastating. An important part of your job is to inform your unit about the impact that arthropods can have on military operations and the ways in which unnecessary exposure to them can be avoided.