Pthirus pubis - Pubic or Crab Louse

Pig Louse

Hemiptera - the true bugs

• Some 55,000 species• Hemielytra type of wing. Anterior half is

leathery while the posterior portion is membranous. Some are wingless

Cimex lectularius - the bed bug

• Cosmopolitan - in the temperate zones• Not a major transmitter of human pathogens.

Mechanically transmit Hepatitis B virus and source of much misery to man.

• Can live without food for as long as 18 months (4 months is common)

• Nocturnal feed on hosts while they sleep (bed bugs), painful bite disrupts sleep

Cimex lectularius - the bed bug

• Dorsoventrally flattened - allows them to hide in tight places, cracks, under loose materials, in thatch houses.

• Control is use of insecticides and remove hiding places.

Reduviidae - The Assassin Bugs

• The assassin bugs - most feed on other insects.– One Subfamily Triatominae contain important

vectors of Trypanosoma cruzi which causes Chagus disease.

– Called “Kissing bugs” often bite on tender parts of the body (lips) and have a bite that does not hurt while feeding. Hurts sometime later.

Reduviidae - The Assassin Bugs

• The most common vectors of T. cruzi are Panstrongylus megistus, Triatoma infestans, and Rhodnius prolixus

• Dogs, cats, rodents are important reservoir hosts in the urban setting and in the Sylvantic cycle the opossum is very important. .

Reduviidae - Kissing Bugs

• Rhodnius prolixus Triatoma infestans

Chagus Disease

• Caused by the protozoan Trypanosoma cruzi.

• Develops in the posterior of the insect infective forms passed out in insect feces.

• Insect defecates when feeds. • Feces with infected forms rubbed into break

in skin or into membranes of eyes.

Pathogenesis of Chagus Disease

• Acute phase - most common in children under 5 years

• Romana's sign• Pseudocysts can form in almost any tissue

Heart muscle ganglion cells are very susceptible and up to 80% of them may be destroyed.

• Death may occur within 3-4 weeks after infection.

Epidemiology• Reduviidae bugs are the most

important link to human transmission

• wild mammals may serve as reservoir hosts, dogs and cats are more important reservoirs for human disease.

Siphonaptera - the fleas

• The combined effects of Nero and Kubla Khan, of Napoleon and Hitler, all the Popes, all the Pharoahs, and all the incumbents of the Ottoman throne are as a fuff of smoke against the typhoon blast of fleas’ rabages through the ages.

• Quote by B. Lehane

Siphonaptera - the fleas

• Important in the transmission of many organisms especially the the plague.

• Morphology - see figures page 554-555. These will used in lab to identify fleas.

• Jumping mechanism - – Can jump more than 100 times body length. – Resulin is a specialized protein that releases 97%

of its stored energy.

Siphonaptera - the fleas

• In general, fleas lack significant host specificity.

• Most fleas do have preferred hosts.• Fleas are grouped as to how much time they

spend on the host.

Types of Fleas

• Spend little time on host (feeding) spend most of time in nest. Some rodent fleas.

• Spend most of time on host but can transfer from host to host. Most fleas.

• Sticktight flea attaches permanently to skin of fowl.

• Chigoe (Tunga penetrans) buries under skin on feet and hands - (see fig 37.12).

Some Important Fleas

• Nosopsyllus fasciatus - northern rat flea - Usually not considered an important plague vector because it seldom bites man.

• Pulex irritans - the human flea - see page 557. Is not host specific and commonly appears on dogs (80% of fleas on dogs were Pulex irritans in Georgia study). Can transmit plague

Some Important Fleas

• Echidnophaga gallinacea is the sticktight flea of poultry. Buries its mouthparts under the skin and remains attached.

• Ctenocephalides canis and C. felis are the dog and cat fleas. Often bite humans. Can be distinguished from other fleas by the presence of genal ctenidium with more than 5 teeth.

Some Important Fleas

• Xenopsylla cheopis - The oriental or tropical rat flea - most important vector for plaque and murine typhus

• Tunga penetrans (chigoe, jigger, chigger, chique, sand flea) commonly penetrates the skin around the base of nails on feet and hands. (See fig 37.12, page 560)

Ctenocephalides felis (cat flea)

Pulex irritans - the Human Flea

Xenopsylla cheopis - oriental rat flea

‘Tunga penetrans

Fleas as Vectors

• Plague – Commonly known as the black death– Caused by bacterium Yersinia pestis (Pasturella

pestis)– Releases toxins that act on the mitochondrial

membranes inhibiting uptake of ions and thus normal functioning of the cellular respiration.

– Primarily a disease of rodents. Infected flea bites man and he becomes infected.

Three Types of Plague

• Bubonic - primary plague in epidemics, demonstrates buboes (large swollen areas in lymph nodes of the groin area or armpits (see fig 37.13, page 561). Fatal in 25-50% of untreated cases.

• Pneumonic plague involves heavy infection of lungs. Is highly contagious and can be spread by breathing, coughing. Often fatal

• Primary septicemic - generalized blood infection. Is often fatal.

Murine Typhus

• Murine typhus • Endemic or flea-borne typhus caused by

Rickettsia mooseri (prowazekii).• Usually rather mild in humans fever, head

and body aches, and rash of 14 days or so duration.

• Xenopsylla cheopis is most important vector.

Following info from Dr. Glenn Songer’s Webpage at

http://microvet.arizona.edu/Courses/MIC420/lecture_notes/yersinia/yersinia_p_history.html

• History of the Plaque- problem since early recorded history- Justinian Pandemic 6th century– Began 540 A.D. in Egypt, spread to Alexandria

then on to Palestine, and to the rest of the world– 10,000 deaths per day at peak in Byzantium

lasted 50 years, killed 100 x 106 people

Black Death Pandemic - From Asia to Europe on the Silk Road

• 14th century: social conditions poor, rat population high, rats and humans lived in close proximity

• First use of "Black Death" probably because of severe cyanosis in terminal plague victims.

• China, India, Syria, ArmeniaMoved via the trade routes to Europe

The Black Plague

• Probably first use of biological weapons bodies of plague victims catapulted into enemy camp.

• Sudden appearance in winter of 1346-1347 in Europe- suspect black rat (Rattus rattus) and its flea Xenopsylla cheopsis. Throughout 14th century, upto 55 million died. (1/3 population)

The Black Death

Great Plague of London - 1665

• Began 1664 - "Just before Christmas”• Peak mortality 7000/week Total mortality of

100,000 (Total population: 500,000) Not isolated to London or England

• May have given rise to children's rhyme: – "Ring Around The Rosies

A Pocket Full Of PosiesAshes, Ashes, All Fall Down"

Prevention of Diseases Carried by Fleas

• Control of fleas - Use of insecticides and light traps that attract fleas.

• General sanitation• Conditions conducive to high rat and flea

populations and human overcrowding contribute to plague outbreaks.

Diptera - the Flies

• More members of this group are involved in the transmission of pathogens than any other Arthropod group.

• General features – These organisms have two wings (Diptera) and a

second pair of halters which function in equilibrium– Have complete or Holometabolous development

(egg, larvae, pupae, adult)

Family Psychodidae - Subfamily Phlebotominae - Phlebotomus

• The sand flies– Weak flies that can fly only short distances and

can not fly when wind is blowing.– Transmits Leishmania causing Kala azar disease

and tropical sore. – Carrions disease (Oroya fever). Caused by the

bacterium Bartonella bacilliformis. It is a visceral form that causes muscle and joint pains, anemia, jaundice, and is sometime fatal.

Culicidae - Mosquitos

• Mosquitos are the most Important insect vectors of human disease?– Have scales on the wing veins and posterior

margin – Have an elongate proboscis– Life cycle includes eggs, larvae (wiggler) pupa

(tumbler), and adult.– Larval forms use siphon tube to breath.

Some Important Mosquitos

• Culex tarsalis - main vector of western equine encephalitis (WEE) and St. Louis encephalitis

• Culex pipiens - are important vectors for filarial worms (Wucheria bancrofti and Dirofilaria immitis).

• Aedes aegypti - the yellow fever mosquito - also dengue, (breakbone fever).

Anopheles sp

• At rest, the head, thorax, and abdomen form a straight line. When they feed, there is a sharp angle toward the host

• Vectors for Plasmodium falciparium, the most important of the human malarias

• Female Anopheles mosquitos are the vectors Anopheles freeborni is a common example.

Anopheles feeding on person

Mosquito Control

• Control of mosquitos comes from two major methods– Destruction of breeding sites - drainage of

swamps, changing water levels, removal of trash (cans, tires, etc.) Mud puddles in Honduras.

– Destruction of the organism - Insecticides, Gambusia (mosquito larvae eating fish), oil on the water.

Mosquito eating fish

Culex pipiens Male

Aedes aegypti - yellow fever mosquito

Culex pipiens and Anopheles punctipennis

Simulidae

• Black flies, buffalo nats• Immature stages aquatic found in cold rapid

flowing streams.• Transmitts Onchocerca volvolus which

causes river blindness among other things

Simulium larva

Tabanidae

• Transmitts Trypanosoma evansi which causes surra in horses, cattle, dogs, etc.

• The deer fly, Chrysops is important in transmission of Loa loa - the African eye worm.

• Often cause significant blood loss.

Tabanidae

• Tabanids as transmitters of pathogens. – Anautogeny - must have blood meal for

development of eggs– Telmophagy feeding habit - pool of blood that

can receive pathogenic organisms.– Large blood meals (feed for long time)– Intermediate feeding (from organism to

organism)

Black Deer Fly Chrysops