Arthropod Transmission Of

Disease

What is an‘Arthropod-borne Disease’?

A disease transmitted by an arthropod

So… “Why is it important for public health staff to understand arthropod-borne diseases?”

‘Top 5’ reasons to address arthropod-borne diseases

5. Arthropod-borne diseases occur world-wide, including Afghanistan

4. They’re making a comeback throughout the world

3. Afghans are highly susceptible to these diseases (both physically and mentally)

2. Very few vaccines exist for these diseases1. MOST IMPORTANT: Military history shows

complacency, and ignorance of these vitally important diseases kills and sickens troops

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OBJECTIVEهدف

Explain disease cycles and control measures of vector-borne diseases.

Overviewمرور

Transmission

Cycles

Types

Let’s use life cycles to study arthropod-borne

diseases

What’s a life cycle?

It’s just a map that shows you how a “germ” infects people

Next slide is an example

Types of Life Cycles

Three-factor cycle - African sleeping sickness (trypanosomiasis) - it involves a human, a fly, and the trypanosomiasis germ.

Trypanosomiasis germ (T.b. gambiense protozoa) in the blood of the infected human is ingested by a fly.

Fly bites an uninfected human and transfers the Trypanosomiasis-causing germ to the human.

1. Host

2. Pathogen

3. Vector

Tse tse fly

Types of Life Cycles

Four-Factor (Complex Cycle) - a disease of animals that can be transmitted to humans

Also known as a complex cycle

Plague bacterium is in the rodent’s blood

Flea ingests bacteria when it feeds on blood

Flea regurgitates bacteria into rodent when it feeds

Some fleas may move to humans, feed, and transmit the plague bacteria.

1. Host 2. Pathogen

3. Vector 4. Reservoir

Terms and Concepts

You need to know the vocabulary of arthropod-borne diseases because:

They use these terms at your public health office (it’s nice to understand the conversation)

The literature you’ll read at work uses these terms (it’s nice to understand your readings)

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Terms and Definitions

Host – person or living animal that provides food and lodging to the infectious agent

Parasite – an organism that lives on or in another organism or gets its food from that organism

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Terms and Definitions

Pathogen – a parasite that causes diseaseArbovirus – virus carried by arthropodsVector – a living non-human carrier of a pathogenReservoir – any person, animal, arthropod, plant, soil or substance in which an infectious agent normally lives and multiplies**In some cases a reservoir can also be a host (i.e. dengue fever)**

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Terms and Definitions

Transmission Mechanisms:Mechanical Disease Transmission – parasite is carried accidentally on or in a vector’s body (but does not go through sexual changes in the vector)

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Terms and Definitions

Transmission Mechanisms:Biological Disease Transmission – occurs when a pathogen multiplies and/or undergoes sexual growth changes in a vector’s body

Malaria

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Terms and Definitions

Inoculation Mechanisms:Active Inoculation – pathogen is introduced into a host by the bite of an infected vectorPassive inoculation – pathogen is introduced to the host by rubbing vector feces or other infective material into a feeding wound, skin abrasion, or mucous membrane

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Terms and Definitions

Transovarial transmission – pathogens are passed on from infected female to her eggs

Female mosquito Mosquito eggs

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Terms and Definitions

Passage of Disease between regions:Imported Disease – disease acquired in one area and diagnosed in another

Introduced Disease – disease acquired in one area, then brought into another area, and acquired by a second individual

A B

A B

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Part 2

Arthropod Transmission Of

Disease

Introduction

We covered Definitions in Part 1 -- Any questions on those?

Apply those concepts to specific vector-borne diseases of particular importance... starting with...

Mosquito – Borne Diseases

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Malaria

An acute & chronic disease caused by parasitic protozoans in the genus Plasmodium.

Transmitted by certain Anopheles species mosquitoes.

A complex 3-factor vector-borne disease of the blood.

>1 pathogen species, vector species, man, complicated ecology

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Four Plasmodium species cause human malaria:

P. falciparum -- malignant tertian malaria.

P. vivax -- benign tertian malaria.

P. malariae -- quartan malaria.

P. ovale -- tertian malaria.

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The Malaria Pathogen Life Cycle Is Complex

The primary (or sexual) cycle is in the mosquito.

Parasites ingested from an infected host develop into sexual forms which mate & reproduce. Infective forms migrate to the mosquito’s salivary glands where they are introduced into the next host while the mosquito is feeding.

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The malaria pathogen life cycle is complex

The secondary (asexual, generative) cycle occurs in humans.

The pathogens initially enter cells in the liver where they continue their development. The parasites then emerge and invade red blood cells. Once in the red blood cells they multiply asexually and produce huge numbers of parasites, which attack additional red blood cells.

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Symptoms

Symptoms occur when red blood cells (RBCs) rupture to release pathogens that have multiplied within them. When enough RBCs are affected, anemia develops.

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Symptoms

In falciparum malaria, RBCs “stick together” causing blocked capillaries, which then rupture -- When this happens in the brain, cerebral hemorrhage may cause brain damage and/or death.

The liver and spleen may also become grossly enlarged.

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Symptoms

Commence 10-28 days after an infective mosquito bite.

Initially anorexia, headache, fever, flu-like symptoms.

After a period, RBCs rupture to release pathogens at the same time, each 2 or 3 days, depending on the species.

Release causes chills, high fever & profuse sweating.

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Symptoms

Other symptoms may include headaches, nausea, vomiting, muscle & joint pains

Over time -- anemia, cerebral hemorrhage, impaired liver function.

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Treatment

Chloriquine

Primaquine

Doxycycline

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Malaria Distribution

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Epidemiology

Malaria is widespread throughout the tropical countries of the world. Transmission can also occur by blood transfusions & hypodermic needles.Communicability lasts as long as malaria pathogens are in the blood.Susceptibility is universal, but a previous case gives some protection.Diagnosis is by finding malaria pathogens in blood by examination of blood smears, or from symptoms.

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Vector

Malaria is biologically transmitted only by certain species of Anopheles mosquitoes Most Anopheles cannot transmit malaria. There are 6 main Anopheles vectors in Afghanistan:

a. Anopheles superpictus

b. A. culicifacies

c. A. stephensi

d. A. hycranus

e. A. pulcherrimus

f. A. fluviatilis

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Prevention

Personal protection from Anopheles mosquito bites -- including use of repellents & chemoprophylaxis.

Reduction of host habitat (if feasible).

Pesticides for vector control (if feasible).

Education on how & when to use the above.

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Dengue

An acute, febrile illness caused by an arbovirus & transmitted by mosquitoes.

A simple 3-factor vector-borne disease.

There are 4 serological types (serotypes) & two clinical forms:

Benign (Classical) Dengue, or “breakbone fever.”

Dengue Hemorrhagic Fever (DHF) or Dengue Shock Syndrome (DSS).

Symptoms

Benign dengue symptoms include:Fever (101°F).

Severe headache, muscle & joint pain (“breakbone”) & sometimes a flat rash.

Commence 5 - 6 days after the infective mosquito bite & last 5 - 7 days. Recovery is usually uneventful.

Patients are infective to another mosquito 1 - 4 days after their symptoms occur.

Symptoms

DHF & DSS symptoms include:

Bleeding of the gums, nosebleeds, gastrointestinal bleeding, & dengue shock syndrome.

Death is most often due to internal bleeding or shock.

Hemorrhaging -- on arm of child

Treatment

Classical dengue

None

Supportive, TLC – aspirin is not advised

DHF/DSS

Intravenous (IV) transfusions & fluids to prevent shock, & with corticosteroids.

Epidemiology

Found throughout much of the tropical world, particularly in Mexico, Caribbean, central America, west Africa, & south Asia.

Dengue Hemorrhagic Fever kills thousands of south Asian children annually.

Epidemiology

Transmitted by the bite of infective Aedes species mosquitoes, principally Aedes aegypti.

Vector

Aedes aegypti, yellow fever mosquito

Daytime biter, weak flyer, never found more than about 400 meters from human habitationNot able to overwinter in cold areas. Larvae are found in water in artificial containers: cans, rain gutters, & particularly rubber tires.

Epidemiology of Dengue

Vectors =Aedes aegypti

Aedes albopictus

Prevention

Personal protection from mosquito bitesIsolating infective people from mosquito vectorsReduction of mosquito habitat (if possible & feasible)Pesticides (if feasible)Education about the above. It’s #1!!!

The Arboviral Encephalitides

“Arthropod Borne Viruses” = Arbovirus

The Arboviral Encephalitides...

Acute infections of the brain and/or spinal cord Encephalitides is the plural of encephalitis -- includes more than one encephalitic disease. Complex four-factor vector-borne diseases. May be mild to fatal

The Arboviral Encephalitides

There are over 100 arboviruses that produce disease in humans. Transmission is by the bite of an infected arthropod (including mosquitoes, sand flies, ticks)

Mosquito-borne Encephalitides

In the Afghanistan there are several types :

Japanese Encephalitis Infections may occur nationwide.

Sindbis Fever Probably not endemic nationwide.

West Nile Virus Probably not endemic to Afghanistan but may be more common in desert environments.

Symptoms/Treatment

Range from asymptomatic, through general flu-like illness, to severe central nervous system (CNS) damage or death.

Usually fever, headaches & drowsiness.Sometimes vomiting, stiff neck, tremors, confusion, & convulsions.Severity varies by species of virus.Incubation period from infective bite to sickness ranges from 2 - 20 days.

Treatment is supportive -- there is no medicine to kill just the virus.

EpidemiologyThe epidemiology of the mosquito-borne encephalitides is complex

Several vectors & reservoirs, & much is unknown.

All humans without previous exposure to a given virus are susceptible to infection Certain viruses “prefer” certain age groups.Mosquitoes cannot pass arboviral encephalitis from one human to another.

Vector

In Afghanistan, arboviral encephalitides are spread only by mosquitoes.

Several species of Aedes, Culex, & others are involved.

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Reservoir ???

Japanese Encephalitis-Birds.

West Nile Virus – Birds.

Sindbis Fever-Birds, rodents.

Many other reservoirs are possible: rodents, bats, reptiles, amphibians, etc.

Prevention

Personal protection from mosquito bites.

Reduction of mosquito habitat (if feasible).

Surveillance for vectors & pesticides for control (if necessary).

Monitoring with sentinel chickens.

Education about the above.

Tick-Borne Diseases

Crimean Congo Hemorrhagic Fever

• Tick-borne disease caused by a Nairovirus in the family Bunyaviridae. It is primarily transmitted by a bite or exposure to hard ticks (Family Ixodidae) in the genus Hyalomma.

Symptoms

Sudden, with initial signs including headache, high fever, back pain, joint pain, stomach pain, and vomiting.

Other symptoms include red eyes, flushed face, a red throat, and red spots on the palate.

Symptoms may also include jaundice, and in severe cases changes in mood and sensory perception.

As the illness progresses, large areas of severe bruising, severe nosebleeds, and uncontrolled bleeding at injection sites can be seen, beginning about on the fourth day of illness and lasting for about two weeks.

Fatality rates in hospitalized patients range from 9% to 50%.

Diagnosis is by laboratory tests and clinical findings.

Treatment

Treatment is primarily supportive, and attention to fluid balance and correction of electrolyte abnormalities, oxygenation, and hemodynamic support, as well as appropriate treatment of secondary infections. The antiviral drug ribavirin has also been used for treatment with some benefit.

Epidemiology

In Afghanistan, there is nationwide evidence of CCHF viral antibodies. Habitats that are conducive to tick occurrence are dry areas, including animal stables, trails, and former pastures.

CCHF is maintained in nature by Hyalomma ticks. Soft ticks (Family Argasidae), such as Ornithodoros lahorensis are also considered secondary vectors and are often found in animal stables. Numerous wild and domestic animals, such as cattle, goats, sheep, and hares, serve as amplifying hosts for the virus.

Epidemiology

CCHF is transmitted to humans biologically by the bite of an infected tick (active inoculation) or exposure to infected blood (passive inoculation). It can be transmitted from human to human by contact with infectious blood or fluids, or improper sterilization of medical equipment.

The transmission period is primarily from May-October.

Animal herders, livestock workers, and slaughter houses in endemic areas area at risk of CCHF. Healthcare workers in endemic areas are also at risk.

VectorCCHF vectors in Afghanistan are:

Hyalomma marginatum (Primary vector)

H. anatolicum, H. detritum, H. dromedarii, H. impeltatum, H. schulzei, and H. asiaticum; also the soft tick Ornithodoros lahorensis (Secondary vectors)

Prevention

Personal protection measures against ticks, including self-inspection & “buddy” inspection.

Tick control -- may be of limited effectiveness & use.

Education.

Miscellaneous Arthropod-Borne

Diseases

Plague

Plague

A zoonotic vector-borne disease caused by the bacterium Yersinia pestisTransmitted by fleas. Historically known as “black death” because of the symptomatic appearance of dark hemorrhagic areas in the skin of infected persons.

Septicemic Plague -- Note

darkening of skin, hence the term “black death.”

Plague

A complex two-, three-, or four-factor disease.

Can take three forms -- bubonic, septicemic, & pneumonic -- depending on the system & organs affected.

Symptoms...Bubonic form (most common)

Swollen lymph nodes draining the flea bite, “buboes” in groin, armpit or neck Buboes may be inflamed, painful, & may ooze.Untreated, mortality rate is 50%, but responds well if treated early.

Plague buboes in axillum

Feline Plague: Sub-maxillary buboes on the neck of a cat

Symptoms

Septicemic form -- “blood” plague.

Dissemination in the blood to various parts of the body.

Can progress rapidly.

Untreated mortality rate is over 90%.

Septicemic plague symptoms -- gangrene of fingers and toes

Symptoms

Pneumonic form -- “plague pneumonia”

Secondary involvement of the lungs.

Person-to-person transmission by sneezing & coughing is a threat, particularly in a hospital environment.

Untreated mortality rate is over 90%.

Treatment

Must be started immediately. A number of antibiotics work well, but penicillin is not particularly useful.Diagnosis is by microscope examination of blood or bubo fluid or by other laboratory tests -- Early diagnosis is essential.

Epidemiology

Distribution is throughout much of the world, although large areas are plague-free. Found in many species of wild & domestic animals.

Some are asymptomatic carriers, others become symptomatic & die quickly -- All are reservoirs.

Epidemiology

Plague can be spread by

Bite of infected flea (vector transmission),

Respiratory aerosols (non-vector transmission)

Blood to blood contact, a form of indirect inoculation (non-vector transmission).

Epidemiology

Plague can thus be --A 4-factor disease (prairie dog to humans by a flea),

or

A 3-factor disease (human to human by flea),

or

A 2-factor disease (human to human by respiratory aerosol or indirect blood to blood inoculation).

Epidemiology

Incubation period 2 - 6 days from flea bite or blood-blood contact.1 - 6 days from aerosol inoculation.

Susceptibility is general. Recovery confers some immunity. Excellent vaccine available.

Separate cycles in nature for Urban (murine) spread by domestic rodents .Rural (sylvatic) spread by wild rodents.

Vector

Many species of vector fleas, some much more efficient than others. Can be transmitted from reservoir to reservoir, reservoir to human, & human to human. Transmission most dangerous when flea’s gut is “blocked” by plug of plague bacteria.

Flea continues to try to feed, regurgitating contaminated blood through the feeding wound into a new host.

Blocked Flea

Prevention

Educate everyone at risk on plague avoidance.

Use personal protection measures.

Implement rodent exclusion & harborage elimination.

Prevention

Control fleas in wild rodent burrows Animal control is not always practical, but if attempted, it’s mandatory that fleas are killed first, so they are not actively seeking a new host when their previous one has been killed.Vaccination of at-risk personnel.Contact protection in hospitals, elsewhere as necessary.

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BreakBreak

“The great scourge of humanity”

Epidemic Typhus

Epidemic Typhus

Caused by the rickettsia Rickettsia prowazekii.Transmitted by the body louse Pediculus humanus humanus. Also known as louse-borne typhus, classical typhus fever, & historically as the “red death.” Complex 3-factor disease

Symptoms...

Sudden onset with chills, fever, headache, pains, prostration.Body rash appears on the 5th or 6th day. Incubation period 7 - 14 days after infection. Lasts 2 - 3 months unless death occurs first.

Symptoms

Toxemia (blood poisoning) pronounced & severe.

Mortality in untreated epidemic typhus can reach 40%.

Diagnosis is by laboratory tests -- clinical diagnosis can be difficult except in epidemic situations.

Treatment

Various antibiotics until one day after fever breaks.

Epidemiology

Potential occurrence throughout most of the world.

Can originate in & be limited to a defined area -- For example, in 1979, there were:

18,364 reported cases worldwide,

18,278 cases were in Africa,

17,499 cases were in Ethiopian refugee camps (over 95% of the cases for that year).

Epidemiology

Non-human reservoir doubtfulNo direct person-to-person transmission.

Infection occurs when louse feces or fluids from crushed lice are rubbed into feeding wounds or other breaks in the skin -- Passive inoculation Transmitted biologically

Epidemiology

Epidemic typhus is a risk whenever poverty creates conditions favoring poor hygiene & crowding.

Risk increases with wars, famines, & natural disasters creating refugees.

Susceptibility is universal, but attack confers long-term immunity.

A vaccine is available.

Vector

Transmitted by the body louse

The head louse is a capable secondary vector of endemic typhus, but the pubic louse is not a vector.

These species of lice live only on humans.

The human body louse, Pediculus humanus

humanus

Prevention

Improve sanitation & personal hygieneChange clothes, wash clothes & bedding in hot water or bake in oven.

Disinsection of clothes on body with insecticidal dusts, or, issuance of permethrin-treated clothingVaccinate personnel at risk.

Leishmaniasis

Leishmaniasis

Caused by protozoans of the genus Leishmania.

Transmitted by sand flies of several species.

A complex 4-factor vector-borne disease.3 species of pathogen

Several vector species

Complex ecology

Leishmaniasis

There are 3 clinically separate types caused by separate species of Leishmania:

CutaneousUta, chiclero ulcer

Mucocutaneous (not know to occur in Afghanistan)Papalomoyo, espundia

Visceral Kala azar, dumdum fever, tropical splenomegaly

Symptoms

Vary with type of infection...

Cutaneous Leishmaniasis

Dry or moist ulcerating lesion (usually single) or nodular lesions (usually multiple)

May last for months, usually leave large scars.

Usually affect ear, face or extremities, unusual on trunkNot fatal but is debilitating & disfiguring.Usually resolve spontaneously in 6 - 12 months.

Cutaneous Leishmaniasis

Mucocutaneous Leishmaniasis

Affects face only -- skin, mucous membranes, muscle & bone.

Severely disfiguring if not diagnosed & treated soon after exposure.

Fatalities result from secondary infections, asphyxiation from dislodged tissue.

Mucocutaneous Leishmaniasis

Untreated caseEarly stage

Visceral Leishmaniasis

Chronic disease of lymphatic system, liver, & spleen, with fever, anemia, & progressive, physical wasting away until the patient dies.

Mortality is up to 95% in untreated cases -- early detection is vital.

Diagnosis

Through biopsy cultures from sores, & microscopic & other laboratory tests.

Treatment

Several medicines are available but early diagnosis is important to prevent disfigurement, or death in the visceral form.

Epidemiology of cutaneous & mucocutaneous forms

Transmission is biological through active inoculation -- through the bite of an infected sand fly.

Non-human reservoirs include dogs, cats, rodents, perhaps other small mammals.

No human-to-human infection except for human-to-human contact of abraded skin.

Epidemiology of cutaneous & mucocutaneous forms

Occurs in pockets throughout Central & South America, Africa, Europe & Asia usually in rural areas.Incubation period is a few days to many months.Susceptibility is universal

Immunity to the cutaneous form develops after lesions heal.

Leishmaniasis Distribution

Vector

Transmitted biologically by several species of Phlebotomus sand flies.

Prevention

Early case detection & treatment.

Chemical & cultural sand fly control.

Personal protection.

Education.

LessonsLearned

Unpredictable

Occurrence of vector-borne diseases can be extremely unpredictable.

Outbreaks of disease caused by arboviruses cannot be predicted based upon history.

A small area may have a major outbreak, although there was not a single case in the area prior to the outbreak & may not be another case in the area for decades afterwards.

The Importance OfVector Surveillance

Disease surveillance is “looking for” a disease.

If we know the disease is in the area we can take precautions to prevent it. With vector-borne diseases we can also survey for the vectors through vector surveillance, & control them before they can spread a significant amount of disease.

Vector-Borne Disease ThreatMilitary Significance

Many areas of the world harbor vector-borne diseases that are only found in those areas & nowhere else.

If these areas are of military interest, we must know what vector-borne diseases occur there so we can prevent them in our personnel.

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Transmission

Cycles

Types

Summary

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