Download File

Notes Unit 20
Arthropodborne Diseases
Structure and Function of Cardiovascular and Lymphatic Systems
The function of the cardiovascular system is to circulate blood through the body’s tissues so it can deliver
certain substances to cells and remove other substances from them. Blood is what flows through the
cardiovascular system. Blood is a mixture of cells and plasma. Here is the function of each of the components
of blood:




Plasma – transports dissolved nutrients to body cells and carries wastes away from the cells.
Red blood cells – carry oxygen to the cells
White blood cells – help defend the body against infection
Platelets – essential to the body’s clotting system
The lymphatic system is an essential part of the circulation of blood. To simplify things, as the blood
circulates, some of the plasma filters out of the blood capillaries into the lymphatic system, and eventually
returned to the heart. The lymphatic system contains a type of white blood cell called a lymphocyte, which also
helps to fight infection. See the diagram of the lymphatic system below:
1
At various points in the lymphatic system are lymph nodes, which contain white blood cells that help clear the
lymph of microorganisms. When they are actively fighting infection, they become swollen and tender; swollen
lymph nodes are called buboes.
Defenses against pathogens include: lack of iron in the blood (which is a requirement for microbial growth),
and phagocytic cells (white blood cells).
Normal Flora of Cardiovascular and Lymphatic System
There should be NO normal flora of either of the systems.
Some Vocabulary Terms You Need to Know







Septicemia – when there are a lot of microorganisms in the blood
Sepsis – the condition resulting from septicemia
Septic shock – when bacteria release endotoxins, and your blood pressure rapidly drops
Endocarditis – an inflammation of the inner layer of the heart
Pericarditis – inflammation of the sac around the heart
Ischemia – when a wound causes the blood supply to be interrupted
Necrosis – tissue death
Important Diseases
1. Bubonic Plague
Causative Organism: Yersinia pestis
Type of Organism: Gram negative, rod shaped bacterium that lives in a flea
Pathogenicity:
Can survive and multiply within phagocytic white blood cells, which means it can
escape detection by our immune system.
Symptoms:
People usually show symptoms 2 to 6 days after getting plague. Symptoms
include fever, chills, weakness, and swollen and painful lymph nodes. A few
people get pneumonia (infection of the lungs) as a first symptom of plague. The
infection then spreads to other parts of the body. If this disease is not treated right
away, many people who get sick will not survive. The mortality rate is 50-75%.
Hallmark:
Buboes on body which are swollen lymph nodes that turn black.
Transmission:
People usually get plague from being bitten by a rodent flea that is carrying the
plague bacterium or by handling an infected animal.
Treatment:
Antibiotics.
2
2. Lyme Disease
Causative Organism:
Type of Organism:
Pathogenicity:
Symptoms:
Hallmark:
Transmission:
Treatment:
Borrelia burgdorferi
Bacteria; spiral-shaped rod that lives in a tick
No special ones.
First symptom is usually a rash that appears at bite site. It is a red area that clears
in the center as it expands to a diameter of 15 cm. Flulike symptoms appear in a
couple of weeks. In the second phase, the heart becomes affected (irregular
heartbeat). Neurological symptoms appear (paralysis, meningitis, encephalitis,
etc). Joint damage, arthritis.
Bulls-eye lesion at site of tick bite
From the bite of a tick
Antibiotics
3. Rocky Mountain Spotted Fever
Causative Organism:
Type of Organism:
Pathogenicity:
Symptoms:
Hallmark:
Transmission:
Treatment:
Rickettsia rickettsii
Bacteria that infects ticks
None
Initial symptoms may include fever, nausea, vomiting, severe headache, muscle
pain, lack of appetite. The rash first appears 2-5 days after the onset of fever and
is often not present or may be very subtle when the patient is initially seen by a
physician. Younger patients usually develop the rash earlier than older patients.
Most often it begins as small, flat, pink, non-itchy spots (macules) on the wrists,
forearms, and ankles. These spots turn pale when pressure is applied and
eventually become raised on the skin. Later signs and symptoms include rash,
abdominal pain, joint pain, diarrhea. The characteristic red, spotted (petechial)
rash of Rocky Mountain spotted fever is usually not seen until the sixth day or
later after onset of symptoms, and this type of rash occurs in only 35% to 60% of
patients with Rocky Mountain spotted fever.
Tick bite; all over body rash
Through bite of a tick.
Antibiotics.
4. West African Trypanosomiasis (Sleeping Sickness)
Causative Organism:
Type of Organism:
Pathogenicity:
Symptoms:
Trypanosoma brucei gambiense
Flagellated protozoan that lives in a tsetse fly
Will cause death if not treated.
A bite by the tsetse fly is often painful. Occasionally, within 1 to 2 weeks, the
infective bite develops into a red sore, also called a chancre. Several weeks to
months later, other symptoms of sleeping sickness occur. These include fever,
rash, swelling around the eye and hands, severe headaches, extreme fatigue,
aching muscles and joints. You may develop swollen lymph nodes on the back of
your neck called Winterbottom's sign. Weight loss occurs as the illness
progresses. Progressive confusion, personality changes, slurred speech,
irritability, loss of concentration, seizures, and difficulty in walking and talking
occurs when infection has invaded the central nervous system. These symptoms
become worse as the illness progresses. Sleeping for long periods of the day and
having insomnia at night is a common symptom. If left untreated, infection
3
Hallmark:
Transmission:
Treatment:
becomes worse and death will occur within several months to years after
infection.
Cause by bite of the tsetse fly; extreme fatigue
Bite of the tsetse fly, found only in Africa.
Medication for protozoans available, but no prevention.
5. Yellow Fever
Causative Organism:
Type of Organism:
Pathogenicity:
Symptoms:
Hallmark:
Transmission:
Treatment:
Yellow Fever Virus
Virus that lives in a mosquito
None.
Fever, chills, headache, nausea, black vomit. Jaundice of the skin, which reflects
liver damage. While most other infections that cause a high fever also cause an
increased heart rate, yellow fever results in an unusual finding, called Faget's sign.
This is the simultaneous occurrence of a high fever with a slowed heart rate.
Mortality rate is 20%.
Because of liver involvement, you turn yellow (jaundice).
From a mosquito that lives in mostly Africa and South America.
None. But there is a vaccine recommended for travelers to these areas.
6. Malaria
Causative Organism:
Type of Organism:
Pathogenicity:
Symptoms:
Hallmark:
Transmission:
Treatment:
Plasmodium sp. (there are 4 different species that affect humans)
Protozoan
Leading cause of death and disease worldwide
Once in the blood, the parasites travel to the liver and enter liver cells to grow and
multiply. During this "incubation period", the infected person has no symptoms.
After as few as 8 days or as long as several months, the parasites leave the liver
cells and enter red blood cells. Once in the cells, they continue to grow and
multiply. After they mature, the infected red blood cells rupture, freeing the
parasites to attack and enter other red blood cells. Toxins released when the red
cells burst are what cause the typical fever, chills, and flu-like malaria symptoms.
Bite of Anopheles mosquito in tropical area; cycles of fever and chills
From the Anopheles mosquito, mostly in tropical areas
Quinine; currently no vaccine available
7. Dengue Fever (Breakbone Fever)
Causative Organism:
Type of Organism:
Pathogenicity:
Symptoms:
Dengue virus
Virus that lives in mosquitoes
Dengue Hemorrhagic Fever is a very severe form that is deadly
High fever, severe headache, backache, joint pains, nausea and vomiting, eye
pain, and rash. Generally, younger children have a milder illness than older
children and adults. Dengue hemorrhagic fever is characterized by a fever that
lasts from 2 to 7 days, with general signs and symptoms that could occur with
many other illnesses (e.g., nausea, vomiting, abdominal pain, and headache). This
stage is followed by hemorrhagic manifestations, tendency to bruise easily or
other types of skin hemorrhages, bleeding nose or gums, and possibly internal
bleeding. The smallest blood vessels (capillaries) become excessively permeable
(“leaky”), allowing the fluid component to escape from the blood vessels. This
4
Transmission:
Treatment:
may lead to failure of the circulatory system and shock, followed by death, if
circulatory failure is not corrected.
Dengue is transmitted to people by the bite of an Aedes mosquito that is infected
with a dengue virus. The mosquito becomes infected with dengue virus when it
bites a person who has dengue or DHF and after about a week can transmit the
virus while biting a healthy person. Dengue cannot be spread directly from person
to person.
None – just supportive care
8. West Nile Virus
Causative Organism:
Type of Organism:
Pathogenicity:
Symptoms:
Transmission:
Treatment:
West Nile Virus
Virus that lives in a mosquito
Potentially serious illness
Develop symptoms between 3 and 14 days after they are bitten by the infected
mosquito. About one in 150 people infected with WNV will develop severe
illness. The severe symptoms can include high fever, headache, neck stiffness,
stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss,
numbness and paralysis. These symptoms may last several weeks, and
neurological effects may be permanent. Up to 20 percent of the people who
become infected have symptoms such as fever, headache, and body aches, nausea,
vomiting, and sometimes swollen lymph glands or a skin rash on the chest,
stomach and back. Symptoms can last for as short as a few days, though even
healthy people have become sick for several weeks. Approximately 80 percent of
people (about 4 out of 5) who are infected with WNV will not show any
symptoms at all.
Most often, WNV is spread by the bite of an infected mosquito. Mosquitoes
become infected when they feed on infected birds. Infected mosquitoes can then
spread WNV to humans and other animals when they bite. In a very small number
of cases, WNV also has been spread through blood transfusions, organ
transplants, breastfeeding and even during pregnancy from mother to baby. WNV
is not spread through casual contact such as touching or kissing a person with the
virus.
No treatment – supportive care.
9. Eastern Equine Encephalitis
Causative Organism:
Type of Organism:
Pathogenicity:
Symptoms:
Hallmark:
Transmission:
Treatment:
EEE Virus
Virus
High fatality rate (35%)
Can range from mild flu-like illness to inflammation of the brain, coma and death.
If survive, can cause severe neurologic deficits.
Mosquito-borne illness that causes brain inflammation.
Through the bite of an infected mosquito, mostly in swampy areas on the East
Coast, which feeds on birds first. Then on horses, and humans.
None – vaccine only.
5
9. Leishmaniasis
Causative Organism: Leishmania sp.
Type of Organism: Protozoa found in sand flies
Pathogenicity:
Visceral leishmaniasis is a severe form of the disease with a 100% fatality rate if
not treated.
Symptoms:
Cutaneous: One or more sores on their skin. The sores can change in size and
appearance over time. They may end up looking somewhat like a volcano, with a
raised edge and central crater (ulcer). Some sores are covered by a scab. The sores
can be painless or painful. Some people have swollen glands near the sores (for
example, under the arm if the sores are on the arm or hand).
Visceral: Usually have fever, weight loss, and an enlarged spleen and liver
(typically, the spleen is bigger than the liver), and some abnormal blood tests. For
example, patients usually have low blood counts, including a low red blood cell
count (anemia), low white blood cell count, and low platelet count.
Transmission:
Bite of infected sand fly
Treatment:
Anti-parasite medicine.
10. Lymphatic Filariasis (Elephantiasis)
Causative Organism:
Type of Organism:
Pathogenicity:
Symptoms:
Transmission:
Treatment:
Wuchereria bancrofti, Brugia malayi
Helminth (worm) that lives in infected mosquito
Hard to cure – can still develop symptoms after the worm is dead
Although the worm damages the lymph system, most infected people are
asymptomatic and will never develop clinical symptoms. A small percentage of
persons will develop swelling of lymph nodes. This is caused by improper
functioning of the lymph system which results in fluid collection and swelling.
This mostly affects the legs, but can also occur in the arms, breasts, and genitalia.
Most people develop these symptoms years after being infected. The swelling and
the decreased function of the lymph system make it difficult for the body to fight
germs and infections. Affected persons will have more bacterial infections in the
skin and lymph system. This causes hardening and thickening of the skin, which
is called elephantiasis. Many of these bacterial infections can be prevented with
appropriate skin hygiene. Men can develop swelling of the scrotum after the death
of an adult worm.
From person to person by mosquito bite
People infected with adult worms can take a yearly dose of medicine that kills the
microscopic worms circulating in the blood. While this drug does not kill all of
the adult worms, it does prevent infected people from giving the disease to
someone else.
6
11. Onchocerciasis (River Blindness)
Causative Organism:
Type of Organism:
Pathogenicity:
Symptoms:
Transmission:
Treatment:
Onchocerca volvulus
Helminth (worm) found in the blackfly
Can cause blindness; 17.7 million people in world are infected
The normal incubation period ranges from 9 to 24 months after the bite of an
infected blackfly. Each female worm can reproduce millions of microfilariae
during her lifetime. Worms can live for 10-15 years. Infected persons may be
without symptoms. Those with symptoms will usually have one or more of the
three manifestations: skin rash, eye lesions, and/or subcutaneous bumps under the
skin. The most serious manifestation consists of lesions in the eye that can
progress to blindness.
Bite of the blackfly, which is found near flowing rivers
Anti-helminth medication
12. Trachoma
Causative Organism:
Type of Organism:
Pathogenicity:
Symptoms:
Hallmark:
Transmission:
Treatment:
Chlamydia trachomatis
Bacteria found in insects
Can cause blindness.
Trachoma is a chronic conjunctivitis that leads to scarring in the conjunctiva and
cornea of the eye. Repeat active infections occur in children < 10 years of age.
Subsequently, conjunctival scarring (cicatricial disease) and inversion of the
eyelashes so they irritate the cornea (trichiasis) develops as a result of earlier
infections. Trichiasis predisposes to corneal ulceration resulting in decreased
vision and blindness.
Severe eye disease mostly in developing countries; leading cause of blindness
Primary: person-to-person transmission by ocular and respiratory secretions.
Secondary: insect vectors such as house flies.
Antibiotic ointments.
7