Diseases exam 2 Flashcards
What is the infectious agent of rubella?
Rubella virus. It is a single stranded RNA enveloped virus
Taxonomy of rubella
It is a member of the togavirus family and a member of the genus Rubivirus
Transmission of rubella
Transmission is person to person. It is transmitted by nasal secretions shortly before and for about a week after the rash appears. The virus is highly infectious
Rubella
Also known as German measles. It is the mildest of the rash causing viral diseases, but can severely impact a fetus. Prior to the vaccine nearly everyone caught rubella, 50% of cases in children and 90% cases are not recognized
Incubation period of rubella
14-21 days, on average about 18 days
Rubella prodromal illness
In adults, there may be a prodromal illness preceding the rash by 1-7 days. People may feel tired, have a headache and fever, have a mild sensitivity to light, conjunctivitis, swollen cervical lymph nodes that occur before rash
Rubella symptoms
Rash appears first on the trunk after 16-21 days after infection- characterized by a mild maculopapular rash. Other symptoms are swollen lymph nodes, fever, sore throat, and feeling tired
Complications of rubella
Arthritis may occur in up to 70% of adult women who are infected. Testicular swelling occurs mainly in adults, but can make males infertile. Other complications include inflammation of nerves, encephalitis, congenital rubella syndrome, and miscarriage
Pathogenesis of rubella
When the virus enters the body, it replicates in the upper respiratory tract and will spread in the bloodstream to the lymphoid tissues, skin, and other organs. The cellular immune response is thought to play a role on the rash and the arthritis symptoms
Diagnosis of rubella
Collect throat (best source), nasal, or urine specimens for viral detection by PCR testing or molecular testing. IgM and IgG antibody titration can be done on blood samples. Clinical diagnosis of rubella (based only on the symptoms) is unreliable- up to half of all infections can be subclinical
Treatment of rubella
No current official treatment is available
How can rubella be prevented?
Vaccination- MMR combined attenuated vaccine. One dose of MMR vaccine is about 97% effective at preventing rubella if exposed to the virus
How does rubella harm a developing fetus?
Caused by rubella virus induced cellular damage and the effect of the virus on dividing cells. Rubella virus is likely transported into the fetal circulation as infected endothelial cell emboli, which can result in infection and damage of fetal organs. The virus can induce damage by apoptosis, probably due to how the virus replicates
When is the risk of congenital rubella syndrome highest?
In the first trimester. The range of abnormalities is correlated with gestational age during maternal rubella infection in the first trimester. If maternal infection occurs after the first trimester, the frequency and severity of fetal damage decreases drastically. This is probably because the fetus has developed humoral and cell mediated immune responses at this point, and has passively received maternal antibodies
Symptoms of congenital rubella syndrome
The triad of congenital rubella syndrome is cataracts, heart defects, and deafness- these defects can be temporary or permanent. In infants with CRS, rubella virus continues to replicate and be excreted. This means that contacts with the infant can be infected
How is congenital rubella syndrome diagnosed?
Rubella IgG and IgM antibodies synthesized by the fetus are detectable at birth in CRS. Diagnosis is made using IgM responses since maternal IgG antibodies are present in the infants’ sera. The virus is secreted in infants with CRS, but it declines progressively in the first year
What is the replication number for rubella?
The R0 for rubella is 3-8, but can be as high as 12 in crowded, developing countries
What is the herd immunity threshold for rubella in the US?
In the US, the herd immunity threshold is 85-88%. Rubella may be easier to eradicate than measles due to its lower R0 value
Why is rubella virus a candidate for global eradication? (3)
- Humans are the only known host
- Accurate diagnostic and molecular assays exist
- There has been demonstrated sustained interruption of endemic transmission in the Americas since 2009
For thousands of years, how did people think malaria was contracted?
For over 2500 years, the idea that malaria fevers were caused by miasmas rising from swamps persisted. The association was because malaria is more common in humid areas- these areas and swamps attracted mosquitos. The world malaria comes from the Italian mal’aria- bad air
Charles Louis Alphonse Laveran
First described the malaria parasite
Malaria is caused by a
Protozoan
Infectious agents of malaria (5)
- Plasmodium falciparum
- Plasmodium vivax- causes 77% of the infections in the Americas
- Plasmodium malariae
- Plasmodium ovale
- Plasmodium knowlesi- most recent, found in Oceania
Plasmodium falciparum
Most deadly and most common in general. Most of the deaths occur in Africa, and this agent is only found in Africa. Resistant to most antimicrobials. Causes the most severe cases of anemia, a common cause of death
Where is malaria common?
Common in developing countries and areas with warm temperatures and high humidity. It is rare in the US, but more common in Africa, central and south America, Dominican Republic, Haiti, and other areas in the Caribbean, Eastern Europe, South Asia, and islands in the Central and South Pacific Ocean (Oceania)
How is malaria transmitted?
Via a mosquito vector. 2 hosts are needed for the parasite to survive- humans and mosquitoes
Hypnozoite
Dormant form in the liver of only certain forms of the parasite. You can’t give blood if you acquire malaria for this reason. A hypnozoite can leave the liver cells and reproduce under certain conditions