Lecture 9 Flashcards
Gastrointestinal (“Enteric”) Viruses
- 70% of gastroenteritis is virus caused (30% bacterial/ parasitic)
1. Mostly transmitted by fecal - oral
- Disease progression is similar
- Symptoms 1-3 days after 1st contact
- similar symptoms (vomiting, diarrhea, nausea, abdominal pain)
- Self-limiting infection (3-4 days) in healthy humans
determining which virus gi disease can only be done in lab
4 types of enteric viruses responsible for most diseases
Rotavirus - diarrhea in kids under 5 (in adults with minor symptoms) (year round/ mostly winter)
Adenovirus - kids under 2 (year round)
Astrovirus- all ages (winter)
Calicviruses (large group/ norovirus) - All ages/ year round
Norovirus (Norwalk Virus)
Naked RNA virus
Found in Norwalk, ohio (viruses with similar features called Norwalk-like)
Fecal-contaminated food/water = source
- cant tell by looking/smelling
- low infectious dose (10-100 virus particles can cause disease)
- Close contact for extended periods = risk (care home[59% causes] , hospitals, day care, cruise)
-300 to 400 outbreaks per year in Canada mostly winter
What defines an outbreak of norovirus
-more than 2 cases linked by common exposure/location over <6 days
How does Norovirus cause disease
- Viruses attach, enter and replicate in intestinal epithelial cells
- lytic infection cycle destroys cells
- new viruses released into feces (re-transmission)
- Localized dmg to gut epithelium (nausea, vomiting, pain, loss of absorptive capacity (diarrhea)
- Self limiting infection (recovery via immune response but no protective immunity)
Clinical features of Norovirus
- 2 to 3 days incubation period before symptoms seen
- 1 to 5 days of diarrhea, nausea, vomiting, abd. pain. (severe in very young/old)
- Severe dehydration is main concern
- tachycardia
- hypotension
- Supportive therapy only (anti virals don’t work)
- fluid replacement/ oral rehydration salts (Na, K, Glucose)
-Shed viruses after 2 weeks of no symptoms (good hygiene important)
Viruses of the Central Nervous System
(Neurotropic viruses diseases) 3
- Encephalitis (inflammation of the brain)
- meningitis (inflammation of protective membrane covering brain)
- Poliomyelitis (destruction of motor neurons in brain, spine)
(Neurotropic viruses)
Viruses =Mumps, measles, rabies, herpes, enteroviruses, polio
Infection usually starts elsewhere (fecal to neurons)
West Nile Virus (WNV)(neurotropic disease)
- small enveloped RNA virus
- Vector borne virus (living carrier)
- Uganda, remained localized to Africa, West Asia, middle east
- 1st outbreak in new York (middle east strain)
West Nile Virus Transmission cycle
-natural host is birds (mostly crow)
Primary transmission cycle is from bird to bird via mosquito
Humans (other animals) are incidental host (bug bite that leads to dead end)
-not enough virus in human blood to re-transmit
Cant transmit through casual contact (only through organ transplants, blood transfusion, childbirth)
WNV Clinical Presentation
80% no symptoms
20 % = West nile fever
- 3 to 14 days after bite
- fever, headache, body ache, rash, swollen glands
- lasts 3 - 4 days then recover with no later effects
- No anti-therapy/ no human vaccine
- Unknown if protective immunity develops
- avoid mosquitos
1% = encephalitis of WNV
Replication in brain
-Headache, high fever, neck stiffness, disorientation, paralysis, seizures
Neurological dmg permanent, symptoms disappear
Blood Borne Viruses
Infect various organs, but presence is detected in bloodstream/bodily fluids
Transmitted by direct contact with fluid
Major BBV
Minor BBV
Health care Worry
Major: Hep B, Hep C, HIV
Minor: Hep A, D, WNV, cytomegalovirus
Hep B = 1 in 3 risk of infection
Hep C = 1 in 30
HIV = 1 in 300
Hepatitis C Virus
Hepatitis = inflammation of liver
-Jaundice, poor appetite, weight loss, fatigue, muscle and joint paint
-Progressive loss of liver function, often requiring liver transplants to avoid death (liver transplants 40% due to Hep C)
First called non-a/b
Enveloped RNA Virus (small genome/10 genes) Rapid Replication (10^12/day) 7 different genotypes (plus >50 subtypes) (DIFFER IN SEQUENCE OF NON-STRUCTURAL GENES)
differ in how well they respond to therapy and are distributed differently throughout the world (eg. North America – Geno. 1; Middle East & Africa – Geno. 4)
Transmission of HCV
Blood borne ( shared needles 65%, exposure, hemodialysis, blood transfusion/ transplant <0.1%
- Household exposure or unprotected sex with HCV+ partner
- Mother fetus transmission
NOT TRANSMITTED BY CASUAL CONTACT:
-Coughing, sneezing, hugging, kissing, Sharing eating utensils or via food or water, biting insects
Progression of Clinical disease (after first contact)
HC -> blood -> liver
Acute infection = 7-8 weeks 30% see symptoms,/70% don’t see symptoms (20% no further symptoms)
80% of acute -> chronic
- > 6 months
- Rate of virus replication slows & severity of symptoms declines
Progression to cirrhosis &/or cancer can take decades (many factors)
In the chronically infected population (HCV)
≈ 70% develop liver disease with mild or no symptoms
→ ≈ 25% develop more severe cirrhosis (scarring) of liver + liver failure
→ ≈ 3% develop liver cancer (hepatocelluar carcinoma)
Diagnosis of HCV via a blood test:
Antibodies against HCV (serology)
(Positive = acute or chronic disease or past exposure to the virus)
HCV nucleic acid amplification test (PCR)
(Positive = virus is present & therefore patient has active disease)
Anti-viral therapy for HCV
Virus has effective anti-virals
Interferon = non-specific anti viral Ribavirin = inhibit replication in cell
Inconvenient dosage/ 3 inject 3 subcutaneous and 2 daily ribavirin
costly
New HCV anti-virals
Harvoni = 2 compounds (Ledipasvir + Sofosbuvir) Block viral replication \
One pill per day, mild side effects
>90 response rate
Can HCV be prevented or cured
No preventative vaccine to date
- Numerous genotypes & sub-types
- Cant do animal ttesing
“Cure” = no virus after 24 weeks
Cure rate after treatment with new anti-virals ≈ 75-95 Success rate for cure depends on: - Overall health of patient - Genotype of the virus (geno. 1 is harder to treat) - Patient compliance with dosing instructions
Why is HCV silent epidemic
Lack of obvious symptoms in many people (70% of those infected don’t know it)
Risk of long-term liver damage even without prior obvious symptoms
Encourage testing for HCV in 50-70 yr old age group (increase awareness)
