Rubella Virus: Epidemiology, Pathogenesis, Effects and Diagnoasis

Introduction

Rubella virus is only member of rubrivirus genes of togavirus family. It is also called as german measeles as it was discovered in german. Rubella virus spherical 40 to 80nm, positive, single stranded RNA virus consist of 30 to35 nm core covered by lipoprotein envelope. The RNA has a molecule of 3*106. It has spherical with spiky hemaggulutinin which has some projections. It is different from other groups of virus. It has three major polypeptides follows. E1-> Viral Hemagglutinin E2-> most specific antigenicity.

Demographics and Epidemiology

Before vaccine era it has epidemic pattern of 6 to 9 year cycles. Worst pandemic happened at last in United states around 1964. Late winter and early spring was its peak incidence. 25% to 50% are asymptomatic. Infection peaks about 5 days before and continous 6 days after rash starts. Vaccination started in 1966. 5 to 9 year old children more prone for infection. Incubation period between 14 and 21 days. Rubella is no less communicable than measles (due to absence of coughing). Infectivity is greatest when rash is erupting. In 1964-1965 there is outbreak of this virus and impact came very seriously many children born with congenial malformation in ear, eye, heart, brain etc. Many went to complication of this virus like Encephalitis, abortion, congenital rubella syndrome unexpected neonatal death too. This make the importance of vaccination. At that first outbreak college students and adult screened and vaccinated. But again in nineteen highly once again the outbreak achieved its own milestones. Two dose of Rubella vaccine introduced and the diseases were in the same control. This vaccination programme also reduced upcoming future emergence of malformed baby. Once the importance of vaccination identified disease itself came in control. But 100%there is no immunity, still is reduced malformation, outbreak it will be strictly followed world wide.

Disease pathogenesis and its clinical manifestation

Virus starts its action in respiratory epithelium and from there its invades and run into native or nearly lymph nodes. In native or nearly lymph nodes, virus start multiplication and ready for complications within ten to seventeen days. Virus runout or comeout from nasopharynx mostly it happens after tenth day of contamination. After rashes start to erode, virus present in body for two weeks. Virus has the highest peak time of contamination between live days before to six days after the visualize of rashes. Once the virus enter the placental tissue is go deep and causes tissue necrosis by reduced blood supply, reducing cell division, chromosomal division reduction and finally it stops the mitosis arrest and it cause protein synthesis stoppage and it indirectly impact on cell division and cell necrosis.

Congenital effects of rubella system vise

1. Cardio vascular system: ventricular septal defect, patent ductus arteriosus, pulmonary artery narrowing and myocarditis.
2. Central nervous system: meningitis, necrosis and calcifications.
3. Eye: small pupil, cataract, iridocyclitis, ciliary body necrosis, glaucoma and retinopathy.
4. Ear: cochlear bleeding, endothelial necrosis, sensori neural hearing loss and it was irreversible too.
5. Respiratory system: interstitial pneumonitis.
6. Liver: hepatic gaint cell malformations, fibrosis, lobular disarrangement, bile stasis it cause neonatal cholestasis some cases it will recover spontaneously or it will leads to cirrohis of liver, but most common infection is cytomegalo virus. In first 6 months rubella igM was diagnostic and after 6 months igG titres will be more relavent.
7. Kidney: interstitial nephritis.
8. Adrenal gland: it causes cortical cytomegly so it may cause unnecessary rise of several steroid hormones and its impact was more serious than viremia.
9. Bone: poor mineralisation of osteoid cause malformed and thinned osteoid.
10. Spleen and lymphnode: extramedullar hematopoeisis occurs as a result of bone marrow invasion. It causes hypersplenism leads to pancytopenia.
11. Thymus: it cause histocytic reaction and also cause absence of germinal centres.
12. Skin: it cause erythropoeisis in dermis.

M Rubella serologic testing

M Rubella positivity even in a single sample of serum in suspected case is confirmatory of an acuteinfection with rubella virus. But the interval between the day of onset of rash and colletion of serum sample for testing plays an important role in determining the sensitivity of the test.

Serum samples collected less than five days after onset of rash test IgM negative but those collected more than five days after onset of rash test IgM positive. So it would be necessary to repeat the test with samples collected after five days of rash onset. IgG positivity: Indicates exposure to wild type rubella virus infection or it may be vaccination. In acute infectionIgG testing of paired samples i. e acute phase serum sample convelecent phase serum sample can be done. If the test shows,

• First type: Rubella seggregative in acute phase and positive in convalescent phase then that seroconversion and confirms acute rubella infection.
• Second type: If IgG rubella positive in acute plan convalescent sample to be collected after 10-14 days, greater than fold increase between acute and convalescent sample indicates acute infection.

As with IgM testing, there is relation between day of rash onset and time of collection of serum samples collected in cases with primary infection in first few days of onset of rash are IgG negative. Whereare samples collected few weeks after rash onset have a high IgG.

Rubella IgG avidity testing: Antibody avidity: This shows the strength of Ag-Ab binding. It increases over time following Ag exposure. Helps to differentiate a recent infection from a past infection. High avidity index indicates past infection and low avidity index indicates acute infection.

Defection of Rubella virus

Rubella virus isolation and RT PCR detection of rubella virus can be done. It is not most commonly used as a confirmatory test but useful for genotyping and epidemiology to track virus transmission, outbreak. The samples used for isolation of rubella virus are nasopharyngeal or threat aspirates collect preferably before five days after onset of rash.