RUBELLA

 

History

           

            Rubella was initially considered to be a form of measles up to the second half of the 19^th century. Rubella is commonly called German measles. It is the 3^rd of the six viral exanthema of childhood, with measles and scarlet fever being first and second respectively.

 

            Rubella was initially thought to be a benign disease (which it is in postnatal infection and in adults) but Australian ophthalmologist Gregg then observed the congenital defects of infants of mothers who had developed rubella early in pregnancy. So, more attention was given to the study of rubella and its vaccination in the 20^th century.

 

 

Classification

 

            Rubella virus belongs to the family Togaviridae and is the only member in the genus Rubivirus.  The family contains two other genera also: Alphavirus and Pestivirus. In contrast to the Alphaviruses, which replicate in arthropods, Rubella virus and Pestivirus do not have invertebrate hosts. Humans are the only hosts for them.

 

            There is only one serotype of Rubella virus which makes it very easy to control the disease by vaccination.

 

 

Morphology

 

            The Rubella virus is a spherical particle measuring 50-70 nm in size. It is surrounded by an envelope carrying hemagglutinin peplomers. The core consists of a single stranded RNA genome, positive sense. (See figure in the last page)

 

            The virus has 3 antigens:

1.      C-protein (Capsid Protein) which is a structural protein.

2.      E₁ protein which is present on the envelope. It has hemagglutinating property.

3.      E₂ protein which is also present on the envelope. Its function is not known.

 

 

Cultivation and host range

 

            The virus can be cultivated in many primary cell cultures and continuous cell cultures. The most common cell lines used include:

1. Vero Cell Line
2. Rabbit Cell Lines
3. Baby Hamster Kidney Cell Lines

 

However, the propagation of the Rubella virus in tissue culture does not produce any reliable or distinctive CPE by light microscopy. The CPE varies widely depending on several other factors. So, detection is done by “Interference assay”, where the propagation of the Rubella virus is inferred by the prevention of superinfection by other viruses which can produce CPE, like Enteroviruses or ECHO viruses. Neutralization tests or immunofluorescence test with specific anti-rubella serum can be done to detect the viral antigens in tissue culture.

 

      Humans are the only hosts for Rubella virus. However, animals esp. monkeys can be experimentally infected but the disease process does not manifest completely in them.

 

 

Resistance

 

            Rubella virus is highly heat labile. It is rapidly inactivated at 56^oC. It can be stored at -60^oC. Usual disinfectants including formalin, ether, chlorine, 70% alcohol can inactivate Rubella virus.

 

 

Epidemiology

 

            The virus is distributed worldwide but clinical disease occurs more in the temperate zones than the tropics. Before vaccination was started, epidemics of rubella occurred every 6 to 9 years & pandemics every 10 to 30 years with 100% infection rate among susceptible. But after immunization, the number of cases has come down considerably (by as much as 99% in the United States of America).

 

 

Pathogenesis

 

            The pathogenesis and the clinical features of Rubella infection can be considered under two headings: postnatal infection and the congenital infection.

 

Postnatal Rubella

 

Source of Infection: Infected persons (including asymptomatic infections), infants with the congenital rubella syndrome

 

Mode of transmission: Inhalation of virus-laden droplets from respiratory secretions of infected persons. The virus is found in the respiratory secretions 1 week before and up to 2 weeks after the appearance of the exanthema (i.e. the rash). In case of infants with congenital rubella syndrome, the viral shedding can go on for up to 20 months also, although within 1 year more than 80% are non-spreaders.

 

Incubation Period: On an average 16-18 days but can range from 14-23 days.

 

Pathogenesis:

 

Following initial infection of cells of the nasopharyngeal 

epithelium, the virus undergoes multiplication in the cells

↓

The virus then reaches the regional lymph nodes and

undergoes multiplication for another 7 to 9 days

↓

Primary viremia then occurs followed by spread to multiple

sites throughout the body where further multiplication takes place

↓

Secondary viremia then occurs 10 to 17 days after infection.

During the secondary viremia, viruria also occurs.

↓

Antibodies start appearing by 16 days and at this time the rash

appears which suggests immunological basis for the rash

↓

The virus is then cleared rapidly within

2 weeks of the appearance of the rash.

 

Clinical Features: More than half of the infections go unnoticed since they are subclinical. In people who develop symptoms, prodromal symptoms may be seen 10-15 days after infection. These include low grade fever, cough, coryza, sore throat, headache, malaise, anorexia, ophthalmalgia, mild conjunctivitis. Tender lymphadenopathy is seen, characteristically involving the sub occipital, posterior auricular and posterior cervical groups.

This is then followed by the development of an exanthema, which appears after an incubation period of 16-18 days. The pruritic erythematous maculopapular rash initially appears on the face and then spreads rapidly to the trunk and distal extremities within 24 hours. During the 2^nd day, it begins to fade and by the end of the 3^rd day, it is resolved completely. Hence, it is also called the “Three-day Measles”. Desquamation of the skin may be seen during convalescence.

Raised ESR and leucopenia may be seen during the rash.

 

Complications: These occur within one week of the disappearance of the rash.

 

1. Acute Polyarticular Arthritis

This occurs in about 40% of the women who are infected while only 10% of the men get this. Symptoms range from joint pain to full blown arthritis – pain, swelling, redness, joint effusions, decreased movements. Circulating immune complexes may be the cause.

 

2. Neurological Involvement

Encephalitis and post-infectious encephalopathy are rare complications but carry 40% mortality rate. Pathogenesis is unclear.

 

3. Hemorrhagic Complications

Thrombocytopenic purpuras can occur especially in children.

 

If the crisis phase in these complications is tided through, complete recovery is the rule.

 

Differential Diagnosis: Rubella can be readily mistaken for scarlet fever, toxoplasmosis, infectious mononucleosis, measles, roseola, erythema infectiosum, enterovirus infections and allergic reactions. So, lab procedures are very important in the diagnosis of the disease.

Immune Response to Postnatal Rubella Infection:

            The immune response is similar to any other typical viral infection.

 

v     IgM antibodies are first produced which can be detected within a few days of onset of rash up to 8 weeks, using Hemagglutination Inhibition (HI) test, Immunofluorescence (IF), Radio Immuno Assay (RIA), ELISA.

 

v     IgG antibodies also appear within a few days of onset of the rash and then persist for life. They can be detected using Latex agglutination, Neutralization test, IF, RIA, ELISA and CFT.

 

Lab Diagnosis:

Specimens Collected: Nasopharyngeal or throat swabs take 6 days before or after the onset of rash, Blood for Serology

 

Methods:

1. Virus Isolation

This is done using green monkey kidney cell lines –Vero cell line. Incubation temperature: 33 – 35^o C. Identification is done by

1. Viral interference to CPE produced by enterovirus
2. Viral Ag can be detected after 3 to 4 days by IF or neutralization test.

 

However virus isolation not recommended because

•     CPE produced is inconspicuous

•     Delay is involved in the method.

 

2. Serology
1. Demonstration of rubella specific IgM Antibodies (by ELISA) is diagnostic of recent infection.
2. A 4 fold rise in rubella specific IgG level between acute and convalescent phase serum (by ELISA) can also be done. For this, Hemagglutination Inhibition test can be done.
3. Viral antigen can be detected by CFT, IF, ELISA

 

 

Treatment: The disease is self-limiting. No specific treatment is required. Complications are managed by supportive treatment and care. Aspirin should not be given to children for treatment for arthritis because Reye’s syndrome may be precipitated.

 

 

 

 

 

 

 

Congenital Rubella Infection

 

            Congenital infection of the fetus occurs when the mother gets infected primarily during pregnancy. The risk varies according to the time of infection during the pregnancy.

 

 

            The rate of congenital anomalies seen during birth or within 2 yrs of birth also differs with the time of the primary infection during pregnancy. If the primary infection takes place in the first trimester, then 85% of the infants show congenital anomalies whereas after 20 weeks of gestation, no congenital anomalies are seen.

 

            So, earlier the infection of the mother, higher is the chance of congenital infection and anomalies.

 

Pathogenesis:

 

During the viremia caused by the primary infection of the mother,

the virus enters the fetal circulation transplacentally

↓

The virus then induces cellular destruction,

vascular injury & vascular insufficiency

↓

Edema, fibrosis and necrosis of the chorionic villi

 also occur, resulting in a small placenta

↓

These lead to Intrauterine Growth Retardation (IUGR)

and hypoplasticity of the affected organs of the fetus

which lead to congenital anomalies.

 

            Once infected in-utero, there is chronic persistence of the virus in the newborn. At birth, the virus can be demonstrated in pharyngeal secretions, multiple organs, CSF, urine, rectal swabs. Viral excretion may last for up to 20 months but the viral shedding goes on decreasing with age.

 

Clinical Features: Unlike those of postnatal Rubella, the clinical manifestations of congenitally acquired Rubella are usually severe. The classic triad of Congenital Rubella Syndrome consists of Cataracts, Cardiac abnormalities and Deafness.

 

            The consequences of in-utero rubella infection can be considered broadly under 3 categories.

1. Transient Sequelae

These usually resolve over a period of weeks. They include dermal erythropoiesis (“Blue berry muffin” rash), chronic rash, thrombocytopenic purpuras, hemolytic anemia, generalized lymphadenopathy, hepatitis, nephritis, myositis, myocarditis, meningoencephalitis and hepatosolenomegaly.

 

2. Permanent Manifestations
1. The most common permanent manifestation is Deafness
2. Others include structural defects of the Cardiovascular system like Patent ductus arteriosus
3. Ophthalmologic findings like cataracts, retinopathy and micropthalmia
4. Permanent neurological impairment  like mental retardation, motor disabilities.

 

3. Delayed Manifestations

Sequelae of congenital rubella that develop in childhood and adulthood but are not present in infancy include endocrinopathies, deafness, ocular damage, vascular effects and progressive rubella panencephalitis. The most important delayed manifestation is Insulin Dependent Diabetes Mellitus (IDDM).

 

 

Immune Response in Congenital Rubella Infection:

 

·        Following maternal rubella infection, the mother produces rubella specific IgM and IgG antibodies. Of these, IgM cannot cross the placenta. But the IgG which can cross the placenta does so only slowly.

·        The fetus also starts producing rubella specific IgM antibodies which can be detected for up to 3 months – 1 year after birth.

·        The fetal IgG also can be demonstrated after birth although it is known to decrease markedly over years. 

 

So, a child born with congenital rubella infection will have a following picture:

ü      Detectable high titres of rubella specific fetal IgM

ü      Detectable high titres of rubella specific IgG which includes both maternal IgG and fetal IgG.

 

 

 

 

Lab Diagnosis of Congenital Rubella Infection:

 

1. In Utero Diagnosis (1^st trimester)
1. Detection of rubella specific IgM antibodies in fetal blood – obtained by cordocentesis. Seropositivity is seen within 19 wks of gestation.
2. Chorionic Villus culture can demonstrate the virus.
3. Immunoblotting using rubella specific monoclonal antibody.
4. Hybridization technique using DNA probes.

 

2. Perinatal Diagnosis
1. Virus Isolation

The virus may be isolated from a variety of sources like urine, throat swabs, bone marrow, CSF obtained from the new born.

 

2. Serology

·        Demonstration of rubella specific IgM Antibodies in infants is diagnostic (by ELISA)

·        Rubella specific maternal IgG may be detected in the initial 6 months, which reach the fetal circulation by passive transfer across the placenta.

 

Treatment:

            Congenital rubella can only be prevented by childhood immunization as to prevent rubella infection during a future pregnancy. If rubella detected in first 3-4 months of pregnancy, then termination of pregnancy is advised. Use of gamma globulin in infected mothers doesn’t prevent fetal transmission.

 

 

 

Prophylaxis of Rubella

 

            This is done by active immunization by a live attenuated vaccine. The live attenuated vaccine contains RA 27/3 strain propagated in human diploid cell lines. It is generally given as a combination (M.M.R) vaccine.

 

MMR Vaccine

 

            It is a live attenuated combined vaccine to eliminate measles, mumps, rubella & Congenital Rubella Syndrome from human population.

 

Components of the Vaccine:

Live attenuated measles virus            Shwarz strain

Live attenuated mumps virus             RIT 4385 strain

Live attenuated rubella virus              Wistar RA 27/3 strain

 

Schedule:

The first dose is given to children at 12 to 15 months after birth. This is followed by a booster dose at 3 – 5 yrs.

                       

Reconstitution and route of administration:

Reconstitution is to be done only with the diluents provided. After reconstitution, it is to be stored at 6 – 8^o C. It is to be discarded after one hour.

 

Advantages of MMR:

1. It helps in reducing the number of clinical visits and injections.
2. Increased acceptance among the patients.
3. Reduces the cost of immunization.

 

Side Effects of the vaccine:

This includes fever, rash, swelling of the glands / cheeks, arthralgia, lymphadenopathy, autism (?)

 

Contraindications:

1. Immunodeficiency
2. Undiagnosed fever
3. Cancer therapy
4. Allergy to egg components
5. Pregnancy is an absolute contraindication in case of adult female patients. Patient should be advised not to become pregnant within 3 months of vaccine administration

 

References

 

1. Clinical Virology, 2^nd ed. 2002 by Douglas D Richman, Richard J Whitley, Fredrick G Hayden. ASM Press
2. Jawetz, Melnick & Adelberg’s Medical Microbiology 23^rd ed. 2004. McGraw Hill Publications.

 

Images