rx64: Transmission

Chicken Pox or Varicella is an acute, highly infectious disease caused by the Varicella–Zoster (V–Z) virus. It is characterized by vesicular rash that may be accompanied by fever and malaise. It is found the world over due to various factors and occurs in both epidemic and endemic forms which has to be controlled. Chicken Pox and Herpes Zoster are now regarded as different hosts with the same etiology. <hr>Prevention & Control of Chicken Pox <hr> Control of Chicken Pox There is no specific treatment for Chicken Pox. The usual control measures are notifications, isolation of cases for about six days or so after the onset of rash, and disinfections of articles soiled by nose and throat discharges. Prevention of Chicken Pox Chicken Pox Chicken Pox Varicella Zoster Immunoglobulin (VZIG). Varicella Zoster Immunoglobulin (VZIG), within 72 hours of exposure has been recommended for prevention. A dose of 1.25 to 5 ml given intramuscularly will modify or prevent the disease. The current recommendation is that it should be reserved for immunosuppressed contacts of acute cases or newborn contacts. It has also been shown to provide some improvement in high–risk children with Varicella. Vaccine for Chicken Pox No serious attempt was made in the past to develop a vaccine against Chicken Pox probably because the disease, in general, was not considered a health priority. A live attenuated vaccine (OKA strain) developed by Takahashi in Japan has been extensively studied in field trials. The frequency of mild local reactions at the site of inoculation is about 1%. A general reaction to the vaccine, mainly rash or mild Varicella may occur. Sero conversion, after vaccination, in healthy sero–negative children is over 90%. The vaccine has proved safe and effective in preventing the disease. However, opinion is divided about the need for a vaccine against Chicken Pox. Some consider that since Chicken Pox is a relatively mild illness, there is little need for a vaccine. Further, it may be disastrous if Chicken Pox is postponed from childhood when it is mild, to adulthood, when it is more severe. One of the major objections to a live vaccine is the potential of the Chicken Pox virus to establish a latent infection; this may produce Zoster in later years more frequently or in a more severe form than the natural disease. <hr>Symptoms of Chicken Pox <hr> The clinical symptoms of Chicken Pox and Small Pox differ which may vary from a mild illness with only a few scattered lesions, to a severe febrile illness with widespread rash. Unapparent infection is estimated to occur in no more than 5% of susceptible children. In a majority of cases, the disease tends to be mild and typical. Laboratory Diagnosis of Chicken Pox Laboratory Diagnosis Laboratory Diagnosis During the Small Pox post–eradication era, the diagnosis of Chicken Pox is of great importance because of its resemblance to mild Small Pox. Laboratory diagnosis is rarely required as clinical signs are usually clearcut. The most rapid and sensitive means of diagnosis is examination of vesicle fluid under the electronic microscope, which shows round particles (brick–shaped in Small Pox) and may be used for cultivation of the virus. Scrapings of the floor of vesicles show multi–nucleated giant cells colored by Giemsa stain (not in Small Pox). Serology is used mainly for epidemiological surveys. <hr>Stages of Chicken Pox <hr> Pre–eruptive Stage Pre-eruptive Stage Pre–eruptive Stage There is sudden onset with mild or moderate fever, pain in the back, shivering and malaise. This stage is very brief, and lasting for about 24 hours. In adults, the prodromal illness is usually more severe and may last for about two to three days before the rash comes out. Eruptive Stage In children, the rash is often the first sign. It appears on the day the fever starts. The distinctive features of the rash are: Centripetal Distribution The rash is symmetrical. It first appears on the trunk where it is abundant, and then on the face, arms and legs, where it is less abundant. Mucosal surfaces (e.g. buccal, pharyngeal) are generally involved. Axilla may be affected, but palms and soles are not usually affected. The density of the eruption diminishes centrifugally. Rapid Evolution The rash advances quickly through the stages of macule, papule, vesicle and scab. In fact, the first to attract attention are often the vesicles filled with clear fluid and looking like “Dewdrops” on the skin. They are superficial in site, with easily ruptured walls and surrounded by an area of inflammation. Usually, they are not umbilicated. The vesicles may form crusts without going through the pustular stage. Many lesions may abort. Scabbing begins four days to a week days after the rash appears. Pleomorphism A characteristic feature of the rash in Chicken Pox is its pleomorphism, that is, all stages of the rash (papules, vesicles and crusts) may be seen simultaneously at one time, in the same area. This is due to the rash appearing in successive crops for four to five days in the same area. Fever The fever does not run high but gets exacerbated with each fresh crop of eruption. Complications with Chicken Pox In most cases, Chicken Pox is a mild, self–limiting disease. The mortality is less than 1% in uncomplicated cases. However, Varicella may be accompanied by severe complications, particularly in immuno–suppressed patients, and may also occur in normal children and adults. These include hemorrhages (varicella hemorrhagica), pneumonia, encephalitis, acute cerebellar ataxia and Reye’s Syndrome (acute encephalopathy associated with fatty degeneration of the viscera, especially the liver). Maternal Varicella during pregnancy may cause fetal wastage and birth defects such as cutaneous scars, atrophied limbs, microcephaly, and low birth weight. Intrauterine infection occurring near term may cause Typical Varicella in the newborn with varying degrees of severity depending on the transfer of maternal–specific lG antibodies. <hr>Mode of Transmission of Chicken Pox <hr> Transmission of Chicken Pox Chicken Pox is transmitted from person to person by droplet infection, and by droplet nuclei. Most patients are infected by “Face to face”, (personal) contact. The portal of entry of the virus is through the respiratory tract. Since the virus is extremely labile, it is unlikely that fomites play a significant role in its transmission. Contact infection undoubtedly plays a role when an individual with Herpes Zoster is an index case. The virus can cross the placental barrier and infect the fetus, a condition known as Congenital Varicella. Incubation Period of Chicken Pox Usually, the incubation period is about 14 to 16 days, although extremes as wide as 21 days have been reported. <hr>Mode of Transmission of Chicken Pox <hr> Agent Factors for Chicken Pox Agent The causative agent of Chicken Pox, V–Z virus is also called, “Human (Alpha) Herpes Virus 3”. Primary infection causes Chicken Pox. Recovery from primary infection is commonly followed by the establishment of latent infection in the sensory ganglia often for decades, without clinical manifestations. When the cell mediated immunity wanes with age or following immuno–suppressive therapy, the virus may reactivate, resulting in zoster, a painful, vesicular, pustular eruption in the distribution of one or more sensory nerve roots. The virus can be grown in tissue culture. Source of Infection Source of InfectionSource of Infection Usually a case of Chicken Pox. The virus occurs in the oropharyngeal secretions and lesions of skin and mucosa. Rarely, the source of infection may be a patient with Herpes Zoster. The virus can be readily isolated from the vesicular fluid during the first three days of the illness. The scabs, however, are not infective. Infectivity The period of communicability of patients with varicella is estimated to range from one to two days before the appearance of rash, and four to five days thereafter. The virus tends to die before the pustular stage. The patient ceases to be infectious once the lesions have crusted. Secondary Attack Rate Chicken Pox is highly communicable. The secondary attack rate in household contacts approaches the 90% mark. Host Factors for Chicken Pox Age Chicken Pox occurs primarily among children under 10 years of age. A few persons escape infection until adulthood. The disease can be severe in normal adults. Immunity One attack gives durable immunity; second attacks are rare. The acquisition of maternal antibodies protects the infant during the first few months of life. No age, however, is exempt in the absence of immunity. The lG antibodies persist for life and their presence is correlated with protection against Varicella. The cell mediated immunity appears to be important in recovery from V–Z infections and in protection against the reactivation of the latent V–Z virus. Pregnancy Infection during pregnancy presents a risk to the fetus and the neonate. Environmental Factors Chicken Pox shows a seasonal trend in India, the disease occurring mostly during the first six months of the year. Overcrowding favors its transmission. In temperate climates, there is little evidence of any seasonal trend. <hr>

Chicken Pox or Varicella is an acute, highly infectious disease caused by the Varicella–Zoster (V–Z) virus. It is characterized by vesicular...

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Chicken Pox

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