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they are caused by distinct viruses that belong to different families ( varicella - zoster virus , a dna virus belonging to the family herpesviridae ; morbilli virus , an rna virus belonging to the family paramyxoviridae ) .
owing to sustained high vaccination coverage with two doses of measles vaccine , at the age of one and seven years , measles are virtually eliminated in croatia . in the last decade
only sporadic imported cases of measles are reported , with the exception of two small outbreaks , which occured in 2004 and 2008 following importation of measles .
since there is no universal chickenpox vaccination in croatia and the number of vaccinated persons upon request is very low , chickenpox is a common childhood disease with an annual incidence of 2530 cases per 1000 children under 15 years of age .
the first symptoms of illness ( fever and rash on the trunk and extremities ) appeared during their stay in italy . upon arrival to croatia , on 5 july , two of the children ( 15 and eight years of age ) were admitted to hospital with suspected measles and chickenpox . both children presented with fever up to 39c , dry cough and confluent macular rash wich was most prominent on the face and neck .
the 15-year - old daughter had prominent retroauricular confluent rash and koplik spots on the buccal mucosa .
five days later , on 10 july an 18-year - old boy from the same family , presented at the infectology clinic with fever up to 39c and dense confluent macular rash , with numerous scabs on the face and entire body .
an epidemiological investigation revealed that he had chickenpox with disease onset at the time of their stay in italy about 15 june .
the epidemiological investigation focused on ten children from the same family . in six children ( including the two hospitalized girls )
blood samples were taken on 14 july and sent to the refence laboratory at the croatian national institute of public health ( cniph ) for measles and varicella - zoster serology testing . based on clinical manifestations and results of serology testing , four of these six children had simultaneous infection with measles and varicella and two children had chickenpox .
four siblings who had no symptoms and had no history of measles immunization were vaccinated with a monovalent measles vaccine following the investigation .
serologic tests were performed at who national measles laboratory , department of virology ( cniph ) .
specific igm and igg antibodies to measles and varicella - zoster virus ( vzv ) were detected using commercial enzyme - linked immunosorbent assay ( virotech , russelsheim , germany ) .
vzv igg positive samples were tested for igg avidity ( euroimmun , lubeck , germany ) .
serologic results are presented in table 1 . in two patients ( patiens 1 and 2 ) varicella infection
two patients ( patients 3 and 4 ) had positive vzv igm antibodies with low igg avidity . for two patients ( patients 5 and 6 ) , paired samples were obtained three weeks later . in both patients ,
varicella infection was confirmed by low igg avidity in the second sample ( table 1 ) . 

table 1serologic results in six patients with suspected measles and varicella infection.patientagesexmeasles virusvaricella - zoster virusigmiggigmiggigg avidity1i11fnegativenegativepositivepositivelow2i12mnegativenegativepositivepositivelow3i15fpositivenegativenegativepositivelow4i8fpositivenegativepositivepositivelow5i18mpositivenegativepositiveequivocal - ii*positivepositivepositivepositivelow6i12fpositivepositivenegativenegative - ii*positivepositivepositiveequivocallow*paired serum samples ( obtained three weeks later ) . paired serum samples ( obtained three weeks later ) .
the epidemiological investigation revealed that none of the ten children were vaccinated against measles ( which is mandatory according to the childhood immunization programme in croatia ) or varicella ( which is not mandatory ) .
the fact that none of the children were vaccinated represents a public health issue in a relatively small migrant population and indicates that vaccination coverage may be low in this population . simultaneous infection and clinical illnesses of a viral and bacterial etiology is a well known fact , as well as co - infections but not simultaneous illness caused by two distinct viruses . however , clinical disease caused by two viruses at the same time is known to be a feature of only a few viruses , notably hiv , hepatitis b and hepatitis c viruses .
our literature search revealed only a few case report of children who had measles and chickenpox at the same time .
all these cases occurred at the time when incidences of both measles and chickenpox were high in the populations .
due to very high incidence rates of chickenpox and still high incidence of measles in countries with low vaccination coverage , one would expect numerous cases of simultaneous disease in the absence of some kind of immunological interference .
the rarity of reports on simultaneous measles and chickenpox illness indicates that recent infection with one virus results in suppression of clinically manifest disease caused by another virus if a person acquires the other infection soon afterward .
the simultaneous illness described in our report is quite unexpected because measles is virtually eliminated in croatia and in earlier decades , when measles was a common childhood disease , we have not identified cases of simultaneous clinical illness caused by measles and chickenpox .
we are reporting on a household outbreak of measles , in which cases of simultaneous measles and chickenpox infection occured in children of a family who resided in italy during the incubation period ( june 2011 ) . in three children , fever and generalized confluent macular rash 
 were the dominant symptoms . 
 serology testing revealed simultaneous measles and chickenpox infection in four children .