Serological analysis reveals circulation of influenza C viruses, Brazil

Análise sorológica revela circulação de vírus influenza C, Rio de Janeiro, RJ

Serological analysis reveals circulation of influenza C viruses, Brazil^*

Análise sorológica revela circulação de vírus influenza C, Rio de Janeiro, RJ

Fernando C Motta, Maristela O Luiz e José NSS Couceiro

Departamento de Virologia do Instituto de Microbiologia Professor Paulo de Góes da Universidade Federal do Rio de Janeiro. Rio de Janeiro, RJ, Brasil

KEYWORDS
Influenzavirus C^#. Hemagglutination inhibition test. ABSTRACT
The circulation of influenza C viruses in Rio de Janeiro, Brazil, was studied when significant levels of antibodies were detected (56.7%) with hemagglutination inhibition test, used as a standard methodology for influenza virus studies. DESCRITORES
Influenzavírus C^#. Testes de inibição da hemaglutinação. RESUMO
Foi estudada no Rio de Janeiro, RJ, Brasil, a circulação de vírus influenza C detectando-se níveis significativos de anticorpos (56,7%) através de reação de inibição de hemaglutinação, o qual é considerada como padrão para estudos em influenzavírus.

Influenza C viruses have been targeted as causal agents of benign clinical cases of influenza throughout the world, and few outbreaks have been observed in children and adults.² Most of the infected individuals normally have symptoms of fever for about two or three days, long lasting nasal discharge, mild cough, headache, malaise, and sore throat.² An age-related incidence of antibodies probable due to multiple infections have been detected by several authors in their studies of the human prevalence of antibodies induced by influenza C virus infections.^2,3

The data reveal a continuous stimulation by recurrent clinical or, more commonly, sub-clinical infections.⁵ Although these authors believe the level of antibodies remains stable for a long period of time, a rapid decline in the antibodies to influenza C viruses has already been demonstrated, which can explain the recurrent aspect of the infections caused by these viruses. This possibility is validated by the presence of low antigenic variability among influenza C viruses⁴ as indicated above.

In an attempt to evaluate the influenza C virus circulation in Rio de Janeiro city, a small community population who sought care at a public university hospital was taken as a study group. We analyzed the specific humoral immunity in 67 sera from adult individuals who received care in the hospital clinic during 1996-1997. They were randomized to be analyzed in regard of their hemagglutination inhibition (HI) titers to influenza C virus.¹ Sera samples were serially diluted from 1:10 to 1:5,120, in triplicates, with subsequent addition of the viral antigen (sample C/Taylor/1233/74) and incubated for 18 h. The final reading was performed after the addition of "A" group human erythrocytes at 1% and new incubation for 2 h. The inhibition titer was considered to be the reciprocal of the highest dilution of the sera in which occurred complete hemagglutination inhibition.¹

The results showed that the circulation of influenza C viruses is actually significant (56.7%). The percentages of HI titers at the threshold considered here (>80) after heat treatment were used as standard. The percentage of titers equal or higher than 80 was 56.7% while the percentage of sera with titers over 1,280 was only 4.5%, though occurred a raising of the HI titers of some sera. In fact, very little changes were detected when samples isolated over 17 years were studied, as it was already observed by Muraki et al,⁴ showing that influenza C viruses are the most stable among influenza viruses. Samples of influenza C viruses possibly circulating in Brazil will be differentiated from the sample used here as standard; however, the reactivity of the antibodies from the analyzed sera indicated that the humoral immunity is always active, revealing that those circulating Brazilian samples of influenza C virus exhibit reasonable antigenic similarity to the standard sample used.⁴ This homogeneity must not be attributed to a long life immunity as can be believed,⁵ situation that associated to the known low genetic variability would be a barrier against the naturally recurrent infections, which are known as typical characteristic of these viruses.

The significant serum positivity, the kindliness of the clinical cases and the persistence character, already observed in infections for these viruses, make us suppose that the importance of these viruses is actually underevaluated. Their role among the agents of respiratory virus diseases deserves further investigation. This kindliness of the infections should still work as a maintenance factor for the circulation of these viruses.

Correspondence to:

José Nelson dos Santos Silva Couceiro

Centro de Ciências da Saúde ¾ Bloco I ¾ subsolo ¾ Sala I0-063 ¾ Caixa Postal 68040

21941-590 Rio de Janeiro, RJ, Brasil

E-mail: [e-mail]

Submitted on 10/2/2000. Approved on 14/2/2000.

• 1. Couceiro JNSS, Paulson JC, Baum LG. Influenza virus strains selectively recognize sialyloligosaccharides on human respiratory epithelium, the role of the host cell in selection of hemagglutinin receptor specificity. Virus Res 1993;29:155-65.
• 2. Katagiri S, Ohizumi A, Homma M. An outbreak of type C influenza in a children's home. J Infect Dis 1983;148:51-6.
• 3. Melles HHB, Takimoto S. Freqüęncia de anticorpos para o vírus da influenza tipo C em habitantes da cidade de Săo Paulo. Rev Inst Adolfo Lutz 1982;42:17-20.
• 4. Muraki Y, Hongo S, Sugawara K, Kitame F, Nakamura K. Evolution of the haemagglutinin-esterase gene of influenza C virus. J Gen Virol 1996;77:673-9.
• 5. O'Callaghan RJ, Gohd RS, Labat DD. Human antibody to Influenza C virus: Its age-related distribution and distinction from receptor analogs. Infect lmmun 1980;30:500-5.

*

Financial support of Finep (institutional grants), Faperj (Process number: E-26 / 150.094 / 99); CNPq (Process number: 520130 / 96-0), FUJB/UFRJ (Process number: 7994-4).

Publication Dates

• Publication in this collection
  06 Aug 2001
• Date of issue
  Apr 2000

History

• Accepted
  14 Feb 2000
• Received
  10 Feb 2000