Reoviruses Workup

Updated: Mar 03, 2017
  • Author: Andrew Stevenson Joel Chandranesan, MBBS; Chief Editor: Mark R Wallace, MD, FACP, FIDSA  more...
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Workup

Laboratory Studies

Routine laboratory tests, such as CBC count, electrolytes, and liver profile, may be needed.

Reovirus

Reoviruses have been shown to replicate in various cell culture types used by laboratories for general viral culture, but these agents are only rarely isolated from clinical samples.

Paired acute- and convalescent-phase serum samples can be used to detect seroconversion via hemagglutination inhibition, complement fixation, or virus neutralization.

Colorado tick fever

Diagnosis of CTF in humans has been established most reliably by isolation of the virus from the erythrocyte fraction of whole blood or by demonstrating the presence of viral antigen in the erythrocytes via the direct fluorescent-antibody technique. The CTF virus has been shown to persist in erythrocytes of patients for as long as 120 days. The virus has been found in cerebrospinal fluid in people with no apparent encephalitis or meningitic involvement. Whole blood specimens shipped unrefrigerated to the laboratory by surface mail are satisfactory for virus isolation. However, virus isolation and identification takes 1-2 weeks from the time of receipt of the specimen. The fluorescent-antibody technique requires special equipment that some laboratories do not possess, and interpretation of the results is subjective.

Detection of antibody is also an adequate tool for diagnosing infection with this virus, but dependence on this method has several drawbacks. Various serologic procedures, such as neutralization tests in suckling and weanling mice, tissue culture neutralization, plaque-reduction methods, complement fixation, and direct immunofluorescence, have been used. Complement fixation antibody titers are low usually, and about 25% of infected individuals do not develop a complement fixation antibody response.

To demonstrate a diagnostically significant change in antibody titer, sera must be obtained at least 1 week after onset and again 3-4 weeks later. The specific neutralizing and complement fixing antibodies appear in the blood between the eighth and 14th days of the illness; neutralizing antibodies have been demonstrated to be present for many years. Blood from acute- or convalescent-phase samples can be inoculated into suckling mice or susceptible cell cultures (eg, baby hamster kidney [BHK] or Vero cells).

PCR techniques have been developed that allow the diagnosis to be established from the first day of symptoms.

Rotavirus

Rotaviruses are fastidious agents to culture and cannot be detected via routine viral isolation techniques. Most HRVs can be cultivated if pretreated with the proteolytic enzyme trypsin and if low levels of trypsin are included in the tissue culture medium. This cleaves an outer capsid protein and facilitates uncoating.

Direct electron microscopy, although the least sensitive technique, affords by far the most rapid method for detecting fecal viruses and has proven to be an especially useful diagnostic and teaching tool when used to test the first available stool sample from acutely ill patients with diarrhea during periods of rotavirus activity.

Direct EIA and on-grid immunoelectron microscopy (IEM) techniques are approximately equivalent in sensitivity and reliability. Compared with the conventional electron microscopy method, both techniques are about 9 times more sensitive in detecting purified SA-11 (simian rotavirus) and 3 times more sensitive in detecting HRV in crude stool samples. The IEM technique is presently the best method for detecting all of the known gastroenteritis viruses, especially in rectal swab specimens, but, with most stool specimens, IEM takes hours longer than direct electron microscopy to provide the same diagnostic result.

The Rotazyme test is a useful tool in the diagnosis of HRV gastroenteritis. Testing should be performed early in the course of the illness. The maximum number of viral particles is found in the stool of infants in the first few days of illness, especially between the second and fifth days. Excretion generally continues for as long as 8 days, with some reports of excretion as late as 23 days and even later in the immunosuppressed population. Because of the decreasing concentrations of viral particles excreted as the patient improves, testing after 23 days may fail to detect viral antigen. Because rotavirus infects the epithelial cells of small intestinal villi, mucosal gut antibodies are the most reliable indicators of immune response following natural rotavirus infection or rotavirus vaccination. In one study, saliva was used as a marker of intestinal immune response following natural rotavirus diarrhea in infants, the reasoning being that primed immunocompetent cells from the gut migrate to distant mucosal sites where they produce antibodies. [21]

Quantitative real-time PCR can also be used in the diagnosis of rotavirus, along with other bacteria and viruses in a multiplex platform. [22]

Usually, no abnormalities of peripheral white blood cell count or significantly elevated numbers of polymorphonuclear leukocytes or immature forms are found. These cells may have higher alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels.

Hypophosphatemia may be present in as many as 50% of cases of rotavirus gastroenteritis. Uric acid levels above 10 mg/dL also can be present. Most patients have mild compensated metabolic acidosis with decreased plasma bicarbonate levels.