Poor Accuracy of Manually Derived Head Computed Tomography Parameters in Predicting Intracranial Hypertension After Nontraumatic Intracranial Hemorrhage

BACKGROUND

The utility of head computed tomography (CT) in predicting elevated intracranial pressure (ICP) is known to be limited in traumatic brain injury; however, few data exist in patients with spontaneous intracranial hemorrhage.

METHODS

We conducted a retrospective review of prospectively collected data in patients with nontraumatic intracranial hemorrhage (subarachnoid hemorrhage [SAH] or intraparenchymal hemorrhage [IPH]) who underwent external ventricular drain (EVD) placement. Head CT scans performed immediately prior to EVD placement were quantitatively reviewed for features suggestive of elevated ICP, including temporal horn diameter, bicaudate index, basal cistern effacement, midline shift, and global cerebral edema. The modified Fisher score (mFS), intraventricular hemorrhage score, and IPH volume were also measured, as applicable. We calculated the accuracy, positive predictive value (PPV), and negative predictive value (NPV) of these radiographic features for the coprimary outcomes of elevated ICP (> 20 mm Hg) at the time of EVD placement and at any time during the hospital stay. Multivariable backward stepwise logistic regression analysis was performed to identify significant radiographic factors associated with elevated ICP.

RESULTS

Of 608 patients with intracranial hemorrhages enrolled during the study time frame, 243 (40%) received an EVD and 165 (n = 107 SAH, n = 58 IPH) had a preplacement head CT scan available for rating. Elevated opening pressure and elevated ICP during hospitalization were recorded in 48 of 152 (29%) and 103 of 165 (62%), respectively. The presence of ≥ 1 radiographic feature had only 32% accuracy for identifying elevated opening pressure (PPV 30%, NPV 58%, area under the curve [AUC] 0.537, 95% asymptotic confidence interval [CI] 0.436-0.637, P = 0.466) and 59% accuracy for predicting elevated ICP during hospitalization (PPV 63%, NPV 40%, AUC 0.514, 95% asymptotic CI 0.391-0.638, P = 0.820). There was no significant association between the number of radiographic features and ICP elevation. Head CT scans without any features suggestive of elevated ICP occurred in 25 of 165 (15%) patients. However, 10 of 25 (40%) of these patients had elevated opening pressure, and 15 of 25 (60%) had elevated ICP during their hospital stay. In multivariable models, mFS (adjusted odds ratio [aOR] 1.36, 95% CI 1.10-1.68) and global cerebral edema (aOR 2.93, 95% CI 1.27-6.75) were significantly associated with elevated ICP; however, their accuracies were only 69% and 60%, respectively. All other individual radiographic features had accuracies between 38 and 58% for identifying intracranial hypertension.

CONCLUSIONS

More than 50% of patients with spontaneous intracranial hemorrhage without radiographic features suggestive of elevated ICP actually had ICP > 20 mm Hg during EVD placement or their hospital stay. Morphological head CT findings were only 32% and 59% accurate in identifying elevated opening pressure and ICP elevation during hospitalization, respectively.

Trajectories of Neurologic Recovery 12 Months After Hospitalization for COVID-19: A Prospective Longitudinal Study

BACKGROUND AND OBJECTIVE

Little is known about trajectories of recovery 12 months after hospitalization for severe COVID-19.

METHODS

We conducted a prospective, longitudinal cohort study of patients with and without neurologic complications during index hospitalization for COVID-19 from March 10, 2020, to May 20, 2020. Phone follow-up batteries were performed at 6 and 12 months after COVID-19 onset. The primary 12-month outcome was the modified Rankin Scale (mRS) score comparing patients with or without neurologic complications using multivariable ordinal analysis. Secondary outcomes included activities of daily living (Barthel Index), telephone Montreal Cognitive Assessment (t-MoCA), and Quality of Life in Neurologic Disorders (Neuro-QoL) batteries for anxiety, depression, fatigue, and sleep. Changes in outcome scores from 6 to 12 months were compared using nonparametric paired-samples sign test.

RESULTS

Twelve-month follow-up was completed in 242 patients (median age 65 years, 64% male, 34% intubated during hospitalization) and 174 completed both 6- and 12-month follow-up. At 12 months, 197/227 (87%) had ≥1 abnormal metric: mRS >0 (75%), Barthel Index <100 (64%), t-MoCA ≤18 (50%), high anxiety (7%), depression (4%), fatigue (9%), or poor sleep (10%). Twelve-month mRS scores did not differ significantly among those with (n = 113) or without (n = 129) neurologic complications during hospitalization after adjusting for age, sex, race, pre-COVID-19 mRS, and intubation status (adjusted OR 1.4, 95% CI 0.8-2.5), although those with neurologic complications had higher fatigue scores (T score 47 vs 44; p = 0.037). Significant improvements in outcome trajectories from 6 to 12 months were observed in t-MoCA scores (56% improved, median difference 1 point; p = 0.002) and Neuro-QoL anxiety scores (45% improved; p = 0.003). Nonsignificant improvements occurred in fatigue, sleep, and depression scores in 48%, 48%, and 38% of patients, respectively. Barthel Index and mRS scores remained unchanged between 6 and 12 months in >50% of patients.

DISCUSSION

At 12 months after hospitalization for severe COVID-19, 87% of patients had ongoing abnormalities in functional, cognitive, or Neuro-QoL metrics and abnormal cognition persisted in 50% of patients without a history of dementia/cognitive abnormality. Only fatigue severity differed significantly between patients with or without neurologic complications during index hospitalization. However, significant improvements in cognitive (t-MoCA) and anxiety (Neuro-QoL) scores occurred in 56% and 45% of patients, respectively, between 6 and 12 months. These results may not be generalizable to those with mild or moderate COVID-19.

Toxic Metabolic Encephalopathy in Hospitalized Patients with COVID-19

Background

Toxic metabolic encephalopathy (TME) has been reported in 7–31% of hospitalized patients with coronavirus disease 2019 (COVID-19); however, some reports include sedation-related delirium and few data exist on the etiology of TME. We aimed to identify the prevalence, etiologies, and mortality rates associated with TME in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-positive patients.

Methods

We conducted a retrospective, multicenter, observational cohort study among patients with reverse transcriptase–polymerase chain reaction-confirmed SARS-CoV-2 infection hospitalized at four New York City hospitals in the same health network between March 1, 2020, and May 20, 2020. TME was diagnosed in patients with altered mental status off sedation or after an adequate sedation washout. Patients with structural brain disease, seizures, or primary neurological diagnoses were excluded. The coprimary outcomes were the prevalence of TME stratified by etiology and in-hospital mortality (excluding comfort care only patients) assessed by using a multivariable time-dependent Cox proportional hazards models with adjustment for age, race, sex, intubation, intensive care unit requirement, Sequential Organ Failure Assessment scores, hospital location, and date of admission.

Results

Among 4491 patients with COVID-19, 559 (12%) were diagnosed with TME, of whom 435 of 559 (78%) developed encephalopathy immediately prior to hospital admission. The most common etiologies were septic encephalopathy (n = 247 of 559 [62%]), hypoxic-ischemic encephalopathy (HIE) (n = 331 of 559 [59%]), and uremia (n = 156 of 559 [28%]). Multiple etiologies were present in 435 (78%) patients. Compared with those without TME (n = 3932), patients with TME were older (76 vs. 62 years), had dementia (27% vs. 3%) or psychiatric history (20% vs. 10%), were more often intubated (37% vs. 20%), had a longer hospital length of stay (7.9 vs. 6.0 days), and were less often discharged home (25% vs. 66% [all P < 0.001]). Excluding comfort care patients (n = 267 of 4491 [6%]) and after adjustment for confounders, TME remained associated with increased risk of in-hospital death (n = 128 of 425 [30%] patients with TME died, compared with n = 600 of 3799 [16%] patients without TME; adjusted hazard ratio [aHR] 1.24, 95% confidence interval [CI] 1.02–1.52, P = 0.031), and TME due to hypoxemia conferred the highest risk (n = 97 of 233 [42%] patients with HIE died, compared with n = 631 of 3991 [16%] patients without HIE; aHR 1.56, 95% CI 1.21–2.00, P = 0.001).

Conclusions

TME occurred in one in eight hospitalized patients with COVID-19, was typically multifactorial, and was most often due to hypoxemia, sepsis, and uremia. After we adjustment for confounding factors, TME was associated with a 24% increased risk of in-hospital mortality.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12028-021-01220-5.

Abstract P100: Hemorrhagic Stroke in the Setting of COVID-19 is Associated With Anticoagulation Use

Introduction: While the thrombotic complications of COVID-19 have been described, there are limited data on its implications in hemorrhagic stroke. The clinical characteristics, underlying stroke mechanism, and outcomes in this group of patients are especially salient as empiric therapeutic anticoagulation becomes increasingly common in the treatment and prevention of thrombotic complications of COVID-19.

Methods: We conducted a retrospective cohort study of patients with hemorrhagic stroke (both non-traumatic intracerebral hemorrhage and spontaneous non-aneurysmal subarachnoid hemorrhage) who were hospitalized between 3/1/20-5/15/20 at a NYC hospital system, during the coronavirus pandemic. We compared the demographic and clinical characteristics of patients with hemorrhagic stroke and COVID-19 to those without COVID-19 admitted to our hospital between 3/1/20-5/15/20 (contemporary controls) and 3/1/19-5/15/19 (historical controls), using Fischer’s exact test and non-parametric testing. We adjusted for multiple comparisons using the Bonferroni method.

Results: During the study period, 19 out of 4071 (0.5%) patients who were hospitalized with COVID-19 had hemorrhagic stroke on imaging. Of all COVID-19 with hemorrhagic stroke, only 3 had non-aneurysmal SAH without intraparenchymal hemorrhage. Among hemorrhagic stroke and COVID-19 patients, coagulopathy was the most common etiology (73.7%); empiric anticoagulation was started in 89.5% vs 4.2% of contemporary and 10.0% of historical controls (both with p =<0.001). Compared to contemporary and historical controls, COVID-19 patients had higher initial NIHSS scores, INR, PTT and fibrinogen levels. These patients also had higher rates of in-hospital mortality [84.6% vs. 4.6%, p =<0.001]. Sensitivity analyses excluding patients with strictly subarachnoid hemorrhage yielded similar results.

Conclusion: We observed an overall low rate of imaging-confirmed hemorrhagic stroke among patients hospitalized with COVID-19. Most hemorrhages in COVID-19 patients occurred in the setting of therapeutic anticoagulation and were associated with increased mortality. Further studies are needed to evaluate the safety and efficacy of therapeutic anticoagulation in COVID-19 patients.

A Prospective Study of Neurologic Disorders in Hospitalized Patients With COVID-19 in New York City

OBJECTIVE

To determine the prevalence and associated mortality of well-defined neurologic diagnoses among patients with coronavirus disease 2019 (COVID-19), we prospectively followed hospitalized severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-positive patients and recorded new neurologic disorders and hospital outcomes.

METHODS

We conducted a prospective, multicenter, observational study of consecutive hospitalized adults in the New York City metropolitan area with laboratory-confirmed SARS-CoV-2 infection. The prevalence of new neurologic disorders (as diagnosed by a neurologist) was recorded and in-hospital mortality and discharge disposition were compared between patients with COVID-19 with and without neurologic disorders.

RESULTS

Of 4,491 patients with COVID-19 hospitalized during the study timeframe, 606 (13.5%) developed a new neurologic disorder in a median of 2 days from COVID-19 symptom onset. The most common diagnoses were toxic/metabolic encephalopathy (6.8%), seizure (1.6%), stroke (1.9%), and hypoxic/ischemic injury (1.4%). No patient had meningitis/encephalitis or myelopathy/myelitis referable to SARS-CoV-2 infection and 18/18 CSF specimens were reverse transcriptase PCR negative for SARS-CoV-2. Patients with neurologic disorders were more often older, male, white, hypertensive, diabetic, intubated, and had higher sequential organ failure assessment (SOFA) scores (all p < 0.05). After adjusting for age, sex, SOFA scores, intubation, history, medical complications, medications, and comfort care status, patients with COVID-19 with neurologic disorders had increased risk of in-hospital mortality (hazard ratio [HR] 1.38, 95% confidence interval [CI] 1.17-1.62, p < 0.001) and decreased likelihood of discharge home (HR 0.72, 95% CI 0.63-0.85, p < 0.001).

CONCLUSIONS

Neurologic disorders were detected in 13.5% of patients with COVID-19 and were associated with increased risk of in-hospital mortality and decreased likelihood of discharge home. Many observed neurologic disorders may be sequelae of severe systemic illness.

Keeping the team together: Transformation of an inpatient neurology service at an urban, multi-ethnic, safety net hospital in New York City during COVID-19

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Neurology teams can care for patients with COVID-19 in lieu of being redeployed.

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Maintaining team structures has advantages to redeployment during pandemic surges.

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Streamlining neurological services increases capacity to care for COVID-19 patients.

The COVID-19 pandemic dramatically affected the operations of New York City hospitals during March and April of 2020. This article describes the transformation of a neurology division at a 450-bed tertiary care hospital in a multi-ethnic community in Brooklyn during this initial wave of COVID-19. In lieu of a mass redeployment of staff to internal medicine teams, we report a novel method for a neurology division to participate in a hospital’s expansion of care for patients with COVID-19 while maintaining existing team structures and their inherent supervisory and interpersonal support mechanisms.

Protocolized Urine Sampling is Associated with Reduced Catheter-associated Urinary Tract Infections: A Pre- and Postintervention Study

Background

Standard urine sampling and testing techniques do not mitigate against detection of colonization, resulting in false positive catheter-associated urinary tract infections (CAUTI). We aimed to evaluate whether a novel protocol for urine sampling and testing reduces rates of CAUTI.

Methods

A preintervention and postintervention study with a contemporaneous control group was conducted at 2 campuses (test and control) of the same academic medical center. The test campus implemented a protocol requiring urinary catheter removal prior to urine sampling from a new catheter or sterile straight catheterization, along with urine bacteria and pyuria screening prior to culture. Primary outcomes were test campus CAUTI rates, compared between each 9-month pre- and postintervention epoch. Secondary outcomes included the percent reductions in CAUTI rates, compared between the test campus and a propensity score–matched cohort at the control campus.

Results

A total of 7991 patients from the test campus were included in the primary analysis, and 4264 were included in the propensity score–matched secondary analysis. In the primary analysis, the number of CAUTI cases per 1000 patients was reduced by 77% (6.6 to 1.5), the number of CAUTI cases per 1000 catheter days was reduced by 63% (5.9 to 2.2), and the number of urinary catheter days per patient was reduced by 37% (1.1 to 0.69; all P values ≤ .001). In the propensity score–matched analysis, the number of CAUTI cases per 1000 patients was reduced by 82% at the test campus, versus 57% at the control campus; the number of CAUTI cases per 1000 catheter days declined by 68% versus 57%, respectively; and the number of urinary catheter days per patient decreased by 44% versus 1%, respectively (all P values &lt; .001).

Conclusions

Protocolized urine sampling and testing aimed at minimizing contamination by colonization was associated with significantly reduced CAUTI infection rates and urinary catheter days.

3 cases of primary intracranial hemorrhage associated with "Molly", a purified form of 3,4-methylenedioxymethamphetamine (MDMA)

3,4-Methylenedioxymethamphetamine (MDMA, or "Ecstasy" in tablet form) is a powerful sympathomimetic drug that is commonly perceived as safer than other stimulants such as methamphetamine or cocaine. "Molly" is a purified form of MDMA that is perceived by users as being even safer, as it is free of adulterants such as methamphetamine. Previously, all reports of intracranial hemorrhages in MDMA abusers were associated with coingestion of other sympathomimetic drugs, or with pre-existing cerebrovascular lesions. We describe a series of three young, otherwise healthy patients with various types of intracranial hemorrhages associated with "Molly" ingestion. All three patients underwent extensive workup including catheter angiography that did not demonstrate aneurysm, arteriovenous malformation, or vasculitis. We suggest that even the purified form of MDMA can cause serious intracranial hemorrhagic complications and should not be thought of as a safe recreational drug.

The acute motor-sensory axonal neuropathy variant of Guillain-Barré syndrome after thoracic spine surgery

Guillain-Barré syndrome (GBS) is the eponym used to describe acute inflammatory polyradiculoneuropathies, which manifest with weakness and diminished reflexes. Although the classic form of GBS is considered to be an ascending demyelinating polyneuropathy, several variants have been described in the literature, including the Miller-Fisher syndrome, acute panautonomic neuropathy, acute motor axonal neuropathy, and acute motor-sensory axonal neuropathy (AMSAN). Few cases of postoperative GBS have been documented, particularly for the AMSAN variant. The authors describe the case of a patient who developed AMSAN after thoracic spine surgery and highlight the importance of investigating new-onset weakness in the postoperative period.

A double-protease-resistant variant of transmissible gastroenteritis virus and its ability to induce lactogenic immunity

A virus resistant to 2 major intestinal proteases (trypsin and alpha-chymotrypsin) was derived from the attenuated Purdue strain of transmissible gastroenteritis virus. Its enzymatic stability was confirmed, in vitro, by exposure to proteolytic enzymes and to porcine intestinal fluids. Vaccination of 5 seronegative pregnant sows with the variant virus by a series of 2 oral and 1 IM inoculations resulted in high titers of neutralizing antibody in serum and colostrum. The mean antibody titer in milk whey decreased 44-fold within 1 week after parturition. At 3 days of age, the 40 pigs delivered by these sows were challenge exposed orally with virulent transmissible gastroenteritis virus. Pigs nursing the 5 vaccinated sows underwent a relatively mild clinical course of illness. The average mortality of these 40 pigs was 33%. Thirty-six pigs which had been raised by 4 nonvaccinated sows had a more severe illness, greater daily weight loss, and higher mortality (92%).

Elaboration of chemotactic substances by alveolar cells: possible mechanisms for the initial neutrophilic response in feline caliciviral pneumonia

In vitro experiments established that the interaction of feline calicivirus (FCV) with alveolar macrophages and pneumocytes results in the generation of chemotactic factors that produce directed migration of neutrophils in Boyden chambers. Factors were produced independent of immune mechanisms and of discernible serum factors. Lysates of noninfected alveolar macrophages and pneumocytes did not possess chemotactic activity, indicating that chemotactic factors were not preformed in these cells. Noninfected alveolar macrophages also elaborated neutrophil chemotactic factors in culture; however, activity was greater when macrophages were infected with FCV. The results of this study suggested that the neutrophilic response in the peripheral portion of the lung of cats exposed to aerosols of FCV was the result of the elaboration of complete chemotactic factors from FCV-infected alveolar cells.

Ultrastructural morphogenesis of acute viral pneumonia produced by feline calicivirus

The ultrastructural morphogenesis of acute viral pneumonia was studied in pathogen-free cats exposed to aerosols of a virulent strain of feline calicivirus. Electron microscopy and fluorescence microscopy indicated that the virus had a marked tropism for alveolar pneumocytes. Viral-induced necrosis of pneumocytes was observed as early as 12 hours after exposure and was associated with acute serofibrinous and neutrophilic inflammation in the distal air exchange tissue. The acute exudative phase abated by 168 hours after exposure. The regenerative phase that followed was characterized by hyperplasia of type II pneumocytes; influx of monocytes, lymphocytes, and plasma cells; and interalveolar and intraalveolar proliferation of fibroblasts. The decrease in pneumocyte injury coincided with the increase in alveolar macrophages and immunocytes. With minor exceptions, feline calicivirus-induced alveolar damage and the subsequent repair resembled toxic alveolar injury produced by oxidant gases. Feline caliciviral pneumonia, therefore, is a naturally occurring example of viral-induced diffuse alveolar damage.

In vitro interaction of alveolar macrophages and pneumocytes with feline respiratory viruses

Feline alveolar macrophages and feline pneumocytes were inoculated in vitro with low multiplicities of either feline calicivirus or feline viral rhinotracheitis virus. Pneumocytes were permissive for both viruses. High titers were attained, and characteristic cytopathic effects developed. Alveolar macrophages were permissive for feline viral rhinotracheitis virus, although the cycle of replication was delayed. Infection of macrophages with feline calicivirus resulted in the production of viral antigens and cytopathic effects; however, viral particles were not detected by electron microscopy, and viral infectivity titers rose only slightly and then fell to undetectable levels by 96 h. The differences in viral susceptibility between these two peripheral pulmonary cell populations that were demonstrated in vitro probably contribute to the differences in pathogenesis of viral rhinotracheitis and calicivirus infections in cats.

Experimentally induced feline chlamydial infection (feline pneumonitis)

Cats exposed to aerosols of feline Chlamydia psittaci developed a disease characterized principally by conjunctivitis. Signs of conjunctivitis appeared between postexposure days (PED) 5 and 10, were often unilateral initially, and persisted for 22 to 45 days. Fever followed the onset of conjunctivitis (PED 11 to 15) and persisted for 3 to 8 days. Signs of mild rhinitis (occasional sneezing and mild serous nasal discharge) occurred in some cats between PED 8 and 37. Neither signs of lower respiratory tract disease nor significant pulmonary lesions were produced by the feline pneumonitis agent. Small foci of pneumonia were detected microscopically in 3 of 6 cats examined between PED 7 and 14. Chlamydiae were identified between PED 7 and 14 in the cytoplasm of epithelial cells in stained conjunctival smears. Conjunctivitis persisted for at least 18 days after chlamydiae no longer were detectable in conjunctival smears. Low levels of chlamydial infectivity, however, still were present in conjunctiva and lung on PED 45.

Diffuse alveolar damage in cats induced by nitrogen dioxide or feline calicivirus

The ultrastructural morphogenesis of pulmonary lesions was studied in cats exposed to either aerosols of feline calicivirus (FCV) or high concentrations of NO2. Both directly injured alveolar lining cells, particularly type I cells. Necrosis of pneumocytes attended by an acute exudative response in the air exchange tissues was evident from 0 through 24 hours after exposure of cats to NO2 and from 12 through 96 hours after infection with FCV. The reparative process following alveolar injury was characterized by regenerative hyperplasia of type II pneumocytes, proliferation of stromal cells, and infiltration of mononuclear cells. Differences in the lesions produced by NO2 and FCV also were encountered. Endothelial necrosis was detected only after NO2 injury, whereas a marked infiltration of neutrophils and immunocytes was observed only after FCV injury. The FCV/NO2 experimental system in cats is well suited for studies of diffuse alveolar damage of toxic and viral etiology.

Feline caliciviral disease: experimental immunoprophylaxis

An attenuated feline calicivirus (FCV) was administered intramuscularly to specific-pathogen-free cats. Vaccination did not cause signs of illness. Oropharyngeal replication of attenuated FCV was not detected, nor was there evidence of virus transmission to contact-control cats. Antiviral neutralizing antibody was present in the serum of all vaccinated cats 7 days after they were given the 2nd intramuscular dose of immunogen. Vaccinated and control cats were challenge exposed to aerosols of a virulent FCV strain. All controls developed severe pneumonia and died within 7 days after this challenge exposure. In the vaccinated cats, signs of illness were absent or minimal; pulmonary lesions were milder and less extensive than those in the control cats. Feline calicivirus was isolated from ocular, nasal, and oropharyngeal swabbings from both control and vaccinated cats after viral challenge. Results indicate protective immunity to FCV disease can be induced by intramuscular administration of an attenuated FCV.

Comparison of canine distemper viral strains: an electron microscopic study

A canine distemper (CD) viral strain, designated R252, originally obtained from a dog with demyelinating encephalomyelitis has been shown to reproduce this disease in gnotobiotic dogs in a high incidence in contradistinction to other CD viral strains which produce an acute fatal disease. Because comparision of R252 strain with the Snyder Hill (SH) and Onderstepoort (Ond) strains revealed differences in in vitro behavior, the 3 viruses were ultrastructurally investigated. The results revealed differences among the 3 viruses: Cytoplasmic nucleocapsid aggregates were characteristic of R252, diffuse aggregates of nucleocapsids were characteristic of SH, and although budding viral particles were recognized in Ond-infected cells, few nucleocapsids were seen in the cytoplasm. Cytoplasmic fibrillar structures were characteristic of R252- and Ond-infected cells. The budding viral particles observed with R252 and SH were similar, whereas Ond budding particles seemed to contain fewer nucleocapsids. Intranuclear inclusions recognized in R252- and SH-infected cultures appeared as areas of clearing of nucleoplasm along with disruption of the nucleolus. The presence of nucleocapsid-like structures was variable. Ultrastructurally, the cytoplasmic inclusions in cells infected with all 3 viruses progressed from focal aggregates of nucleocapsids to electron-dense bodies.

Induction of immunity to feline caliciviral disease

Six specific-pathogen-free cats were exposed by aerosol to a feline calicivirus of low virulence (F-9 virus). Homotypic (anti-F-9) seroconversion occurred in all cats by postexposure day 14. The serum of one cat on postexposure day 14 and four of six cats on postexposure day 35 neutralized feline picornavirus isolate no. 225 (FPV-255), a virulent feline calicivirus. Homologous antiviral activity was detected before the appearance of heterologous (anti-FPV-255) activity and always was present in higher titer. Protective immunity was evaluated on postexposure day 35 by aerosol challenge with FPV-255. The pyrexia, depression, dyspnea, oral ulcers, and severe pneumonia produced in two susceptible specific-pathogen-free cats by exposure to FPV-255 did not occur in the cats that had been infected previously with F-9 vir. The study demonstrates that heterotypic protective immunity to feline calicivirus disease can be induced by prior infection with feline calicivirus of low virulence.

Biological properties of a canine distemper virus isolate associated with demyelinating encephalomyelitis

A canine distemper virus (CDV), DESIGNATED R252, originally recovered from a dog with demyelinating encephalomyelitis was shown to reproduce this disease in gnotobiotic dogs with a high incidence as compared to other CDV strains, which produced an acute fatal infection. In this investigation, R252 was propagated for the first time in Vero cells and compared to two known strains of CDV, Snyder-Hill (SH) and Onderstepoort (Ond). The results of this study revealed that intracellular R252 accumulated more slowly than either SH or Ond. There was extensive destruction of Vero monolayers infected with either R252 or SH. Each virus induced the formation of intracytoplasmic and intranuclear inclusions. Ond infection resulted in minimal cytopathic changes and intracytoplasmic inclusions. Immunofluorescence studies indicated that the spread of R252 infection within the monolayers was intermediate between the rapidly spreading SH and slowly spreading Ond. R252-infected cells developed characteristic immunofluorescent cytoplasmic inclusions. Initially, each stained homogeneously and later appeared as a non fluorescent body surrounded by a fluorescent ring. This characteristic pattern of fluorescence was observed only infrequently in thelate stage of SH infection and was absent in Ond-infected cultures. Reciprocal neutralization studies indicated that the three strains are of one serotype. These findings suggest that R252-CDV has biological properties which differ from two other strains of CDV and which may have bearing upon the in vivo capability of this virus to produce demyelinating encephalomyelitis.

Experimentally induced feline calicivirus infection: clinical signs and lesions

Sixty-six specific-pathogen-free cats were allotted to 10 groups and exposed by aerosol to 10 feline calicivirus (FCV) isolates. Viruses of different virulence were identified. The more virulent FCV caused pyrexia, depression, dyspnea, pneumonia, vesicles, or ulcers of the tongue and ulceration of the hard palate and nostrils. The FCV of low virulence caused similar lesions of the tongue, palate, and nostrils but little or no malaise, pyrexia, or pneumonia. Lesions produced by FCV usually were confined to the oral mucosa, tonsils, and lungs. Lesions in the nasal or trachea were associated with 2 of the 10 FCV tested.

Differences in acute and convalescent-phase antibodies of cats infected with feline picornaviruses

Complement fixation inhibiting and complement-fixing antibodies were demonstrated in sera from cats during the acute and convalescent stages, respectively, of feline picornavirus infections. Complement-fixing antibody activity was present in 19S and 7S globulins, whereas complement fixation inhibiting antibody activity was confined to the 7S globulins. Sera with complement-fixing antibody and sera with complement fixation inhibiting antibody were also shown to have neutralizing and precipitating antibodies. In a study of antibody responses to homotypic and heterotypic strains of feline picornavirus, less serological cross-reactions were observed between strains of feline picornavirus in sera from cats in the acute phase of feline picornavirus infection than in the convalescent phase. The temporal relationship of complement fixation inhibiting and complement-fixing antibody responses of cats after acute viral respiratory infections is contrasted with previously observed antibody response in cats to feline leukemia virus.

Lesions produced by feline picornaviruses of different virulence in pathogen-free cats

Sixteen pathogen-free cats were exposed by aerosol to either of two feline picornavirus isolates. The isolates used were picornavirus-255 and kidney-cell-degenerating virus. These viruses were selected to represent picornavirus prototypes of high and low virulence, respectively. Picornavirus-255 consistently produced depression, anorexia, and pneumonia. There were no lesions in the upper respiratory tract or conjunctiva, nor were there clinical signs of upper respiratory disease. The pulmonary lesions began as multifocal exudative pneumonia that progressed rapidly to interstitial pneumonia characterized by marked adenomatoid proliferation of pneumocytes. Three weeks after exposure the pulmonary lesions were principally resolved. It also produced discrete lingual and palatine ulcers that were easily detected. Experimental infection with kidney-cell-degenerating virus resulted only in transient fever and tiny vesicles and ulcerations of the lingual and tonsillar mucosae that could easily escape detection. No significant respiratory lesions were induced by kidney cell degenerating virus.