key: cord-0795691-02qy72vt
authors: Hoshino, Y.; Scott, F. W.
title: Coronavirus-like particles in the feces of normal cats
date: 1980
journal: Arch Virol
DOI: 10.1007/bf01320772
sha: e1c3354f75b855ae6ef95b8501437170e4093c8f
doc_id: 795691
cord_uid: 02qy72vt

Coronavirus-like particles, morphologically indistinguishable from coronavirus-like particles seen in human, canine, and simian feces, were detected by electron microscopy in the feces from both feline infectious peritonitis antibody-positive and antibody-negative cats.

of this clarified fecal suspension were mixed with 20 drops of distilled water, one drop of 0.1 percent bovine serum albumin, and three to 4 drops of 4 percent phosphotungstic acid (PTA) a d j u s t e d to p H 7.0. This mixture was applied to a carbon parlodion-eoated 200 mesh copper grid with a nebulizer, and examined in a Philips 201 electron microscope a t 80 kV. Samples t h a t were negative for virus particles b y this method were re-examined b y the following uttracentrifugation method. The 10 percent to 20 percent fecal suspension was clarified at 6,000 r p m (3,000 × g) for 30 minutes, the s u p e r n a t a n t fluid was removed and ultmcentrifuged at 35,000 r p m (80,000×g) for one hour. The pellet was resuspended in one to 2 drops of distilled water, negatively stained with 2 percent P T A p H 7.0, and examined b y electron microscopy (EM). 

Indirect irnmunofluorescent test ( I I F T ) was performed for measuring serum a n t i b o d y titers for F I P virus, using a canine neurofibrosarcoma cell line infected with transmissible gastroenteritis (TGE) virus, Shizuoka strain, as antigen. Table t summarizes the results of EM and I I F T .

~Iarked pleomorphism occurred in the virus-like particles (Fig. 1 ). R o u g h l y t h e y can be grouped into four morphological types: 1. small (90 to 100 n m inelusive of projections) spherical particles ( Fig. 2A) , 2. small elongated (90 to 100×210 to 290 nm) particles (Fig. 2B ), 3. m e d i u m to large (150 to 300 nm) spherical and ellipsoidal particles ( Fig. 2C and 2D) , and 4. pleomorphic particles (Fig. 2 E and 2F ). The surface projections which measured a p p r o x i m a t e l y 25 n m in length were made up of spherical or teardrop-like knobs attached to the partieles with thin stalks. Sometimes these thin stalks appeared to protrude outwardly beyond the knobs (Fig. 2D) . In spite of a considerable variation in shape and size of the particles, lengths of the surface projections were uniform. This consistency in the length of surface projections has also been reported with avain infectious bronchitis virus (IBV), mouse hepatitis virus (MHV), and human coronavirus strain 229E (6) . Morphologically this feline enteric eoronavirus-like particle is indistinguishable from enteric coronavirus-like particles of humans (3, 13, 14) , dogs (17) , and monkeys (2) . They are different in the surface projection morphology from F I P virus (8, 11, 12) , human respiratory coronavirus, canine coronavirus, TGE virus of pigs, calf diarrhea eoronavirus, IBV, MHV, rat coronavirus, turkey enteric coronavirus, hemagglutinating encephalomyelitis virus of pigs, and the third enteric porcine eoronavirus designated CV777 (16) . CArL and EGGLESTONE (2) speculate that "there may therefore be two subgroups of coronavirus distinguishable by their projection morphology --one group possessing the classical petal-shaped projections and the other possessing projections consisting of spherical or teardrop-like knobs attached to the particle by a thin stalk". A third type of surface projection, fairly large spherical knob, has been reported for Lundc virus, a coronavirus-like agent isolated in Norway (20) associated with seabirds and the tick Ixodes uriae. A filiform projection without distal ends form the fourth type of projection which has been reported for FIPV (8) , TGE virus (22) , and porcine epidemic diarrhea type II virus (5). Fig. 1 . Electron mierograph of negatively stained eoronavirus-like particles in a typical field seen in the feline fecal sample. Small, medium, large, and pleomorphie particles are seen. Some particles appear to have lost several surface projections (arrows). Bar represents 100 nm Table 1 shows that coronavirus-Iike particles were visualized in feces from both F I P antibody-positive and antibody-negative cats, although most F I P antibody-negative cats were also free from these particles. Morphologically this eoronavirus-like particle appears to be different from F I P virus. I t m a y either be Fig. 2 . Electron mierographs of negatively stained eoronavirus-like particles in fecal samples. Bar represents 100 rim. A Small spherical particles. B Small elongated particle. C Large spherical particle. Surface projections appear to protrude outwardly beyond the knobs (arrows). D Large ellipsoidM particle. Typical teardrop-like surface projections are seen (arrow). E and ~Y Pleomorphic particles a v a r i a n t of F I P virus or a second feline eoronavirus. Possibility exists t h a t this coronavirus-like particle m a y be connected with one or more manifestations of a new disease eomplex called k i t t e n m o r t a l i t y complex (KMC) (18) , which causes unusually high incidences of reproductive failure and death of young kittens in m a n y eatteries t h r o u g h o u t the U n i t e d States. B o t h MDC breeding colonies from which we obtained experimental eats have suffered from KlV[C.

Follow up fecal samples were still positive over a period of one m o n t h (Table 1 ) which suggests persistent excretion of these coronavirus-like particles.

As this is the first report of enteric coronavirus-Iike particles, it is unknown how widespread t h e y are in eat populations. I t is of interest from the point of view of n a t u r a l history and the ecology of viruses t h a t morphologically indistinguishable enteric coronavirus-like particles are found in eats, dogs, monkeys, and humans.

A pilot s t u d y at Cornell Feline Research L a b o r a t o r y d e m o n s t r a t e d the prop a g a t i o n of this enteric coronavirus-like particles in small intestinal organ cultures of the eat. F u r t h e r studies on possible relationships between feline enteric eoronavirus-like particles and F I P virus, transmission, and pathogenesis of this enteric eoronavirus-like particles are in progress in our laboratory.

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Authors' address : Dr. Y. t{os~IINO, Department of Microbiology