When a characteristic physical particle has been obtained, it should fulfill the following criteria before it is identified as a virus particle: 鉴定病毒颗粒需满足以下条件/标准：

1. The particle can be obtained only from infected cells or tissues.  

2. Particles obtained from various sources are identical regardless of the cellular origin in which the virus is grown.

3. Particles contain nucleic acid (DNA or RNA), the sequence of which is not the same as the species of host cells from which the particles were obtained.

4. The degree of infective activity of the preparation varies directly with the number of particles present.

5. Destruction of the physical particle by chemical or physical means is associated with a loss of viral activity.

6. Certain properties of the particles and infectivity must be shown to be identical (eg, their sedimentation behavior in the ultracentrifuge and their pH stability curves).

7. Antisera prepared against the infectious virus should react with the characteristic particle and vice versa. Direct observation of an unknown virus can be accomplished by electron microscopic examination of aggregate formation in a mixture of antisera and crude viral suspension.

8. The particles should be able to induce the characteristic disease in vivo (if such experiments are feasible).

9. Passage of the particles in tissue culture should result in the production of progeny with biologic and antigenic properties of the virus. 

以上转自：Jawetz, Melnick, & Adelberg’s Medical Microbiology （Twenty-Eighth Edition），CHAPTER 29

科赫法则

One of the landmarks in the history of infectious diseases was the development of the Henle–Koch postulates that established the evidence required to prove a causal relationship between a particular infectious agent and a particular disease. These simple postulates were originally drawn up for bacteria, but were revised in 1937 by Thomas Rivers and again in 1982 by Alfred Evans in attempts to accommodate the special problem of proving disease causation by viruses. In many cases, virologists have had to rely on indirect causal evidence, with associations based on epidemiology and patterns of antibody prevalence among populations.

Koch's postulates were reworked again in 1996 by David Relman and David Fredricks as more and more genomic sequencing criteria came to dominate the subject.

如何确认某种病毒是导致特定疾病的病因？怎样证明某种疾病是由特定病毒感染引起的？

Fredricks and Relman’s Molecular Guidelines For Causal Association

1. Strength of the association. Are viral nucleic acid sequences detected in most (all) cases of disease?

2. Specificity of the association. Are viral nucleic acid sequences localized to diseased tissues, and not to healthy tissues? Is the frequency of virus infection reduced significantly in healthy individuals?

3. Response to treatment. Does the copy number of viral nucleic acid sequences fall with resolution of illness or

effective treatment, and increase if the disease relapses?

4. Temporality. Does infection with the virus precede and predict disease onset?

5. Plausibility. Do the known biological properties of the virus make sense in terms of the disease?

6. Biological gradient. Is the amount of virus higher in patients with severe disease than it is in persons with mild disease? Is the amount of virus higher in diseased tissues than in healthy tissues?

7. Consistency. Are these findings reproducible by multiple laboratories and by multiple investigators?

以上转自：Fenner and White’s Medical Virology（Fifth Edition），CHAPTER 2