A recent study has provided evidence that two types of equine (horse) herpes viruses have an unusually broad host range. This fact supports which of the following statements?

a. The lytic cylce occurs in horses while the lysogenic cycle occurs only in other species.

b. The virus is transmitted from one host to another by mosquitoes.

c. In a population of horses, many of the individuals will become infected

d. Horses, rhinoceroses, and polar bear can become infected

e. In an individual horse, many different type of cells will be infected

According to the answer key, the answer is D. My question is why isn't E also a correct answer? I thought host range means "the range of cells that can act as a host to a virus".

  • $\begingroup$ A host is an organism, not a cell of an organism. $\endgroup$ – mgkrebbs Mar 9 '17 at 16:19
  • $\begingroup$ Welcome to Biology.SE. Please do not just upload images but make the effort to rewrite the text. Images are not searchable and is a trouble for people with visual impair. Also, your title is not helpful. Of course the post will contain a question, so it is useless to use the word question in the title. Try to be more specific. $\endgroup$ – Remi.b Mar 9 '17 at 16:34
  • $\begingroup$ You must provide text for questions otherwise they will be removed as they cannot be indexed properly. A scan is not acceptable. $\endgroup$ – David Mar 9 '17 at 16:36
  • $\begingroup$ I think this is a good question because it highlights a critical pitfall in any field of science: making broad assumptions with too little or poor data. It also in part highlights poor test questions/mentoring that lead people into these pitfalls. See in my comments on Yordan's answer. $\endgroup$ – CKM Mar 10 '17 at 15:03

"host" refers to the organism as a whole. So two types of equine herpes viruses have an unusually broad host range means here that these two viruses have the particular ability to infect various animals, and not only horses.

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  • $\begingroup$ And yet that statement still doesn't support any of the possible answers. Is that a fussy assumption? $\endgroup$ – CKM Mar 9 '17 at 16:35
  • $\begingroup$ @CMosychuk My guess is that the question is badely put. It should have been more like 'Based on this fact, which of the following statements can be considered as true?'. Then d. is the correct answer because the fact that these viruses have a broad host range is enough to explain why polar bear and rhinos can also be infected. However, it is kind of a circular reasoning. $\endgroup$ – Flo Mar 9 '17 at 17:33

The correct answer is D and there is nothing wrong with the question. @user34748, the very definition of host range is the range of species a virus can infect, not cell types. See the Wikipedia definition of host as used in biology: In biology, a host is an organism that harbors a parasitic, a mutual, or a commensal symbiont, typically providing nourishment and shelter. This is why the answer is D, not E. If the question specified host cell types, then E would have been the correct answer.

The problem is that you are supposed to know the definition before you go to exam and host has very clear definition in parasitology in general as the organism the infectious organism infects, not its cell types! In fact if the answer was to be E the very structure of the question had to be changed to include a special close specifying it is host cell types, not the hosts themselves the question is about. And this is clearly not the case here. This is why the answer is D, not E. Even from a testological point of view there is nothing wrong with the question. The methodology used to compose it is within the limits of what you are expected to know and the reasoning you are expected to be able to use. It's legitimate virology question.

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  • $\begingroup$ As I understand it, the correct answer is that multiple species (polar bear, rhino, horse) can get infected because these viruses have a broad host range. But I guess that the very definition of having a broad host range is being able to infect various hosts. So, in the end the reason why d. is correct is that d. is correct... $\endgroup$ – Flo Mar 9 '17 at 20:41
  • $\begingroup$ No, the reason why D is correct is because you definition you should have known before entering this exam is " In biology, a host is an organism that harbors a parasitic, a mutual, or a commensal symbiont, typically providing nourishment and shelter." If you knew this definition, you should not have had any problems choosing D as answer. See definitions are important in biology, if you don't pay enough attention to them you can easily make mistakes later on in both interpreting and even noticing important tendencies in your data. You should have paid attention to the definition of host! $\endgroup$ – Yordan Yordanov Mar 9 '17 at 21:33
  • $\begingroup$ Basically the entire question revolves around knowing or not what the definition of host is in virology. If you have considered that host is always an organism and not just a single cell you would never had failed the question and ask it here. I advise you the next time you go take a test-learn your definitions better. Hope you make good lesson out of this experience. $\endgroup$ – Yordan Yordanov Mar 9 '17 at 21:37
  • $\begingroup$ Well, I did not fail the question, because I did not take the exam. I'm not the OP, I'm just confused by the way the question is asked. And for that matter, I am well aware that definitions are important in biology, as in every other field of science. $\endgroup$ – Flo Mar 9 '17 at 22:43
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    $\begingroup$ Without explicitly demonstrating the virus in a polar bear or rhinoceros, how would the statement "a virus has more than one host species" lead you to assume a polar bear or a rhinoceros can be infected? Why not bobcats or barn owls? That requires more data than this question provides, and here's the actual paper being referenced (1, 2). You can see how they can make that assumption, QED. $\endgroup$ – CKM Mar 10 '17 at 14:55

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