Agricultural Shows; a virus' dream?

This week saw the annual event when farmers descend from all parts of Scotland to compare their animals: The Royal Highland Show. I went along and, after a while wandering around the tractors, had a look around the livestock. Looking at the plethora of pampered sheep and cattle, a few things occurred to me. 

First was a half-hearted feeling of 'missed opportunity'. Sheep in particular, but also cattle, had come from across Scotland (and beyond). Imagine if a blood sample of every animal had been taken. Schmallenberg virus (SBV) is known to have reached, and circulated, in Scotland, but nobody knows to what extent. Perhaps testing these animals may have given a cross-section of SBV distribution across Scotland. Maybe even an idea of variation in breed susceptibility; although there's nothing really suggesting that such differences exist.

Show time: a Jacob sheep gets a final trim in the sheep yard prior to showing at the Royal Highland Show.

Second was considering the potential for transmission and dissemination of pathogens across wide geographical areas. In 2001 in the UK the dispersal of Foot and Mouth Disease Virus to various regions was due, at least in part, to the mixing and distribution of sheep from Hexham Market. Agricultural shows represent a similar type of mixing event, and last for days rather than hours. In the case of Foot and Mouth, the clinical signs are mild in sheep, thus allowing infected animals to go unnoticed.

Bringing animals to the show with clinical signs of disease is unlikely to happen as the idea is obviously to show the best animals. That restricts the possibility of infectious animals to those in a pre-clinical incubation stage. However, shows lasting for several days gives sufficient time in which to develop a viraemia and allow transmission, either via direct contact, fomites or vectors. Unsurprisingly there are already studies on the role of agricultural shows. One regarding UK shows (Webb, 2006) revealed competitors at shows to form a large network, with some competitors travelling to shows up to 600 km apart. Clearly there is potential, but thus far nothing seems to have been nailed down showing an outbreak resulting from mixing at agricultural shows.

The impact of time-between shows: the number of days between shows affects the network, no time limit results in a mass network (a) whereas time limits of 14 days (b), 10 days (c) or 7 days (d) reduce the number of nodes, effectively separating shows and breaking links. From Webb 2006.

Third was the zoonotic potential.
It is well established that  cross-species transmission of zoonotic pathogens occurs at the interface between the animal source and humans. These shows represent perfect scenarios for such interactions. Largely absent from the Royal Highland Show were pigs, which have previously been shown to be a source of influenza A infection. Pigs may therefore represent more of a risk due to their ability to sustain various zoonotic agents. Likewise shows where chickens and ducks are present, offering the possibility for the transmission of avian influenza.  

Odd choice: A sheep decides a coat is preferable to hay.

The idea of catching bugs from farm animals at these kind of events, as well as at petting farms for kids etc., is not new. And it is true, infections do happen. The knee-jerk response of a modern nanny state society, at least in the UK, would therefore dictate the banning of such scenarios, including all agricultural shows without question. But this is another case of putting risk into perspective; of all the millions of animals, and the millions of contacts with humans that have happened at these shows over the years, how many infections have occurred, or at least been serious enough to cause alarm? The simple answer: not many. For now though, the relative importance that agricultural shows play in the transmission, evolution and species transfer of viruses remains largely unknown.

Webb, C.R. (2006) Investigating the potential spread of infectious diseases of sheep via agricultural shows in Great Britain. Epidemiol Infect. 134(1)31-40. doi: 10.1017/S095026880500467X

Françoise Barré-Sinoussi visits the Centre for Virus Research

Few stories in virology can have been more frequently or comprehensively covered as the early days of the HIV/AIDS epidemic. Randy Shilts' 'And the Band Played On' is surely one of the most detailed accounts and, whilst massive, provides insights into what went on in the first few years of the epidemic. If you don't fancy reading the book, there's always the resulting film to watch, although it concentrates much more on the heroics of the epidemiologist Don Francis. 

And The Band Played On: Don Francis fights HIV in the face of politics and business.

There are so many aspects discussed both in the book/film and in general about the discovery of HIV as the cause of AIDS, but for me it is the politics which strikes the hardest. The political scene was set for the emergence of a disease like AIDS; a disease emerging largely in sections of society which a conservative government would rather not acknowledge. The original CDC Morbidity and Mortality Weekly Report  MMWR) is rather poignant, now that we know what it represented - I've pasted it at the end (copied from the CDC Website). 

Scientifically, politics became an issue too. A rather bitter rivalry built up between two particular virology groups as everyone raced to figure out the ultimate cause of AIDS. Now it seems obvious that it was a virus attacking T lymphocytes, but at the time things were much more unknown. As an example, one red herring in the early days was poppers/alkyl nitrates as a result of their association with homosexual bathhouses. Ultimately the rivalry ended in dispute as to who had discovered the viral cause of AIDS - something that, in theory, should have taken second place over concentrating on doing something about it. In the end, the French group lead by Luc Montagnier, (as opposed to the US group lead by Robert Gallo) are generally regarded as being the discovers of HIV - the cause of AIDS - and Montagnier won the Nobel Prize in Physiology or Medicine in 2008. Together in receiving the prize was Françoise Barré-Sinoussi. In 1983 Barré-Sinoussi published a paper in Science reporting the isolation of a retrovirus from a suspected patient - effectively reporting the viral cause of AIDS.

The first step was isolating the virus. Cells from a lymph node biopsy from the patient were cultured in growth medium. Samples were taken over several days, and tested for reverse transcriptase (RT) activity (a hallmark of retroviruses). After 15 days they detected RT activity, suggesting a retrovirus was present. When some of the 'infected' cells were mixed with healthy cells, RT activity was again detected, but only after 15 days, therefore suggesting that transmission had occurred. Media without the cells could also infect umbilical cord lymphocytes, and when these were looked at using electron microscopy, viruses could be seen budding from the cells.

HIV budding from the cell membrane

Importantly, Barré-Sinoussi showed that, in addition to isolating a virus with a predilection for human T cells, it was different to the known human T cell leukaemia viruses (HTLV) discovered to that date (largely based upon serum cross-reactivity, but also the fact that this new virus killed the T cells, as opposed to causing cancer in the case of HTLV-I and -II), backing up data that the genetic sequence was distinct from HTLV-I and -II . Altogether the data pointed towards a retrovirus as being behind AIDS. 

Françoise Barré-Sinoussi receives the Nobel Prize for Physiology or Medicine in  2008.

Gallo was at times vilified, some might argue rightly so, but equally his work on T cells and viruses was fundamental towards the ability to isolate the virus in the first place. Thankfully things have placated somewhat and, when he visited the CVR, he gave an interesting talk about his views on what it is going to take to make a good HIV vaccine. My expectation is that Françoise Barré-Sinoussi's story will be equally enthralling.


The following MMRW essentially represents the first report of HIV:

Pneumocystis Pneumonia -- Los Angeles

MMWR 1981;30:250-2 (June 5, 1981)

In the period October 1980-May 1981, 5 young men, all active homosexuals, were treated for biopsy-confirmed Pneumocystis carinii pneumonia at 3 different hospitals in Los Angeles, California. Two of the patients died. All 5 patients had laboratory-confirmed previous or current cytomegalovirus (CMV) infection and candidal mucosal infection. Case reports of these patients follow.

Patient 1: A previously healthy 33-year-old man developed P. carinii pneumonia and oral mucosal candidiasis in March 1981 after a 2-month history of fever associated with elevated liver enzymes, leukopenia, and CMV viruria. The serum complement-fixation CMV titer in October 1980 was 256; in May 1981 it was 32.* The patient's condition deteriorated despite courses of treatment with trimethoprim-sulfamethoxazole (TMP/SMX), pentamidine, and acyclovir. He died May 3, and postmortem examination showed residual P. carinii and CMV pneumonia, but no evidence of neoplasia.

Patient 2: A previously healthy 30-year-old man developed P. carinii pneumonia in April 1981 after 5-month history of fever each day and of elevated liver-function tests, CMV viruria, and documented seroconversion to CMV, i.e., an acute-phase titer of 16 and a convalescent-phase titer of 28* in anticomplement immunofluorescence tests. Other features of his illness included leukopenia and mucosal candidiasis. His pneumonia responded to a course of intravenous TMP/SMX, but, as of the latest reports, he continues to have a fever each day.

Patient 3: A 30-year-old man was well until January 1981 when he developed esophageal and oral candidiasis that responded to Amphotericin B treatment. He was hospitalized in February 1981 for P. carinii pneumonia that responded to oral TMP/SMX. His esophageal candidiasis recurred after the pneumonia was diagnosed, and he was again given Amphotericin B. The CMV complement-fixation titer in March 1981 was 8. Material from an esophageal biopsy was positive for CMV.

Patient 4: A 29-year-old man developed P. carinii pneumonia in February 1981. He had had Hodgkins disease 3 years earlier, but had been successfully treated with radiation therapy alone. He did not improve after being given intravenous TMP/SMX and corticosteroids and died in March. Postmortem examination showed no evidence of Hodgkins disease, but P. carinii and CMV were found in lung tissue.

Patient 5: A previously healthy 36-year-old man with a clinically diagnosed CMV infection in September 1980 was seen in April 1981 because of a 4-month history of fever, dyspnea, and cough. On admission he was found to have P. carinii pneumonia, oral candidiasis, and CMV retinitis. A complement-fixation CMV titer in April 1981 was 128. The patient has been treated with 2 short courses of TMP/SMX that have been limited because of a sulfa-induced neutropenia. He is being treated for candidiasis with topical nystatin.

The diagnosis of Pneumocystis pneumonia was confirmed for all 5 patients ante-mortem by closed or open lung biopsy. The patients did not know each other and had no known common contacts or knowledge of sexual partners who had had similar illnesses. The 5 did not have comparable histories of sexually transmitted disease. Four had serologic evidence of past hepatitis B infection but had no evidence of current hepatitis B surface antigen. Two of the 5 reported having frequent homosexual contacts with various partners. All 5 reported using inhalant drugs, and 1 reported parenteral drug abuse. Three patients had profoundly depressed in vitro proliferative responses to mitogens and antigens. Lymphocyte studies were not performed on the other 2 patients.

Reported by MS Gottlieb, MD, HM Schanker, MD, PT Fan, MD, A Saxon, MD, JD Weisman, DO, Div of Clinical Immunology-Allergy, Dept of Medicine, UCLA School of Medicine; I Pozalski, MD, Cedars-Mt. Sinai Hospital, Los Angeles; Field Services Div, Epidemiology Program Office, CDC.

Barre-Sinoussi, F., Chermann, J., Rey, F., Nugeyre, M., Chamaret, S., Gruest, J., Dauguet, C., Axler-Blin, C., Vezinet-Brun, F., Rouzioux, C., Rozenbaum, W., & Montagnier, L. (1983). Isolation of a T-lymphotropic retrovirus from a patient at risk for acquired immune deficiency syndrome (AIDS) Science, 220 (4599), 868-871 DOI: 10.1126/science.6189183

Tick-borne encephalitis virus....in milk

Based upon the name, Tick-borne encephalitis virus (TBEV) would be expected to be transmitted by ticks. And it appears it is. But it can also be spread by milk/milk products. A recent paper has reported a case in Slovenia where 3/4 people who drank the milk of a goat (later found to be positive for TBEV) became ill. TBEV is a flavivirus and is present in many parts of Europe, with incidence levels in recent years of up to 18.6 cases/100,000 people.

Unpasteurised cheese - a potential source of TBEV infection

Transmission of TBEV in unpasteurised milk hasn't previously been reported in Slovenia specifically, but it was already known that TBEV can be transmitted in raw dairy products. In a recent study, four people had drank unpasteurised colostrum from a goat, three of whom subsequently became sick, having symptoms of fever, malaise, headache, nausea and tremor. Although TBEV RNA couldn't be detected in the blood of any of the three patients, they all had antibodies. IgG and IgM isotypes were detected by ELISA, and the serum was neutralising for the virus. The fourth person, who didn't become ill, had been vaccinated against TBEV and had good antibody titres against TBEV, although IgG titres taken at different intervals suggested they'd received a boost, presumably as a result of drinking the infected milk.

Goats, not sheep seem to be the culprits when it comes to harbouring TBEV in their milk

The authors took samples from the 9 goats and 9 sheep on the farm, and tested them for evidence of TBEV.
Perhaps unsurprisingly, 5/9 goat sera  and 1/4 goat milk samples were positive for TBEV antibodies. The suspect goat whose milk had been drunk prior to the patients becoming sick was also shown to have RNA (indicative of virus) in both the blood and milk, confirming that the goat had evidence of actual viral antigen.

None of the sheep samples were positive, which I find one of the most intriguing points - do ticks prefer goats, or is there species specificity when it comes to TBEV?

According to the authors, drinking unpasteurised milk is fashionable as part of a 'natural lifestyle'. Based upon this paper, the risk of contracting TBEV (as well as other pathogens) would therefore also be part of the natural lifestyle; that's an interesting choice of lifestyle.

Hudopisk, N., Korva, M., Janet, E., Simetinger, M., Grgič-Vitek, M., Gubenšek, J., Natek, V., Kraigher, A., Strle, F., & Avšič-Županc, T. (2013). Tick-borne Encephalitis Associated with Consumption of Raw Goat Milk, Slovenia, 2012 Emerging Infectious Diseases, 19 (5) DOI: 10.3201/eid1905.121442

Schmallenberg virus...where are we at: Part 3. Vaccine time

As Bluetongue virus 8 was making its way to the UK in 2007 I was asked by a farmer whether or not he should vaccinate when the vaccine became available. 100% yes was the answer, and would be now. BTV-8 was a particularly virulent strain, resulting in mass death in sheep and even (unusually for BTV) causing disease and deaths in cattle. Bluetongue had never before been to the UK, so the entire herd was susceptible to the virus. The result was that, whilst East Anglia experienced a few outbreaks in 2007, the vaccine prevented recrudescence of the virus in 2008; unlike what happened on the continent after 2007, where BTV overwintered from 2006 and erupted in 2007 to cause the largest outbreak of BTV in history.

Bluetongue virus did eventually reach the UK, but vaccination stopped it from progressing

This week saw the news that a vaccine for Schmallenberg virus will be available from Merck by the summer. The obvious assumption is that every farmer will be desperate to vaccinate. That would be no surprise considering the damage it's done this past year, in particular to the sheep industry where countless lambs have been lost as a result of the disease.

But the same question now arises - should you vaccinate? This time the situation is very different. We've had it. Would vaccinating now be the equivalent of the metaphorical slamming the stable door after the horse has bolted etc.? If current reports from the continent equate to the UK, then the majority of cows and sheep will be immune, in which case a vaccine might be of limited value. There will however be some naive animals which somehow avoided becoming infected, and once maternal antibody has waned this years offspring will be open to infection.So vaccinate, right?

In the case of human diseases, the choice to vaccinate is generally simple; vaccinate. Similarly, most horse  and pet owners would probably also vaccinate their animals in the face of an emerging disease (assuming a vaccine were available). Farming is different though; farming is to make money. The option to vaccinate is no longer based upon sentimentality, but business. How much do you stand to lose if there's an outbreak, relative to how much it costs to vaccinate when there's only the possibility of an outbreak? In the case of BTV the evidence from the continent was that it would be devastating. The choice to vaccinate was clear.

With SBV however, does it make sense from a business perspective to spend a lot of money to vaccinate the flock/herd? Say 90% of the animals are immune - a reasonable guess based upon studies on the continent. To begin with this level of seroprevalence already makes it more difficult for an outbreak to persist. Ignoring that, and assuming the extent of infection will be the same as last year, 9% of the flock would in theory become infected. If in turn we assume only 10-20% of those infected would be affected clinically, that's only 1-2% of the overall flock/herd.

You're fired: does it make business sense to vaccinate animals when there might not be any need?

In a flock of 1000 animals, 10 animals may be affected. Is that a sufficient number to warrant vaccinating 1000 sheep? Would you vaccinate a herd of 500 cattle on the basis there might be 5 cases of acute disease? Clearly such numbers are approximate, and may be wide of reality, but they're realistic enough to shows there's a difficult choice to make. I can't advise on whether or not to vaccinate, but I do know it's going to be a tricky choice for those involved.

poly(A) messages; lost in translation

From a virus' perspective, how do you translate your own messenger RNA (mRNA), whilst not allowing your host cell to continue manufacturing its own proteins, including those that might be detrimental to virus survival? It's a problem viruses have found various ways to overcome, often by manipulating the biology of the mRNAs, which have the following structure:

The classical polyadenylated mRNA ready for translation

Simply, an eIF4F cap-binding complex binds to the cap and a poly(A) binding protein (PABP) interacts with the poly(A) tail. The PABP in turn interacts with eIF4G of the cap binding complex, thus circularising the mRNA for  efficient translation to occur.

The translation complex showing circularisation enabled by PABP linking the poly(A) tail to eIF4G.

A good way in which to specifically translate viral messenger RNAs is to  make the viral mRNAs different in such a way that viral mRNAs are the most efficiently translated mRNAs. Picornaviruses (e.g. polio, foot and mouth disease) and flaviviruses (e.g. West Nile, Hepatitis C), genomes contain an internal ribosome entry site (IRES), which allows ribosome attachment and subsequent translation in the absence of the 5' cap; get rid of the ability of the cell to translate capped mRNAs and suddenly the viral mRNAs are preferentially translated.

Rotaviruses target the other end. Rotavirus mRNAs all end in a specific sequence ....GACC instead of a poly(A) tail. One of the viral non-structural proteins, NSP3, has been shown to act in similar fashion to PABP; NSP3 specifically binds RNAs ending in this sequence (i.e. rotaviral mRNAs), and also binds the cap-binding complex in place of PABP, but with higher affinity than PABP. The overall result is that polyadenylated mRNAs are outcompeted by rotaviral mRNAs. NSP3 also seems to be responsible for PABP accumulating in the nucleus, where it is unable to translate cytoplasmic mRNAs. Even so, there is evidence that rotaviral mRNA translation appears to be independent of NSP3.

A paper has just come out looking into the location of poly(A), i.e. cellular, mRNAs in rotavirus infected cells.
The first question was, where do you find poly(A) mRNAs in infected cells? Using fluorescence in situ hybridisation (FISH) the authors found poly(A) containing mRNAs to accumulate in the nucleus of cells, thus preventing their translation. Removing NSP3 using RNA silencing prevented this from happening, so that poly(A) mRNAs were then found in the cytoplasm, just as in uninfected cells.

Rotavirus (and NSP3) retain polyadenylated mRNA in the nucleus. Oligo (dT) probes detects polyadenylated (i.e. cell-like) mRNA. Normally the mRNA is distributed throughout the cell (top) in infected cells, signal is only observed in the nucleus (middle row) whereas when NSP3 is silenced, the nuclear block is apparently released (bottom).

Next there is an intriguing finding that, perhaps surprisingly, the untranslated regions (UTRs) of rotaviral mRNAs do not influence how well that particular transcript is translated, as luciferase reporter RNAs with host-cell UTRs were not translated any less efficiently than reporter RNAs with rotaviral UTRs. Most strikingly though, was the fact that the overall efficiency of translation appeared to be enhanced in infected cells, implying that the translation machinery is altered upon infection. These mRNAs were directly transfected into the cytoplasm, which isn't how cellular mRNAs originate. To look at this, the authors used two ways of supplying mRNA to the translation machinery, either directly into the cytoplasm, where they again found it to be more efficiently translated in infected cells, or allowed the cell to transcribe it from a plasmid, in which case they observed a decrease in expression as as result of rotavirus infection. Silencing of NSP3 released this apparent inhibition, with the infected cells appearing more like uninfected cells. Together this all leads to the conclusion that, rather than NSP3 affecting the translation of mRNAs directly, the inhibition of poly(A)-dependent translation is due to a lack of export of newly transcribed RNA.

RNA translation in the presence of Rotavirus: (A) when RNA is  transcribed in the nucleus (and needs to be exported for translation), infection suppresses translation, whereas mRNA transfected into cytoplasm implies that rotavirus infection enhances the translation efficiency of the translational machinery. (B) Suppression of rotavirus NSP3 by RNA silencing removes the block imposed upon protein expression from a plasmid.

The authors checked the location of cellular mRNAs too, and found that they too accumulated in the nucleus of infected cells, whereas in mock-infected cells the mRNAs were found in the cytoplasm. Again, when NSP3 was silenced, this block disappeared.

What happens to the polyadenylated mRNAs which accumulate in the nucleus (alongside the normally cytoplasmic PABP which is also retained in the nucleus)? By looking at the length of the RNAs, and using oligos which target the poly(A) tail, they found that the poly(A) tails were increased in length; an observation in line with data showing that PABP accumulation in the nucleus results in hyperadenylation and nuclear retention of RNAs.

Finally, the authors looked to see whether there were more cellular mRNAs in the nucleus compared to the cytoplasm in infected cells. They found that the cytoplasm of infected cells contained 50% less polyadenylated mRNAs. All of this leads to a scenario in which a translationally very active cytoplasm is (comparatively) free of cellular, polyadenylated mRNAs, into which the virus transcribes masses of its own mRNAs; essentially the viral mRNAs now have the cell's translational machinery to themselves, and all of this apparently orchestrated by NSP3.

As a strategy it makes sense; simply get rid of the host's RNAs.

 Rubio, R., Mora, S., Romero, P., Arias, C., & Lopez, S. (2013). Rotavirus Prevents the Expression of Host Responses by Blocking the Nucleocytoplasmic Transport of Polyadenylated mRNAs Journal of Virology, 87 (11), 6336-6345 DOI: 10.1128/​JVI.00361-13
Piron, M. (1998). Rotavirus RNA-binding protein NSP3 interacts with eIF4GI and evicts the poly(A) binding protein from eIF4F The EMBO Journal, 17 (19), 5811-5821 DOI: 10.1093/emboj/17.19.5811

Gold Rush: what the Hoffman crew face

In the four weeks recuperating with a sling from shoulder surgery there's only so much reading and one-handed typing you can do; enter Gold Rush. I found out about this from a research fellow who's arrived from New York. For anyone not familiar (being British I clearly wasn't), this is a reality TV show on the Discovery  Channel following a team of guys from Oregon who pursue the American dream by heading to Alaska aiming to mine gold, with a slight obsession for a 'glory hole'. Inspirational stuff.

Todd Hoffman (centre) and his team head to Alasksa

At one point, Todd and his crew in Alaska seemed to be having issues with mosquitoes, and these could potentially carry arboviruses, (if there were any there to begin with). The water source was rightly another point of concern; it's clearly not just pure virgin meltwater up there.

Gold mining's a dangerous business: as well as the machinery, Alaska also has plenty of inquisitive bears. There's also the added danger of being in the wilderness. One of the prime causes for virus emergence is generally accepted as being encroachment into thus far untouched environments. Disturbing forests or other   

forms of wilderness bring humans into contact with nature, resulting in opportunities for spillover events to occur. As a fairly recent example, and sticking with the mining theme, miners in Uganda experienced an outbreak of Marburg haemorrhagic fever in 2007. In this case just four miners contracted Marburg virus, a very unpleasant virus related to Ebolavirus. As the authors point out though, as long as you go in the cave/mine without protection from the bat secretions (the suspected source of virus), then you'll be at risk. Is the risk worth it? That's going to very much depend on your perspective; a virologist in Scotland is inevitably going to have a different view than someone depending on the mine for their livelihood.

So Todd, if you feel the need to go prospecting in Africa, watch out for those bats.

Coke, formalin, tea...save your horse from African horse sickness!

African horse sickness (AHS) is arguably the most lethal infectious disease of horses. Like Bluetongue virus, AHS virus is an Orbivirus in the Reoviridae family of dsRNA viruses. Also like BTV (and the bunyavirus Schmallenberg virus), it's an arbovirus that is spread between mammalian hosts by Culicoides midges. 

African horse sickness: the lungs fill with fluid and the horse essentially dies  by drowning.  If a horse develops the pulmonary form of the disease, the likelihood is the horse will die.

After recent experiences of BTV and Schmallenberg virus, it's not an unreasonable question to ask whether AHSV would be capable of a similarly large outbreak in Europe. Spain has previously experienced AHSV, but it's never persisted and spread to the extent of the recent BTV and SBV epizootics in Northern Europe.  Though an outbreak is a possibility, BTV and SBV are viruses of ruminants, particularly cattle and sheep, and whilst the midges which feed on cattle and sheep are competent to transmit these viruses, that's no guarantee that similar dynamics would be seen for AHSV. There are also many more sheep and cattle than there are horses, which would also make an AHSV outbreak harder to establish. Nevertheless, the devastating annual experience of AHSV in South Africa suggests that, given the right conditions, an outbreak could happen. Horse-lovers beware.

What can you do? Vaccination? There are both live attenuated and inactivated vaccines for AHSV, but because demand is low most pharmaceutical companies don't formulate them. The most commonly used are the South African live attenuated strains; unfortunately the efficacy isn't great, and if the horses are vaccinated during the midge season they can result in an outbreak.

That leaves therapy. Unsurprisingly people will try anything to save their horse, including some questionable as well the logical approaches (although I'm no pharmacist). I've come across the following, not all of them recommended by a vet:

• Allergex tablets. 
• Vitamin C.
• Tioctan Vet.
• Phosamine or any other Vitamin B Co-injectable.
• Brewers Yeast (can use 2 teaspoons Marmite 3 x per day as a substitute).
• A good probiotic.
• Himalayan Rock Salt.
• Colloidal Silver, a homeopathy classic
• Coca Cola or liquid molasses added to the water to encourage drinking.
• Hydrogen Peroxide 35% in the drinking water of all horses in the yard. 
• DCA immune booster.
• Immune boosting herbs.
• The AHS herbal treatment kit.
• Bute replacement herbs (containing cortisone).
• Eco-Heal, Eco-Lung and Eco-heart.
• Miracle mineral supplement (MMS).
• Salix.
• Dimethyl sulphoxide (DMSO).
• Solal ribose.
• Infrared lamp.
• Oxygen blanket.
• Bio-Electro-Magnetic_Energy_Regulation (BEMER).
• Sub-cutaneous Dettol injections.
• Essential oils (rubbed between the back legs).
• Rooibos tea.

Coke: for AHSV maybe it works, maybe it doesn't, but it's still bad for their teeth. 

The 'cure' I find most concerning though is the intravenous injection of formalin. This seems to be based on historic rumours rather than anything else; one possibility is apparently that it stops the blood vessels from becoming leaky. On the other hand, it's toxic, and I find it surprising that this would even be considered.

Someone with more knowledge of therapies than me please explain, but looking around there doesn't seem to be masses of scientific support for many of these treatments.

At the end of the day though, I really don't blame the owners. If your horse is infected with a virus which is going to kill >90% of those it infects, surely anything's worth a shot!