Fighting the ASF disease: Vaccines vs surveillance

African Swine Fever (ASF) continues to reduce the productivity of the swine industry of the country. According to the World Organization for Animal Health (WOAH), the disease has affected several regions of the world including East Asia, exacting “massive losses in pig populations and drastic economic consequences.”  Caused by the ASF virus, the disease can be passed on to other pigs through animal feeds, pork products, and even by the “clothes, boots, wheels, and other materials” used by those, who work in or in the neighborhood of pig farms.

The disease has come in several waves in the Philippines, its first outbreak being in 2019. In 2020, our pig herd was reduced by about 3.08 million heads from a pre-disease inventory of 13.8 million. That sharp drop reflected higher pig mortality due to ASF, boosted by pig farmers depopulating their farms to cut down their respective financial losses to ASF. The first wave of ASF in 2019 cut the number of backyard pig farms by half and commercial farms of the country by 40%, most intensively in the pig-producing Region 3.

In the next two years, outbreaks or spread of the disease had not been observed — it was as if the disease had been effectively contained. But according to one Department of Agriculture (DA) official, that might have been because farmers internalized their management of the diseases to avoid the costly process of following the protocols of the Bureau of Animal Industry (BAI) to contain the disease.

The DA issued regulations on national zoning and pig inventory movements for the prevention and control of ASF¹ and mandatory culling of pigs in red zones, the ground zero of the disease outbreaks². While necessary for animals no longer fit to be consumed and whose movements risk spreading the disease to the rest of the pig population, mandatory depopulation cost pig producers as they cannot recover their costs in raising pigs, despite the subsidy the National Government provides for their losses.

The costlier repercussion of the mandatory depopulation of animals in red zones is that a substantial number of pigs ordered to be culled may turn out to have been healthy pigs and may likely have commanded their normal values in the market. But without accurate information about what pigs deserve to be destroyed and which can still be destined for the market, regulators must lean on avoiding the higher cost of an uncontrolled spread of the ASF virus to the rest of the province or country. Without data, mandatory depopulation of animals in red zones appears to be the less risky move to take.

These regulations are still in place, but somehow the industry has learned how to deal with the costly threat of pig depopulation by abiding by DA’s regulation on how the marketing of pigs must be done to contain the spread of the disease.  According to these protocols, those pigs in no-ASF green zones can be marketed with a clearance, to be issued by authorized laboratories, affirming the absence of the disease.  The clearance allows producers to sell their pigs to the rest of the Philippines.  The clearance is valid for a period of six months.

The pigs in between red and green zones are allowed to be marketed — but only in the province where the animals are raised. This clearance is good for three months.

An equilibrium had descended on the industry, where pig farmers effectively avoided mandatory culling. Reporting of mortalities or of ASF symptoms could be avoided with marketing clearance procedures, whose validity can be questioned. A permit valid for at least three to six months, precludes the possibility that pig mortalities or at least symptoms of ASF were observed in these farms, which must be reported to the BAI. Industry players have been willing to pay a significant amount for getting such marketing clearances to avoid the costlier mandatory culling of pig farms where mortalities had been observed. Accredited private sector laboratories can process applications for these clearances, receiving the clearance fees which run to the tens of thousands of pesos.

Thus, it came to pass that in the two years after the first wave of ASF, the country had seemed to have eliminated ASF. But we did not. In 2022, the second major outbreak of the disease was observed in Iloilo and Negros Occidental. Eventually it spread to Cebu. And that is when we learned that ASF has continued to spread to other parts of the country.

ASF SURVEILLANCE 1.0
I call these protocols to control the ASF virus ASF Surveillance 1.0. Aside from the pig farmers internalizing their observations and responses to the disease to avoid the costly culling of pigs (sick or healthy) in red zones, regulators are ineffectively surveilling the country’s pig farms. LGU biosecurity officers surveille their area weekly to observe clinical signs of the disease, such as sudden death or animals with fever.  Such surveillance, supported by clinical observations, is like regulating the industry blindly.

Nonetheless, if ASF symptoms are observed, the surveillance officials must report these signs to the Province Veterinary Officer, who would organize a task force to undertake a disease investigation to confirm the presence of the virus.  Once confirmed, a wide area around ground zero is declared a red zone and animals may be culled and products derived from the swine restricted to move only within the area.

To confirm the presence of the virus, biological samples are moved from the affected areas to animal disease diagnostic laboratories, which have RT-Polymerase chain reaction (RT PCR). It is prescribed that confirmation be done using RT PCRs.  But this movement of samples can spread the disease to other areas.

There are 12 regional animal disease diagnostic laboratories (RADDL), one ADDL for the National Capital Region (NCR), and seven private laboratories. This forms a bottleneck and raises the cost of trading pork or live pigs. Private commercial farms are complaining about the fees charged by these laboratories, which are reportedly at P35,000. Small farmers would not have the incentive to comply with the regulation with only the few heads that they produce. Furthermore, the owners must wait five to seven days for the results. The lag time can cause the spread of the virus in affected areas.

ASF VIRUS VACCINE
After the spread of the disease in Western and Central Visayas, the BAI refocused its strategy to controlling the disease using the ASF virus vaccine.

The WOAH has advised its members that there is as yet no known effective and stable vaccine for the virus, and that an effective surveillance system continues to be the crucial approach to curtail the spread of ASF and eventually to eradicate the virus. Despite this, the BAI conducted a limited trial of the vaccine in 2024 in partnership with the vaccine’s importer.

The efficacy and safety of the Vietnamese ASF vaccine maybe questionable because the US Department of Agriculture – Animal and Plant Health Inspection Service, which produced the virus strain that was processed into the vaccine in Vietnam, delisted the said ASF strain from its “Selected Regulatory Exclusions List” as these were evaluated to potentially pose a severe threat to animal health and animal products. Despite this, AVAC, the Vietnamese vaccine developer and exporter to the Philippines of the vaccine, continued to process the virus strain and commercialized it globally.

It turns out that AVAC restricted the use of its ASF vaccine to obtain a 92% efficacy. The following are the conditions it should be used under:

1. The pigs to be vaccinated must be ASF Free.

2. The AVAC incubation period is 28 days. There is no guarantee if pigs will get infected before this.

3. Only healthy pigs of four to 10 weeks old may safely be vaccinated.

4. No other vaccines (for other diseases) must be given to vaccinated pigs within two weeks before or two weeks after the 28-day incubation period of the AVAC vaccine.

5. The vaccine must not be used to immunize boars or sows. Either may pass on the virus to their offspring. Sows may likely to have abortions.

The following are some comments/observations shared by a non-Vietnamese user of the AVAC vaccine.

1. Other diseases which were previously controlled or which had vaccines — e.g., PRRS, PCV, mycoplasma — flared up.

2. All the pregnant sows which were vaccinated had abortions and 80% of the sows died after the abortions.

3. ASF deaths before AVAC vaccination came to 1,000 pigs/day; after vaccination the number rose to 5,000 to 8,000/day indicating increased virulence of previous episodes, as well as the flare up of other diseases as mentioned above.

4. DNA analysis done before and after AVAC vaccination revealed the dominance of the AVAC ASF virus strain among pigs that died, not the original strain present before AVAC vaccination.

These concerns about the virus seriously call for a thorough evaluation of the efficacy and safety of the ASF vaccine. The trial conducted by the BAI and the virus importer in 2023 reported that it was successful. It said that there were no mortalities. But with all due respect, there is a conflict of interest in such a trial as it involved the importer. 

It was very helpful that the Chairperson of the Senate Agriculture Committee, Senator Cynthia Villar, conducted a public hearing on ASF in August this year. With it, we were able to focus our attention on the concerns surrounding the vaccine from Vietnam. For months before the hearing, stakeholders had heard about the significant importation of the vaccine, reportedly amounting to 3,000 doses, by a private sector firm. Allegedly, once the Food and Drug Administration issues the importer a Certificate of Product Registry, those doses can be commercially sold to vaccinate the country’s pig inventory.

The committee did urge the players to be extra careful in introducing the vaccine without the necessary evaluation of its safety and efficacy. That put down the introduction of the virus,  but only for a while.

RESUMED INTEREST IN THE ASF VACCINE
The next stimuli for bringing the vaccine into the country was the third major outbreak of ASF, this time in Batangas, the country’s largest provincial pig producer. The DA seemed compelled to pursue the application of the ASF vaccine to finally eliminate, or at least reduce effectively, the incidence of ASF in the country.

Batangas is the largest supplier of pork to the NCR. Because of its port in Batangas City, the province is also an entry point of pigs from the Visayas and Mindanao into the NCR. As of this writing, I gathered that 70% of the provincial pig inventory was killed by the virus or culled to arrest the spread of the disease.

In my view, if the industry and government do not do something smarter than what they are doing now to contain the virus, in the next few months we may observe the end of our once vibrant pig industry. It will puncture the government’s fight against food price inflation. Pork is a major supplier of protein to the population, and we expect pork prices to inflate without our pig industry.

In latest report about the ASF vaccine (to be honest, unverified by me), the DA did a trial of the vaccine on 40 pigs in the town of Lobo, Batangas. Reportedly, 10 of the vaccinated pigs died. This report seemed to contradict an assessment by a DA official whom I texted to find out about its ongoing program to conduct trials on the vaccine in Batangas. According to this official, the report from the field was encouraging toward the use of the vaccine.

If the report about Lobo is verified, a 10% mortality rate linked to the use of the virus is significant. The DA should be extra careful in introducing the vaccine. It may end up destroying the pig industry altogether.

There is even more disturbing information about the vaccine. Reportedly, the DA obtained funding worth P150 million to conduct more trials in other towns of Batangas.  The regulator of the vaccine, the Food and Drugs Administration, issued a certificate of product registry of the ASF vaccine.

These trials do not seem so widespread as to cost the taxpayers over P100 million. Farmers seemed resistant to using the vaccine in their farms, slowing down the implementation of the trials. Farmers had heard about the lack of efficacy and safety of the vaccine. Moreover, the vaccination procedure requires weeks of testing to ensure qualification of the animals to be vaccinated. These disrupted the normal operation of the farms affected, a reason why farmers are not eager to use the vaccine. I am not sure if, despite these concerns, the importation of the vaccines this year had gone through.

Then there is an even more concerning report that in 2025, the vaccine will be deployed to more pig farms in the country. The budget this time is P350 million. I think the DA, which is conducting the vaccine deployment, should be careful as it may end up wasting public money on a program that the industry seems to resist. Vaccines, after all, expire after a period.

What is even more upsetting — if true — is the cost. The DA reportedly is buying each dose of the vaccine at P400, but the price in Vietnam is only about P100. Perhaps the DA must renegotiate its cost to import these vaccines and must import the amount that it can effectively deploy to those farms which are open and ready to using the vaccine.

SURVEILLANCE 2.0
I have a few ideas to improve our surveillance system

1. We must use mobile PCRs or mPCRs to conduct on-site testing, instead of waiting to observe clinical signs of the presence of the virus. Onsite testing generates qualitative results, evidencing the sample tested has or does not have the virus. With this device, we manage the ASF disease by exception. The device can produce onsite results in at most two hours after testing. Only those pigs with positive results are to be confirmed and analyzed for the viral load and virulence of the virus.

2. We must deputize the municipalities/cities to conduct onsite testing. This solves the problem of lack of manpower for surveillance.

3. LGUs deputized to implement the surveillance system may be allowed to charge fees to recover the cost.

4. The provincial LGUs must be deputized to verify positive results of onsite testing in the province with qPCRs, following WOAH protocols. In some provinces like Batangas, the regional animal disease diagnostic labs may serve as verifiers of the disease.

5. Samples of positive results are transported as DNA and not biological form to avoid the spread of the disease.

6. Provincial LGUs must maintain a database of the incidence of the disease in the province.

7. An ICT application is to be developed to send the testing results in real time to the province. This allows a buildup of the data about the disease incidence and allows authorities to know more about the spread of the disease in the province.

¹ See Administrative Circular (AC) No 12 s 2019

² See AC 22 s 2019

Ramon L. Clarete is a professor at the University of the Philippines School of Economics.