Overview

Requirement Definition

To detect the risk of avian influenza infection, it would, of course, be ideal to directly sense the presence of the influenza virus within the poultry farm. Detectable evidence of the virus could be the proteins or nucleic acids it leaves behind.

A lateral flow test, which uses mucus collected from humans or suspect chickens, is a simple and rapid method that is actually widespread for detecting viral proteins, indicating whether a person or chicken is infected with influenza. In this test, antibodies against the viral protein attach to secondary antibodies on a control line, making the influenza virus detectable through visible results. However, such a simple test requires a relatively high concentration of viral protein for detection. It is not practical to routinely collect mucus from chickens on a farm to continuously perform this type of test.

Unlike proteins, nucleic acids can be amplified from a minuscule amount using methods like PCR, making them detectable. By collecting the influenza RNA contained in tiny airborne water droplets within the poultry house, amplifying it, and then testing it, we could estimate the risk of avian influenza spread. When detecting RNA, unlike direct protein detection, numerous steps are required, from nucleic acid extraction to amplification. However, if the steps following extraction are performed externally, the on-site burden at the poultry farm can be minimized. The device would only need to automatically collect the RNA from the air. Furthermore, the DETECTR method [2] can be considered for detecting the amplified RNA. In the DETECTR method, CRISPR-Cas12a recognizes and cleaves the target sequence, which in turn causes collateral cleavage of nearby single-stranded DNA reporters, leading to a recognizable signal indicating the presence of the target RNA. In fact, systems using this approach to detect viruses have been established [3] and may hold high potential as a rapid and accurate detection method. Similarly, the CRISPR-Cas3 system [4], which also uses a CRISPR-Cas system, might be applicable. [a] This method also holds the potential for rapid and highly specific detection of influenza.

Based on the above, the device we are attempting to create is one that automatically collects airborne viral RNA within a poultry farm. The necessary performance characteristics for creating a filter that can easily and consistently collect viruses at the farm site are summarized as follows:

• High Virus Collection Efficiency
  It must collect minute amounts of airborne influenza virus.
• Durability and Low Maintenance
  A simple mechanism for virus collection is preferable.
• Low Cost
  Even if we use a filter to collect the virus, we want to keep the running costs down.
• Simple Operation
  To avoid adding to the burden on farm workers, the operation should be simple and self-contained.

Design & Methods

The overall concept for the filter we have created is as follows: Ambient air passes through a narrow channel where it is cooled, causing fine airborne water droplets (condensation) to be collected [b] [c]. The virus is then collected by filtering out the viruses contained within these water droplets.

For instance, consider using this filter inside a poultry house with an ambient temperature of 25°C and 50% humidity, where the air passing through the cooling unit (described later) is cooled to 10°C. Assuming the filter circulates 2 L of air per minute (120 L per hour).

Based on Tetens' equation (or August-Roche-Magnus equation based on Tetens' parameters) for saturated vapor pressure e(t) = 6.1078 × 10^{(7.5T/(T+237.3))}, the amount of water expected to condense in 4 hours is approximately 0.50 g.

The possibility of detecting airborne viruses exists if viruses or their fragments are present in the 0.50 g of water collected in a single cycle.

While this device uses chilled water to cool the air, using a compressor to absorb heat and cool the air down to nearly 0°C could collect approximately 1.6 g of water in a single cycle under the same assumptions as above—about three times the volume.

The filter we created operates on a five-hour cycle. For the first four hours, the filter takes in outside air and collects fine water droplets in the air by cooling. After circulating the outside air for four hours, the filter then circulates the accumulated water derived from the outside air for 30 minutes. It is expected that the water contains viruses. The accumulated water is filtered, and the viruses are collected on the filter. It is considered good to use a high-performance filter such as N100 so that virus particles and their fragments can be collected as completely as possible. Since it is used in water, oil resistance will not be necessary. In the last 30 minutes, the filter stops. During this 30-minute period, the user collects the viruses that have been collected inside the filter. In this process, the user only needs to operate the filter and collect the viruses collected in the filter after four and a half hours, so the series of operations is hardly a burden at the poultry farm site.

In addition, the advantage of first collecting water and then filtering the water instead of filtering the air directly is that it may be possible to improve the virus collection efficiency by using molecules that strongly adsorb viruses only in water.

The filter we created consists of three major sections. The first is the upper section of the filter, where outside air is taken in and fine water droplets in the air are condensed and collected by cooling. The second is the section where the fine water droplets in the air, which have been condensed and gathered, are stored and filtered, and viruses and their fragments contained in the fine water droplets in the air are collected. The last section is two pumps outside the filter, which are used to circulate the fine water droplets in the air that have been collected and gathered, and the cooling water for cooling. Here, we explain the design and methods of these three sections respectively.

Upper Section

The Upper Section of the device is composed of three main parts.

The first part is the lid, which has a fan attached to it to draw and push air into the filter unit. The lid is made of transparent polyvinyl chloride (PVC) to allow for easy viewing of the interior.

The second part is the main body of the upper section. This part contains an internal space for collecting the air and an inner water reservoir to hold the water used to wash down the collected condensate (and viruses). Externally, it has an attached water tank for the chilled water used to cool the air. The bottom of this main body is narrowed to ensure that the air passing through is sufficiently cooled. The interior surface is also coated with silicone to help the collected water drain easily.

The third part is the component responsible for cooling the ambient air. A copper tube is spirally wound around this part. As chilled water passes through this copper tube, the air is continuously cooled. This part functions by being screwed and inserted into the hole of the main body of the upper section and connected to the small chilled water tank.

These parts are designed to be easily disassembled, which enhances the ease of maintenance when the device is used in a real poultry farm environment.

Lower Section

The lower section consists of three parts. The first part is designed to store the water that has condensed in the upper section, fallen down, and accumulated. This is the main part of the lower section. A drainage channel is located at the bottom, and the water discharged through this channel is pumped back to the upper section. An exhaust port equipped with a fan allows efficient exhaust.

The main part of the lower section performs both exhaust and drainage. Exhaust is carried out by the fan, and drainage is performed using the pump as the power source. During drainage, viruses are filtered out.

The second part is a screw that corresponds to the first part and firmly secures the filter to it.

This screw corresponds to the drainage hole of the main part of the lower section. It is color-coded with the main part.

The third part is the filter. In poultry farms, the presence of viruses can be inspected by regularly collecting this filter, placing it in an ethanol solution, and outsourcing the analysis. It is also possible to increase virus collection efficiency by attaching antibodies against the influenza virus to the filter. The lower section can be easily separated from the upper section, and the filter can be collected simply by removing the screw.

References