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By Dr. Priyom Bose, Ph.D. Reviewed by Danielle Ellis, B.Sc.

What happens after HIV infection?
Evolution of HIV diagnostic assays
Conclusions
References
Further reading

Acquired immunodeficiency syndrome (AIDS) is caused by the human immunodeficiency virus (HIV) that attacks the body’s immune system, making it vulnerable to all infections. One of the major concerns of the early AIDS epidemic that began in 1981 was the lack of proper diagnostic measures to identify infected individuals.1 Since the development of the first HIV diagnostic assay in 1985, scientists have continued to improve diagnostic accuracy, detection speed, and cost.

Image Credit: Hanna Karpiak/Shutterstock.com What happens after HIV infection?

The immune system produces antibodies after encountering harmful foreign substances or antigens. HIV infects the vital cells associated with immunity, such as macrophages, helper T cells, and dendritic cells, and disrupts their function. The three important HIV antigens are p24, gp 41, and gp 120.2

HIV is a slow-replicating retrovirus that is transmitted through sexual intercourse, sharing an infected needle, or by blood transfer.3 After HIV infection, the viral load cannot be measured immediately due to low plasma load. Typically, the viral RNA can be measured within 10 to 12 days after infection.4

Antibodies to p24 and gp 41 are the first serological markers used to detect HIV infection. IgG antibodies appear approximately three weeks after infection. In the majority of HIV-infected individuals, HIV antibodies appear to circulate within 1 to 2 months of the infection. However, in a few cases, it may take up to six months to appear at a detectable level.5 Evolution of HIV diagnostic assays

Over the years, scientists have developed many immunoassays and nucleic acid amplification tests (NAATs) to accurately and high-throughput HIV diagnosis. These tests are broadly divided into two categories, namely, screening and confirmatory tests. Typically, HIV tests are performed on blood, oral fluids, or urine samples.6

HIV screening is performed by various immunoassays that focus on detecting IgG antibodies against HIV-1 antigens in the serum. Techniques such as Western blot, line immunoassay (LIA), and recombinant immunoblot are used as confirmatory tests.7 Some of the important HIV diagnostic assays are discussed below: Serological testing for HIV

In the mid-1980s, simple serological tests for HIV antibodies were developed based on culture-derived viral antigen preparation.7 These tests enabled HIV diagnosis and assessed blood and blood product supplies. Since the early assays, various serological assays have been developed that aided simple/rapid testing, high-throughput screening, confirmatory tests, incidence determination, and epidemiological surveillance. Since its first development, five generations of enzyme immunoassays (EIAs) have emerged based on varied antigen preparations and detection chemistries.8

First-generation assays: The first-generation EIAs detect IgG antibodies from antigens derived from whole viral lysates of HIV-positive cultures. Since crude antigen lysate contains impurities, this method exhibited reduced specificity and high false positivity. In contrast, immunofluorescence assays or Western blotting (WB) have shown higher specificity and lower false positivity.

Second-generation assays: Second-generation assays involve the use of recombinant proteins or synthetic peptides derived from the immunodominant regions (IDR) of HIV-1 proteins and gp36 of HIV-2, which increases sensitivity and decreases false positivity.

Third-generation assays: Third-generation assays, including the Genetic Systems HIV-1/HIV-2 Plus O EIA, use a variety of antigens to detect HIV-1 and -2 antibodies in the serum. A major advantage of third-generation sandwich format assays is their ability to detect HIV-1 IgM antibodies early, enabling quicker HIV diagnosis.

Fourth-generation assays: The fourth-generation EIAs, including the Abbott Architect HIV Ag/Ab Combo assay, utilize fully automated chemiluminescent microparticle technology that can instantaneously identify antibodies to HIV-1 and HIV-2 and HIV-1 p24 antigen. This technique has further allowed early HIV diagnosis. Other advantages of fourth-generation high-throughput assays are their capacity to perform more than 150 tests per hour and their ability to test specimens immediately upon arrival and generate results within 30 minutes.  These assays are suitable for facilities, such as blood banks, that handle high volumes of blood samples.

Fifth-generation assays: Fifth-generation assays, such as the Bio-Rad BioPlex 2200 HIV Ag-Ab assay, use magnetic beads coated with p24 monoclonal antibodies and epitopes specific for HIV-1 and HIV-2. This type of assay has a major advantage in  that it can confirm HIV infection in a single test. Interested in Assay Kits? Explore Equipment Here

Despite the advancements in EIA assays, the challenges associated with the generation of false positive results persist. Therefore, EIA-reactive specimen is typically retested with supplemental tests, such as Western Blot. Rapid diagnostic tests Related StoriesSweden exceeds UNAIDS HIV goals but faces new challengesNutrition's pivotal role in combating tuberculosis: addressing N-AIDS for better outcomes

The first HIV rapid test was available in the early 1990s. It determined an individual's serostatus before surgery, maternal labor/delivery, and organ transplant. Rapid diagnostics is based on immunochromatographic technology that uses blood from finger pricks to assess HIV status. 9 This test can provide results in less than 30 minutes and can be used in point-of-care (POC) settings. Since this test presents both false positive and negative results, it is essential to confirm the findings with laboratory-based HIV assays.

The main advantage of this technique is that any non-laboratory staff can perform it in a primary health care center. Even though decentralization of HIV diagnostic services has increased HIV test service in remote areas, it has been challenged by the lack of national guidelines, waste disposal, inventory management, and quality assurance (QA) monitoring.10

HIV self-testing, based on rapid testing methods, has allowed individuals who would otherwise refrain from testing in fear of discrimination to perform the test privately and start proper intervention. The World Health Organization (WHO) has prequalified several HIV rapid tests for HIV self-testing, including the Insti HIV-1/HIV-2 antibody tests and the Oraquick rapid HIV-1/2 antibody test.10 Nucleic acid test (NAT)

The NAT identifies HIV nucleic acid, i.e., either RNA or proviral DNA, in the blood sample. This test is based on the principles of polymerase chain reaction (PCR), nucleic acid sequence-based amplification, or ligase chain reaction.11 This test has proved to be vital in situations when an antibody against HIV is absent in serum. NAT is also performed in newborns of HIV-infected mothers. Unlike other assays, this test can detect HIV even after recent or possible exposure to the virus. Furthermore, NAT can quantify viral load.

Revolutions in Infectious Disease Testing Conclusions

The advancements in HIV diagnostic assays have played a vital role in identifying, staging, and monitoring infected individuals, even when they are under antiretroviral therapy. These assays have played an important role in surveillance and identification of transmission hot spots. Extraordinary progress in HIV testing methodologies has not only reduced false positives but decreased assessment time as well. References Sharp PM, Hahn BH. Origins of HIV and the AIDS pandemic. Cold Spring Harb Perspect Med. 2011;1(1):a006841. doi: 10.1101/cshperspect.a006841. Foster JE., et al. Viruses as Pathogens: Animal Viruses, With Emphasis on Human Viruses. Viruses. 2018; 157-187. doi.org/10.1016/B978-0-12-811257-1.00007-3 Dasgupta A, Wahed. Human immunodeficiency virus (HIV) and hepatitis testing. Clinical Chemistry, Immunology and Laboratory Quality Control (Second Edition). 2021; 513-533. doi.org/10.1016/B978-0-12-815960-6.00015-7 Konrad BP, et al. On the duration of the period between exposure to HIV and detectable infection. Epidemics. 2017; 20, 73-83. doi.org/10.1016/j.epidem.2017.03.002 Davis LE. Acute viral meningitis and encephalitis. Infections of the Nervous System, 1987; 156-176. doi.org/10.1016/B978-0-407-02293-5.50014-3 Pant PN. Oral fluid-based rapid HIV testing: issues, challenges and research directions. Expert Review of Molecular Diagnostics. 2007; 7 (4), 325-328, DOI: 10.1586/14737159.7.4.325 Abdullah DM, et al. The contemporary immunoassays for HIV diagnosis: a concise overview. Asian Biomed (Res Rev News). 2023;17(1):3-12. doi: 10.2478/abm-2023-0038. Alexander TS. Human Immunodeficiency Virus Diagnostic Testing: 30 Years of Evolution. Clin Vaccine Immunol. 2016;23(4):249-53. doi: 10.1128/CVI.00053-16. Aidoo S, et al. Suitability of a rapid immunochromatographic test for detection of antibodies to human immunodeficiency virus in Ghana, West Africa. J Clin Microbiol. 2001;39(7):2572-5. doi: 10.1128/JCM.39.7.2572-2575.2001. Parekh BS, et al. Diagnosis of Human Immunodeficiency Virus Infection. Clin Microbiol Rev. 2018;32(1):e00064-18. doi: 10.1128/CMR.00064-18. Garrett, P. E. Quality control for nucleic acid tests: Common ground and special issues. Journal of Clinical Virology. 2001; 20(1-2), 15-21. doi.org/10.1016/S1386-6532(00)00150-5

Further ReadingAll HIV ContentThe Economic Impacts of AIDSRecent Advancements in Treating HIV

Last Updated: Nov 29, 2024

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BYD takes the spotlight in the heart of Europe after sales surge by +750% in April

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BYD takes the spotlight in the heart of Europe after sales surge by +750% in April

China’s EV leader is quickly making a name for itself in Europe. In April, BYD outsold Tesla in Germany and the UK as sales surged in the region. With new models on the way, this looks to be just the start of BYD’s global sales run.

BYD sales outpace Tesla in Germany and the UK in April

BYD is like a freight train right now. There’s no slowing its roll. The company sold over 380,000 new energy vehicles (NEVs) last month, up 21% from April 2024.

Like most Chinese automakers, BYD reports NEV sales, or electric (EV) and plug-in hybrid (PHEV) vehicles. Since it stopped making gas-powered cars in 2022, BYD has focused entirely on EVs and PHEVs. So far, it has paid off.

For the first time in over a year, BYD’s electric vehicles outsold its plug-in models. Last month, the company sold over 195,000 electric cars (+45% YOY) and nearly 176,000 (+0%) PHEVs.

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Although its EVs got most of the attention, BYD sold over 79,000 vehicles overseas last month, its fifth straight month of growth. Through April, the company has sold over 285,000 vehicles in overseas markets, more than doubling from last year.

BYD-sales-Germany-April
BYD launches Sealion 7 smart electric SUV at 2024 Paris Motor Show (Source: BYD)

According to the latest sales numbers released by the German federal road traffic agency, KBA, BYD even outsold Tesla in Germany, Europe’s largest auto market.

BYD sold 1,566 vehicles in Germany last month, an over eightfold (+756%) increase from April 2024. In comparison, Tesla’s sales fell 46% with just 855 cars sold in Germany last month.

BYD-sales-Germany-April
Michael Shu, Managing Director of BYD Europe, speaks at the IAA (Source: BYD)

Closing the gap in Europe

Through the first four months of 2025, BYD sold 2,791 vehicles (+385%) in Germany, while Tesla remains ahead at 5,820 (-60%).

And it’s not just in Germany. BYD outsold Tesla in the UK last month as well. Data from SMNT shows BYD sold 2,511 vehicles in April 2025. Tesla only sold 512 vehicles in the UK last month.

BYD-overseas-EV-sales
BYD’s wide-reaching electric vehicle portfolio (Source: BYD)

BYD is quickly closing in on Tesla in the UK. Through April, BYD sold 11,782 vehicles while Tesla’s sales reached 12,986 vehicles.

Will China’s EV leader overtake Tesla in Europe? With several new vehicles rolling out, BYD is poised to see even more demand later this year. After launching its luxury Denza brand last month, BYD’s cheapest EV, the Seagull, is set to arrive later this year.

BYD-Seagull-EV
BYD Seagull EV (Dolphin Mini) Source: BYD

BYD will launch the low-cost EV later this year in Europe under the name Dolphin Surf with prices starting under £20,000 ($26,000). In China, the Seagull starts at under $10,000 (69,800 yuan) and was BYD’s top seller last month with over 55,000 units sold.

According to forecasts from S&P Global Mobility, BYD’s sales are expected to double in Europe from 83,000 last year to 186,000 in 2025. By 2029, that number could reach upwards of 400,000.

As it looks to drive growth this year, BYD is aggressively expanding overseas. BYD’s fourth car transport ship, the “BYD Shenzhen,” officially set sail last week with enough room for 9,200 vehicles. It is now the world’s largest.

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Game-changing Lectric XP4 next-gen electric bike launched, shocking industry once again

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Game-changing Lectric XP4 next-gen electric bike launched, shocking industry once again

In true Lectric style, North America’s largest e-bike company just unveiled the latest generation of its best-selling electric bike in a high-energy, adrenaline-fueled product launch this morning. The Lectric XP4 is the newest generation of the ultra-popular e-bike line, and once again brings a shocking level of upgrades at price points never before seen in the industry.

To put it simply, Lectric has done it again; they’ve absolutely crushed it and set a new high watermark for value in the US folding e-bike market.

The XP line is the best-selling electric bike in the US, so this was bound to be a hotly-anticipated launch. With roughly 1 out of every 10 electric bikes sold in the US being a Lectric XP (out of many hundreds of models available in the market), any new launch in the product line was set to grab eyeballs. And despite the extremely high expectations, Lectric appears to have risen to not only meet them but likely exceed what most could have expected at this price point.

The launch of the new XP4 actually includes a pair of launches, with the base 500W model offering the same $999 price tag we’ve come to know ever since the XP 2.0 days. A new long-range XP4, which swaps the 10.4Ah battery for a massive 17.5Ah battery and upgrades the motor to 750W, bares only a slightly higher $1,299 price tag.

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“Because this model is so important to us and our riding community, we were determined to hold the line on price,” said Lectric eBikes co-founder and CEO Levi Conlow. “While other e-bike companies continue to raise prices and launch new products at higher price points, we know riders are going to appreciate Lectric going against the grain and making huge improvements for the same entry price we set more than four years ago.”

Levi isn’t paying lip service there, either. Both models share a number of key upgrades covering everything from the hardware design to the included componentry, and even the riding feel.

Both models include a new in-house designed torque sensor, offering smoother and more responsive pedal assist across the full range of power levels. A new 56-tooth chainring is larger and provides a more comfortable pedal cadence at higher speeds, meaning those taking advantage of the Class 3-capable 28 mph (45 km/h) speed can do so without their feet needing to spin uncomfortably fast.

The handlebars now feature an upgraded TFT color display with a built in USB-C port for phone and device charging. Having personally tested the e-bike yesterday, I can attest to just how beautifully designed the TFT screen truly is, providing much more information to the rider yet in a neatly laid out way that keeps it clear and easy to read, even in bright sunlight.

My full first ride experience will be coming soon, but first let’s continue with what makes these models so new and innovative.

The frame has been redesigned with a novel rack setup, a larger main frame tube to accommodate the longer-range battery, and a new handlebar stem that provides a more comfortable reach in the cockpit. That rear rack adds to both the bike’s appearance and utility, providing a color and styling accent but also offering more compatibility for accessories mounted to its round tubes while still maintaining the boxier tubes consistent with the design legacy across the XP models’ successive frames.

New hydraulic disc brakes were developed specifically for Lectric and provide punchier stops than the previous version’s hydraulic disc brakes. The brakes’ model number of 602 even pays subtle homage to the area code in Phoenix, Lectric’s headquarters.

The transmission also received an upgrade, with the lower tier 7-speed Tourney derailleur getting replaced with a step up in Shimano’s hierarchy to an 8-speed Altus.

Other hardware improvements on the bike include the quick-release pedals, which have been redesigned, increasing the quality and making them easier to use. The new derailleur is matched with new trigger shifters on the right side of the handlebars paired with Lectric’s upgraded locking ergonomic bar ends. The new shifters and bar ends required a new throttle though, resulting in an updated left-side paddle-style thumb throttle.

The lighting on the XP4 has also been upgraded, now including rear turn signals.

The keyway for locking the battery has been relocated to the non-drive side of the main tube, making it easier to access, and is located next to a newly designed cover for the charging port and on/off button for the battery.

Like all of Lectric’s e-bikes, the XP4 is compliant with UL2849, and the two battery sizes are both compatible with a 5A fast charger that provides a full recharge in either 2 or 3.5 hours for the smaller or larger battery option.

New 20×3.0 tires include a mixed-terrain tread with a novel design that creates a smoother center patch for quieter riding on smooth surfaces like asphalt but retains enough knobbiness on the edges for better grip in off-road riding conditions. The tires’ quiet ride has been specifically designed to complement the ultra-quiet Stealth motor that Lectric has brought from its other models to the new XP4.

Unlike the XP 3.0 that had previously been available in just white or black, the new XP4 comes in multiple color options, a nod to customers who often asked the company for more variety in colorways. The XP4 now includes color options of Stratus White, Tempest Gray, Raindrop Blue, and Pine Green. The bike is also available in two frame styles of standard and step-over.

Pre-orders are now open for the XP4, priced at either $999 or $1,299 for the 500W and 750W versions, with shipping expected to begin next month.

Electrek’s Take

It’s hard to overstate how big of a deal the XP4’s launch is, especially considering that the starting price has remained the same affordable $999. At a time when tariffs are forcing other companies to increase prices, the XP4 stands head and shoulders above other folding e-bikes in the US market, not just on price but also on features.

If you take the $1,299 long-range version with the 750W motor and 840Wh battery, it’s easy to see how far ahead it is of the competition. If the only thing Lectric had done was put that big battery and torque sensor in it, the bike already would have surpassed any other leading brand’s folding e-bike on value. There just isn’t another torque sensor-based 840Wh folding e-bike out there at this price point. But then Lectric went so much further. All of the additions are like a mountain of cherries on top of an already alluring XP4 sundae. From the beautiful new TFT display to the super punchy new brakes, from the upgraded derailleur to the quieter tires and motor, from the easy-to-use quick-release pedals to the improved ergonomics of the handlebars – it’s just more heaped on top of more.

The one feature I wish they would have included would have been Apple FindMy integration to allow for easy tracking of a lost or stolen e-bike. Trust me, I tried to plant the bug in Lectric co-founder and Chief Innovation Officer Robby Deziel’s ear, but to no avail. Oh well, maybe but there’s still hope for including location tracking on the XP5.

There’s one thing for sure though: Everyone else is still competing for second place against Lectric. That’s nothing new, but now the gap between Lectric and others has continued to grow. There was already no better option when it comes to bang-for-your-buck in the folding e-bike space, and now Lectric has grown that value gap even further.

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Amazon’s Zoox robotaxi unit issues software recall after recent Las Vegas crash

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Amazon's Zoox robotaxi unit issues software recall after recent Las Vegas crash

A Zoox autonomous robotaxi in San Francisco, California, US, on Wednesday, Dec. 4, 2024. 

David Paul Morris | Bloomberg | Getty Images

Amazon‘s Zoox issued a software recall for 270 of its robotaxis after a crash in Las Vegas last month, the company said Tuesday.

The recall surrounds a defect with the vehicle’s automated driving system that could cause it to inaccurately predict the movement of another car, increasing “the risk of a crash,” according to a report submitted to the National Highway Traffic Safety Administration.

Zoox submitted the recall after an April 8 incident in Las Vegas where an unoccupied Zoox robotaxi collided with a passenger vehicle, the NHTSA report states. There were no injuries in the crash and only minor damage occurred to both vehicles.

“After analysis and rigorous testing, Zoox identified the root cause,” the company said in a blog post. “We issued a software update that was implemented across all Zoox vehicles. All Zoox vehicles on the road today, including our purpose-built robotaxi and test fleet, have the updated software.”

Zoox paused all driverless vehicle operations while it reviewed the incident. It’s since resumed operations after rolling out the software update.

Read more CNBC Amazon coverage

Amazon acquired Zoox in 2020 for over $1 billion, announcing at the time that the deal would help bring the self-driving technology company’s “vision for autonomous ride-hailing to reality.” However, Amazon has fallen far behind Alphabet‘s Waymo, which has robotaxi services operating in multiple U.S. markets. Tesla has also announced plans to launch a robotaxi offering in Austin in June, though the company has missed many prior target dates for releasing its technology.

Zoox has been testing its robotaxis in Las Vegas, Nevada, and Foster City, California. Last month, Zoox began testing a small fleet of retrofitted vehicles in Los Angeles.

Last month, NHTSA closed a probe into two crashes involving Toyota Highlanders equipped with Zoox’s autonomous vehicle technology. The agency opened the probe last May after the vehicles braked suddenly and were rear-ended by motorcyclists, which led to minor injuries.

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