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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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UK-US pact neither a free-trade agreement nor broad trade deal of Brexiteer dreams

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UK-US pact neither a free-trade agreement nor broad trade deal of Brexiteer dreams

Sir Keir Starmer was at home in Downing Street, watching Arsenal lose in the Champions League, when he got a call from Donald Trump that he thought presented the chance to snatch victory from the jaws of trading defeat.

The president’s call was a characteristic last-minute flex intended to squeeze a little more out of the prime minister.

It was enough to persuade Sir Keir and his business secretary Jonathan Reynolds, dining with industry bosses across London at Mansion House, that they had to seize the opportunity.

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The result, hurriedly announced via presidential conference call, is not the broad trade deal of Brexiteer dreams, and is certainly not a free-trade agreement.

It’s a narrow agreement that secures immediate relief for a handful of sectors most threatened by Mr Trump’s swingeing tariffs, with a promise of a broader renegotiation of “reciprocal” 10% tariffs to come.

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‘A fantastic, historic day’

Most pressing was the car industry, which Mr Reynolds said was facing imminent announcements of “very difficult news” at Britain’s biggest brands, including Jaguar Land Rover, which sounds like code for redundancies.

In place of the 25% tariffs imposed last month, a 10% tariff will apply to a quota of 100,000 vehicles a year, less than the 111,000 exported to the US in 2024, but close enough for a deal.

It still leaves the car sector far worse off than it was before “liberation day”, but, with one in four exports crossing the Atlantic, ministers reason it’s better than no deal, and crucially offers more favourable terms than any major US trading partner can claim.

For steel and aluminium zero tariffs were secured, along with what sounds like a commitment to work with the US to prevent Chinese dumping. That is a clear win and fundamental for the ailing industries in Britain, though modest in broad terms, with US exports worth only around £400m a year.

US and UK announced trade deal
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US and UK announced trade deal

In exchange, the UK has had to open up access to food and agricultural products, starting with beef and ethanol, used for fuel and food production.

In place of tariff quotas on beef that applied on either side (12% in the UK and 20% in America) 13,000 tonnes of beef can flow tariff-free in either direction, around 1.5% of the UK market.

The biggest wins

Crucially, sanitary and phytosanitary (SPS) production standards that apply to food and animal products, and prevent the sale of hormone-treated meat, will remain. Mr Trump even suggested the US was moving towards “no chemical” European standards.

This may be among the biggest wins, as it leaves open the prospect of an easing of SPS checks on trade with the European Union, a valuable reduction in red tape that is the UK’s priority in reset negotiations with Brussels.

Farmers also believe the US offers an opportunity for their high-quality, grass-fed beef, though there is concern that the near-doubling of ethanol quotas is a threat to domestic production.

Technology deals to come?

There were broad commitments to do deals on technology, AI and an “economic security blanket”, and much hope rests on the US’s promise of “preferential terms” when it comes to pharmaceuticals and other sectors.

There was no mention of proposed film tariffs, still unclear even in the Oval Office.

Taken together, officials describe these moves as “banking sectoral wins” while they continue to try and negotiate down the remaining tariffs.

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The challenge from here is that Mr Trump’s “reciprocal” tariff is not reciprocal at all. As commerce secretary Howard Lutnick proudly pointed out in the Oval Office, tariffs on US trade have fallen to less than 2%, while the UK’s have risen to 10%.

As a consequence, UK exporters remain in a materially worse position than they were at the start of April, though better than it was before the president’s call, and for now, several British industries have secured concessions that no other country can claim.

From a protectionist, capricious president, this might well be the best deal on offer.

Quite what incentive Mr Trump will have to renegotiate the blanket tariff, and what the UK has left to give up by way of compromise, remains to be seen. Sir Keir will hope that, unlike the vanquished Arsenal, he can turn it round in the second leg.

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Why Ukraine’s European allies will be nervously watching VE Day events in Red Square

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Why Ukraine's European allies will be nervously watching VE Day events in Red Square

Donald Trump has a soft spot for military spectacles and autocrats.

He will be looking on with envy as Vladimir Putin parades both in Moscow today, with Chinese leader Xi Jinping flying in to join Victory Day events in Red Square.

European allies of Ukraine will be watching nervously, wary of anything that could upturn the delicate quest for peace.

President Trump‘s patience with peddling his much vaunted “peace deal” has been wearing thin and allies had feared Ukraine could be punished for it.

That would have been grotesquely unfair, of course. Ukraine has bent over backwards to accommodate Mr Trump’s one-sided diplomacy that has so far seemed to favour the aggressor in this obscene war.

Russian army soldiers marching during a dress rehearsal for Victory Day parade in St. Petersburg on 7 May. Pic: AP/Dmitri Lovetsky
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Pic: AP

True, the Trump proposal does not agree to Russian annexation of all the land already taken by force and stops short of ordering the complete demilitarisation of Ukraine, but otherwise the proposals are pretty much everything that Moscow has asked for.

The deal is being pushed by Steve Witkoff, Mr Trump’s golf partner turned chief negotiator, a man regarded by diplomats as out of his depth and lost in the rough when it comes to the arts of statecraft.

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Like his president, Mr Witkoff has a history of doing business with Russian oligarchs, an apparently starry-eyed view of the Russian leader and has called Ukraine a “false country”.

Moment of truth approaching

Mr Witkoff and Mr Trump have so far given Mr Putin the benefit of the doubt, but a moment of truth is approaching. While Ukraine has agreed to a longer ceasefire in principle, Mr Putin will not.

Ukraine’s European allies feared that Mr Trump was about to despair of progress, blame Ukraine and take US military support with him.

Then came the minerals agreement between the US and Ukraine. The breakthrough gave the US president something to show for his efforts and assuaged his desire for some kind of deal. He seems to have moved on for now, at least, and approved the first $50m of arms sales to Ukraine.

Russian Air Force fly over Red Square, leaving trails of smoke in the colors of the Russian national flag during rehearsal. Pic: AP/Alexander Zemlianichenko
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Members of the Russian Air Force fly over Red Square during the rehearsal. Pic: AP

But these remain a tense few days ahead with plenty at stake.

Mr Putin’s self-declared three-day ceasefire raises the spectre paradoxically of escalation if either side breaks it.

The Russian lull is seen here in Kyiv as little more than a ploy.

If the Russian leader was serious about giving peace a chance, they say, he would have signed up to the permanent ceasefire being proposed by the Trump team.

Besides, Russia broke the last truce in Easter as soon as it had begun and used it to carry out surveillance and reinforcement operations says Kyiv. Why risk another pointless pause that is exploited by the invaders?

Escalation possible

If Russia plays the same games this time and Ukraine retaliates, there could be a significant escalation. Likewise, with any Ukrainian drone attack on Moscow during Victory Day.

Any major flare-up will not be looked on favourably by the US president if it upstages his first trip abroad this presidency, a three-day tour of the Middle East.

For now, his attention is not so much on the Ukraine conflict and he is no longer issuing threats to walk away and stop supporting the Ukrainians.

Russian servicemen march towards the Red Square before Victory Day military parade general rehearsal on 7 May. Pic: AP/Pavel Bednyakov
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Russian servicemen march towards Red Square in the rehearsal. Pic: AP

Read more from Sky News:
Ukraine and Russia accuse each other of breaching ceasefire
Putin prepares to host dozens of world leaders for Victory Day parade

That will be a relief here in the Ukrainian capital. They would be unwise to do anything to reengage him, for now at least.

Their European allies, though, know American involvement in this war appears to be receding.

Can they fill the vacuum?

This week, they remember the sacrifices made to bring peace and security to their continent 80 years ago.

Can they find the political will and unity to do so again, even without America?

Astonishingly, given all we have been through, that is still an open question.

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India will respond ‘in exactly the same light’ if Pakistan retaliates, high commissioner tells Sky News

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India will respond 'in exactly the same light' if Pakistan retaliates, high commissioner tells Sky News

India will respond to any escalation from Pakistan “proportionally and in exactly the same light”, the country’s high commissioner has told Sky News.

Weeks after 26 tourists were shot dead by gunmen in Indian-controlled Kashmir last month, India carried out missile strikes in Pakistan and Islamabad-administered parts of the disputed region.

On Wednesday, India said it hit nine “terrorist infrastructure” sites, while Pakistan said it was not involved in the April attack and the sites were not militant bases.

Pakistan’s Prime Minister Shehbaz Sharif has since vowed that India will “now have to pay the price” for their “blatant mistake,” and skirmishes have also been reported along the Line of Actual Control (LAC).

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Speaking to Sky’s The World with Yalda Hakim on Thursday, India’s high commissioner to the UK, Vikram Doraiswami, said “the original escalation is Pakistan’s sponsored terror groups’ attack on civilians”.

India strikes ‘reasonable,’ says high commissioner

He then insisted India’s strikes in Pakistan and Kashmir were “precise, targeted, reasonable and moderate,” adding: “It was focused principally and solely on terrorist infrastructure.

“We made it abundantly clear that the object of this exercise was clearly to avoid military escalation.

“A fact that was actually acknowledged – in a left-handed way of course – by the Pakistani side in terms of their own statements, which said the airspace hadn’t been violated.”

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India awaits Pakistan’s response

Pakistan chose ‘to escalate the matter’

The high commissioner also said about claims Pakistan shot down Indian aircraft with Chinese-made fighter jets: “If it satisfies Pakistan’s ego to say that they’ve done something, they could have used that as an off-ramp to move on.

“Clearly they’ve chosen not to, and they’ve chosen to escalate the matter.”

A boy collects papers from the debris of a residential house damaged by a cross-border shelling in Gingal village near the Line of Control (LoC) between India and Pakistan, in Indian Kashmir's Baramulla district, May 9, 2025. REUTERS/Stringer
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A boy collects papers from the debris of a damaged house in Gingal village. Pic: Reuters

And when asked about Pakistan’s threats of retaliation, Mr Doraiswami said: “We’re not looking for an escalation, but if Pakistan responds, as we have done, we will respond proportionally and in exactly the same light.”

He then referenced the border skirmishes, saying: “I do want to remind everybody: For the last 15 days, they’ve also opened artillery fire along the Line of Actual Control… That’s led to civilian casualties.”

Read more:
The story of India and Pakistan’s deadly conflict
How India and Pakistan’s militaries match up

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It comes after India said Pakistan attacked its military stations in the Kashmir region with drones and missiles on Thursday.

The country’s defence ministry said stations at Jammu, Pathankot and Udhampur were “targeted by Pakistani-origin” weapons, and added “the threats were swiftly neutralised”.

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