Hospitals in Pakistan’s largest city, Karachi, are brimming with chikungunya virus patients.

Major government hospitals throughout the city are reporting 500 to 750 suspected cases of the mosquito-borne disease every day, as noted by local media earlier this month, further straining an already struggling public health system.

But what is chikungunya, how does it spread, and why has it hit Pakistan’s most populous city so badly?

What is chikungunya?

Chikungunya is a viral disease that is spread through the bite of infected Aedes aegypti mosquitos. These mosquitos also carry and spread dengue and the Zika virus.

The name, chikungunya, derives from a word in the Kimakonde language, spoken in Tanzania and Mozambique, meaning “to become contorted”.

How bad is the chikungunya outbreak in Pakistan?

In recent months, severe cases of chikungunya have been reported in Karachi, particularly among elderly patients and those with diabetes, according to a report from Aga Khan University Hospital.

Complications include neurological issues like paralysis and coma, as well as heart and eye problems. These severe cases often require intensive care and mechanical ventilation, with uncertain recovery prospects and a risk of prolonged hospitalisation or death.

According to government records seen by Al Jazeera, 172 people in Karachi tested positive for polymerase chain reaction (PCR) tests between May and September. Of 956 people suspected of having the virus, 713 were tested. However, the actual number of cases is likely much higher.

Many people are diagnosed without the PCR test, relying instead on matching symptoms and blood tests that show low platelet counts, which can be caused by chikungunya.

Shoaib Khan, general physician at a private hospital in Karachi’s Nazimabad, told The Express Tribune newspaper that the high test cost had also prevented patients from getting a proper diagnosis.

The PCR test for the virus is available at a few private hospitals and costs 7,000 rupees ($25) to 8,000 rupees ($28) in a country where the per capita monthly income was $118 back in 2021, according to World Bank data, making it unaffordable for many people.

One of Karachi’s government hospitals, the Jinnah Postgraduate Medical Centre, provides free tests for chikungunya, Muslim Shah, a city resident who visited the facility on Thursday, told Al Jazeera. Karachi has a population of around 20 million people, according to the 2023 census.

Shah told Al Jazeera that the hospital does not have a separate chikungunya ward, and the patients hospitalised with the mosquito-borne virus are in general wards, without mosquito nets.

Chikungunya and dengue are expected to remain severe until December, Abdul Wahid Rajput, director of the Sindh Infectious Diseases Hospital and Research Centre, told The Express Tribune.

Residents in Karachi and Lahore, where mosquito-borne viruses are common, have blamed the government for not regularly carrying out fogging, which involves spraying disinfectant to eradicate mosquitoes.

How does chikungunya spread?

If an infected mosquito bites a healthy human, it injects the virus into the bloodstream.

If a non-infected mosquito bites a person who is already infected, it sucks the virus from that person’s blood and becomes a carrier capable of transmitting the virus to others through bites.

Health authorities warn that the risk of the virus spreading from an infected person – via a carrier mosquito – is the highest during the first week of infection. The virus does not directly spread from human to human.

This cycle likely began after mosquitos bit infected animals. Chikungunya naturally exists in wild animals (like monkeys) that serve as a virus reservoir.

What are chikungunya symptoms?

Fever and joint pain are the most common symptoms. While fatal cases are rare, joint pain can be severe and continue for months.

Infected people might also have headaches, nausea, fatigue, muscle pain, joint swelling, or a rash.

“It started off with me feeling pain in my wrist. The kind that you get when you sleep on your wrist funny,” 23-year-old Karachi resident Nawal Malik, who contracted the virus in late September, told Al Jazeera.

Malik’s mother, colleague, and neighbour also contracted the virus around the same time.

Soon, all of Malik’s joints were hurting, including her fingers and knuckles. Besides joint pain, she experienced nausea, low blood pressure, heart palpitations, pain behind her eyes, chills and high-grade fever.

“For any other infection, the fever usually breaks when you take medicines for it, but for us with chikungunya, the fever would come back quickly after breaking,” she said, talking about the experience of herself and her mother.

As of Wednesday, it has been about three weeks since Malik recovered from the virus, but she still experiences acute ankle pain.

For her mother, 63, the virus was “much more severe”. She has previously been diagnosed with osteoarthritis and diabetes.

“For her, the joint pain was really horrible; it is the worst pain I’ve ever seen her in,” she said, adding that her mother’s joints continue to hurt weeks after recovery.

Symptoms usually begin three to seven days after an infected mosquito bites you. Many people recover within a week to a few weeks. After that, a person will likely have life-long immunity from the virus.

Chikungunya symptoms are similar to those of dengue and the Zika virus. As a result, chikungunya is often misdiagnosed, say experts, including the World Health Organisation.

How is chikungunya treated?

While there are no specific medicines to treat it, rest, fluids, and pain relievers may help alleviate symptoms, according to the Centers for Disease Control and Prevention (CDC) in the United States.

However, not all pain relievers are safe during a suspected infection. The CDC advises against taking non-steroidal anti-inflammatory drugs (NSAIDs) until dengue has been ruled out, as they can increase the risk of bleeding. In severe cases, dengue patients can have internal or external bleeding complications.

Common examples of NSAIDs include ibuprofen, Advil, and aspirins.

Over-the-counter medicines such as acetaminophen or paracetamol are acceptable as they reduce pain and fever, but do not have anti-inflammatory effects.

How can one protect against chikungunya?

Health authorities support protecting oneself against mosquito bites as the most effective strategy against the spread of chikungunya.

This may involve wearing long sleeves and pants, applying mosquito repellants, removing standing water, and staying in closed, air-conditioned spaces indoors or behind mosquito netting when outdoors.

Is there a vaccine?

A single-dose chikungunya vaccine (IXCHIQ) is available in the United States. According to a November 2023 article by the US Food and Drug Administration (FDA), it is approved for individuals 18 years and older and at a higher risk of exposure to the virus. In June 2024, Ixchiq received market authorisation in Canada and in July, in Europe.

However, Meeran Yousuf, spokesperson for the Sindh Health Department, said that Pakistan usually only uses vaccines authorised by the WHO, which has not approved a chikungunya vaccine so far.

People at higher risk of severe symptoms include newborns, seniors and people with medical conditions such as diabetes or high blood pressure.

Where has it spread?

In 2024, some 460,000 Chikungunya virus cases have been reported worldwide, along with 170 associated deaths, according to the European Centre for Disease Prevention and Control (ECDC).

According to the ECDC, countries with the highest number of cases in 2024 included Brazil, with 391,754 reported cases and India, with 69,439 reported cases.

The virus was first identified in what is now Tanzania – then known as Tanganyika – in 1952 and has since been reported in 118 countries, according to the World Health Organization.

In Africa, Southeast Asia, the Indian subcontinent, the Pacific Region and the tropical regions of the Americas, it has become endemic.

An endemic virus consistently exists within a specific geographic area or population. Outbreaks, in this case, are predictable over time, unlike global pandemics, which are more widespread.

Brazil, Paraguay, Argentina and Bolivia are some countries with the most cases, according to the European CDC.

Sporadic outbreaks have also been reported in locations with the Aedes aegypti mosquito, such as Yemen and Italy. France reported one non-travel-related chikungunya infection in August.

What is the government doing?

Meeran Yousuf, spokesperson for the Sindh Health Department, told Al Jazeera that the government is carrying out “multiple spray activities” throughout the province of Sindh, where Karachi is located.

These efforts aim to eradicate the mosquito responsible for spreading chikungunya.

In addition, the government is carrying out awareness campaigns. “We’re also doing larvicidal activities,” Yousuf added. A larvacide is a type of insecticide that kills mosquitos in their immature larvae and pupae stages, preventing them from developing into biting adults, according to the CDC.