"Super rats" - bigger and smarter rodents than before - are thriving in gutters across Johannesburg.
Rat expert Diederik van't Hof, who has been catching the rodents for almost a decade and has a BSc in zoology, says a record-sized 661g brown "Ratzilla" was caught in Msawawa in Kya Sand recently. The previous record, according to his research, was 500g.
But the city's environmental health department says it is more concerned about the increase in the number of rats in the city."There is evidence that rat-bite incidents in the city are increasing and that is an indication that there are more rodents, which is a huge concern," said Jan van Niekerk, operational manager at the auxiliary services of the city's environmental health department.
Van't Hof said the reason for the increase in the number of the "super" rodents was due to their high-protein diet from people's food waste, and the vitamin content of pet food, which rats often steal.
Rats were changing their behaviour and were learning not to eat poisonous bait that made them sick.
He said there was also more food.
"The amount of waste in a lot of townships makes [food] readily available for rats. It is high-protein food. In the suburbs it is dog or cat food that contains vitamin K, which is also an antidote to poison."
Van Niekerk said that while there was no scientific evidence that rats were changing genetically, reports from city officials show that the rodents were biting residents at a rate of at least a dozen incidents a day. Authorities were struggling to deal with the problem.Rat bites were more prevalent in summer between October and April, he said.
"This is because it is the rats' peak breeding season and their aggression levels are higher."
The biting was a concern because rats were not only biting in defence but also feeding on people, in many cases on babies.
This puts people at risk of contracting rat-bite fever and other diseases, according to John Frean of the Centre for Emerging Zoonotic and Parasitic Diseases at the National Institute for Communicable Diseases.
But a new outbreak of plague in the city remained unlikely, he said.
"There is no further evidence of plague since the report we released more than two years ago, and we have surveillance at a level that we would pick it up quickly [if it arose]," said Frean.
Rats can breed just 18 hours after delivering a litter and are reproducing faster than the city's environmental health department can exterminate them. City officials kill thousands of rats each month through a number of interventions, but can't tell exactly how many rats there are in the metro.
Charlotte Mokoatle, head of the department of environmental health at the University of Johannesburg, said the battle against rats would be won only when officials and communities addressed the factors that provided harbour for rats...