Rats have a role in the spread of many human pathogens, heightened by to their close
association with humans.
Contamination of stored produce and animal feed with rodent urine and faeces may
transmit disease to both humans and livestock. Recent research has shown that rats
caught on farms carry a surprising number of disease causing organisms. These include
cryptosporidiosis (63%), toxoplasmosis (35%), leptospirosis (14%) and listeriosis (11%).
The full results are shown in Table 1.
Cryptosporidiosis is a particular concern because rats can be implicated in the
contamination of cattle foodstuffs that in turn leads to cattle slurry contaminating
watercourses from which drinking water is extracted.
Cryptosporidiosis causes intestinal illness in humans and several other mammals.
Symptoms are abdominal cramps and watery diarrhoea. In healthy people these
symptoms last only one to two weeks. There is currently no cure.
In 2001 there were more than 4400 reported human cases of cryptosporidiosis in the
UK.
Toxoplasmosis is a parasitic disease caused by a protozoan a single-celled animal. It
is a common illness in both animals and humans throughout the world. In human cases
it can cause spontaneous abortion and birth defects. In animals, Toxoplasma is an
important cause of ovine abortion.
In 2001, 129 laboratory-confirmed cases of toxoplasmosis were reported. Serological
surveys indicate that voluntary laboratory reports underestimate the level of infection.
Leptospirosis is a bacterial disease that affects humans and animals. It is a notifiable
disease in humans throughout the UK and causes a wide range of symptoms ranging
from flu-like fevers, headaches, chills and vomiting.
In the cattle and pig industries it causes major economic losses through its adverse
effects on the reproductive performance of these animals. In the dairy industry it can
adversely affect milk yields and fertility.
In 2001 there were 48 confirmed reports of leptospirosis among humans in the UK.
Leptospirosis may be fatal if not treated promptly.
Listeriosis causes symptoms ranging from mild, flu-like illnesses to severe,
life-threatening infections such as septicaemia and meningo-encephalitis. Those at
highest risk are pregnant women, the elderly and the immuno-compromised.
In 2001, 153 cases of human listeriosis were diagnosed in the UK.
Food safety is paramount and the focus nowadays starts on the farm and ends on the
fork. It is more important than ever to ensure that there is no contamination at any stage
of the food chain. Farm assurance schemes specify that approved rodent control
programmes are effectively carried out.
There are also economic reasons why rats need to be controlled.
In a 24-hour period, a Norway rat can pass 12 to 16 ml of urine and produce 50
droppings. This will damage and spoil food in store. The cost of the contaminated food
is considered to be greater than the cost of the food eaten.
This is borne out by a study that claimed that 70% of a tonne of wheat had been spoiled
by 10 to 26 rats during a 12 to 28 week period, although only 4.4% had actually been
eaten. The associated costs are highly significant.
Rats can cause considerable damage to property and buildings. It has been estimated
that the most significant economic damage on farms comes from the gnawing of
electrical cables; around 50% of farm fires are caused by this.
Based on today´s prices, the damage on farms caused by rats is estimated to cost the
UK farming industry £14 to £28 million a year.
Table 1. Diseases transmitted from Norway rats to man
| Parasite | Disease of Man | % rats carrying disease |
| Helminths | ||
| Capillaria spp | Capillariasis | 23 |
| Toxocara cati | Toxocariasis | 15 |
| Hymenolepis nana | Rat tapeworm | 11 |
| Bacteria | ||
| Leptospira spp | Leptospirosis | 14 |
| Listeria spp | Listeriosis | 11 |
| Yersinia enterocolitica | Yersiniosis | 11 |
| Pasteurella spp | Pasteurellosis | 6 |
| Pseudomonas spp | Melioidosis | 4 |
| Coxiella burnetii (antibodies) | Q Fever | 34 |
| Protozoa | ||
| Cryptosporidium parvum | Cryptosporidiosis | 63 |
| Toxoplasma gondii | Toxoplasmosis | 35 |
| Virus (antibodies) | ||
| Hantavirus | Hantaan-fever | 4 |
